Fix value interactions.

Adapt all Commodore machines to 6502Mk2.

.github/workflows/build.yml

@@ -17,7 +17,9 @@ jobs:
         xcode-version: latest-stable
     - name: Make
       working-directory: OSBindings/Mac
-      run: xcodebuild CODE_SIGN_IDENTITY=-
+      run: |
+        xcodebuild -downloadComponent MetalToolchain
+        xcodebuild CODE_SIGN_IDENTITY=-
 
   build-sdl-cmake:
     name: SDL UI / cmake / ${{ matrix.os }}
@@ -37,6 +39,7 @@ jobs:
             sudo apt-get --fix-missing install cmake gcc-10 libsdl2-dev
             ;;
           macOS)
+            brew uninstall cmake
             brew install cmake sdl2
             ;;
         esac

Activity/Source.hpp

@@ -14,7 +14,7 @@ namespace Activity {
 
 class Source {
 public:
-	virtual void set_activity_observer(Observer *observer) = 0;
+	virtual void set_activity_observer(Observer *) = 0;
 };
 
 }

Analyser/Dynamic/ConfidenceCounter.cpp

@@ -10,7 +10,7 @@
 
 using namespace Analyser::Dynamic;
 
-float ConfidenceCounter::get_confidence() {
+float ConfidenceCounter::confidence() const {
 	return float(hits_) / float(hits_ + misses_);
 }
 

Analyser/Dynamic/ConfidenceCounter.hpp

@@ -20,7 +20,7 @@ namespace Analyser::Dynamic {
 class ConfidenceCounter: public ConfidenceSource {
 public:
 	/*! @returns The computed probability, based on the history of events. */
-	float get_confidence() final;
+	float confidence() const final;
 
 	/*! Records an event that implies this is the appropriate class: pushes probability up towards 1.0. */
 	void add_hit();

Analyser/Dynamic/ConfidenceSource.hpp

@@ -17,7 +17,7 @@ namespace Analyser::Dynamic {
 	program is handed to an Atari 2600 then its confidence should grow towards 1.0.
 */
 struct ConfidenceSource {
-	virtual float get_confidence() = 0;
+	virtual float confidence() const = 0;
 };
 
 }

Analyser/Dynamic/ConfidenceSummary.cpp

@@ -22,10 +22,10 @@ ConfidenceSummary::ConfidenceSummary(
 	weight_sum_ = std::accumulate(weights.begin(), weights.end(), 0.0f);
 }
 
-float ConfidenceSummary::get_confidence() {
+float ConfidenceSummary::confidence() const {
 	float result = 0.0f;
 	for(std::size_t index = 0; index < sources_.size(); ++index) {
-		result += sources_[index]->get_confidence() * weights_[index];
+		result += sources_[index]->confidence() * weights_[index];
 	}
 	return result / weight_sum_;
 }

Analyser/Dynamic/ConfidenceSummary.hpp

@@ -30,7 +30,7 @@ public:
 		const std::vector<float> &weights);
 
 	/*! @returns The weighted sum of all sources. */
-	float get_confidence() final;
+	float confidence() const final;
 
 private:
 	const std::vector<ConfidenceSource *> sources_;

Analyser/Dynamic/MultiMachine/Implementation/MultiProducer.cpp

@@ -106,5 +106,5 @@ void MultiTimedMachine::run_for(const Time::Seconds duration) {
 		if(machine->get_confidence() >= 0.01f) machine->run_for(duration);
 	});
 
-	if(delegate_) delegate_->did_run_machines(this);
+	if(delegate_) delegate_->did_run_machines(*this);
 }

Analyser/Dynamic/MultiMachine/Implementation/MultiProducer.hpp

@@ -60,7 +60,7 @@ public:
 		been received.
 	*/
 	struct Delegate {
-		virtual void did_run_machines(MultiTimedMachine *) = 0;
+		virtual void did_run_machines(MultiTimedMachine &) = 0;
 	};
 	/// Sets @c delegate as the receiver of delegate messages.
 	void set_delegate(Delegate *const delegate) {

Analyser/Dynamic/MultiMachine/Implementation/MultiSpeaker.cpp

@@ -60,24 +60,24 @@ void MultiSpeaker::set_output_volume(const float volume) {
 	}
 }
 
-void MultiSpeaker::speaker_did_complete_samples(Speaker *const speaker, const std::vector<int16_t> &buffer) {
+void MultiSpeaker::speaker_did_complete_samples(Speaker &speaker, const std::vector<int16_t> &buffer) {
 	auto delegate = delegate_.load(std::memory_order_relaxed);
 	if(!delegate) return;
 	{
 		std::lock_guard lock_guard(front_speaker_mutex_);
-		if(speaker != front_speaker_) return;
+		if(&speaker != front_speaker_) return;
 	}
 	did_complete_samples(this, buffer, stereo_output_);
 }
 
-void MultiSpeaker::speaker_did_change_input_clock(Speaker *const speaker) {
+void MultiSpeaker::speaker_did_change_input_clock(Speaker &speaker) {
 	auto delegate = delegate_.load(std::memory_order_relaxed);
 	if(!delegate) return;
 	{
 		std::lock_guard lock_guard(front_speaker_mutex_);
-		if(speaker != front_speaker_) return;
+		if(&speaker != front_speaker_) return;
 	}
-	delegate->speaker_did_change_input_clock(this);
+	delegate->speaker_did_change_input_clock(*this);
 }
 
 void MultiSpeaker::set_new_front_machine(::Machine::DynamicMachine *const machine) {
@@ -87,6 +87,6 @@ void MultiSpeaker::set_new_front_machine(::Machine::DynamicMachine *const machin
 	}
 	auto delegate = delegate_.load(std::memory_order_relaxed);
 	if(delegate) {
-		delegate->speaker_did_change_input_clock(this);
+		delegate->speaker_did_change_input_clock(*this);
 	}
 }

Analyser/Dynamic/MultiMachine/Implementation/MultiSpeaker.hpp

@@ -42,8 +42,8 @@ public:
 	void set_output_volume(float) override;
 
 private:
-	void speaker_did_complete_samples(Speaker *speaker, const std::vector<int16_t> &buffer) final;
-	void speaker_did_change_input_clock(Speaker *speaker) final;
+	void speaker_did_complete_samples(Speaker &, const std::vector<int16_t> &buffer) final;
+	void speaker_did_change_input_clock(Speaker &) final;
 	MultiSpeaker(const std::vector<Outputs::Speaker::Speaker *> &speakers);
 
 	std::vector<Outputs::Speaker::Speaker *> speakers_;

Analyser/Dynamic/MultiMachine/MultiMachine.cpp

@@ -12,9 +12,7 @@
 #include <algorithm>
 
 namespace {
-
-Log::Logger<Log::Source::MultiMachine> logger;
-
+using Logger = Log::Logger<Log::Source::MultiMachine>;
 }
 
 using namespace Analyser::Dynamic;
@@ -68,11 +66,11 @@ bool MultiMachine::would_collapse(const std::vector<std::unique_ptr<DynamicMachi
 		(machines.front()->timed_machine()->get_confidence() >= 2.0f * machines[1]->timed_machine()->get_confidence());
 }
 
-void MultiMachine::did_run_machines(MultiTimedMachine *) {
+void MultiMachine::did_run_machines(MultiTimedMachine &) {
 	std::lock_guard machines_lock(machines_mutex_);
 
-	if constexpr (logger.enabled) {
-		auto line = logger.info();
+	if constexpr (Logger::InfoEnabled) {
+		auto line = Logger::info();
 		for(const auto &machine: machines_) {
 			auto timed_machine = machine->timed_machine();
 			line.append("%0.4f %s; ", timed_machine->get_confidence(), timed_machine->debug_type().c_str());

Analyser/Dynamic/MultiMachine/MultiMachine.hpp

@@ -62,7 +62,7 @@ public:
 	void *raw_pointer() final;
 
 private:
-	void did_run_machines(MultiTimedMachine *) final;
+	void did_run_machines(MultiTimedMachine &) final;
 
 	std::vector<std::unique_ptr<DynamicMachine>> machines_;
 	std::recursive_mutex machines_mutex_;

Analyser/Machines.hpp

@@ -18,6 +18,7 @@ enum class Machine {
 	AtariST,
 	Amiga,
 	Archimedes,
+	BBCMicro,
 	ColecoVision,
 	Electron,
 	Enterprise,

Analyser/Static/Acorn/Disk.cpp

@@ -44,7 +44,7 @@ std::unique_ptr<Catalogue> Analyser::Static::Acorn::GetDFSCatalogue(const std::s
 		case 3: catalogue->bootOption = Catalogue::BootOption::ExecBOOT;	break;
 	}
 
-	for(std::size_t file_offset = 8; file_offset < final_file_offset; file_offset += 8) {
+	for(std::size_t file_offset = 8; file_offset <= final_file_offset; file_offset += 8) {
 		File new_file;
 		char name[10];
 		snprintf(name, 10, "%c.%.7s", names->samples[0][file_offset + 7] & 0x7f, &names->samples[0][file_offset]);

Analyser/Static/Acorn/File.hpp

@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <cstdint>
 #include <memory>
 #include <string>
 #include <vector>

Analyser/Static/Acorn/StaticAnalyser.cpp

@@ -19,6 +19,23 @@
 
 using namespace Analyser::Static::Acorn;
 
+namespace {
+bool is_basic(const File &file) {
+	std::size_t pointer = 0;
+	const uint8_t *const data = file.data.data();
+	const std::size_t data_size = file.data.size();
+	while(true) {
+		if(pointer >= data_size-1 || data[pointer] != 0x0d) {
+			return false;
+		}
+		if((data[pointer+1]&0x7f) == 0x7f) break;
+		pointer += data[pointer+3];
+	}
+	return true;
+}
+
+}
+
 static std::vector<std::shared_ptr<Storage::Cartridge::Cartridge>>
 AcornCartridgesFrom(const std::vector<std::shared_ptr<Storage::Cartridge::Cartridge>> &cartridges) {
 	std::vector<std::shared_ptr<Storage::Cartridge::Cartridge>> acorn_cartridges;
@@ -68,11 +85,22 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(
 	TargetPlatform::IntType,
 	bool
 ) {
-	auto target8bit = std::make_unique<ElectronTarget>();
-	auto targetArchimedes = std::make_unique<ArchimedesTarget>();
+	const auto early_exit = [](auto &ptr) {
+		TargetList list;
+		list.push_back(std::move(ptr));
+		return list;
+	};
 
-	// Copy appropriate cartridges to the 8-bit target.
-	target8bit->media.cartridges = AcornCartridgesFrom(media.cartridges);
+	auto targetElectron = std::make_unique<ElectronTarget>();
+	auto targetBBC = std::make_unique<BBCMicroTarget>();
+	auto targetArchimedes = std::make_unique<ArchimedesTarget>();
+	int bbc_hits = 0;
+	int electron_hits = 0;
+	bool format_prefers_bbc = false;
+
+	// Copy appropriate cartridges to the 8-bit targets.
+	targetElectron->media.cartridges = AcornCartridgesFrom(media.cartridges);
+	targetBBC->media.cartridges = AcornCartridgesFrom(media.cartridges);
 
 	// If there are tapes, attempt to get data from the first.
 	if(!media.tapes.empty()) {
@@ -80,35 +108,15 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(
 		auto serialiser = tape->serialiser();
 		std::vector<File> files = GetFiles(*serialiser);
 
-		// continue if there are any files
+		// Continue only if there are any files.
 		if(!files.empty()) {
-			bool is_basic = true;
-
-			// If a file is execute-only, that means *RUN.
-			if(files.front().flags & File::Flags::ExecuteOnly) {
-				is_basic = false;
-			}
-
-			// Check also for a continuous threading of BASIC lines; if none then this probably isn't BASIC code,
-			// so that's also justification to *RUN.
-			if(is_basic) {
-				std::size_t pointer = 0;
-				uint8_t *const data = &files.front().data[0];
-				const std::size_t data_size = files.front().data.size();
-				while(true) {
-					if(pointer >= data_size-1 || data[pointer] != 0x0d) {
-						is_basic = false;
-						break;
-					}
-					if((data[pointer+1]&0x7f) == 0x7f) break;
-					pointer += data[pointer+3];
-				}
-			}
-
 			// Inspect first file. If it's protected or doesn't look like BASIC
 			// then the loading command is *RUN. Otherwise it's CHAIN"".
-			target8bit->loading_command = is_basic ? "CHAIN\"\"\n" : "*RUN\n";
-			target8bit->media.tapes = media.tapes;
+			targetElectron->loading_command =
+				(files.front().flags & File::Flags::ExecuteOnly) || !is_basic(files.front()) ? "*RUN\n" : "CHAIN\"\"\n";
+			targetElectron->media.tapes = media.tapes;
+
+			// TODO: my BBC Micro doesn't yet support tapes; evaluate here in the future.
 		}
 	}
 
@@ -123,25 +131,67 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(
 		// 8-bit options: DFS and Hugo-style ADFS.
 		if(dfs_catalogue || (adfs_catalogue && !adfs_catalogue->has_large_sectors && adfs_catalogue->is_hugo)) {
 			// Accept the disk and determine whether DFS or ADFS ROMs are implied.
-			// Use the Pres ADFS if using an ADFS, as it leaves Page at &EOO.
-			target8bit->media.disks = media.disks;
-			target8bit->has_dfs = bool(dfs_catalogue);
-			target8bit->has_pres_adfs = bool(adfs_catalogue);
+
+			// Electron: use the Pres ADFS if using an ADFS, as it leaves Page at &E00.
+			targetElectron->media.disks = media.disks;
+			targetElectron->has_dfs = bool(dfs_catalogue);
+			targetElectron->has_pres_adfs = bool(adfs_catalogue);
+
+			// BBC: only the 1770 DFS is currently supported, so use that.
+			targetBBC->media.disks = media.disks;
+			targetBBC->has_1770dfs = bool(dfs_catalogue);
+			targetBBC->has_adfs = bool(adfs_catalogue);
+
+			// Special case: if there's only one file, and it is called CPMDISC,
+			// select a BBC with the Z80 second processor.
+			const auto &files = dfs_catalogue ? dfs_catalogue->files : adfs_catalogue->files;
+			if(files.size() == 1 && files[0].name == "$.CPMDISC") {
+				targetBBC->tube_processor = BBCMicroTarget::TubeProcessor::Z80;
+				return early_exit(targetBBC);
+			}
 
 			// Check whether a simple shift+break will do for loading this disk.
 			const auto bootOption = (dfs_catalogue ?: adfs_catalogue)->bootOption;
 			if(bootOption != Catalogue::BootOption::None) {
-				target8bit->should_shift_restart = true;
+				targetBBC->should_shift_restart = targetElectron->should_shift_restart = true;
 			} else {
-				target8bit->loading_command = "*CAT\n";
+				// Otherwise: if there's only one BASIC program then chain it.
+				// Failing that, do a *CAT to be communicative.
+
+				const File *sole_basic_file = nullptr;
+				for(const auto &file: dfs_catalogue ? dfs_catalogue->files : adfs_catalogue->files) {
+					if(is_basic(file)) {
+						if(!sole_basic_file) {
+							sole_basic_file = &file;
+						} else {
+							sole_basic_file = nullptr;
+							break;
+						}
+					}
+				}
+
+				targetBBC->loading_command = targetElectron->loading_command =
+					sole_basic_file ? "CHAIN \"" + sole_basic_file->name + "\"\n" : "*CAT\n";
 			}
 
-			// Check whether adding the AP6 ROM is justified.
-			// For now this is an incredibly dense text search;
-			// if any of the commands that aren't usually present
-			// on a stock Electron are here, add the AP6 ROM and
-			// some sideways RAM such that the SR commands are useful.
-			for(const auto &file: dfs_catalogue ? dfs_catalogue->files : adfs_catalogue->files) {
+			// Further special case: if any of the files have a top word of 0x0003 then
+			// they're for a 6502 second processor, so provide a BBC with one of those.
+			for(const auto &file: files) {
+				if((file.load_address >> 16) == 3) {
+					targetBBC->tube_processor = BBCMicroTarget::TubeProcessor::WDC65C02;
+					return early_exit(targetBBC);
+				}
+			}
+
+			// Add a slight preference for the BBC over the Electron, all else being equal, if this is a DFS floppy.
+			format_prefers_bbc = bool(dfs_catalogue);
+
+			for(const auto &file: files) {
+				// Electron: check whether adding the AP6 ROM is justified.
+				// For now this is an incredibly dense text search;
+				// if any of the commands that aren't usually present
+				// on a stock Electron are here, add the AP6 ROM and
+				// some sideways RAM such that the SR commands are useful.
 				for(const auto &command: {
 					"AQRPAGE", "BUILD", "DUMP", "FORMAT", "INSERT", "LANG", "LIST", "LOADROM",
 					"LOCK", "LROMS", "RLOAD", "ROMS", "RSAVE", "SAVEROM", "SRLOAD", "SRPAGE",
@@ -149,10 +199,60 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(
 					"VERIFY", "ZERO"
 				}) {
 					if(std::search(file.data.begin(), file.data.end(), command, command+strlen(command)) != file.data.end()) {
-						target8bit->has_ap6_rom = true;
-						target8bit->has_sideways_ram = true;
+						targetElectron->has_ap6_rom = true;
+						targetElectron->has_sideways_ram = true;
 					}
 				}
+
+				// Look for any 'BBC indicators', i.e. direct access to BBC-specific hardware.
+				// Also currently a dense search.
+
+				const auto hits = [&](const std::initializer_list<uint16_t> collection) {
+					int hits = 0;
+					for(const auto address: collection) {
+						const uint8_t sta_address[3] = {
+							0x8d, uint8_t(address & 0xff), uint8_t(address >> 8)
+						};
+
+						if(std::search(
+							file.data.begin(), file.data.end(),
+							std::begin(sta_address), std::end(sta_address)
+						) != file.data.end()) {
+							++hits;
+						}
+
+						// I think I'll want std::ranges::contains_subrange if/when building for C++23.
+					}
+					return hits;
+				};
+
+				bbc_hits += hits({
+					// The video control registers.
+					0xfe20, 0xfe21,
+
+					// The system VIA.
+					0xfe40, 0xfe41, 0xfe42, 0xfe43, 0xfe44, 0xfe45, 0xfe46, 0xfe47,
+					0xfe48, 0xfe49, 0xfe4a, 0xfe4b, 0xfe4c, 0xfe4d, 0xfe4e, 0xfe4f,
+
+					// The user VIA.
+					0xfe60, 0xfe61, 0xfe62, 0xfe63, 0xfe64, 0xfe65, 0xfe66, 0xfe67,
+					0xfe68, 0xfe69, 0xfe6a, 0xfe6b, 0xfe6c, 0xfe6d, 0xfe6e, 0xfe6f,
+				});
+				// BASIC for "MODE7".
+				static constexpr uint8_t mode7[] = {0xeb, 0x37};
+				bbc_hits += std::search(
+							file.data.begin(), file.data.end(),
+							std::begin(mode7), std::end(mode7)
+						) != file.data.end();
+
+				electron_hits += hits({
+					// ULA addresses that aren't also the BBC's CRTC.
+					0xfe03, 0xfe04, 0xfe05,
+					0xfe06, 0xfe07, 0xfe08,
+					0xfe09, 0xfe0a, 0xfe0b,
+					0xfe0c, 0xfe0d, 0xfe0e,
+					0xfe0f,
+				});
 			}
 		} else if(adfs_catalogue) {
 			// Archimedes options, implicitly: ADFS, non-Hugo.
@@ -167,8 +267,8 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(
 				// Take whatever else comes with a preference for things that don't
 				// have 'boot' or 'read' in them (the latter of which will tend to be
 				// read_me or read_this or similar).
-				constexpr char read[] = "read";
-				constexpr char boot[] = "boot";
+				static constexpr char read[] = "read";
+				static constexpr char boot[] = "boot";
 				const auto has = [&](const char *begin, const char *end) {
 					return  std::search(
 						file.name.begin(), file.name.end(),
@@ -197,28 +297,38 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(
 	// Enable the Acorn ADFS if a mass-storage device is attached;
 	// unlike the Pres ADFS it retains SCSI logic.
 	if(!media.mass_storage_devices.empty()) {
-		target8bit->has_pres_adfs = false;	// To override a floppy selection, if one was made.
-		target8bit->has_acorn_adfs = true;
+		targetElectron->has_pres_adfs = false;	// To override a floppy selection, if one was made.
+		targetElectron->has_acorn_adfs = true;
 
 		// Assume some sort of later-era Acorn work is likely to happen;
 		// so ensure *TYPE, etc are present.
-		target8bit->has_ap6_rom = true;
-		target8bit->has_sideways_ram = true;
+		targetElectron->has_ap6_rom = true;
+		targetElectron->has_sideways_ram = true;
 
-		target8bit->media.mass_storage_devices = media.mass_storage_devices;
+		targetElectron->media.mass_storage_devices = media.mass_storage_devices;
 
 		// Check for a boot option.
-		const auto sector = target8bit->media.mass_storage_devices.front()->get_block(1);
+		const auto sector = targetElectron->media.mass_storage_devices.front()->get_block(1);
 		if(sector[0xfd]) {
-			target8bit->should_shift_restart = true;
+			targetElectron->should_shift_restart = true;
 		} else {
-			target8bit->loading_command = "*CAT\n";
+			targetElectron->loading_command = "*CAT\n";
 		}
 	}
 
 	TargetList targets;
-	if(!target8bit->media.empty()) {
-		targets.push_back(std::move(target8bit));
+	if(!targetElectron->media.empty() && !targetBBC->media.empty()) {
+		if(bbc_hits > electron_hits || (bbc_hits == electron_hits && format_prefers_bbc)) {
+			targets.push_back(std::move(targetBBC));
+		} else {
+			targets.push_back(std::move(targetElectron));
+		}
+	} else {
+		if(!targetElectron->media.empty()) {
+			targets.push_back(std::move(targetElectron));
+		} else if(!targetBBC->media.empty()) {
+			targets.push_back(std::move(targetBBC));
+		}
 	}
 	if(!targetArchimedes->media.empty()) {
 		targets.push_back(std::move(targetArchimedes));

Analyser/Static/Acorn/Target.hpp

@@ -9,6 +9,7 @@
 #pragma once
 
 #include "Analyser/Static/StaticAnalyser.hpp"
+#include "Reflection/Enum.hpp"
 #include "Reflection/Struct.hpp"
 #include <string>
 
@@ -36,6 +37,32 @@ private:
 	}
 };
 
+struct BBCMicroTarget: public ::Analyser::Static::Target, public Reflection::StructImpl<BBCMicroTarget> {
+	std::string loading_command;
+	bool should_shift_restart = false;
+
+	bool has_1770dfs = false;
+	bool has_adfs = false;
+	bool has_sideways_ram = true;
+	bool has_beebsid = false;
+
+	ReflectableEnum(TubeProcessor, None, WDC65C02, Z80);
+	TubeProcessor tube_processor = TubeProcessor::None;
+
+	BBCMicroTarget() : Analyser::Static::Target(Machine::BBCMicro) {}
+
+private:
+	friend Reflection::StructImpl<BBCMicroTarget>;
+	void declare_fields() {
+		DeclareField(has_1770dfs);
+		DeclareField(has_adfs);
+		DeclareField(has_sideways_ram);
+		DeclareField(has_beebsid);
+		AnnounceEnum(TubeProcessor);
+		DeclareField(tube_processor);
+	}
+};
+
 struct ArchimedesTarget: public ::Analyser::Static::Target, public Reflection::StructImpl<ArchimedesTarget> {
 	std::string main_program;
 

Analyser/Static/AmstradCPC/StaticAnalyser.cpp

@@ -16,9 +16,18 @@
 
 #include <algorithm>
 #include <cstring>
+#include <unordered_set>
 
 namespace {
 
+std::string rtrimmed(const std::string &input) {
+	auto trimmed = input;
+	trimmed.erase(std::find_if(trimmed.rbegin(), trimmed.rend(), [](const char ch) {
+		return !std::isspace(ch);
+	}).base(), trimmed.end());
+	return trimmed;
+}
+
 bool strcmp_insensitive(const char *a, const char *b) {
 	if(std::strlen(a) != std::strlen(b)) return false;
 	while(*a) {
@@ -104,58 +113,85 @@ void InspectCatalogue(
 		return;
 	}
 
-	// If only one file is [potentially] BASIC, run that one; otherwise if only one has a suffix
-	// that AMSDOS allows to be omitted, pick that one.
-	int basic_files = 0;
-	int implicit_suffixed_files = 0;
+	const auto run_name = [&]() -> std::optional<std::string> {
+		// Collect:
+		//
+		//	1. a set of all files that can be run without specifying an extension plus their appearance counts;
+		//	2. a set of all BASIC file names.
+		std::unordered_map<std::string, int> candidates;
+		std::unordered_set<std::string> basic_names;
+		for(std::size_t c = 0; c < candidate_files.size(); c++) {
+			// Files with nothing but spaces in their name can't be loaded by the user, so disregard them.
+			if(
+				(candidate_files[c]->type == "   " && candidate_files[c]->name == "        ") ||
+				!is_implied_extension(candidate_files[c]->type)
+			) {
+				continue;
+			}
 
-	std::size_t last_basic_file = 0;
-	std::size_t last_implicit_suffixed_file = 0;
-
-	for(std::size_t c = 0; c < candidate_files.size(); c++) {
-		// Files with nothing but spaces in their name can't be loaded by the user, so disregard them.
-		if(candidate_files[c]->type == "   " && candidate_files[c]->name == "        ")
-			continue;
-
-		// Check for whether this is [potentially] BASIC.
-		if(candidate_files[c]->data.size() >= 128 && !((candidate_files[c]->data[18] >> 1) & 7)) {
-			basic_files++;
-			last_basic_file = c;
-		}
-
-		// Check suffix for emptiness.
-		if(is_implied_extension(candidate_files[c]->type)) {
-			implicit_suffixed_files++;
-			last_implicit_suffixed_file = c;
-		}
-	}
-	if(basic_files == 1 || implicit_suffixed_files == 1) {
-		std::size_t selected_file = (basic_files == 1) ? last_basic_file : last_implicit_suffixed_file;
-		target->loading_command = RunCommandFor(*candidate_files[selected_file]);
-		return;
-	}
-
-	// One more guess: if only one remaining candidate file has a different name than the others,
-	// assume it is intended to stand out.
-	std::map<std::string, int> name_counts;
-	std::map<std::string, std::size_t> indices_by_name;
-	std::size_t index = 0;
-	for(const auto &file : candidate_files) {
-		name_counts[file->name]++;
-		indices_by_name[file->name] = index;
-		index++;
-	}
-	if(name_counts.size() == 2) {
-		for(const auto &pair : name_counts) {
-			if(pair.second == 1) {
-				target->loading_command = RunCommandFor(*candidate_files[indices_by_name[pair.first]]);
-				return;
+			++candidates[candidate_files[c]->name];
+			if(candidate_files[c]->data.size() >= 128 && !((candidate_files[c]->data[18] >> 1) & 7)) {
+				basic_names.insert(candidate_files[c]->name);
 			}
 		}
-	}
 
-	// Desperation.
-	target->loading_command = "cat\n";
+		// Only one candidate total.
+		if(candidates.size() == 1) {
+			return candidates.begin()->first;
+		}
+
+		// Only one BASIC candidate.
+		if(basic_names.size() == 1) {
+			return *basic_names.begin();
+		}
+
+		// Exactly two candidate names, but only one is a unique name.
+		if(candidates.size() == 2) {
+			const auto item1 = candidates.begin();
+			const auto item2 = std::next(item1);
+
+			if(item1->second == 1 && item2->second != 1) {
+				return item1->first;
+			}
+			if(item2->second == 1 && item1->second != 1) {
+				return item2->first;
+			}
+		}
+
+		// Remove from candidates anything that is just a suffixed version of
+		// another name, as long as the other name is three or more characters.
+		std::vector<std::string> to_remove;
+		for(const auto &lhs: candidates) {
+			const auto trimmed = rtrimmed(lhs.first);
+			if(trimmed.size() < 3) {
+				continue;
+			}
+
+			for(const auto &rhs: candidates) {
+				if(lhs.first == rhs.first) {
+					continue;
+				}
+
+				if(rhs.first.find(trimmed) == 0) {
+					to_remove.push_back(rhs.first);
+				}
+			}
+		}
+		for(const auto &candidate: to_remove) {
+			candidates.erase(candidate);
+		}
+		if(candidates.size() == 1) {
+			return candidates.begin()->first;
+		}
+
+		return {};
+	} ();
+
+	if(run_name.has_value()) {
+		target->loading_command = "run\"" + rtrimmed(*run_name) + "\n";
+	} else {
+		target->loading_command = "cat\n";
+	}
 }
 
 bool CheckBootSector(

Analyser/Static/Commodore/StaticAnalyser.cpp

@@ -258,7 +258,7 @@ analyse_starting_address(uint16_t starting_address) {
 		case 0x1c01:
 			// TODO: assume C128.
 		default:
-			Log::Logger<Log::Source::CommodoreStaticAnalyser>().error().append(
+			Log::Logger<Log::Source::CommodoreStaticAnalyser>::error().append(
 				"Unrecognised loading address for Commodore program: %04x", starting_address);
 			[[fallthrough]];
 		case 0x1001:

Analyser/Static/Commodore/Tape.cpp

@@ -9,6 +9,8 @@
 #include "Tape.hpp"
 #include "Storage/Tape/Parsers/Commodore.hpp"
 
+#include <algorithm>
+
 using namespace Analyser::Static::Commodore;
 
 std::vector<File> Analyser::Static::Commodore::GetFiles(Storage::Tape::TapeSerialiser &serialiser, TargetPlatform::Type type) {
@@ -37,7 +39,7 @@ std::vector<File> Analyser::Static::Commodore::GetFiles(Storage::Tape::TapeSeria
 					header = parser.get_next_header(serialiser);
 					if(!header) continue;
 					if(header->type != Storage::Tape::Commodore::Header::DataBlock) break;
-					std::copy(header->data.begin(), header->data.end(), std::back_inserter(new_file.data));
+					std::ranges::copy(header->data, std::back_inserter(new_file.data));
 				}
 			}
 			break;

Analyser/Static/Disassembler/Z80.cpp

@@ -60,11 +60,11 @@ private:
 	bool overrun_ = false;
 };
 
-constexpr uint8_t x(uint8_t v) { return v >> 6; }
-constexpr uint8_t y(uint8_t v) { return (v >> 3) & 7; }
-constexpr uint8_t q(uint8_t v) { return (v >> 3) & 1; }
-constexpr uint8_t p(uint8_t v) { return (v >> 4) & 3; }
-constexpr uint8_t z(uint8_t v) { return v & 7; }
+constexpr uint8_t x(const uint8_t v) { return v >> 6; }
+constexpr uint8_t y(const uint8_t v) { return (v >> 3) & 7; }
+constexpr uint8_t q(const uint8_t v) { return (v >> 3) & 1; }
+constexpr uint8_t p(const uint8_t v) { return (v >> 4) & 3; }
+constexpr uint8_t z(const uint8_t v) { return v & 7; }
 
 Instruction::Condition condition_table[] = {
 	Instruction::Condition::NZ,		Instruction::Condition::Z,
@@ -92,7 +92,7 @@ Instruction::Location RegisterTableEntry(
 	Instruction &instruction,
 	const bool needs_indirect_offset
 ) {
-	constexpr Instruction::Location register_table[] = {
+	static constexpr Instruction::Location register_table[] = {
 		Instruction::Location::B,	Instruction::Location::C,
 		Instruction::Location::D,	Instruction::Location::E,
 		Instruction::Location::H,	Instruction::Location::L,

Analyser/Static/PCCompatible/Target.hpp

@@ -27,6 +27,10 @@ constexpr bool is_at(const Model model) {
 	return model >= Model::AT;
 }
 
+constexpr bool has_ide(const Model model) {
+	return model >= Model::AT;
+}
+
 struct Target: public Analyser::Static::Target, public Reflection::StructImpl<Target> {
 	ReflectableEnum(VideoAdaptor,
 		MDA,

Analyser/Static/StaticAnalyser.cpp

@@ -9,6 +9,7 @@
 #include "StaticAnalyser.hpp"
 
 #include <algorithm>
+#include <bit>
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
@@ -52,6 +53,7 @@
 #include "Storage/Disk/DiskImage/Formats/HFE.hpp"
 #include "Storage/Disk/DiskImage/Formats/IPF.hpp"
 #include "Storage/Disk/DiskImage/Formats/IMD.hpp"
+#include "Storage/Disk/DiskImage/Formats/JFD.hpp"
 #include "Storage/Disk/DiskImage/Formats/MacintoshIMG.hpp"
 #include "Storage/Disk/DiskImage/Formats/MSA.hpp"
 #include "Storage/Disk/DiskImage/Formats/NIB.hpp"
@@ -66,6 +68,7 @@
 #include "Storage/MassStorage/Formats/DSK.hpp"
 #include "Storage/MassStorage/Formats/HDV.hpp"
 #include "Storage/MassStorage/Formats/HFV.hpp"
+#include "Storage/MassStorage/Formats/VHD.hpp"
 
 // State Snapshots
 #include "Storage/State/SNA.hpp"
@@ -205,6 +208,7 @@ static Media GetMediaAndPlatforms(const std::string &file_name, TargetPlatform::
 	accumulator.try_standard<Disk::DiskImageHolder<Disk::AcornADF>>(TargetPlatform::Acorn, "adf");
 	accumulator.try_standard<Disk::DiskImageHolder<Disk::AmigaADF>>(TargetPlatform::Amiga, "adf");
 	accumulator.try_standard<Disk::DiskImageHolder<Disk::AcornADF>>(TargetPlatform::Acorn, "adl");
+	accumulator.try_standard<Disk::DiskImageHolder<Disk::JFD>>(TargetPlatform::Archimedes, "jfd");
 
 	accumulator.try_standard<Cartridge::BinaryDump>(TargetPlatform::AllCartridge, "bin");
 
@@ -299,6 +303,8 @@ static Media GetMediaAndPlatforms(const std::string &file_name, TargetPlatform::
 
 	accumulator.try_standard<Tape::UEF>(TargetPlatform::Acorn, "uef");
 
+	accumulator.try_standard<MassStorage::VHD>(TargetPlatform::PCCompatible, "vhd");
+
 	accumulator.try_standard<Disk::DiskImageHolder<Disk::WOZ>>(TargetPlatform::DiskII, "woz");
 
 	return accumulator.media;
@@ -340,13 +346,7 @@ TargetList Analyser::Static::GetTargets(const std::string &file_name) {
 	TargetPlatform::IntType potential_platforms = 0;
 	Media media = GetMediaAndPlatforms(file_name, potential_platforms);
 
-	// TODO: std::popcount here.
-	int total_options = 0;
-	TargetPlatform::IntType mask = 1;
-	while(mask) {
-		total_options += bool(potential_platforms & mask);
-		mask <<= 1;
-	}
+	int total_options = std::popcount(potential_platforms);
 	const bool is_confident = total_options == 1;
 	// i.e. This analyser `is_confident` if file analysis suggested only one potential target platform.
 	// The machine-specific static analyser will still run in case it can provide meaningful annotations on

CMakeLists.txt

@@ -5,7 +5,7 @@ project(CLK
 	VERSION 24.01.22
 )
 
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 

ClockReceiver/ClockReceiver.hpp

@@ -128,12 +128,7 @@ public:
 
 	forceinline constexpr T operator -() const						{	return T(- length_);				}
 
-	forceinline constexpr bool operator <(const T &rhs) const		{	return length_ < rhs.length_;		}
-	forceinline constexpr bool operator >(const T &rhs) const		{	return length_ > rhs.length_;		}
-	forceinline constexpr bool operator <=(const T &rhs) const		{	return length_ <= rhs.length_;		}
-	forceinline constexpr bool operator >=(const T &rhs) const		{	return length_ >= rhs.length_;		}
-	forceinline constexpr bool operator ==(const T &rhs) const		{	return length_ == rhs.length_;		}
-	forceinline constexpr bool operator !=(const T &rhs) const		{	return length_ != rhs.length_;		}
+	auto operator <=>(const WrappedInt &) const = default;
 
 	forceinline constexpr bool operator !() const					{	return !length_;					}
 	// bool operator () is not supported because it offers an implicit cast to int,

ClockReceiver/DeferredValue.hpp

@@ -16,10 +16,10 @@ template <int DeferredDepth, typename ValueT> class DeferredValue {
 private:
 	static_assert(sizeof(ValueT) <= 4);
 
-	constexpr int elements_per_uint32 = sizeof(uint32_t) / sizeof(ValueT);
-	constexpr int unit_shift = sizeof(ValueT) * 8;
-	constexpr int insert_shift = (DeferredDepth & (elements_per_uint32 - 1)) * unit_shift;
-	constexpr uint32_t insert_mask = ~(0xffff'ffff << insert_shift);
+	static constexpr int elements_per_uint32 = sizeof(uint32_t) / sizeof(ValueT);
+	static constexpr int unit_shift = sizeof(ValueT) * 8;
+	static constexpr int insert_shift = (DeferredDepth & (elements_per_uint32 - 1)) * unit_shift;
+	static constexpr uint32_t insert_mask = ~(0xffff'ffff << insert_shift);
 
 	std::array<uint32_t, (DeferredDepth + elements_per_uint32 - 1) / elements_per_uint32> backlog;
 

ClockReceiver/JustInTime.hpp

@@ -325,7 +325,7 @@ public:
 	/// Flushes all accumulated time.
 	inline void flush() {
 		if(!is_flushed_) {
-			task_queue_.flush();
+			task_queue_.lock_flush();
 			object_.run_for(time_since_update_.template flush<TargetTimeScale>());
 			is_flushed_ = true;
 		}

Components/1770/1770.cpp

@@ -8,11 +8,11 @@
 
 #include "1770.hpp"
 
-#include "Storage/Disk/Encodings/MFM/Constants.hpp"
 #include "Outputs/Log.hpp"
+#include "Storage/Disk/Encodings/MFM/Constants.hpp"
 
 namespace {
-Log::Logger<Log::Source::WDFDC> logger;
+using Logger = Log::Logger<Log::Source::WDFDC>;
 }
 
 using namespace WD;
@@ -31,10 +31,10 @@ void WD1770::write(const int address, const uint8_t value) {
 			if((value&0xf0) == 0xd0) {
 				if(value == 0xd0) {
 					// Force interrupt **immediately**.
-					logger.info().append("Force interrupt immediately");
+					Logger::info().append("Force interrupt immediately");
 					posit_event(int(Event1770::ForceInterrupt));
 				} else {
-					logger.error().append("TODO: force interrupt");
+					Logger::error().append("TODO: force interrupt");
 					update_status([] (Status &status) {
 						status.type = Status::One;
 					});
@@ -101,19 +101,20 @@ uint8_t WD1770::read(const int address) {
 				if(status_.type == Status::One)
 					status |= (status_.spin_up ? Flag::SpinUp : 0);
 			}
-//			logger.info().append("Returned status %02x of type %d", status, 1+int(status_.type));
+//			Logger::info().append("Returned status %02x of type %d", status, 1+int(status_.type));
 			return status;
 		}
 		case 1:
-			logger.info().append("Returned track %d", track_);
+			Logger::info().append("Returned track %d", track_);
 			return track_;
 		case 2:
-			logger.info().append("Returned sector %d", sector_);
+			Logger::info().append("Returned sector %d", sector_);
 			return sector_;
 		case 3:
 			update_status([] (Status &status) {
 				status.data_request = false;
 			});
+//			Logger::info().append("Returned data %02x; [drq:%d]", data_, status_.data_request);
 		return data_;
 	}
 }
@@ -132,26 +133,46 @@ void WD1770::run_for(const Cycles cycles) {
 	}
 }
 
-#define WAIT_FOR_EVENT(mask)	resume_point_ = __LINE__; interesting_event_mask_ = int(mask); return; case __LINE__:
-#define WAIT_FOR_TIME(ms)		resume_point_ = __LINE__; delay_time_ = ms * 8000; WAIT_FOR_EVENT(Event1770::Timer);
-#define WAIT_FOR_BYTES(count)	resume_point_ = __LINE__; distance_into_section_ = 0; WAIT_FOR_EVENT(Event::Token); if(get_latest_token().type == Token::Byte) distance_into_section_++; if(distance_into_section_ < count) { interesting_event_mask_ = int(Event::Token); return; }
-#define BEGIN_SECTION()	switch(resume_point_) { default:
-#define END_SECTION()	(void)0; }
+#include <iostream>
 
-#define READ_ID()	\
-		if(new_event_type == int(Event::Token)) {	\
-			if(!distance_into_section_ && get_latest_token().type == Token::ID) {\
-				set_data_mode(DataMode::Reading);	\
-				++distance_into_section_;	\
-			} else if(distance_into_section_ && distance_into_section_ < 7 && get_latest_token().type == Token::Byte) {	\
-				header_[distance_into_section_ - 1] = get_latest_token().byte_value;	\
-				++distance_into_section_;	\
-			}	\
+void WD1770::posit_event(const int new_event_type) {
+#define WAIT_FOR_EVENT(mask) {							\
+	interesting_event_mask_ = int(mask);				\
+	static constexpr int location = __COUNTER__ + 1;	\
+	resume_point_ = location;							\
+	return;												\
+	case location:										\
+		(void)0;										\
+}
+
+#define WAIT_FOR_TIME(ms)				\
+	delay_time_ = ms * 8000;			\
+	WAIT_FOR_EVENT(Event1770::Timer);
+
+#define WAIT_FOR_BYTES(count)											\
+	distance_into_section_ = 0;											\
+	WAIT_FOR_EVENT(Event::Token);										\
+	distance_into_section_ += get_latest_token().type == Token::Byte;	\
+	if(distance_into_section_ < count) {								\
+		RESUME_WAIT(Event::Token);										\
+	}
+
+#define RESUME_WAIT(mask)		interesting_event_mask_ = int(mask); return;
+
+#define BEGIN_SECTION()			switch(resume_point_) { default:
+#define END_SECTION()			(void)0; }
+
+	const auto READ_ID = [&] {
+		if(new_event_type == int(Event::Token)) {
+			if(!distance_into_section_ && get_latest_token().type == Token::ID) {
+				set_data_mode(DataMode::Reading);
+				++distance_into_section_;
+			} else if(distance_into_section_ && distance_into_section_ < 7 && get_latest_token().type == Token::Byte) {
+				header_[distance_into_section_ - 1] = get_latest_token().byte_value;
+				++distance_into_section_;
+			}
 		}
-
-#define CONCATENATE(x, y) x ## y
-#define INDIRECT_CONCATENATE(x, y) TOKENPASTE(x, y)
-#define LINE_LABEL INDIRECT_CONCATENATE(label, __LINE__)
+	};
 
 #define SPIN_UP()	\
 		set_motor_on(true);	\
@@ -160,24 +181,6 @@ void WD1770::run_for(const Cycles cycles) {
 		WAIT_FOR_EVENT(Event1770::IndexHoleTarget);	\
 		status_.spin_up = true;
 
-// +--------+----------+-------------------------+
-// !	    !	       !          BITS           !
-// ! TYPE   ! COMMAND  !  7  6	5  4  3  2  1  0 !
-// +--------+----------+-------------------------+
-// !	 1  ! Restore  !  0  0	0  0  h  v r1 r0 !
-// !	 1  ! Seek     !  0  0	0  1  h  v r1 r0 !
-// !	 1  ! Step     !  0  0	1  u  h  v r1 r0 !
-// !	 1  ! Step-in  !  0  1	0  u  h  v r1 r0 !
-// !	 1  ! Step-out !  0  1	1  u  h  v r1 r0 !
-// !	 2  ! Rd sectr !  1  0	0  m  h  E  0  0 !
-// !	 2  ! Wt sectr !  1  0	1  m  h  E  P a0 !
-// !	 3  ! Rd addr  !  1  1	0  0  h  E  0  0 !
-// !	 3  ! Rd track !  1  1	1  0  h  E  0  0 !
-// !	 3  ! Wt track !  1  1	1  1  h  E  P  0 !
-// !	 4  ! Forc int !  1  1	0  1 i3 i2 i1 i0 !
-// +--------+----------+-------------------------+
-
-void WD1770::posit_event(const int new_event_type) {
 	if(new_event_type == int(Event::IndexHole)) {
 		index_hole_count_++;
 		if(index_hole_count_target_ == index_hole_count_) {
@@ -198,7 +201,7 @@ void WD1770::posit_event(const int new_event_type) {
 
 	if(new_event_type == int(Event1770::ForceInterrupt)) {
 		interesting_event_mask_ = 0;
-		resume_point_ = 0;
+		resume_point_ = IdleResumePoint;
 		update_status([] (Status &status) {
 			status.type = Status::One;
 			status.data_request = false;
@@ -209,12 +212,29 @@ void WD1770::posit_event(const int new_event_type) {
 		interesting_event_mask_ &= ~new_event_type;
 	}
 
+// +--------+----------+-------------------------+
+// !	    !	       !          BITS           !
+// ! TYPE   ! COMMAND  !  7  6	5  4  3  2  1  0 !
+// +--------+----------+-------------------------+
+// !	 1  ! Restore  !  0  0	0  0  h  v r1 r0 !
+// !	 1  ! Seek     !  0  0	0  1  h  v r1 r0 !
+// !	 1  ! Step     !  0  0	1  u  h  v r1 r0 !
+// !	 1  ! Step-in  !  0  1	0  u  h  v r1 r0 !
+// !	 1  ! Step-out !  0  1	1  u  h  v r1 r0 !
+// !	 2  ! Rd sectr !  1  0	0  m  h  E  0  0 !
+// !	 2  ! Wt sectr !  1  0	1  m  h  E  P a0 !
+// !	 3  ! Rd addr  !  1  1	0  0  h  E  0  0 !
+// !	 3  ! Rd track !  1  1	1  0  h  E  0  0 !
+// !	 3  ! Wt track !  1  1	1  1  h  E  P  0 !
+// !	 4  ! Forc int !  1  1	0  1 i3 i2 i1 i0 !
+// +--------+----------+-------------------------+
+
 	BEGIN_SECTION()
 
 	// Wait for a new command, branch to the appropriate handler.
-	case 0:
+	case IdleResumePoint:
 	wait_for_command:
-		logger.info().append("Idle...");
+		Logger::info().append("Idle...");
 		set_data_mode(DataMode::Scanning);
 		index_hole_count_ = 0;
 
@@ -231,7 +251,7 @@ void WD1770::posit_event(const int new_event_type) {
 			status.track_zero = false;	// Always reset by a non-type 1; so reset regardless and set properly later.
 		});
 
-		logger.info().append("Starting %02x", command_);
+		Logger::info().append("Starting %02x", command_);
 
 		if(!(command_ & 0x80)) goto begin_type_1;
 		if(!(command_ & 0x40)) goto begin_type_2;
@@ -261,7 +281,7 @@ void WD1770::posit_event(const int new_event_type) {
 			status.data_request = false;
 		});
 
-		logger.info().append("Step/Seek/Restore with track %d data %d", track_, data_);
+		Logger::info().append("Step/Seek/Restore with track %d data %d", track_, data_);
 		if(!has_motor_on_line() && !has_head_load_line()) goto test_type1_type;
 
 		if(has_motor_on_line()) goto begin_type1_spin_up;
@@ -341,7 +361,7 @@ void WD1770::posit_event(const int new_event_type) {
 		READ_ID();
 
 		if(index_hole_count_ == 6) {
-			logger.info().append("Nothing found to verify");
+			Logger::info().append("Nothing found to verify");
 			update_status([] (Status &status) {
 				status.seek_error = true;
 			});
@@ -359,7 +379,7 @@ void WD1770::posit_event(const int new_event_type) {
 			}
 
 			if(header_[0] == track_) {
-				logger.info().append("Reached track %d", track_);
+				Logger::info().append("Reached track %d", track_);
 				update_status([] (Status &status) {
 					status.crc_error = false;
 				});
@@ -432,7 +452,7 @@ void WD1770::posit_event(const int new_event_type) {
 		READ_ID();
 
 		if(index_hole_count_ == 5) {
-			logger.info().append("Failed to find sector %d", sector_);
+			Logger::info().append("Failed to find sector %d", sector_);
 			update_status([] (Status &status) {
 				status.record_not_found = true;
 			});
@@ -442,12 +462,12 @@ void WD1770::posit_event(const int new_event_type) {
 			distance_into_section_ = 0;
 			set_data_mode(DataMode::Scanning);
 
-			logger.info().append("Considering %d/%d", header_[0], header_[2]);
+			Logger::info().append("Considering %d/%d", header_[0], header_[2]);
 			if(		header_[0] == track_ && header_[2] == sector_ &&
 					(has_motor_on_line() || !(command_&0x02) || ((command_&0x08) >> 3) == header_[1])) {
-				logger.info().append("Found %d/%d", header_[0], header_[2]);
+				Logger::info().append("Found %d/%d", header_[0], header_[2]);
 				if(get_crc_generator().get_value()) {
-					logger.info().append("CRC error; back to searching");
+					Logger::info().append("CRC error; back to searching");
 					update_status([] (Status &status) {
 						status.crc_error = true;
 					});
@@ -505,18 +525,18 @@ void WD1770::posit_event(const int new_event_type) {
 			set_data_mode(DataMode::Scanning);
 
 			if(get_crc_generator().get_value()) {
-				logger.info().append("CRC error; terminating");
+				Logger::info().append("CRC error; terminating");
 				update_status([] (Status &status) {
 					status.crc_error = true;
 				});
 				goto wait_for_command;
 			}
 
-			logger.info().append("Finished reading sector %d", sector_);
+			Logger::info().append("Finished reading sector %d", sector_);
 
 			if(command_ & 0x10) {
 				sector_++;
-				logger.info().append("Advancing to search for sector %d", sector_);
+				Logger::info().append("Advancing to search for sector %d", sector_);
 				goto test_type2_write_protection;
 			}
 			goto wait_for_command;
@@ -600,7 +620,7 @@ void WD1770::posit_event(const int new_event_type) {
 			sector_++;
 			goto test_type2_write_protection;
 		}
-		logger.info().append("Wrote sector %d", sector_);
+		Logger::info().append("Wrote sector %d", sector_);
 		goto wait_for_command;
 
 
@@ -818,7 +838,7 @@ void WD1770::update_status(const std::function<void(Status &)> updater) {
 			(status_.busy != old_status.busy) ||
 			(status_.data_request != old_status.data_request) ||
 			(status_.interrupt_request != old_status.interrupt_request);
-		if(did_change) delegate_->wd1770_did_change_output(this);
+		if(did_change) delegate_->wd1770_did_change_output(*this);
 	} else updater(status_);
 
 	if(status_.busy != old_status.busy) update_clocking_observer();

Components/1770/1770.hpp

@@ -66,9 +66,8 @@ public:
 	/// @returns The current value of the DRQ line output.
 	inline bool get_data_request_line() const		{	return status_.data_request;		}
 
-	class Delegate {
-		public:
-			virtual void wd1770_did_change_output(WD1770 *wd1770) = 0;
+	struct Delegate {
+		virtual void wd1770_did_change_output(WD1770 &) = 0;
 	};
 	inline void set_delegate(Delegate *delegate)	{	delegate_ = delegate;				}
 
@@ -125,9 +124,12 @@ private:
 	};
 	void posit_event(int type);
 	int interesting_event_mask_;
-	int resume_point_ = 0;
 	Cycles::IntType delay_time_ = 0;
 
+	// Current state machine stap pointer.
+	static constexpr int IdleResumePoint = 0;
+	int resume_point_ = IdleResumePoint;
+
 	// ID buffer
 	uint8_t header_[6];
 

Components/5380/ncr5380.cpp

@@ -11,7 +11,7 @@
 #include "Outputs/Log.hpp"
 
 namespace {
-Log::Logger<Log::Source::NCR5380> logger;
+using Logger = Log::Logger<Log::Source::NCR5380>;
 }
 // TODO:
 //
@@ -25,7 +25,7 @@ NCR5380::NCR5380(SCSI::Bus &bus, const int clock_rate) :
 	bus_(bus),
 	clock_rate_(clock_rate) {
 	device_id_ = bus_.add_device();
-	bus_.add_observer(this);
+	bus_.add_observer(*this);
 
 	// TODO: use clock rate and expected phase. This implementation currently
 	// provides only CPU-driven polling behaviour.
@@ -36,7 +36,7 @@ NCR5380::NCR5380(SCSI::Bus &bus, const int clock_rate) :
 void NCR5380::write(const int address, const uint8_t value, bool) {
 	switch(address & 7) {
 		case 0:
-			logger.info().append("[0] Set current SCSI bus state to %02x", value);
+			Logger::info().append("[0] Set current SCSI bus state to %02x", value);
 
 			data_bus_ = value;
 			if(dma_request_ && dma_operation_ == DMAOperation::Send) {
@@ -45,7 +45,7 @@ void NCR5380::write(const int address, const uint8_t value, bool) {
 		break;
 
 		case 1: {
-			logger.info().append("[1] Initiator command register set: %02x", value);
+			Logger::info().append("[1] Initiator command register set: %02x", value);
 			initiator_command_ = value;
 
 			bus_output_ &= ~(Line::Reset | Line::Acknowledge | Line::Busy | Line::SelectTarget | Line::Attention);
@@ -61,7 +61,7 @@ void NCR5380::write(const int address, const uint8_t value, bool) {
 		} break;
 
 		case 2:
-			logger.info().append("[2] Set mode: %02x", value);
+			Logger::info().append("[2] Set mode: %02x", value);
 			mode_ = value;
 
 			// bit 7: 1 = use block mode DMA mode (if DMA mode is also enabled)
@@ -102,27 +102,27 @@ void NCR5380::write(const int address, const uint8_t value, bool) {
 		break;
 
 		case 3:
-			logger.info().append("[3] Set target command: %02x", value);
+			Logger::info().append("[3] Set target command: %02x", value);
 			target_command_ = value;
 			update_control_output();
 		break;
 
 		case 4:
-			logger.info().append("[4] Set select enabled: %02x", value);
+			Logger::info().append("[4] Set select enabled: %02x", value);
 		break;
 
 		case 5:
-			logger.info().append("[5] Start DMA send: %02x", value);
+			Logger::info().append("[5] Start DMA send: %02x", value);
 			dma_operation_ = DMAOperation::Send;
 		break;
 
 		case 6:
-			logger.info().append("[6] Start DMA target receive: %02x", value);
+			Logger::info().append("[6] Start DMA target receive: %02x", value);
 			dma_operation_ = DMAOperation::TargetReceive;
 		break;
 
 		case 7:
-			logger.info().append("[7] Start DMA initiator receive: %02x", value);
+			Logger::info().append("[7] Start DMA initiator receive: %02x", value);
 			dma_operation_ = DMAOperation::InitiatorReceive;
 		break;
 	}
@@ -146,15 +146,15 @@ void NCR5380::write(const int address, const uint8_t value, bool) {
 uint8_t NCR5380::read(const int address, bool) {
 	switch(address & 7) {
 		case 0:
-			logger.info().append("[0] Get current SCSI bus state: %02x", (bus_.get_state() & 0xff));
+			Logger::info().append("[0] Get current SCSI bus state: %02x", (bus_.state() & 0xff));
 
 			if(dma_request_ && dma_operation_ == DMAOperation::InitiatorReceive) {
 				return dma_acknowledge();
 			}
-		return uint8_t(bus_.get_state());
+		return uint8_t(bus_.state());
 
 		case 1:
-			logger.info().append(
+			Logger::info().append(
 				"[1] Initiator command register get: %c%c",
 				arbitration_in_progress_ ? 'p' : '-',
 				lost_arbitration_ ? 'l' : '-');
@@ -169,15 +169,15 @@ uint8_t NCR5380::read(const int address, bool) {
 			(lost_arbitration_ ? 0x20 : 0x00);
 
 		case 2:
-			logger.info().append("[2] Get mode");
+			Logger::info().append("[2] Get mode");
 		return mode_;
 
 		case 3:
-			logger.info().append("[3] Get target command");
+			Logger::info().append("[3] Get target command");
 		return target_command_;
 
 		case 4: {
-			const auto bus_state = bus_.get_state();
+			const auto bus_state = bus_.state();
 			const uint8_t result =
 				((bus_state & Line::Reset)			? 0x80 : 0x00) |
 				((bus_state & Line::Busy)			? 0x40 : 0x00) |
@@ -187,12 +187,12 @@ uint8_t NCR5380::read(const int address, bool) {
 				((bus_state & Line::Input)			? 0x04 : 0x00) |
 				((bus_state & Line::SelectTarget)	? 0x02 : 0x00) |
 				((bus_state & Line::Parity)			? 0x01 : 0x00);
-			logger.info().append("[4] Get current bus state: %02x", result);
+			Logger::info().append("[4] Get current bus state: %02x", result);
 			return result;
 		}
 
 		case 5: {
-			const auto bus_state = bus_.get_state();
+			const auto bus_state = bus_.state();
 			const uint8_t result =
 				(end_of_dma_ ? 0x80 : 0x00) |
 				((dma_request_ && state_ == ExecutionState::PerformingDMA) ? 0x40 : 0x00)	|
@@ -202,16 +202,16 @@ uint8_t NCR5380::read(const int address, bool) {
 				/* b2 = busy error */
 				((bus_state & Line::Attention) ? 0x02 : 0x00) |
 				((bus_state & Line::Acknowledge) ? 0x01 : 0x00);
-			logger.info().append("[5] Get bus and status: %02x", result);
+			Logger::info().append("[5] Get bus and status: %02x", result);
 			return result;
 		}
 
 		case 6:
-			logger.info().append("[6] Get input data");
+			Logger::info().append("[6] Get input data");
 		return 0xff;
 
 		case 7:
-			logger.info().append("[7] Reset parity/interrupt");
+			Logger::info().append("[7] Reset parity/interrupt");
 			irq_ = false;
 		return 0xff;
 	}
@@ -242,7 +242,7 @@ void NCR5380::update_control_output() {
 	}
 }
 
-void NCR5380::scsi_bus_did_change(SCSI::Bus *, const SCSI::BusState new_state, const double time_since_change) {
+void NCR5380::scsi_bus_did_change(SCSI::Bus &, const SCSI::BusState new_state, const double time_since_change) {
 	/*
 		When connected as an Initiator with DMA Mode True,
 		if the phase lines I//O, C//D, and /MSG do not match the
@@ -350,7 +350,7 @@ bool NCR5380::dma_request() {
 }
 
 uint8_t NCR5380::dma_acknowledge() {
-	const uint8_t bus_state = uint8_t(bus_.get_state());
+	const uint8_t bus_state = uint8_t(bus_.state());
 
 	dma_acknowledge_ = true;
 	dma_request_ = false;
@@ -370,7 +370,7 @@ void NCR5380::dma_acknowledge(const uint8_t value) {
 }
 
 bool NCR5380::phase_matches() const {
-	const auto bus_state = bus_.get_state();
+	const auto bus_state = bus_.state();
 	return
 		(target_output() & (Line::Message | Line::Control | Line::Input)) ==
 		(bus_state & (Line::Message | Line::Control | Line::Input));

Components/5380/ncr5380.hpp

@@ -78,7 +78,7 @@ private:
 	SCSI::BusState target_output() const;
 	void update_control_output();
 
-	void scsi_bus_did_change(SCSI::Bus *, SCSI::BusState new_state, double time_since_change) final;
+	void scsi_bus_did_change(SCSI::Bus &, SCSI::BusState, double) final;
 	bool phase_matches() const;
 };
 

Components/6522/6522.hpp

@@ -60,10 +60,9 @@ public:
 */
 class IRQDelegatePortHandler: public PortHandler {
 public:
-	class Delegate {
-		public:
-			/// Indicates that the interrupt status has changed for the IRQDelegatePortHandler provided.
-			virtual void mos6522_did_change_interrupt_status(void *irq_delegate) = 0;
+	struct Delegate {
+		/// Indicates that the interrupt status has changed for the IRQDelegatePortHandler provided.
+		virtual void mos6522_did_change_interrupt_status(void *irq_delegate) = 0;
 	};
 
 	/// Sets the delegate that will receive notification of changes in the interrupt line.

Components/6522/Implementation/6522Implementation.hpp

@@ -23,7 +23,7 @@ template <typename T> void MOS6522<T>::access(const int address) {
 			}
 		break;
 
-		case 0xf:
+//		case 0xf:
 		case 0x1:
 			// In both handshake and pulse modes, CA2 goes low on any read or write of Port A.
 			if(handshake_modes_[0] != HandshakeMode::None) {
@@ -57,14 +57,17 @@ template <typename T> void MOS6522<T>::write(int address, const uint8_t value) {
 			bus_handler_.run_for(time_since_bus_handler_call_.flush<HalfCycles>());
 			bus_handler_.template set_port_output<Port::A>(value, registers_.data_direction[0]);
 
-			if(handshake_modes_[1] != HandshakeMode::None) {
-				set_control_line_output<Port::A, Line::Two>(LineState::Off);
-			}
+			// Avoid handshaking if this was via address 0xf.
+			if(address == 0x1) {
+				if(handshake_modes_[1] != HandshakeMode::None) {
+					set_control_line_output<Port::A, Line::Two>(LineState::Off);
+				}
 
-			registers_.interrupt_flags &= ~(
-				InterruptFlag::CA1ActiveEdge |
-				((registers_.peripheral_control&0x02) ? 0 : InterruptFlag::CB2ActiveEdge)
-			);
+				registers_.interrupt_flags &= ~(
+					InterruptFlag::CA1ActiveEdge |
+					((registers_.peripheral_control&0x02) ? 0 : InterruptFlag::CB2ActiveEdge)
+				);
+			}
 			reevaluate_interrupts();
 		break;
 
@@ -144,10 +147,11 @@ template <typename T> void MOS6522<T>::write(int address, const uint8_t value) {
 			reevaluate_interrupts();
 		break;
 		case 0xe:	// Interrupt enable register ('IER').
-			if(value&0x80)
+			if(value&0x80) {
 				registers_.interrupt_enable |= value;
-			else
+			} else {
 				registers_.interrupt_enable &= ~value;
+			}
 			reevaluate_interrupts();
 		break;
 	}
@@ -195,9 +199,10 @@ template <typename T> uint8_t MOS6522<T>::read(int address) {
 			registers_.interrupt_flags &= ~(InterruptFlag::CB1ActiveEdge | InterruptFlag::CB2ActiveEdge);
 			reevaluate_interrupts();
 		return get_port_input<Port::B>(registers_.data_direction[1], registers_.output[1], registers_.auxiliary_control & 0x80);
-		case 0xf:
-		case 0x1:	// Read Port A ('IRA').
+		case 0x1:	// Read Port A ('IRA') [with handshaking].
 			registers_.interrupt_flags &= ~(InterruptFlag::CA1ActiveEdge | InterruptFlag::CA2ActiveEdge);
+			[[fallthrough]];
+		case 0xf:	// Read Port A ('IRA') [without handshaking].
 			reevaluate_interrupts();
 		return get_port_input<Port::A>(registers_.data_direction[0], registers_.output[0], 0);
 
@@ -245,8 +250,10 @@ uint8_t MOS6522<T>::get_port_input(
 ) {
 	bus_handler_.run_for(time_since_bus_handler_call_.flush<HalfCycles>());
 	const uint8_t input = bus_handler_.template get_port_input<port>();
-	output = (output & ~timer_mask) | (registers_.timer_port_b_output & timer_mask);
-	return (input & ~output_mask) | (output & output_mask);
+
+	// Force any timer-adjusted PB7 to be visible even if the pin is set as input.
+	output = (input & ~output_mask) | (output & output_mask);
+	return (output & ~timer_mask) | (registers_.timer_port_b_output & timer_mask);
 }
 
 template <typename T> T &MOS6522<T>::bus_handler() {

Components/6526/6526.hpp

@@ -83,7 +83,7 @@ private:
 
 	bool serial_line_did_produce_bit(Serial::Line<true> *line, int bit) final;
 
-	Log::Logger<Log::Source::MOS6526> log;
+	using Logger = Log::Logger<Log::Source::MOS6526>;
 };
 
 }

Components/6526/Implementation/6526Implementation.hpp

@@ -129,7 +129,7 @@ void MOS6526<BusHandlerT, personality>::write(int address, const uint8_t value)
 
 		// Shift control.
 		case 12:
-			log.error().append("TODO: write to shift register");
+			Logger::error().append("TODO: write to shift register");
 		break;
 
 		// Logically unreachable.

Components/6526/Implementation/6526Storage.hpp

@@ -125,11 +125,11 @@ private:
 	uint32_t alarm_ = 0xff'ffff;
 
 public:
-	template <int byte> void write(uint8_t v) {
+	template <int byte> void write(const uint8_t v) {
 		if constexpr (byte == 3) {
 			return;
 		}
-		constexpr int shift = byte << 3;
+		static constexpr int shift = byte << 3;
 
 		// Write to either the alarm or the current value as directed;
 		// writing to any part of the current value other than the LSB
@@ -147,7 +147,7 @@ public:
 		if constexpr (byte == 3) {
 			return 0xff;	// Assumed. Just a guess.
 		}
-		constexpr int shift = byte << 3;
+		static constexpr int shift = byte << 3;
 
 		if constexpr (byte == 2) {
 			latch_ = value_ | 0xff00'0000;
@@ -163,7 +163,7 @@ public:
 		return result;
 	}
 
-	bool advance(int count) {
+	bool advance(const int count) {
 		// The 8250 uses a simple binary counter to replace the
 		// 6526's time-of-day clock. So this is easy.
 		const uint32_t distance_to_alarm = (alarm_ - value_) & 0xff'ffff;
@@ -221,8 +221,7 @@ struct MOS6526Storage {
 			control = v;
 
 			if(v&2) {
-				Log::Logger<Log::Source::MOS6526> log;
-				log.error().append("UNIMPLEMENTED: PB strobe");
+				Log::Logger<Log::Source::MOS6526>::error().append("UNIMPLEMENTED: PB strobe");
 			}
 		}
 

Components/6560/6560.cpp

@@ -12,10 +12,9 @@
 
 using namespace MOS::MOS6560;
 
-AudioGenerator::AudioGenerator(Concurrency::AsyncTaskQueue<false> &audio_queue) :
+AudioGenerator::AudioGenerator(Outputs::Speaker::TaskQueue &audio_queue) :
 	audio_queue_(audio_queue) {}
 
-
 void AudioGenerator::set_volume(const uint8_t volume) {
 	audio_queue_.enqueue([this, volume]() {
 		volume_ = int16_t(volume) * range_multiplier_;
@@ -97,19 +96,29 @@ constexpr uint8_t noise_pattern[] = {
 	0xf0, 0xe1, 0xe0, 0x78, 0x70, 0x38, 0x3c, 0x3e, 0x1e, 0x3c, 0x1e, 0x1c, 0x70, 0x3c, 0x38, 0x3f,
 };
 
-#define shift(r) shift_registers_[r] = \
-	(shift_registers_[r] << 1) | (((shift_registers_[r]^0x80)&control_registers_[r]) >> 7)
-#define increment(r) shift_registers_[r] = (shift_registers_[r]+1)%8191
-#define update(r, m, up) \
-	counters_[r]++; if((counters_[r] >> m) == 0x80) { up(r); counters_[r] = unsigned(control_registers_[r]&0x7f) << m; }
-// Note on slightly askew test: as far as I can make out, if the value in the register is 0x7f then what's supposed to
-// happen is that the 0x7f is loaded, on the next clocked cycle the Vic spots a 0x7f, pumps the output, reloads, etc. No
-// increment ever occurs. It's conditional. I don't really want two conditionals if I can avoid it so I'm incrementing
-// regardless and testing against 0x80. The effect should be the same: loading with 0x7f means an output update every
-// cycle, loading with 0x7e means every second cycle, etc.
-
 template <Outputs::Speaker::Action action>
 void AudioGenerator::apply_samples(const std::size_t number_of_samples, Outputs::Speaker::MonoSample *const target) {
+	const auto shift = [&](const int r) {
+		shift_registers_[r] =
+			(shift_registers_[r] << 1) | (((shift_registers_[r] ^ 0x80) & control_registers_[r]) >> 7);
+	};
+	const auto increment = [&](const int r) {
+		shift_registers_[r] = (shift_registers_[r] + 1) % 8191;
+	};
+	const auto update = [&](const int r, const int m, auto &&up) {
+		++counters_[r];
+
+		if((counters_[r] >> m) == 0x80) {
+			up(r);
+			counters_[r] = unsigned(control_registers_[r]&0x7f) << m;
+		}
+		// Note on slightly askew test: as far as I can make out, if the value in the register is 0x7f then what's
+		// supposed to happen is that the 0x7f is loaded, on the next clocked cycle the Vic spots a 0x7f, pumps the
+		// output, reloads, etc. No increment ever occurs. It's conditional. I don't really want two conditionals if I
+		// can avoid it so I'm incrementing regardless and testing against 0x80. The effect should be the same: loading
+		// with 0x7f means an output update every cycle, loading with 0x7e means every second cycle, etc.
+	};
+
 	for(unsigned int c = 0; c < number_of_samples; ++c) {
 		update(0, 2, shift);
 		update(1, 1, shift);
@@ -138,7 +147,7 @@ template void AudioGenerator::apply_samples<Outputs::Speaker::Action::Store>(
 template void AudioGenerator::apply_samples<Outputs::Speaker::Action::Ignore>(
 	std::size_t, Outputs::Speaker::MonoSample *);
 
-void AudioGenerator::set_sample_volume_range(std::int16_t range) {
+void AudioGenerator::set_sample_volume_range(const std::int16_t range) {
 	range_multiplier_ = int16_t(range / 64);
 }
 

Components/6560/6560.hpp

@@ -19,7 +19,7 @@ namespace MOS::MOS6560 {
 // audio state
 class AudioGenerator: public Outputs::Speaker::BufferSource<AudioGenerator, false> {
 public:
-	AudioGenerator(Concurrency::AsyncTaskQueue<false> &audio_queue);
+	AudioGenerator(Outputs::Speaker::TaskQueue &audio_queue);
 
 	void set_volume(uint8_t);
 	void set_control(int channel, uint8_t value);
@@ -30,7 +30,7 @@ public:
 	void set_sample_volume_range(std::int16_t);
 
 private:
-	Concurrency::AsyncTaskQueue<false> &audio_queue_;
+	Outputs::Speaker::TaskQueue &audio_queue_;
 
 	unsigned int counters_[4] = {2, 1, 0, 0};	// create a slight phase offset for the three channels
 	unsigned int shift_registers_[4] = {0, 0, 0, 0};
@@ -64,8 +64,7 @@ public:
 	MOS6560(BusHandler &bus_handler) :
 			bus_handler_(bus_handler),
 			crt_(65*4, 1, Outputs::Display::Type::NTSC60, Outputs::Display::InputDataType::Luminance8Phase8),
-			audio_generator_(audio_queue_),
-			speaker_(audio_generator_)
+			audio_(Cycles(4))
 	{
 		// default to s-video output
 		crt_.set_display_type(Outputs::Display::DisplayType::SVideo);
@@ -75,11 +74,11 @@ public:
 	}
 
 	~MOS6560() {
-		audio_queue_.flush();
+		audio_.stop();
 	}
 
 	void set_clock_rate(const double clock_rate) {
-		speaker_.set_input_rate(float(clock_rate / 4.0));
+		audio_.speaker().set_input_rate(float(clock_rate / 4.0));
 	}
 
 	void set_scan_target(Outputs::Display::ScanTarget *const scan_target) {
@@ -95,11 +94,11 @@ public:
 		return crt_.get_display_type();
 	}
 	Outputs::Speaker::Speaker *get_speaker() {
-		return &speaker_;
+		return &audio_.speaker();
 	}
 
 	void set_high_frequency_cutoff(const float cutoff) {
-		speaker_.set_high_frequency_cutoff(cutoff);
+		audio_.speaker().set_high_frequency_cutoff(cutoff);
 	}
 
 	/*!
@@ -161,10 +160,10 @@ public:
 
 		switch(output_mode) {
 			case OutputMode::PAL:
-				crt_.set_visible_area(Outputs::Display::Rect(0.1f, 0.07f, 0.9f, 0.9f));
+				crt_.set_fixed_framing(Outputs::Display::Rect(0.1f, 0.07f, 0.9f, 0.9f));
 			break;
 			case OutputMode::NTSC:
-				crt_.set_visible_area(Outputs::Display::Rect(0.05f, 0.05f, 0.9f, 0.9f));
+				crt_.set_fixed_framing(Outputs::Display::Rect(0.05f, 0.05f, 0.9f, 0.9f));
 			break;
 		}
 
@@ -180,7 +179,7 @@ public:
 	*/
 	inline void run_for(const Cycles cycles) {
 		// keep track of the amount of time since the speaker was updated; lazy updates are applied
-		cycles_since_speaker_update_ += cycles;
+		audio_ += cycles;
 
 		auto number_of_cycles = cycles.as_integral();
 		while(number_of_cycles--) {
@@ -377,8 +376,7 @@ public:
 		Causes the 6560 to flush as much pending CRT and speaker communications as possible.
 	*/
 	inline void flush() {
-		update_audio();
-		audio_queue_.perform();
+		audio_.perform();
 	}
 
 	/*!
@@ -420,14 +418,12 @@ public:
 			case 0xb:
 			case 0xc:
 			case 0xd:
-				update_audio();
-				audio_generator_.set_control(address - 0xa, value);
+				audio_->set_control(address - 0xa, value);
 			break;
 
 			case 0xe:
-				update_audio();
 				registers_.auxiliary_colour = colours_[value >> 4];
-				audio_generator_.set_volume(value & 0xf);
+				audio_->set_volume(value & 0xf);
 			break;
 
 			case 0xf: {
@@ -467,14 +463,7 @@ private:
 	BusHandler &bus_handler_;
 	Outputs::CRT::CRT crt_;
 
-	Concurrency::AsyncTaskQueue<false> audio_queue_;
-	AudioGenerator audio_generator_;
-	Outputs::Speaker::PullLowpass<AudioGenerator> speaker_;
-
-	Cycles cycles_since_speaker_update_;
-	void update_audio() {
-		speaker_.run_for(audio_queue_, Cycles(cycles_since_speaker_update_.divide(Cycles(4))));
-	}
+	Outputs::Speaker::PullLowpassSpeakerQueue<Cycles, AudioGenerator> audio_;
 
 	// register state
 	struct {

Components/6845/CRTC6845.hpp

@@ -9,28 +9,43 @@
 #pragma once
 
 #include "ClockReceiver/ClockReceiver.hpp"
+#include "Numeric/SizedInt.hpp"
 
 #include <cstdint>
 #include <cstdio>
 
+//
+// WARNING: code is in flux. I'm attempting to use hoglet's FPGA implementation at
+// https://github.com/hoglet67/BeebFpga/blob/master/src/common/mc6845.vhd as an authoritative guide to proper behaviour,
+// having found his Electron ULA to be excellent. This is starting by mapping various bits of internal state here
+// to hoglet's equivalents; cf. comments.
+//
+
 namespace Motorola::CRTC {
 
+using RefreshAddress = Numeric::SizedInt<14>;
+using LineAddress = Numeric::SizedInt<5>;
+
+using SyncCounter = Numeric::SizedInt<4>;
+using CharacterAddress = Numeric::SizedInt<8>;
+using RowAddress = Numeric::SizedInt<7>;
+
 struct BusState {
 	bool display_enable = false;
-	bool hsync = false;
-	bool vsync = false;
+	bool hsync = false;		// hs
+	bool vsync = false;		// vs
 	bool cursor = false;
-	uint16_t refresh_address = 0;
-	uint16_t row_address = 0;
+	RefreshAddress refresh;
+	LineAddress line;
 
 	// Not strictly part of the bus state; provided because the partition between 6845 and bus handler
 	// doesn't quite hold up in some emulated systems where the two are integrated and share more state.
-	int field_count = 0;
+	Numeric::SizedInt<5> field_count = 0;		// field_counter
 };
 
 class BusHandler {
-	public:
-		void perform_bus_cycle(const BusState &) {}
+public:
+	void perform_bus_cycle(const BusState &) {}
 };
 
 enum class Personality {
@@ -39,14 +54,8 @@ enum class Personality {
 	UM6845R,	// Type 1 in CPC parlance. Status register, fixed-length VSYNC.
 	MC6845,		// Type 2. No status register, fixed-length VSYNC, no zero-length HSYNC.
 	AMS40226,	// Type 3. Status is get register, fixed-length VSYNC, no zero-length HSYNC.
-
-	EGA,		// Extended EGA-style CRTC; uses 16-bit addressing throughout.
 };
 
-constexpr bool is_egavga(const Personality p) {
-	return p >= Personality::EGA;
-}
-
 // https://www.pcjs.org/blog/2018/03/20/ advises that "the behavior of bits 5 and 6 [of register 10, the cursor start
 // register is really card specific".
 //
@@ -54,10 +63,10 @@ constexpr bool is_egavga(const Personality p) {
 enum class CursorType {
 	/// No cursor signal is generated.
 	None,
+	/// Built-in 6845 style: 00 => no blinking; 01 => no cursor; 10 => slow blink; 11 => fast blink
+	Native,
 	/// MDA style: 00 => symmetric blinking; 01 or 10 => no blinking; 11 => short on, long off.
 	MDA,
-	/// EGA style: ignore the bits completely.
-	EGA,
 };
 
 // TODO UM6845R and R12/R13; see http://www.cpcwiki.eu/index.php/CRTC#CRTC_Differences
@@ -67,7 +76,7 @@ public:
 	CRTC6845(BusHandlerT &bus_handler) noexcept :
 		bus_handler_(bus_handler), status_(0) {}
 
-	void select_register(uint8_t r) {
+	void select_register(const uint8_t r) {
 		selected_register_ = r;
 	}
 
@@ -85,65 +94,64 @@ public:
 		if(selected_register_ == 16 || selected_register_ == 17) status_ &= ~0x40;
 
 		if(personality == Personality::UM6845R && selected_register_ == 31) return dummy_register_;
-		if(selected_register_ < 12 || selected_register_ > 17) return 0xff;
-		return registers_[selected_register_];
+
+		// Registers below 12 are write-only; no registers are defined above position 17
+		// (other than the UM6845R-specific test register as per above).
+		//
+		// Per the BBC Wiki, attempting to read such a register results in 0.
+		if(selected_register_ < 12 || selected_register_ > 17) return 0x00;
+
+		return registers_[selected_register_.get()];
 	}
 
 	void set_register(const uint8_t value) {
-		static constexpr bool is_ega = is_egavga(personality);
-
-		const auto load_low = [value](uint16_t &target) {
-			target = (target & 0xff00) | value;
-		};
-		const auto load_high = [value](uint16_t &target) {
-			constexpr uint8_t mask = RefreshMask >> 8;
-			target = uint16_t((target & 0x00ff) | ((value & mask) << 8));
-		};
-
-		switch(selected_register_) {
+		switch(selected_register_.get()) {
 			case 0:	layout_.horizontal.total = value;		break;
 			case 1: layout_.horizontal.displayed = value;	break;
 			case 2:	layout_.horizontal.start_sync = value;	break;
 			case 3:
-				layout_.horizontal.sync_width = value & 0xf;
+				layout_.horizontal.sync_width = value;
 				layout_.vertical.sync_lines = value >> 4;
 				// TODO: vertical sync lines:
 				// "(0 means 16 on some CRTC. Not present on all CRTCs, fixed to 16 lines on these)"
 			break;
-			case 4:	layout_.vertical.total = value & 0x7f;		break;
-			case 5:	layout_.vertical.adjust = value & 0x1f;		break;
-			case 6:	layout_.vertical.displayed = value & 0x7f;	break;
-			case 7:	layout_.vertical.start_sync = value & 0x7f;	break;
+			case 4:	layout_.vertical.total = value;			break;
+			case 5:	layout_.vertical.adjust = value;		break;
+			case 6:	layout_.vertical.displayed = value;		break;
+			case 7:	layout_.vertical.start_sync = value;	break;
 			case 8:
 				switch(value & 3) {
-					default:	layout_.interlace_mode_ = InterlaceMode::Off;					break;
-					case 0b01:	layout_.interlace_mode_ = InterlaceMode::InterlaceSync;			break;
-					case 0b11:	layout_.interlace_mode_ = InterlaceMode::InterlaceSyncAndVideo;	break;
+					default:	layout_.interlace_mode_ = InterlaceMode::Off;			break;
+					case 0b01:	layout_.interlace_mode_ = InterlaceMode::Sync;			break;
+					case 0b11:	layout_.interlace_mode_ = InterlaceMode::SyncAndVideo;	break;
 				}
 
 				// Per CPC documentation, skew doesn't work on a "type 1 or 2", i.e. an MC6845 or a UM6845R.
-				if(personality != Personality::UM6845R && personality != Personality::MC6845) {
-					switch((value >> 4)&3) {
-						default:	display_skew_mask_ = 1;		break;
-						case 1:		display_skew_mask_ = 2;		break;
-						case 2:		display_skew_mask_ = 4;		break;
-					}
-				}
+//				if(personality != Personality::UM6845R && personality != Personality::MC6845) {
+//					switch((value >> 4)&3) {
+//						default:	display_skew_mask_ = 1;		break;
+//						case 1:		display_skew_mask_ = 2;		break;
+//						case 2:		display_skew_mask_ = 4;		break;
+//					}
+//				}
 			break;
-			case 9:	layout_.vertical.end_row = value & 0x1f;	break;
+			case 9:	layout_.vertical.end_line = value;	break;
 			case 10:
-				layout_.vertical.start_cursor = value & 0x1f;
-				layout_.cursor_flags = (value >> 5) & 3;
+				layout_.vertical.start_cursor = value;
+				layout_.cursor_flags = value >> 5;
+				update_cursor_mask();
 			break;
 			case 11:
-				layout_.vertical.end_cursor = value & 0x1f;
+				layout_.vertical.end_cursor = value;
 			break;
-			case 12:	load_high(layout_.start_address);	break;
-			case 13:	load_low(layout_.start_address);	break;
-			case 14:	load_high(layout_.cursor_address);	break;
-			case 15:	load_low(layout_.cursor_address);	break;
+			case 12:	layout_.start_address.template load<8>(value);	break;
+			case 13:	layout_.start_address.template load<0>(value);	break;
+			case 14:	layout_.cursor_address.template load<8>(value);	break;
+			case 15:	layout_.cursor_address.template load<0>(value);	break;
 		}
 
+		// Take redundant copies of all registers, limited to their actual bit sizes,
+		// to proffer up if the registers are read.
 		static constexpr uint8_t masks[] = {
 			0xff,	// Horizontal total.
 			0xff,	// Horizontal display end.
@@ -152,24 +160,24 @@ public:
 					// EGA: b0–b4: end of horizontal blank;
 					// b5–b6: "Number of character clocks to delay start of display after Horizontal Total has been reached."
 
-			is_ega ? 0xff : 0x7f,	// Start horizontal retrace.
+			0x7f,	// Start horizontal retrace.
 			0x1f, 0x7f, 0x7f,
-			0xff, 0x1f, 0x7f, 0x1f,
-			uint8_t(RefreshMask >> 8), uint8_t(RefreshMask),
-			uint8_t(RefreshMask >> 8), uint8_t(RefreshMask),
+			0xfc, 0x1f, 0x7f, 0x1f,
+			uint8_t(RefreshAddress::Mask >> 8), uint8_t(RefreshAddress::Mask),
+			uint8_t(RefreshAddress::Mask >> 8), uint8_t(RefreshAddress::Mask),
 		};
 
 		if(selected_register_ < 16) {
-			registers_[selected_register_] = value & masks[selected_register_];
+			registers_[selected_register_.get()] = value & masks[selected_register_.get()];
 		}
-		if(selected_register_ == 31 && personality == Personality::UM6845R) {
+		if(selected_register_.get() == 31 && personality == Personality::UM6845R) {
 			dummy_register_ = value;
 		}
 	}
 
 	void trigger_light_pen() {
-		registers_[17] = bus_state_.refresh_address & 0xff;
-		registers_[16] = bus_state_.refresh_address >> 8;
+		registers_[17] = bus_state_.refresh.get() & 0xff;
+		registers_[16] = bus_state_.refresh.get() >> 8;
 		status_ |= 0x40;
 	}
 
@@ -180,179 +188,291 @@ public:
 			// ordered so that whatever assignments result don't affect any subsequent conditionals
 
 
-			// Do bus work.
-			bus_state_.cursor = is_cursor_line_ &&
-				bus_state_.refresh_address == layout_.cursor_address;
-			bus_state_.display_enable = character_is_visible_ && line_is_visible_;
-			bus_handler_.perform_bus_cycle(bus_state_);
+			//
+			// External bus activity.
+			//
+				bus_state_.line = line_is_interlaced_ ? (line_ & LineAddress::IntT(~1)) | (odd_field_ ? 1 : 0) : line_;
+				bus_state_.display_enable = character_is_visible_ && row_is_visible_;
+				bus_state_.cursor = (cursor_mask_ && is_cursor_line_ && bus_state_.refresh == layout_.cursor_address)
+					&& bus_state_.display_enable;
+
+				bus_handler_.perform_bus_cycle(bus_state_);
+
+				bus_state_.refresh = refresh_;	// Deliberate: do this after bus activity.
+												// TODO: is this a hack?
+
 
 			//
-			// Shared, stateless signals.
+			// Shared signals.
 			//
-				const bool character_total_hit = character_counter_ == layout_.horizontal.total;
-				const uint8_t lines_per_row =
-					layout_.interlace_mode_ == InterlaceMode::InterlaceSyncAndVideo ?
-						layout_.vertical.end_row & ~1 : layout_.vertical.end_row;
-				const bool row_end_hit = bus_state_.row_address == lines_per_row && !is_in_adjustment_period_;
-				const bool was_eof = eof_latched_;
+				const bool character_total_hit = character_counter_ == layout_.horizontal.total;		// r00_h_total_hit
+				const auto lines_per_row =
+					layout_.interlace_mode_ == InterlaceMode::SyncAndVideo ?
+						layout_.vertical.end_line & LineAddress::IntT(~1) : layout_.vertical.end_line;	// max_scanline
+				const bool line_end_hit = line_ == lines_per_row && !is_in_adjustment_period_;	// max_scanline_hit
 				const bool new_frame =
-					character_total_hit && was_eof &&
+					character_total_hit && eof_latched_ &&
 					(
 						layout_.interlace_mode_ == InterlaceMode::Off ||
-						!odd_field_
-					);
+						!bus_state_.field_count.bit<0>() ||
+						extra_line_
+					);		// new_frame
 
-			//
-			// Horizontal.
-			//
-
-				// Update horizontal sync.
-				if(bus_state_.hsync) {
-					++hsync_counter_;
-					bus_state_.hsync = hsync_counter_ != layout_.horizontal.sync_width;
-				}
-				if(character_counter_ == layout_.horizontal.start_sync) {
-					hsync_counter_ = 0;
-					bus_state_.hsync = true;
-				}
-
-				// Check for end-of-line.
-				character_reset_history_ <<= 1;
-				if(character_total_hit) {
-					character_counter_ = 0;
-					character_is_visible_ = true;
-					character_reset_history_ |= 1;
-				} else {
-					character_counter_++;
-				}
-
-				// Check for end of visible characters.
-				if(character_counter_ == layout_.horizontal.displayed) {
-					character_is_visible_ = false;
-				}
-
-			//
-			// End-of-frame.
-			//
-
-				if(character_total_hit) {
-					if(was_eof) {
-						eof_latched_ = eom_latched_ = is_in_adjustment_period_ = false;
-						adjustment_counter_ = 0;
-					} else if(is_in_adjustment_period_) {
-						adjustment_counter_ = (adjustment_counter_ + 1) & 31;
-					}
-				}
-
-				if(character_reset_history_ & 2) {
-					eom_latched_ |= row_end_hit && row_counter_ == layout_.vertical.total;
-				}
-
-				if(character_reset_history_ & 4 && eom_latched_) {
-					// TODO: I don't believe the "add 1 for interlaced" test here is accurate;
-					// others represent the extra scanline as additional state, presumably because
-					// adjust total might be reprogrammed at any time.
-					const auto adjust_length =
-						layout_.vertical.adjust + (layout_.interlace_mode_ != InterlaceMode::Off && odd_field_ ? 1 : 0);
-					is_in_adjustment_period_ |= adjustment_counter_ != adjust_length;
-					eof_latched_ |= adjustment_counter_ == adjust_length;
-				}
-
-			//
-			// Vertical.
-			//
-
-				// Sync.
-				const bool vsync_horizontal =
-					(!odd_field_ && !character_counter_) ||
-					(odd_field_ && character_counter_ == (layout_.horizontal.total >> 1));
-				if(vsync_horizontal) {
-					if((row_counter_ == layout_.vertical.start_sync && !bus_state_.row_address) || bus_state_.vsync) {
-						bus_state_.vsync = true;
-						vsync_counter_ = (vsync_counter_ + 1) & 0xf;
-					} else {
-						vsync_counter_ = 0;
-					}
-
-					if(vsync_counter_ == layout_.vertical.sync_lines) {
-						bus_state_.vsync = false;
-					}
-				}
-
-				// Row address.
-				if(character_total_hit) {
-					if(was_eof) {
-						bus_state_.row_address = 0;
-						eof_latched_ = eom_latched_ = false;
-					} else if(row_end_hit) {
-						bus_state_.row_address = 0;
-					} else if(layout_.interlace_mode_ == InterlaceMode::InterlaceSyncAndVideo) {
-						bus_state_.row_address = (bus_state_.row_address + 2) & ~1 & 31;
-					} else {
-						bus_state_.row_address = (bus_state_.row_address + 1) & 31;
-					}
-				}
-
-				// Row counter.
-				row_counter_ = next_row_counter_;
-				if(new_frame) {
-					next_row_counter_ = 0;
-					is_first_scanline_ = true;
-				} else {
-					next_row_counter_ = row_end_hit && character_total_hit ?
-						(next_row_counter_ + 1) : next_row_counter_;
-					is_first_scanline_ &= !row_end_hit;
-				}
-
-				// Vertical display enable.
-				if(is_first_scanline_) {
-					line_is_visible_ = true;
-					odd_field_ = bus_state_.field_count & 1;
-				} else if(line_is_visible_ && row_counter_ == layout_.vertical.displayed) {
-					line_is_visible_ = false;
-					++bus_state_.field_count;
-				}
-
-
-				// Cursor.
-				if constexpr (cursor_type != CursorType::None) {
-					// Check for cursor enable.
-					is_cursor_line_ |= bus_state_.row_address == layout_.vertical.start_cursor;
-					is_cursor_line_ &= bus_state_.row_address != layout_.vertical.end_cursor;
-
-					switch(cursor_type) {
-						// MDA-style blinking.
-						// https://retrocomputing.stackexchange.com/questions/27803/what-are-the-blinking-rates-of-the-caret-and-of-blinking-text-on-pc-graphics-car
-						// gives an 8/8 pattern for regular blinking though mode 11 is then just a guess.
-						case CursorType::MDA:
-							switch(layout_.cursor_flags) {
-								case 0b11: is_cursor_line_ &= (bus_state_.field_count & 8) < 3;	break;
-								case 0b00: is_cursor_line_ &= bool(bus_state_.field_count & 8);	break;
-								case 0b01: is_cursor_line_ = false;								break;
-								case 0b10: is_cursor_line_ = true;								break;
-								default: break;
-							}
-						break;
-					}
-				}
 
 			//
 			// Addressing.
 			//
 
+				// Start-of-line address: seeded with the programmed display start address upon a new frame;
+				// otherwise copied from the refresh address at the end of each line of characters.
+				const auto initial_line_address = line_address_;
 				if(new_frame) {
-					bus_state_.refresh_address = layout_.start_address;
+					line_address_ = layout_.start_address;
+				} else if(character_counter_ == layout_.horizontal.displayed && line_end_hit) {
+					line_address_ = refresh_;
+				}
+
+				// Refresh address: seeded with the programmed display start address upon a new frame;
+				// otherwise copied from the start-of-line address is a new line is about to start;
+				// otherwise incremented across the line.
+				if(new_frame) {
+					refresh_ = layout_.start_address;
 				} else if(character_total_hit) {
-					bus_state_.refresh_address = line_address_;
+					refresh_ = initial_line_address;
 				} else {
-					bus_state_.refresh_address = (bus_state_.refresh_address + 1) & RefreshMask;
+					++refresh_;
+				}
+
+				//
+				// Per hoglet: b0 does not vary within a line even if you switch in/out of interlaced mode.
+				// He reproduces the same with extra state, which probably doesn't exist on the real device.
+				// This implementation follows his lead.
+				//
+				if(character_total_hit) {
+					line_is_interlaced_ = layout_.interlace_mode_ == InterlaceMode::SyncAndVideo;
+				}
+
+			//
+			// Sync.
+			//
+
+				// Vertical sync.
+				//
+				// Counter:
+				// Sync width of 0 => 16 lines of sync.
+				// Triggered by the row counter becoming equal to the sync start position, regardless of when.
+				// Subsequently increments at the start of each line.
+				const bool hit_vsync = row_counter_ == layout_.vertical.start_sync;		// vs_hit
+				const bool is_vsync_rising_edge = hit_vsync && !hit_vsync_last_;
+				hit_vsync_last_ = hit_vsync;
+
+				// Select odd or even sync depending on the field.
+				// (Noted: the reverse-odd-test is intentional)
+				bus_state_.vsync = (layout_.interlace_mode_ != InterlaceMode::Off && !odd_field_) ?
+					vsync_odd_ : vsync_even_;
+
+				// Odd sync copies even sync, but half a line later.
+				if(character_counter_ == layout_.horizontal.total >> 1) {
+					vsync_odd_ = vsync_even_;
+				}
+
+				// Even sync begins on the rising edge of vsync, then continues until the counter hits its proper
+				// target, one cycle after reset of the horizontal counter.
+				if(is_vsync_rising_edge) {
+					vsync_even_ = true;
+				} else if(vsync_counter_ == layout_.vertical.sync_lines && character_reset_history_.bit<0>()) {
+					vsync_even_ = false;
+				}
+
+				// The vsync counter is zeroed by the rising edge of sync but subsequently increments immediately
+				// upon reset of the horizontal counter.
+				if(is_vsync_rising_edge) {
+					vsync_counter_ = 0;
+				} else if(character_total_hit) {
+					++vsync_counter_;
+				}
+
+				// Horizontal sync.
+				//
+				// A sync width of 0 should mean that no sync is observed.
+				// Hitting the start sync condition while sync is already ongoing should have no effect.
+				if(bus_state_.hsync) {
+					++hsync_counter_;
+				} else {
+					hsync_counter_ = 0;
+				}
+				if(hsync_counter_ == layout_.horizontal.sync_width) {
+					bus_state_.hsync = false;
+				} else if(character_counter_ == layout_.horizontal.start_sync) {
+					bus_state_.hsync = true;
+				}
+
+
+			//
+			// Horizontal.
+			//
+
+				// Check for visible characters; visibility starts in the first column and continues
+				if(!character_counter_) {
+					character_is_visible_ = true;
+				}
+				if(character_counter_ == layout_.horizontal.displayed || character_total_hit) {
+					character_is_visible_ = false;
+				}
+
+				// Check for end-of-line.
+				//
+				// character_reset_history_ is used because some events are defined to occur one or two
+				// cycles after end-of-line regardless of whether an additional end of line is hit in
+				// the interim.
+				if(character_total_hit) {
+					character_counter_ = 0;
+				} else {
+					++character_counter_;
+				}
+
+
+			//
+			// Vertical.
+			//
+
+				// Update line counter (which also counts the vertical adjust period).
+				//
+				// Counts in steps of 2 only if & 3) mode is InterlaceMode::SyncAndVideo and this is
+				// not the adjustment period. Otherwise counts in steps of 1.
+				if(new_frame) {
+					line_ = 0;
+				} else if(character_total_hit) {
+					line_ = next_line_;
+				}
+
+				if(line_end_hit) {
+					next_line_ = 0;
+				} else if(is_in_adjustment_period_ || layout_.interlace_mode_ != InterlaceMode::SyncAndVideo) {
+					next_line_ = line_ + 1;
+				} else {
+					next_line_ = (line_ + 2) & LineAddress::IntT(~1);
+				}
+
+				// Update row counter.
+				//
+				// Very straightforward: tests at end of line whether row end has also been hit. If so, increments.
+				row_counter_ = next_row_counter_;
+				if(new_frame) {
+					next_row_counter_ = 0;
+				} else if(character_total_hit && line_end_hit) {
+					next_row_counter_ = row_counter_ + 1;
+				}
+
+				// Vertical display enable.
+				if(is_first_scanline_) {
+					row_is_visible_ = true;
+					odd_field_ = bus_state_.field_count.bit<0>();
+				} else if(row_is_visible_ && row_counter_ == layout_.vertical.displayed) {
+					row_is_visible_ = false;
+					++bus_state_.field_count;
+					update_cursor_mask();
+				}
+
+
+			//
+			// End-of-frame.
+			//
+
+				if(new_frame) {
+					is_in_adjustment_period_ = false;
+				} else if(character_total_hit && eom_latched_ && will_adjust_) {
+					is_in_adjustment_period_ = true;
 				}
 
 				if(new_frame) {
-					line_address_ = layout_.start_address;
-				} else if(character_counter_ == layout_.horizontal.displayed && row_end_hit) {
-					line_address_ = bus_state_.refresh_address;
+					is_first_scanline_ = true;
+				} else if(character_total_hit) {
+					is_first_scanline_ = false;
 				}
+
+				// The extra-line flag holds true for a single line if one is needed to complete
+				// an odd interlaced field.
+				if(
+					character_total_hit &&
+					eof_latched_ &&
+					layout_.interlace_mode_ != InterlaceMode::Off &&
+					bus_state_.field_count.bit<0>() &&
+					!extra_line_
+				) {
+					extra_line_ = true;
+				} else if(character_total_hit) {
+					extra_line_ = false;
+				}
+
+				// EOF (end of field) marks the end of the regular set of scans, including the adjustment area.
+				// It doesn't include the extra line added during odd interlaced fields.
+				if(new_frame) {
+					eof_latched_ = false;
+				} else if(eom_latched_ && !will_adjust_ && character_reset_history_.bit<2>()) {
+					eof_latched_ = true;
+				}
+
+				// Will-adjust indicates whether an adjustment area is upcoming; if so then it occurs after EOM.
+				if(new_frame) {
+					will_adjust_ = false;
+				} else if(character_reset_history_.bit<1>() && eom_latched_) {
+					if(next_line_ == layout_.vertical.adjust) {
+						will_adjust_ = false;
+					} else {
+						will_adjust_ = true;
+					}
+				}
+
+				// EOM (end of main) marks the end of the visible set of rows, prior to any adjustment area.
+				// It is set one cycle after the most-recent start of line.
+				if(new_frame) {
+					eom_latched_ = false;
+				} else if(character_reset_history_.bit<0>() && line_end_hit && row_counter_ == layout_.vertical.total) {
+					eom_latched_ = true;
+				}
+
+			//
+			// Cursor
+			//
+				cursor_history_ <<= 1;
+				if constexpr (cursor_type != CursorType::None) {
+					if(character_total_hit) {
+						// This is clearly a nonsense test; there's absolutely no reason a real 6845 would do anything
+						// other than equality comparisons, to maintain internal state.
+						//
+						// ... that said, I have been unable to reconcile:
+						//
+						//	1. the PCjs results on real MC6845Ps that show wraparound cursors
+						//		Cf. https://www.pcjs.org/blog/2018/03/20/ ; and
+						//	2. the expectations of the BBC Micro (which sets an out-of-range stop line for its cursor
+						//		right at initial boot) and various pieces of its software (including but
+						//		not limited to Arcadians, which uses in-range numbers but has start > end and expects
+						//		the cursor correspondingly to be hidden).
+						//
+						// I also note that the two BBC FPGA implementations I glanced at, hoglet's and Mister's, use
+						// fictional range comparisons.
+						//
+						// But, on the other hand, Tom Seddon remarks at https://github.com/tom-seddon/6845-tests that
+						// "Looks like the cursor switches on when cursor is off and raster matches R10, and switches
+						// off when cursor is on and raster matches R11."
+						//
+						// (but also seems to use a range test in his software implementation?)
+						is_cursor_line_ =
+							line_ >= layout_.vertical.start_cursor &&
+							line_ <= layout_.vertical.end_cursor;
+					}
+				}
+
+
+			//
+			// Event history.
+			//
+
+				// Somewhat of a fiction, this keeps a track of recent character resets because
+				// some events are keyed on 1 cycle after last reset, 2 cycles after last reset, etc.
+				character_reset_history_ <<= 1;
+				character_reset_history_ |= character_total_hit;
 		}
 	}
 
@@ -361,78 +481,117 @@ public:
 	}
 
 private:
-	static constexpr uint16_t RefreshMask = (personality >= Personality::EGA) ? 0xffff : 0x3fff;
-
 	BusHandlerT &bus_handler_;
 	BusState bus_state_;
 
 	enum class InterlaceMode {
+		/// No interlacing.
 		Off,
-		InterlaceSync,
-		InterlaceSyncAndVideo,
-	};
-	enum class BlinkMode {
-		// TODO.
+		/// Provide interlaced sync, but just scan out the exact same display for each field.
+		Sync,
+		/// Provide interlaced sync and scan even/odd lines depending on field.
+		SyncAndVideo,
 	};
+
+	// Comments on the right provide the corresponding signal name in hoglet's VHDL implementation.
 	struct {
 		struct {
-			uint8_t total;
-			uint8_t displayed;
-			uint8_t start_sync;
-			uint8_t sync_width;
+			CharacterAddress total;			// r00_h_total
+			CharacterAddress displayed;		// r01_h_displayed
+			CharacterAddress start_sync;	// r02_h_sync_pos
+			SyncCounter sync_width;			// r03_h_sync_width
 		} horizontal;
 
 		struct {
-			uint8_t total;
-			uint8_t displayed;
-			uint8_t start_sync;
-			uint8_t sync_lines;
-			uint8_t adjust;
+			RowAddress total;			// r04_v_total
+			RowAddress displayed;		// r06_v_displayed
+			RowAddress start_sync;		// r07_v_sync_pos
+			SyncCounter sync_lines;		// r03_v_sync_width
+			LineAddress adjust;			// r05_v_total_adj
 
-			uint8_t end_row;
-			uint8_t start_cursor;
-			uint8_t end_cursor;
+			LineAddress end_line;		// r09_max_scanline_addr
+			LineAddress start_cursor;	// r10_cursor_start
+			LineAddress end_cursor;		// r11_cursor_end
 		} vertical;
 
-		InterlaceMode interlace_mode_ = InterlaceMode::Off;
-		uint8_t end_row() const {
-			return interlace_mode_ == InterlaceMode::InterlaceSyncAndVideo ? vertical.end_row & ~1 : vertical.end_row;
-		}
+		InterlaceMode interlace_mode_ = InterlaceMode::Off;		// r08_interlace
 
-		uint16_t start_address;
-		uint16_t cursor_address;
-		uint16_t light_pen_address;
-		uint8_t cursor_flags;
+		RefreshAddress start_address;		// r12_start_addr_h + r13_start_addr_l
+		RefreshAddress cursor_address;		// r14_cursor_h + r15_cursor_l
+		RefreshAddress light_pen_address;	// r16_light_pen_h + r17_light_pen_l
+		Numeric::SizedInt<2> cursor_flags;	// r10_cursor_mode
 	} layout_;
 
 	uint8_t registers_[18]{};
 	uint8_t dummy_register_ = 0;
-	int selected_register_ = 0;
+	Numeric::SizedInt<5> selected_register_ = 0;
 
-	uint8_t character_counter_ = 0;
-	uint32_t character_reset_history_ = 0;
-	uint8_t row_counter_ = 0, next_row_counter_ = 0;
-	uint8_t adjustment_counter_ = 0;
+	CharacterAddress character_counter_;		// h_counter
+	Numeric::SizedInt<3> character_reset_history_;	// sol
+	RowAddress row_counter_;					// row_counter
+	RowAddress next_row_counter_;				// row_counter_next
+	LineAddress line_;							// line_counter
+	LineAddress next_line_;						// line_counter_next
+	RefreshAddress refresh_;					// ma_i
 
-	bool character_is_visible_ = false;
-	bool line_is_visible_ = false;
+	bool character_is_visible_ = false;			// h_display
+	bool row_is_visible_ = false;				// v_display
 	bool is_first_scanline_ = false;
 	bool is_cursor_line_ = false;
+	bool cursor_mask_ = false;
 
-	int hsync_counter_ = 0;
-	int vsync_counter_ = 0;
-	bool is_in_adjustment_period_ = false;
+	SyncCounter hsync_counter_;					// h_sync_counter
+	SyncCounter vsync_counter_;					// v_sync_counter
+	bool will_adjust_ = false;					// in_adj
+	bool is_in_adjustment_period_ = false;		// adj_in_progress
 
-	uint16_t line_address_ = 0;
+	RefreshAddress line_address_;				// ma_row
 	uint8_t status_ = 0;
 
-	int display_skew_mask_ = 1;
-	unsigned int character_is_visible_shifter_ = 0;
+//	int display_skew_mask_ = 1;
 
-	bool eof_latched_ = false;
-	bool eom_latched_ = false;
-	uint16_t next_row_address_ = 0;
-	bool odd_field_ = false;
+	bool eof_latched_ = false;					// eof_latched
+	bool eom_latched_ = false;					// eom_latched
+	bool odd_field_ = false;					// odd_field
+	bool extra_line_ = false;					// extra_scanline
+
+	bool hit_vsync_last_ = false;				// vs_hit_last
+	bool vsync_even_ = false;					// vs_even
+	bool vsync_odd_ = false;					// vs_odd
+
+	Numeric::SizedInt<3> cursor_history_;	// cursor0, cursor1, cursor2 [TODO]
+	bool line_is_interlaced_ = false;
+
+	void update_cursor_mask() {
+		switch(cursor_type) {
+			case CursorType::None:
+			break;
+
+			// MDA-style blinking.
+			// https://retrocomputing.stackexchange.com/questions/27803/what-are-the-blinking-rates-of-the-caret-and-of-blinking-text-on-pc-graphics-car
+			// gives an 8/8 pattern for regular blinking though mode 11 is then just a guess.
+			case CursorType::MDA:
+				switch(layout_.cursor_flags.get()) {
+					case 0b11: cursor_mask_ = (bus_state_.field_count & 8) < 3;	break;
+					case 0b00: cursor_mask_ = bus_state_.field_count.bit<3>();	break;
+					case 0b01: cursor_mask_ = false;							break;
+					case 0b10: cursor_mask_ = true;								break;
+					default: break;
+				}
+			break;
+
+			// Standard built-in 6845 blinking.
+			case CursorType::Native:
+				switch(layout_.cursor_flags.get()) {
+					case 0b00: cursor_mask_ = true;								break;
+					case 0b01: cursor_mask_ = false;							break;
+					case 0b10: cursor_mask_ = bus_state_.field_count.bit<3>();	break;
+					case 0b11: cursor_mask_= bus_state_.field_count.bit<4>();	break;
+					default: break;
+				}
+			break;
+		}
+	}
 };
 
 }

Components/6850/6850.cpp

@@ -8,6 +8,7 @@
 
 #include "6850.hpp"
 
+#include <bit>
 #include <cassert>
 
 using namespace Motorola::ACIA;
@@ -141,11 +142,8 @@ int ACIA::expected_bits() {
 	return 1 + data_bits_ + stop_bits_ + (parity_ != Parity::None);
 }
 
-uint8_t ACIA::parity(uint8_t value) {
-	value ^= value >> 4;
-	value ^= value >> 2;
-	value ^= value >> 1;
-	return value ^ (parity_ == Parity::Even);
+uint8_t ACIA::parity(const uint8_t value) {
+	return (std::popcount(value) & 1) ^ (parity_ == Parity::Even);
 }
 
 bool ACIA::serial_line_did_produce_bit(Serial::Line<false> *, const int bit) {

Components/68901/MFP68901.cpp

@@ -14,9 +14,7 @@
 #include "Outputs/Log.hpp"
 
 namespace {
-
-Log::Logger<Log::Source::MFP68901> logger;
-
+using Logger = Log::Logger<Log::Source::MFP68901>;
 }
 
 using namespace Motorola::MFP68901;
@@ -65,11 +63,11 @@ uint8_t MFP68901::read(int address) {
 		case 0x11:	case 0x12:	return get_timer_data(address - 0xf);
 
 		// USART block: TODO.
-		case 0x13:		logger.error().append("Read: sync character generator");	break;
-		case 0x14:		logger.error().append("Read: USART control");				break;
-		case 0x15:		logger.error().append("Read: receiver status");			break;
-		case 0x16:		logger.error().append("Read: transmitter status");		break;
-		case 0x17:		logger.error().append("Read: USART data");				break;
+		case 0x13:		Logger::error().append("Read: sync character generator");	break;
+		case 0x14:		Logger::error().append("Read: USART control");				break;
+		case 0x15:		Logger::error().append("Read: receiver status");			break;
+		case 0x16:		Logger::error().append("Read: transmitter status");			break;
+		case 0x17:		Logger::error().append("Read: USART data");					break;
 	}
 	return 0x00;
 }
@@ -114,7 +112,7 @@ void MFP68901::write(int address, const uint8_t value) {
 		return;
 	}
 
-	constexpr int timer_prescales[] = {
+	static constexpr int timer_prescales[] = {
 		1, 4, 10, 16, 50, 64, 100, 200
 	};
 
@@ -170,11 +168,11 @@ void MFP68901::write(int address, const uint8_t value) {
 		break;
 
 		// USART block: TODO.
-		case 0x13:		logger.error().append("Write: sync character generator");	break;
-		case 0x14:		logger.error().append("Write: USART control");				break;
-		case 0x15:		logger.error().append("Write: receiver status");			break;
-		case 0x16:		logger.error().append("Write: transmitter status");			break;
-		case 0x17:		logger.error().append("Write: USART data");					break;
+		case 0x13:		Logger::error().append("Write: sync character generator");	break;
+		case 0x14:		Logger::error().append("Write: USART control");				break;
+		case 0x15:		Logger::error().append("Write: receiver status");			break;
+		case 0x16:		Logger::error().append("Write: transmitter status");		break;
+		case 0x17:		Logger::error().append("Write: USART data");				break;
 	}
 
 	update_clocking_observer();
@@ -221,7 +219,7 @@ HalfCycles MFP68901::next_sequence_point() {
 // MARK: - Timers
 
 void MFP68901::set_timer_mode(const int timer, const TimerMode mode, const int prescale, const bool reset_timer) {
-	logger.error().append("Timer %d mode set: %d; prescale: %d", timer, mode, prescale);
+	Logger::error().append("Timer %d mode set: %d; prescale: %d", timer, mode, prescale);
 	timers_[timer].mode = mode;
 	if(reset_timer) {
 		timers_[timer].prescale_count = 0;
@@ -399,7 +397,7 @@ int MFP68901::acknowledge_interrupt() {
 
 	int selected = 0;
 	while((1 << selected) != mask) ++selected;
-//	logger.error().append("Interrupt acknowledged: %d", selected);
+//	Logger::error().append("Interrupt acknowledged: %d", selected);
 	return (interrupt_vector_ & 0xf0) | uint8_t(selected);
 }
 

Components/68901/MFP68901.hpp

@@ -16,8 +16,8 @@
 namespace Motorola::MFP68901 {
 
 class PortHandler {
-	public:
-		// TODO: announce changes in output.
+public:
+	// TODO: announce changes in output.
 };
 
 /*!

Components/8272/Status.hpp

@@ -91,12 +91,12 @@ public:
 	void set(const MainStatus flag, const bool value) {
 		set(uint8_t(flag), value, main_status_);
 	}
-	void start_seek(const int drive)	{	main_status_ |= 1 << drive;	}
-	void set(const Status0 flag)		{	set(uint8_t(flag), true, status_[0]);	}
-	void set(const Status1 flag)		{	set(uint8_t(flag), true, status_[1]);	}
-	void set(const Status2 flag)		{	set(uint8_t(flag), true, status_[2]);	}
+	void start_seek(const int drive)		{	main_status_ |= 1 << drive;	}
+	void set(const Status0 flag)			{	set(uint8_t(flag), true, status_[0]);	}
+	void set(const Status1 flag)			{	set(uint8_t(flag), true, status_[1]);	}
+	void set(const Status2 flag)			{	set(uint8_t(flag), true, status_[2]);	}
 
-	void set_status0(uint8_t value)	{	status_[0] = value;	}
+	void set_status0(const uint8_t value)	{	status_[0] = value;	}
 
 	//
 	// Flag getters.

Components/8272/i8272.cpp

@@ -11,9 +11,8 @@
 #include "Outputs/Log.hpp"
 
 namespace {
-
-Log::Logger<Log::Source::i8272> logger;
-
+using Logger = Log::Logger<Log::Source::i8272>;
+constexpr int ms_to_cycles(const int x) { return x * 8000; }
 }
 
 using namespace Intel::i8272;
@@ -59,14 +58,18 @@ void i8272::run_for(const Cycles cycles) {
 				drives_[c].step_rate_counter %= (8000 * step_rate_time_);
 				while(steps--) {
 					// Perform a step.
-					int direction = (drives_[c].target_head_position < drives_[c].head_position) ? -1 : 1;
-					logger.info().append("Target %d versus believed %d", drives_[c].target_head_position, drives_[c].head_position);
+					const int direction = (drives_[c].target_head_position < drives_[c].head_position) ? -1 : 1;
 					select_drive(c);
 					get_drive().step(Storage::Disk::HeadPosition(direction));
 					if(drives_[c].target_head_position >= 0) drives_[c].head_position += direction;
 
+					Logger::info().append(
+						"Drive %d: seeking %d but seemingly at %d", c, drives_[c].target_head_position, drives_[c].head_position);
+
 					// Check for completion.
 					if(seek_is_satisfied(c)) {
+						Logger::info().append(
+							"Drive %d: seek satisfied", c, drives_[c].target_head_position, drives_[c].head_position);
 						drives_[c].phase = Drive::CompletedSeeking;
 						drives_seeking_--;
 						break;
@@ -140,52 +143,73 @@ uint8_t i8272::read(const int address) {
 	}
 }
 
-#define BEGIN_SECTION()	switch(resume_point_) { default:
+void i8272::posit_event(const int event_type) {
+
+#define BEGIN_SECTION()	switch(resume_point_) { default: case IdleResumePoint:
 #define END_SECTION()	}
 
-#define MS_TO_CYCLES(x)			x * 8000
-#define WAIT_FOR_EVENT(mask)	resume_point_ = __LINE__; interesting_event_mask_ = int(mask); return; case __LINE__:
-#define WAIT_FOR_TIME(ms)		resume_point_ = __LINE__; interesting_event_mask_ = int(Event8272::Timer); delay_time_ = MS_TO_CYCLES(ms); is_sleeping_ = false; update_clocking_observer(); case __LINE__: if(delay_time_) return;
+#define WAIT_FOR_EVENT(mask)	{							\
+	static constexpr int location = __COUNTER__ + 1;		\
+	resume_point_ = location;								\
+	interesting_event_mask_ = int(mask);					\
+	return;													\
+	case location:											\
+		(void)0;											\
+}
+
+#define WAIT_FOR_TIME(ms)	{								\
+	static constexpr int location = __COUNTER__ + 1;		\
+	interesting_event_mask_ = int(Event8272::Timer);		\
+	delay_time_ = ms_to_cycles(ms);							\
+	is_sleeping_ = false;									\
+	update_clocking_observer();								\
+	resume_point_ = location;								\
+	[[fallthrough]];										\
+	case location:											\
+	if(delay_time_) return;									\
+}
 
 #define PASTE(x, y) x##y
-#define CONCAT(x, y) PASTE(x, y)
+#define LABEL(x, y) PASTE(x, y)
 
 #define FIND_HEADER()	\
 	set_data_mode(DataMode::Scanning);	\
-	CONCAT(find_header, __LINE__): WAIT_FOR_EVENT(int(Event::Token) | int(Event::IndexHole)); \
+	LABEL(find_header, __LINE__): WAIT_FOR_EVENT(int(Event::Token) | int(Event::IndexHole)); \
 	if(event_type == int(Event::IndexHole)) { index_hole_limit_--; }	\
-	else if(get_latest_token().type == Token::ID) goto CONCAT(header_found, __LINE__);	\
+	else if(get_latest_token().type == Token::ID) goto LABEL(header_found, __LINE__);	\
 	\
-	if(index_hole_limit_) goto CONCAT(find_header, __LINE__);	\
-	CONCAT(header_found, __LINE__):	(void)0;\
+	if(index_hole_limit_) goto LABEL(find_header, __LINE__);	\
+	LABEL(header_found, __LINE__):	(void)0;\
 
 #define FIND_DATA()	\
 	set_data_mode(DataMode::Scanning);	\
-	CONCAT(find_data, __LINE__): WAIT_FOR_EVENT(int(Event::Token) | int(Event::IndexHole)); \
+	LABEL(find_data, __LINE__): WAIT_FOR_EVENT(int(Event::Token) | int(Event::IndexHole)); \
 	if(event_type == int(Event::Token)) { \
-		if(get_latest_token().type == Token::Byte || get_latest_token().type == Token::Sync) goto CONCAT(find_data, __LINE__);	\
+		if(get_latest_token().type == Token::Byte || get_latest_token().type == Token::Sync) \
+			goto LABEL(find_data, __LINE__);	\
 	}
 
 #define READ_HEADER()	\
 	distance_into_section_ = 0;	\
 	set_data_mode(DataMode::Reading);	\
-	CONCAT(read_header, __LINE__): WAIT_FOR_EVENT(Event::Token); \
+	LABEL(read_header, __LINE__): WAIT_FOR_EVENT(Event::Token); \
 	header_[distance_into_section_] = get_latest_token().byte_value;	\
 	distance_into_section_++; \
-	if(distance_into_section_ < 6) goto CONCAT(read_header, __LINE__);	\
+	if(distance_into_section_ < 6) goto LABEL(read_header, __LINE__);	\
 
-#define SET_DRIVE_HEAD_MFM()	\
-	active_drive_ = command_.target().drive;	\
-	active_head_ = command_.target().head;	\
-	select_drive(active_drive_);	\
-	get_drive().set_head(active_head_);	\
-	set_is_double_density(command_.target().mfm);
+	const auto SET_DRIVE_HEAD_MFM = [&] {
+		active_drive_ = command_.target().drive;
+		active_head_ = command_.target().head;
+		select_drive(active_drive_);
+		get_drive().set_head(active_head_);
+		set_is_double_density(command_.target().mfm);
+	};
 
 #define WAIT_FOR_BYTES(n) \
 	distance_into_section_ = 0;	\
-	CONCAT(wait_bytes, __LINE__): WAIT_FOR_EVENT(Event::Token);	\
+	LABEL(wait_bytes, __LINE__): WAIT_FOR_EVENT(Event::Token);	\
 	if(get_latest_token().type == Token::Byte) distance_into_section_++;	\
-	if(distance_into_section_ < (n)) goto CONCAT(wait_bytes, __LINE__);
+	if(distance_into_section_ < (n)) goto LABEL(wait_bytes, __LINE__);
 
 #define LOAD_HEAD()	\
 	if(!drives_[active_drive_].head_is_loaded[active_head_]) {	\
@@ -198,18 +222,20 @@ uint8_t i8272::read(const int address) {
 		}	\
 	}
 
-#define SCHEDULE_HEAD_UNLOAD()	\
-	if(drives_[active_drive_].head_is_loaded[active_head_]) {\
-		if(drives_[active_drive_].head_unload_delay[active_head_] == 0) {	\
-			head_timers_running_++;	\
-			is_sleeping_ = false;	\
-			update_clocking_observer();	\
-		}	\
-		drives_[active_drive_].head_unload_delay[active_head_] = MS_TO_CYCLES(head_unload_time_);\
-	}
+	const auto SCHEDULE_HEAD_UNLOAD = [&] {
+		if(drives_[active_drive_].head_is_loaded[active_head_]) {
+			if(drives_[active_drive_].head_unload_delay[active_head_] == 0) {
+				++head_timers_running_;
+				is_sleeping_ = false;
+				update_clocking_observer();
+			}
+			drives_[active_drive_].head_unload_delay[active_head_] = ms_to_cycles(head_unload_time_);
+		}
+	};
 
-void i8272::posit_event(const int event_type) {
-	if(event_type == int(Event::IndexHole)) index_hole_count_++;
+	if(event_type == int(Event::IndexHole)) {
+		++index_hole_count_;
+	}
 	if(event_type == int(Event8272::NoLongerReady)) {
 		status_.set(Status0::NotReady);
 		goto abort;
@@ -234,7 +260,7 @@ void i8272::posit_event(const int event_type) {
 	wait_for_complete_command_sequence:
 			status_.set(MainStatus::DataReady, true);
 			status_.set(MainStatus::DataIsToProcessor, false);
-			WAIT_FOR_EVENT(Event8272::CommandByte)
+			WAIT_FOR_EVENT(Event8272::CommandByte);
 
 			if(!command_.has_command()) {
 				goto wait_for_complete_command_sequence;
@@ -258,8 +284,8 @@ void i8272::posit_event(const int event_type) {
 						drives_seeking_--;
 					}
 				}
-				// Establishes the drive and head being addressed, and whether in double density mode; populates the internal
-				// cylinder, head, sector and size registers from the command stream.
+				// Establishes the drive and head being addressed, and whether in double density mode; populates
+				// the internal cylinder, head, sector and size registers from the command stream.
 				is_executing_ = true;
 				if(!dma_mode_) {
 					status_.set(MainStatus::InNonDMAExecution, true);
@@ -309,17 +335,17 @@ void i8272::posit_event(const int event_type) {
 		// the index hole limit is breached or a sector is found with a cylinder, head, sector and size equal to the
 		// values in the internal registers.
 			index_hole_limit_ = 2;
-//			logger.info().append("Seeking " << PADDEC(0) << cylinder_ << " " << head_ " " << sector_ << " " << size_);
+//			Logger::info().append("Seeking " << PADDEC(0) << cylinder_ << " " << head_ " " << sector_ << " " << size_);
 		find_next_sector:
 			FIND_HEADER();
 			if(!index_hole_limit_) {
 				// Two index holes have passed wihout finding the header sought.
-//				logger.info().append("Not found");
+//				Logger::info().append("Not found");
 				status_.set(Status1::NoData);
 				goto abort;
 			}
 			index_hole_count_ = 0;
-//			logger.info().append("Header");
+//			Logger::info().append("Header");
 			READ_HEADER();
 			if(index_hole_count_) {
 				// This implies an index hole was sighted within the header. Error out.
@@ -330,26 +356,30 @@ void i8272::posit_event(const int event_type) {
 				// This implies a CRC error in the header; mark as such but continue.
 				status_.set(Status1::DataError);
 			}
-//			logger.info().append("Considering %02x %02x %02x %02x [%04x]", header_[0], header_[1], header_[2], header_[3], get_crc_generator().get_value());
-			if(header_[0] != cylinder_ || header_[1] != head_ || header_[2] != sector_ || header_[3] != size_) goto find_next_sector;
+//			Logger::info().append(
+//				"Considering %02x %02x %02x %02x [%04x]",
+//					header_[0], header_[1], header_[2], header_[3], get_crc_generator().get_value());
+			if(header_[0] != cylinder_ || header_[1] != head_ || header_[2] != sector_ || header_[3] != size_) {
+				goto find_next_sector;
+			}
 
 			// Branch to whatever is supposed to happen next
-//			logger.info().append("Proceeding");
+//			Logger::info().append("Proceeding");
 			switch(command_.command()) {
 				default:
 				case Command::ReadData:
 				case Command::ReadDeletedData:
 				goto read_data_found_header;
 
-				case Command::WriteData:	// write data
-				case Command::WriteDeletedData:	// write deleted data
+				case Command::WriteData:
+				case Command::WriteDeletedData:
 				goto write_data_found_header;
 			}
 
 
 	// Performs the read data or read deleted data command.
 	read_data:
-//			logger.info().append("Read [deleted] data [%02x %02x %02x %02x ... %02x %02x]",
+//			Logger::info().append("Read [deleted] data [%02x %02x %02x %02x ... %02x %02x]",
 //				command_[2],
 //				command_[3],
 //				command_[4],
@@ -390,8 +420,8 @@ void i8272::posit_event(const int event_type) {
 			distance_into_section_ = 0;
 			set_data_mode(Reading);
 
-		// Waits for the next token, then supplies it to the CPU by: (i) setting data request and direction; and (ii) resetting
-		// data request once the byte has been taken. Continues until all bytes have been read.
+		// Waits for the next token, then supplies it to the CPU by: (i) setting data request and direction; and
+		// (ii) resetting data request once the byte has been taken. Continues until all bytes have been read.
 		//
 		// TODO: consider DTL.
 		read_data_get_byte:
@@ -439,7 +469,7 @@ void i8272::posit_event(const int event_type) {
 			goto post_st012chrn;
 
 	write_data:
-//			logger.info().append("Write [deleted] data [%02x %02x %02x %02x ... %02x %02x]",
+//			Logger::info().append("Write [deleted] data [%02x %02x %02x %02x ... %02x %02x]",
 //				command_[2],
 //				command_[3],
 //				command_[4],
@@ -480,7 +510,7 @@ void i8272::posit_event(const int event_type) {
 				goto write_loop;
 			}
 
-			logger.info().append("Wrote %d bytes", distance_into_section_);
+			Logger::info().append("Wrote %d bytes", distance_into_section_);
 			write_crc();
 			expects_input_ = false;
 			WAIT_FOR_EVENT(Event::DataWritten);
@@ -496,10 +526,11 @@ void i8272::posit_event(const int event_type) {
 	// Performs the read ID command.
 	read_id:
 		// Establishes the drive and head being addressed, and whether in double density mode.
-//			logger.info().append("Read ID [%02x %02x]", command_[0], command_[1]);
+//			Logger::info().append("Read ID [%02x %02x]", command_[0], command_[1]);
 
-		// Sets a maximum index hole limit of 2 then waits either until it finds a header mark or sees too many index holes.
-		// If a header mark is found, reads in the following bytes that produce a header. Otherwise branches to data not found.
+		// Sets a maximum index hole limit of 2 then waits either until it finds a header mark or sees too many
+		// index holes. If a header mark is found, reads in the following bytes that produce a header. Otherwise
+		// branches to data not found.
 			index_hole_limit_ = 2;
 			FIND_HEADER();
 			if(!index_hole_limit_) {
@@ -518,7 +549,7 @@ void i8272::posit_event(const int event_type) {
 
 	// Performs read track.
 	read_track:
-//			logger.info().append("Read track [%02x %02x %02x %02x]"
+//			Logger::info().append("Read track [%02x %02x %02x %02x]"
 //				command_[2],
 //				command_[3],
 //				command_[4],
@@ -563,7 +594,7 @@ void i8272::posit_event(const int event_type) {
 
 	// Performs format [/write] track.
 	format_track:
-			logger.info().append("Format track");
+			Logger::info().append("Format track");
 			if(get_drive().is_read_only()) {
 				status_.set(Status1::NotWriteable);
 				goto abort;
@@ -607,7 +638,7 @@ void i8272::posit_event(const int event_type) {
 				break;
 			}
 
-			logger.info().append("W: %02x %02x %02x %02x, %04x",
+			Logger::info().append("W: %02x %02x %02x %02x, %04x",
 				header_[0], header_[1], header_[2], header_[3], get_crc_generator().get_value());
 			write_crc();
 
@@ -640,15 +671,15 @@ void i8272::posit_event(const int event_type) {
 		goto post_st012chrn;
 
 	scan_low:
-		logger.error().append("Scan low unimplemented!!");
+		Logger::error().append("Scan low unimplemented!!");
 		goto wait_for_command;
 
 	scan_low_or_equal:
-		logger.error().append("Scan low or equal unimplemented!!");
+		Logger::error().append("Scan low or equal unimplemented!!");
 		goto wait_for_command;
 
 	scan_high_or_equal:
-		logger.error().append("Scan high or equal unimplemented!!");
+		Logger::error().append("Scan high or equal unimplemented!!");
 		goto wait_for_command;
 
 	// Performs both recalibrate and seek commands. These commands occur asynchronously, so the actual work
@@ -679,11 +710,11 @@ void i8272::posit_event(const int event_type) {
 				// up in run_for understands to mean 'keep going until track 0 is active').
 				if(command_.command() != Command::Recalibrate) {
 					drives_[drive].target_head_position = command_.seek_target();
-					logger.info().append("Seek to %d", command_.seek_target());
+					Logger::info().append("Seek to %d", command_.seek_target());
 				} else {
 					drives_[drive].target_head_position = -1;
 					drives_[drive].head_position = 0;
-					logger.info().append("Recalibrate");
+					Logger::info().append("Recalibrate");
 				}
 
 				// Check whether any steps are even needed; if not then mark as completed already.
@@ -696,7 +727,6 @@ void i8272::posit_event(const int event_type) {
 
 	// Performs sense interrupt status.
 	sense_interrupt_status:
-			logger.info().append("Sense interrupt status");
 			{
 				// Find the first drive that is in the CompletedSeeking state.
 				int found_drive = -1;
@@ -711,12 +741,12 @@ void i8272::posit_event(const int event_type) {
 				if(found_drive != -1) {
 					drives_[found_drive].phase = Drive::NotSeeking;
 					status_.set_status0(uint8_t(found_drive | uint8_t(Status0::SeekEnded)));
-//					status_.end_sense_interrupt_status(found_drive, 0);
-//					status_.set(Status0::SeekEnded);
 
 					result_stack_ = { drives_[found_drive].head_position, status_[0]};
+					Logger::info().append("Sense interrupt status: returning %02x %02x", result_stack_[0], result_stack_[1]);
 				} else {
 					result_stack_ = { 0x80 };
+					Logger::info().append("Sense interrupt status: returning %02x", result_stack_[0]);
 				}
 			}
 			goto post_result;
@@ -724,7 +754,7 @@ void i8272::posit_event(const int event_type) {
 	// Performs specify.
 	specify:
 		// Just store the values, and terminate the command.
-			logger.info().append("Specify");
+			Logger::info().append("Specify");
 			step_rate_time_ = command_.specify_specs().step_rate_time;
 			head_unload_time_ = command_.specify_specs().head_unload_time;
 			head_load_time_ = command_.specify_specs().head_load_time;
@@ -735,7 +765,7 @@ void i8272::posit_event(const int event_type) {
 			goto wait_for_command;
 
 	sense_drive_status:
-			logger.info().append("Sense drive status");
+			Logger::info().append("Sense drive status");
 			{
 				int drive = command_.target().drive;
 				select_drive(drive);
@@ -775,7 +805,7 @@ void i8272::posit_event(const int event_type) {
 	// last thing in it will be returned first.
 	post_result:
 //			{
-//				auto line = logger.info();
+//				auto line = Logger::info();
 //				line.append("Result to %02x, main %02x", command_[0] & 0x1f, main_status_);
 //				for(std::size_t c = 0; c < result_stack_.size(); c++) {
 //					line.append(" %02x", result_stack_[result_stack_.size() - 1 - c]);

Components/8272/i8272.hpp

@@ -72,9 +72,11 @@ private:
 	};
 	void posit_event(int type) final;
 	int interesting_event_mask_ = int(Event8272::CommandByte);
-	int resume_point_ = 0;
 	bool is_access_command_ = false;
 
+	static constexpr int IdleResumePoint = 0;
+	int resume_point_ = 0;
+
 	// The counter used for ::Timer events.
 	Cycles::IntType delay_time_ = 0;
 

Components/8530/z8530.cpp

@@ -13,9 +13,7 @@
 using namespace Zilog::SCC;
 
 namespace {
-
-Log::Logger<Log::Source::SCC> logger;
-
+using Logger = Log::Logger<Log::Source::SCC>;
 }
 
 void z8530::reset() {
@@ -54,7 +52,7 @@ std::uint8_t z8530::read(const int address) {
 
 			case 2:		// Handled non-symmetrically between channels.
 				if(address & 1) {
-					logger.error().append("Unimplemented: register 2 status bits");
+					Logger::error().append("Unimplemented: register 2 status bits");
 				} else {
 					result = interrupt_vector_;
 
@@ -111,11 +109,11 @@ void z8530::write(const int address, const std::uint8_t value) {
 			case 2:	// Interrupt vector register; used only by Channel B.
 					// So there's only one of these.
 				interrupt_vector_ = value;
-				logger.info().append("Interrupt vector set to %d", value);
+				Logger::info().append("Interrupt vector set to %d", value);
 			break;
 
 			case 9:	// Master interrupt and reset register; there is also only one of these.
-				logger.info().append("Master interrupt and reset register: %02x", value);
+				Logger::info().append("Master interrupt and reset register: %02x", value);
 				master_interrupt_control_ = value;
 			break;
 		}
@@ -152,7 +150,7 @@ uint8_t z8530::Channel::read(const bool data, const uint8_t pointer) {
 	if(data) {
 		return data_;
 	} else {
-		logger.info().append("Control read from register %d", pointer);
+		Logger::info().append("Control read from register %d", pointer);
 		// Otherwise, this is a control read...
 		switch(pointer) {
 			default:
@@ -237,10 +235,10 @@ void z8530::Channel::write(const bool data, const uint8_t pointer, const uint8_t
 		data_ = value;
 		return;
 	} else {
-		logger.info().append("Control write: %02x to register %d", value, pointer);
+		Logger::info().append("Control write: %02x to register %d", value, pointer);
 		switch(pointer) {
 			default:
-				logger.info().append("Unrecognised control write: %02x to register %d", value, pointer);
+				Logger::info().append("Unrecognised control write: %02x to register %d", value, pointer);
 			break;
 
 			case 0x0:	// Write register 0 — CRC reset and other functions.
@@ -248,13 +246,13 @@ void z8530::Channel::write(const bool data, const uint8_t pointer, const uint8_t
 				switch(value >> 6) {
 					default:	/* Do nothing. */		break;
 					case 1:
-						logger.error().append("TODO: reset Rx CRC checker.");
+						Logger::error().append("TODO: reset Rx CRC checker.");
 					break;
 					case 2:
-						logger.error().append("TODO: reset Tx CRC checker.");
+						Logger::error().append("TODO: reset Tx CRC checker.");
 					break;
 					case 3:
-						logger.error().append("TODO: reset Tx underrun/EOM latch.");
+						Logger::error().append("TODO: reset Tx underrun/EOM latch.");
 					break;
 				}
 
@@ -262,24 +260,24 @@ void z8530::Channel::write(const bool data, const uint8_t pointer, const uint8_t
 				switch((value >> 3)&7) {
 					default:	/* Do nothing. */		break;
 					case 2:
-//						logger.info().append("reset ext/status interrupts.");
+//						Logger::info().append("reset ext/status interrupts.");
 						external_status_interrupt_ = false;
 						external_interrupt_status_ = 0;
 					break;
 					case 3:
-						logger.error().append("TODO: send abort (SDLC).");
+						Logger::error().append("TODO: send abort (SDLC).");
 					break;
 					case 4:
-						logger.error().append("TODO: enable interrupt on next Rx character.");
+						Logger::error().append("TODO: enable interrupt on next Rx character.");
 					break;
 					case 5:
-						logger.error().append("TODO: reset Tx interrupt pending.");
+						Logger::error().append("TODO: reset Tx interrupt pending.");
 					break;
 					case 6:
-						logger.error().append("TODO: reset error.");
+						Logger::error().append("TODO: reset error.");
 					break;
 					case 7:
-						logger.error().append("TODO: reset highest IUS.");
+						Logger::error().append("TODO: reset highest IUS.");
 					break;
 				}
 			break;
@@ -304,7 +302,7 @@ void z8530::Channel::write(const bool data, const uint8_t pointer, const uint8_t
 					b1 = 1 => transmit buffer empty interrupt is enabled; 0 => it isn't.
 					b0 = 1 => external interrupt is enabled; 0 => it isn't.
 				*/
-				logger.info().append("Interrupt mask: %02x", value);
+				Logger::info().append("Interrupt mask: %02x", value);
 			break;
 
 			case 0x2:	// Write register 2 - interrupt vector.
@@ -319,7 +317,7 @@ void z8530::Channel::write(const bool data, const uint8_t pointer, const uint8_t
 					case 2:		receive_bit_count = 6;	break;
 					case 3:		receive_bit_count = 8;	break;
 				}
-				logger.info().append("Receive bit count: %d", receive_bit_count);
+				Logger::info().append("Receive bit count: %d", receive_bit_count);
 
 				/*
 					b7,b6:
@@ -425,6 +423,6 @@ void z8530::update_delegate() {
 	const bool interrupt_line = get_interrupt_line();
 	if(interrupt_line != previous_interrupt_line_) {
 		previous_interrupt_line_ = interrupt_line;
-		if(delegate_) delegate_->did_change_interrupt_status(this, interrupt_line);
+		if(delegate_) delegate_->did_change_interrupt_status(*this, interrupt_line);
 	}
 }

Components/8530/z8530.hpp

@@ -43,7 +43,7 @@ public:
 		/*!
 			Communicates that @c scc now has the interrupt line status @c new_status.
 		*/
-		virtual void did_change_interrupt_status(z8530 *, bool new_status) = 0;
+		virtual void did_change_interrupt_status(z8530 &, bool new_status) = 0;
 	};
 
 	/*!
@@ -54,7 +54,7 @@ public:
 	void set_delegate(Delegate *const delegate) {
 		if(delegate_ == delegate) return;
 		delegate_ = delegate;
-		delegate_->did_change_interrupt_status(this, get_interrupt_line());
+		delegate_->did_change_interrupt_status(*this, get_interrupt_line());
 	}
 
 	/*

Components/9918/Implementation/9918.cpp

@@ -23,7 +23,7 @@ namespace {
 constexpr unsigned int CRTCyclesPerLine = 1365;
 constexpr unsigned int CRTCyclesDivider = 4;
 
-Log::Logger<Log::Source::TMS9918> logger;
+using Logger = Log::Logger<Log::Source::TMS9918>;
 
 }
 
@@ -74,9 +74,9 @@ TMS9918<personality>::TMS9918() {
 	this->crt_.set_display_type(Outputs::Display::DisplayType::RGB);
 
 	if constexpr (is_yamaha_vdp(personality)) {
-		this->crt_.set_visible_area(Outputs::Display::Rect(0.07f, 0.065f, 0.875f, 0.875f));
+		this->crt_.set_fixed_framing(Outputs::Display::Rect(0.07f, 0.065f, 0.875f, 0.875f));
 	} else {
-		this->crt_.set_visible_area(Outputs::Display::Rect(0.07f, 0.0375f, 0.875f, 0.875f));
+		this->crt_.set_fixed_framing(Outputs::Display::Rect(0.07f, 0.0375f, 0.875f, 0.875f));
 	}
 
 	// The TMS remains in-phase with the NTSC colour clock; this is an empirical measurement
@@ -226,7 +226,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 				// TODO: where did this magic constant come from? https://www.smspower.org/forums/17970-RoadRashHow#111000 mentioned in passing
 				// that "the vertical scroll register is latched at the start of the active display" and this is two clocks before that, so it's
 				// not uncompelling. I can just no longer find my source.
-				constexpr auto latch_time = LineLayout<personality>::EndOfLeftBorder - 2;
+				static constexpr auto latch_time = LineLayout<personality>::EndOfLeftBorder - 2;
 				static_assert(latch_time > 0);
 				if(this->fetch_pointer_.column < latch_time && end_column >= latch_time) {
 					if(!this->fetch_pointer_.row) {
@@ -683,13 +683,7 @@ void Base<personality>::output_border(int cycles, [[maybe_unused]] const uint32_
 		return;
 	}
 
-	// If the border colour is 0, that can be communicated
-	// more efficiently as an explicit blank.
-	if(border_colour) {
-		crt_.output_level<uint32_t>(cycles, border_colour);
-	} else {
-		crt_.output_blank(cycles);
-	}
+	crt_.output_level<uint32_t>(cycles, border_colour);
 }
 
 // MARK: - External interface.
@@ -843,7 +837,7 @@ void Base<personality>::commit_register(int reg, const uint8_t value) {
 				Storage<personality>::solid_background_ = value & 0x20;
 				Storage<personality>::sprites_enabled_ = !(value & 0x02);
 				if(value & 0x01) {
-					logger.error().append("TODO: Yamaha greyscale");
+					Logger::error().append("TODO: Yamaha greyscale");
 				}
 				// b7: "1 = input on colour bus, enable mouse; 1 = output on colour bus, disable mouse" [documentation clearly in error]
 				// b6: 1 = enable light pen
@@ -860,7 +854,7 @@ void Base<personality>::commit_register(int reg, const uint8_t value) {
 				// TODO: on the Yamaha, at least, tie this interrupt overtly to vertical state.
 
 				if(value & 0x08) {
-					logger.error().append("TODO: Yamaha interlace mode");
+					Logger::error().append("TODO: Yamaha interlace mode");
 				}
 
 				// b7: 1 = 212 lines of pixels; 0 = 192
@@ -924,7 +918,7 @@ void Base<personality>::commit_register(int reg, const uint8_t value) {
 			case 20:
 			case 21:
 			case 22:
-//				logger.error().append("TODO: Yamaha colour burst selection; %02x", value);
+//				Logger::error().append("TODO: Yamaha colour burst selection; %02x", value);
 				// Documentation is "fill with 0s for no colour burst; magic pattern for colour burst"
 			break;
 
@@ -1010,7 +1004,7 @@ void Base<personality>::commit_register(int reg, const uint8_t value) {
 				// Kill the command immediately if it's done in zero operations
 				// (e.g. a line of length 0).
 				if(!Storage<personality>::command_ && (value >> 4)) {
-					logger.error().append("TODO: Yamaha command %02x", value);
+					Logger::error().append("TODO: Yamaha command %02x", value);
 				}
 
 				// Seed timing information if a command was found.
@@ -1211,7 +1205,7 @@ uint8_t TMS9918<personality>::read(const int address) {
 template <Personality personality>
 int Base<personality>::fetch_line() const {
 	// This is the proper Master System value; TODO: what's correct for Yamaha, etc?
-	constexpr int row_change_position = 31;
+	static constexpr int row_change_position = 31;
 
 	return
 		(this->fetch_pointer_.column < row_change_position)

Components/9918/Implementation/9918Base.hpp

@@ -87,8 +87,8 @@ template <Personality personality> struct Base: public Storage<personality> {
 	/// applicable @c memory_mask.
 	template <int shift, int length = 8> void install_field(AddressT &target, const uint8_t source) {
 		static_assert(length > 0 && length <= 8);
-		constexpr auto source_mask = (1 << length) - 1;
-		constexpr auto mask = AddressT(~(source_mask << shift));
+		static constexpr auto source_mask = (1 << length) - 1;
+		static constexpr auto mask = AddressT(~(source_mask << shift));
 		target = (
 			(target & mask) |
 			AddressT((source & source_mask) << shift)
@@ -545,8 +545,8 @@ template <Personality personality> struct Base: public Storage<personality> {
 					if(Storage<personality>::cram_is_selected_) {
 						// Adjust the palette. In a Master System blue has a slightly different
 						// scale; cf. https://www.retrorgb.com/sega-master-system-non-linear-blue-channel-findings.html
-						constexpr uint8_t rg_scale[] = {0, 85, 170, 255};
-						constexpr uint8_t b_scale[] = {0, 104, 170, 255};
+						static constexpr uint8_t rg_scale[] = {0, 85, 170, 255};
+						static constexpr uint8_t b_scale[] = {0, 104, 170, 255};
 						Storage<personality>::colour_ram_[address & 0x1f] = palette_pack(
 							rg_scale[(read_ahead_buffer_ >> 0) & 3],
 							rg_scale[(read_ahead_buffer_ >> 2) & 3],

Components/9918/Implementation/Draw.hpp

@@ -93,8 +93,8 @@ void Base<personality>::draw_sprites(
 		assert(!buffer.is_filling);
 	}
 
-	constexpr uint32_t sprite_colour_selection_masks[2] = {0x00000000, 0xffffffff};
-	constexpr int colour_masks[16] = {0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
+	static constexpr uint32_t sprite_colour_selection_masks[2] = {0x00000000, 0xffffffff};
+	static constexpr int colour_masks[16] = {0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
 	const int sprite_width = sprites_16x16_ ? 16 : 8;
 	const int shifter_target = sprite_width << 1;
 	const int pixel_width = sprites_magnified_ ? sprite_width << 1 : sprite_width;
@@ -526,7 +526,7 @@ void Base<personality>::draw_yamaha(const uint8_t y, int start, int end) {
 		}
 	}
 
-	constexpr std::array<uint32_t, 16> graphics7_sprite_palette = {
+	static constexpr std::array<uint32_t, 16> graphics7_sprite_palette = {
 		palette_pack(0b00000000, 0b00000000, 0b00000000),	palette_pack(0b00000000, 0b00000000, 0b01001001),
 		palette_pack(0b00000000, 0b01101101, 0b00000000),	palette_pack(0b00000000, 0b01101101, 0b01001001),
 		palette_pack(0b01101101, 0b00000000, 0b00000000),	palette_pack(0b01101101, 0b00000000, 0b01001001),

Components/9918/Implementation/Fetch.hpp

@@ -407,8 +407,8 @@ struct TextSequencer {
 			return;
 		} else {
 			// For the 120 slots in between follow a three-step pattern of:
-			constexpr int offset = cycle - 30;
-			constexpr auto column = AddressT(offset / 3);
+			static constexpr int offset = cycle - 30;
+			static constexpr auto column = AddressT(offset / 3);
 			switch(offset % 3) {
 				case 0:		// (1) fetch tile name.
 					fetcher.fetch_name(column);
@@ -457,16 +457,16 @@ struct CharacterSequencer {
 
 		// Body of line: tiles themselves, plus some additional potential sprites.
 		if(cycle >= 27 && cycle < 155) {
-			constexpr int offset = cycle - 27;
-			constexpr int block = offset >> 2;
-			constexpr int sub_block = offset & 3;
+			static constexpr int offset = cycle - 27;
+			static constexpr int block = offset >> 2;
+			static constexpr int sub_block = offset & 3;
 			switch(sub_block) {
 				case 0:	character_fetcher.fetch_name(block);	break;
 				case 1:
 					if(!(block & 3)) {
 						character_fetcher.base->do_external_slot(to_internal<personality, Clock::TMSMemoryWindow, Clock::FromStartOfSync>(cycle));
 					} else {
-						constexpr int sprite = 8 + ((block >> 2) * 3) + ((block & 3) - 1);
+						static constexpr int sprite = 8 + ((block >> 2) * 3) + ((block & 3) - 1);
 						sprite_fetcher.fetch_y(sprite);
 					}
 				break;
@@ -549,9 +549,9 @@ struct SMSSequencer {
 		}
 
 		if(cycle >= 25 && cycle < 153) {
-			constexpr int offset = cycle - 25;
-			constexpr int block = offset >> 2;
-			constexpr int sub_block = offset & 3;
+			static constexpr int offset = cycle - 25;
+			static constexpr int block = offset >> 2;
+			static constexpr int sub_block = offset & 3;
 
 			switch(sub_block) {
 				default: break;
@@ -561,7 +561,7 @@ struct SMSSequencer {
 					if(!(block & 3)) {
 						fetcher.base->do_external_slot(to_internal<personality, Clock::TMSMemoryWindow, Clock::FromStartOfSync>(cycle));
 					} else {
-						constexpr int sprite = (8 + ((block >> 2) * 3) + ((block & 3) - 1)) << 1;
+						static constexpr int sprite = (8 + ((block >> 2) * 3) + ((block & 3) - 1)) << 1;
 						fetcher.posit_sprite(sprite);
 						fetcher.posit_sprite(sprite+1);
 					}

Components/9918/Implementation/LineLayout.hpp

@@ -29,49 +29,49 @@ template <Personality personality, typename Enable = void> struct LineLayout;
 //		* text mode on all VDPs adjusts border width.
 
 template <Personality personality> struct LineLayout<personality, std::enable_if_t<is_classic_vdp(personality)>> {
-	constexpr static int StartOfSync		= 0;
-	constexpr static int EndOfSync			= 26;
-	constexpr static int StartOfColourBurst	= 29;
-	constexpr static int EndOfColourBurst	= 43;
-	constexpr static int EndOfLeftErase		= 50;
-	constexpr static int EndOfLeftBorder	= 63;
-	constexpr static int EndOfPixels		= 319;
-	constexpr static int EndOfRightBorder	= 334;
+	static constexpr int StartOfSync		= 0;
+	static constexpr int EndOfSync			= 26;
+	static constexpr int StartOfColourBurst	= 29;
+	static constexpr int EndOfColourBurst	= 43;
+	static constexpr int EndOfLeftErase		= 50;
+	static constexpr int EndOfLeftBorder	= 63;
+	static constexpr int EndOfPixels		= 319;
+	static constexpr int EndOfRightBorder	= 334;
 
-	constexpr static int CyclesPerLine		= 342;
+	static constexpr int CyclesPerLine		= 342;
 
-	constexpr static int TextModeEndOfLeftBorder	= 69;
-	constexpr static int TextModeEndOfPixels		= 309;
+	static constexpr int TextModeEndOfLeftBorder	= 69;
+	static constexpr int TextModeEndOfPixels		= 309;
 
-	constexpr static int ModeLatchCycle		= 36;	// Just a guess; correlates with the known 144 for the Yamaha VDPs,
+	static constexpr int ModeLatchCycle		= 36;	// Just a guess; correlates with the known 144 for the Yamaha VDPs,
 													// and falls into the collection gap between the final sprite
 													// graphics and the initial tiles or pixels.
 
 	/// The number of internal cycles that must elapse between a request to read or write and
 	/// it becoming a candidate for action.
-	constexpr static int VRAMAccessDelay = 6;
+	static constexpr int VRAMAccessDelay = 6;
 };
 
 template <Personality personality> struct LineLayout<personality, std::enable_if_t<is_yamaha_vdp(personality)>> {
-	constexpr static int StartOfSync		= 0;
-	constexpr static int EndOfSync			= 100;
-	constexpr static int StartOfColourBurst	= 113;
-	constexpr static int EndOfColourBurst	= 167;
-	constexpr static int EndOfLeftErase		= 202;
-	constexpr static int EndOfLeftBorder	= 258;
-	constexpr static int EndOfPixels		= 1282;
-	constexpr static int EndOfRightBorder	= 1341;
+	static constexpr int StartOfSync		= 0;
+	static constexpr int EndOfSync			= 100;
+	static constexpr int StartOfColourBurst	= 113;
+	static constexpr int EndOfColourBurst	= 167;
+	static constexpr int EndOfLeftErase		= 202;
+	static constexpr int EndOfLeftBorder	= 258;
+	static constexpr int EndOfPixels		= 1282;
+	static constexpr int EndOfRightBorder	= 1341;
 
-	constexpr static int CyclesPerLine		= 1368;
+	static constexpr int CyclesPerLine		= 1368;
 
-	constexpr static int TextModeEndOfLeftBorder	= 294;
-	constexpr static int TextModeEndOfPixels		= 1254;
+	static constexpr int TextModeEndOfLeftBorder	= 294;
+	static constexpr int TextModeEndOfPixels		= 1254;
 
-	constexpr static int ModeLatchCycle		= 144;
+	static constexpr int ModeLatchCycle		= 144;
 
 	/// The number of internal cycles that must elapse between a request to read or write and
 	/// it becoming a candidate for action.
-	constexpr static int VRAMAccessDelay = 16;
+	static constexpr int VRAMAccessDelay = 16;
 };
 
 }

Components/9918/Implementation/Storage.hpp

@@ -202,6 +202,7 @@ protected:
 						} else {
 							return Event::Type::External;
 						}
+					break;
 					case 6:
 						if((block & 3) != 3) {
 							return Event::Type::External;
@@ -280,11 +281,11 @@ protected:
 				const int block = offset / 32;
 				const int sub_block = offset & 31;
 				switch(sub_block) {
-					case 0:		if(block > 0) return Event(Event::Type::Name, uint8_t(block - 1));
-					case 6:		if((sub_block & 3) != 3) return Event::Type::External;
-					case 12:	if(block < 32) return Event(Event::Type::SpriteY, uint8_t(block));
-					case 18:	if(block > 0) return Event(Event::Type::Pattern, uint8_t(block - 1));
-					case 24:	if(block > 0) return Event(Event::Type::Colour, uint8_t(block - 1));
+					case 0:		if(block > 0) return Event(Event::Type::Name, uint8_t(block - 1));		break;
+					case 6:		if((sub_block & 3) != 3) return Event::Type::External;					break;
+					case 12:	if(block < 32) return Event(Event::Type::SpriteY, uint8_t(block));		break;
+					case 18:	if(block > 0) return Event(Event::Type::Pattern, uint8_t(block - 1));	break;
+					case 24:	if(block > 0) return Event(Event::Type::Colour, uint8_t(block - 1));	break;
 				}
 			}
 

Components/9918/Implementation/YamahaCommands.hpp

@@ -18,8 +18,8 @@ struct Vector {
 	int v[2]{};
 
 	template <int offset, bool high> void set(const uint8_t value) {
-		constexpr uint8_t mask = high ? (offset ? 0x3 : 0x1) : 0xff;
-		constexpr int shift = high ? 8 : 0;
+		static constexpr uint8_t mask = high ? (offset ? 0x3 : 0x1) : 0xff;
+		static constexpr int shift = high ? 8 : 0;
 		v[offset] = (v[offset] & ~(mask << shift)) | ((value & mask) << shift);
 	}
 

Components/AY38910/AY38910.cpp

@@ -91,7 +91,7 @@ void AY38910SampleSource<is_stereo>::set_sample_volume_range(const std::int16_t
 	// from the YM's datasheet, showing a clear power curve, and fitting that to observed
 	// values reported elsewhere.
 	const float max_volume = float(range) / 3.0f;	// As there are three channels.
-	constexpr float root_two = 1.414213562373095f;
+	static constexpr float root_two = 1.414213562373095f;
 	for(int v = 0; v < 32; v++) {
 		volumes_[v] = int(max_volume / powf(root_two, float(v ^ 0x1f) / 3.18f));
 	}

Components/DiskII/DiskII.cpp

@@ -8,6 +8,7 @@
 
 #include "DiskII.hpp"
 
+#include <bit>
 #include <cstdio>
 #include <cstring>
 
@@ -62,11 +63,7 @@ void DiskII::set_control(const Control control, const bool on) {
 		if(stepper_mask_&4) direction += (((stepper_position_ - 4) + 4)&7) - 4;
 		if(stepper_mask_&8) direction += (((stepper_position_ - 6) + 4)&7) - 4;
 
-		// TODO: when adopting C++20, replace with std::popcount.
-		int bits_set = stepper_mask_;
-		bits_set = (bits_set & 0x5) + ((bits_set >> 1) & 0x5);
-		bits_set = (bits_set & 0x3) + ((bits_set >> 2) & 0x3);
-
+		const int bits_set = std::popcount(uint8_t(stepper_mask_));
 		direction /= bits_set;
 
 		// Compare to the stepper position to decide whether that pulls in the current cog notch,

Components/DiskII/DiskIIDrive.cpp

@@ -8,6 +8,8 @@
 
 #include "DiskIIDrive.hpp"
 
+#include <bit>
+
 using namespace Apple::Disk;
 
 DiskIIDrive::DiskIIDrive(const int input_clock_rate) :
@@ -29,7 +31,7 @@ void DiskIIDrive::set_control_lines(const int lines) {
 		if(lines&2) direction += (((stepper_position_ - 2) + 4)&7) - 4;
 		if(lines&4) direction += (((stepper_position_ - 4) + 4)&7) - 4;
 		if(lines&8) direction += (((stepper_position_ - 6) + 4)&7) - 4;
-		const int bits_set = (lines&1) + ((lines >> 1)&1) + ((lines >> 2)&1) + ((lines >> 3)&1);
+		const int bits_set = std::popcount(uint8_t(lines));
 		direction /= bits_set;
 
 		// Compare to the stepper position to decide whether that pulls in the

Components/DiskII/IWM.cpp

@@ -24,7 +24,7 @@ namespace {
 	constexpr int SEL		= 1 << 8;	/*	This is an additional input, not available on a Disk II, with a
 											confusingly-similar name to SELECT but a distinct purpose. */
 
-	Log::Logger<Log::Source::IWM> logger;
+	using Logger = Log::Logger<Log::Source::IWM>;
 }
 
 IWM::IWM(int clock_rate) :
@@ -53,7 +53,7 @@ uint8_t IWM::read(const int address) {
 
 	switch(state_ & (Q6 | Q7 | ENABLE)) {
 		default:
-			logger.info().append("Invalid read\n");
+			Logger::info().append("Invalid read\n");
 		return 0xff;
 
 		case 0:
@@ -62,9 +62,11 @@ uint8_t IWM::read(const int address) {
 
 			if(data_register_ & 0x80) {
 				data_register_ = 0;
-//				logger.info().append("Reading data: %02x", result);
+//				Logger::info().append("Reading data: %02x", result);
+			} else {
+//				Logger::info().append("Spurious read?");
 			}
-//			logger.info().append("Reading data register: %02x", result);
+//			Logger::info().append("Reading data register: %02x", result);
 
 			return result;
 		}
@@ -97,7 +99,7 @@ uint8_t IWM::read(const int address) {
 				bit 6: 1 = write state (0 = underrun has occurred; 1 = no underrun so far).
 				bit 7: 1 = write data buffer ready for data (1 = ready; 0 = busy).
 			*/
-//			logger.info().append("Reading write handshake: %02x", 0x3f | write_handshake_);
+//			Logger::info().append("Reading write handshake: %02x", 0x3f | write_handshake_);
 		return 0x3f | write_handshake_;
 	}
 
@@ -128,9 +130,9 @@ void IWM::write(const int address, const uint8_t input) {
 
 			// TEMPORARY. To test for the unimplemented mode.
 			if(input&0x2) {
-				logger.info().append("Switched to asynchronous mode");
+				Logger::info().append("Switched to asynchronous mode");
 			} else {
-				logger.info().append("Switched to synchronous mode");
+				Logger::info().append("Switched to synchronous mode");
 			}
 
 			switch(mode_ & 0x18) {
@@ -139,8 +141,8 @@ void IWM::write(const int address, const uint8_t input) {
 				case 0x10:		bit_length_ = Cycles(32);		break;	// slow mode, 8Mhz
 				case 0x18:		bit_length_ = Cycles(16);		break;	// fast mode, 8Mhz
 			}
-			logger.info().append("Mode is now %02x", mode_);
-			logger.info().append("New bit length is %d", bit_length_.as<int>());
+			Logger::info().append("Mode is now %02x", mode_);
+			Logger::info().append("New bit length is %d", bit_length_.as<int>());
 		break;
 
 		case Q7|Q6|ENABLE:	// Write data register.
@@ -254,7 +256,7 @@ void IWM::run_for(const Cycles cycles) {
 					drives_[active_drive_]->run_for(Cycles(1));
 					++cycles_since_shift_;
 					if(cycles_since_shift_ == bit_length_ + error_margin) {
-//						logger.info().append("Shifting 0 at %d ", cycles_since_shift_.as<int>());
+//						Logger::info().append("Shifting 0 at %d ", cycles_since_shift_.as<int>());
 						propose_shift(0);
 					}
 				}
@@ -288,11 +290,11 @@ void IWM::run_for(const Cycles cycles) {
 					if(!(write_handshake_ & 0x80)) {
 						shift_register_ = next_output_;
 						output_bits_remaining_ = 8;
-//						logger.info().append("Next byte: %02x", shift_register_);
+//						Logger::info().append("Next byte: %02x", shift_register_);
 					} else {
 						write_handshake_ &= ~0x40;
 						if(drives_[active_drive_]) drives_[active_drive_]->end_writing();
-						logger.info().append("Overrun; done.");
+						Logger::info().append("Overrun; done.");
 						output_bits_remaining_ = 1;
 					}
 
@@ -348,7 +350,7 @@ void IWM::select_shift_mode() {
 		shift_register_ = next_output_;
 		write_handshake_ |= 0x80 | 0x40;
 		output_bits_remaining_ = 8;
-		logger.info().append("Seeding output with %02x", shift_register_);
+		Logger::info().append("Seeding output with %02x", shift_register_);
 	}
 }
 
@@ -362,7 +364,7 @@ void IWM::process_event(const Storage::Disk::Drive::Event &event) {
 	switch(event.type) {
 		case Storage::Disk::Track::Event::IndexHole: return;
 		case Storage::Disk::Track::Event::FluxTransition:
-//			logger.info().append("Shifting 1 at %d", cycles_since_shift_.as<int>());
+//			Logger::info().append("Shifting 1 at %d", cycles_since_shift_.as<int>());
 			propose_shift(1);
 		break;
 	}
@@ -371,8 +373,8 @@ void IWM::process_event(const Storage::Disk::Drive::Event &event) {
 void IWM::propose_shift(const uint8_t bit) {
 	// TODO: synchronous mode.
 
-//	logger.info().append("Shifting at %d", cycles_since_shift_.as<int>());
-//	logger.info().append("Shifting input");
+//	Logger::info().append("Shifting at %d", cycles_since_shift_.as<int>());
+//	Logger::info().append("Shifting input");
 
 	// See above for text from the IWM patent, column 7, around line 35 onwards.
 	// The error_margin here implements the 'before' part of that contract.
@@ -387,7 +389,7 @@ void IWM::propose_shift(const uint8_t bit) {
 
 	shift_register_ = uint8_t((shift_register_ << 1) | bit);
 	if(shift_register_ & 0x80) {
-//		if(data_register_ & 0x80) logger.info().append("Byte missed");
+//		if(data_register_ & 0x80) Logger::info().append("Byte missed");
 		data_register_ = shift_register_;
 		shift_register_ = 0;
 	}

Components/I2C/I2C.cpp

@@ -13,9 +13,7 @@
 using namespace I2C;
 
 namespace {
-
-Log::Logger<Log::Source::I2C> logger;
-
+using Logger = Log::Logger<Log::Source::I2C>;
 }
 
 void Bus::set_data(const bool pulled) {
@@ -52,7 +50,7 @@ void Bus::set_clock_data(const bool clock_pulled, const bool data_pulled) {
 	if(peripheral_bits_) {
 		// Trailing edge of clock => bit has been consumed.
 		if(!prior_clock && clock_) {
-			logger.info().append("<< %d", (peripheral_response_ >> 7) & 1);
+			Logger::info().append("<< %d", (peripheral_response_ >> 7) & 1);
 			--peripheral_bits_;
 			peripheral_response_ <<= 1;
 
@@ -68,10 +66,10 @@ void Bus::set_clock_data(const bool clock_pulled, const bool data_pulled) {
 		// A data transition outside of a clock cycle implies a start or stop.
 		in_bit_ = false;
 		if(data_) {
-			logger.info().append("S");
+			Logger::info().append("S");
 			signal(Event::Start);
 		} else {
-			logger.info().append("W");
+			Logger::info().append("W");
 			signal(Event::Stop);
 		}
 	} else if(clock_ != prior_clock) {
@@ -85,10 +83,10 @@ void Bus::set_clock_data(const bool clock_pulled, const bool data_pulled) {
 			in_bit_ = false;
 
 			if(data_) {
-				logger.info().append("0");
+				Logger::info().append("0");
 				signal(Event::Zero);
 			} else {
-				logger.info().append("1");
+				Logger::info().append("1");
 				signal(Event::One);
 			}
 		}

Components/OPx/Implementation/KeyLevelScaler.hpp

@@ -18,8 +18,8 @@ public:
 		this is used to select a key scaling rate if key-rate scaling is enabled.
 	*/
 	void set_period(const int period, const int octave) {
-		constexpr int key_level_scales[16] = {0, 48, 64, 74, 80, 86, 90, 94, 96, 100, 102, 104, 106, 108, 110, 112};
-		constexpr int masks[2] = {~0, 0};
+		static constexpr int key_level_scales[16] = {0, 48, 64, 74, 80, 86, 90, 94, 96, 100, 102, 104, 106, 108, 110, 112};
+		static constexpr int masks[2] = {~0, 0};
 
 		// A two's complement assumption is embedded below; the use of masks relies
 		// on the sign bit to clamp to zero.
@@ -33,7 +33,7 @@ public:
 	*/
 	void set_key_scaling_level(const int level) {
 		// '7' is just a number large enough to render all possible scaling coefficients as 0.
-		constexpr int key_level_scale_shifts[4] = {7, 1, 2, 0};
+		static constexpr int key_level_scale_shifts[4] = {7, 1, 2, 0};
 		shift_ = key_level_scale_shifts[level];
 	}
 

Components/OPx/Implementation/PhaseGenerator.hpp

@@ -24,8 +24,8 @@ public:
 		Advances the phase generator a single step, given the current state of the low-frequency oscillator, @c oscillator.
 	*/
 	void update(const LowFrequencyOscillator &oscillator) {
-		constexpr int vibrato_shifts[4] = {3, 1, 0, 1};
-		constexpr int vibrato_signs[2] = {1, -1};
+		static constexpr int vibrato_shifts[4] = {3, 1, 0, 1};
+		static constexpr int vibrato_signs[2] = {1, -1};
 
 		// Get just the top three bits of the period_.
 		const int top_freq = period_ >> (precision - 3);
@@ -61,7 +61,7 @@ public:
 		plus the degree of feedback to apply
 	*/
 	void apply_feedback(const LogSign first, const LogSign second, const int level) {
-		constexpr int masks[] = {0, ~0, ~0, ~0, ~0, ~0, ~0, ~0};
+		static constexpr int masks[] = {0, ~0, ~0, ~0, ~0, ~0, ~0, ~0};
 		phase_ += ((second.level(precision) + first.level(precision)) >> (8 - level)) & masks[level];
 	}
 
@@ -72,7 +72,7 @@ public:
 	void set_multiple(const int multiple) {
 		// This encodes the MUL -> multiple table given on page 12,
 		// multiplied by two.
-		constexpr int multipliers[] = {
+		static constexpr int multipliers[] = {
 			1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 20, 24, 24, 30, 30
 		};
 		assert(multiple < 16);

Components/OPx/Implementation/WaveformGenerator.hpp

@@ -22,8 +22,8 @@ public:
 	/*!
 		@returns The output of waveform @c form at [integral] phase @c phase.
 	*/
-	static constexpr LogSign wave(Waveform form, int phase) {
-		constexpr int waveforms[4][4] = {
+	static constexpr LogSign wave(const Waveform form, const int phase) {
+		int waveforms[4][4] = {
 			{1023, 1023, 1023, 1023},	// Sine: don't mask in any quadrant.
 			{511, 511, 0, 0},			// Half sine: keep the first half intact, lock to 0 in the second half.
 			{511, 511, 511, 511},		// AbsSine: endlessly repeat the first half of the sine wave.

Components/OPx/OPLL.cpp

@@ -314,7 +314,11 @@ void OPLL::update_all_channels() {
 		envelope_generators_[c + 9].update(oscillator_);
 	}
 
-#define VOLUME(x)	int16_t(((x) * total_volume_) >> 12)
+	const auto volume = [&](const int x) {
+		return int16_t(
+			(x * total_volume_) >> 12
+		);
+	};
 
 	if(rhythm_mode_enabled_) {
 		// Advance the rhythm envelope generators.
@@ -323,32 +327,32 @@ void OPLL::update_all_channels() {
 		}
 
 		// Fill in the melodic channels.
-		output_levels_[3] = VOLUME(melodic_output(0));
-		output_levels_[4] = VOLUME(melodic_output(1));
-		output_levels_[5] = VOLUME(melodic_output(2));
+		output_levels_[3] = volume(melodic_output(0));
+		output_levels_[4] = volume(melodic_output(1));
+		output_levels_[5] = volume(melodic_output(2));
 
-		output_levels_[9] = VOLUME(melodic_output(3));
-		output_levels_[10] = VOLUME(melodic_output(4));
-		output_levels_[11] = VOLUME(melodic_output(5));
+		output_levels_[9] = volume(melodic_output(3));
+		output_levels_[10] = volume(melodic_output(4));
+		output_levels_[11] = volume(melodic_output(5));
 
 		// Bass drum, which is a regular FM effect.
-		output_levels_[2] = output_levels_[15] = VOLUME(bass_drum());
+		output_levels_[2] = output_levels_[15] = volume(bass_drum());
 		oscillator_.update_lfsr();
 
 		// Tom tom, which is a single operator.
-		output_levels_[1] = output_levels_[14] = VOLUME(tom_tom());
+		output_levels_[1] = output_levels_[14] = volume(tom_tom());
 		oscillator_.update_lfsr();
 
 		// Snare.
-		output_levels_[6] = output_levels_[16] = VOLUME(snare_drum());
+		output_levels_[6] = output_levels_[16] = volume(snare_drum());
 		oscillator_.update_lfsr();
 
 		// Cymbal.
-		output_levels_[7] = output_levels_[17] = VOLUME(cymbal());
+		output_levels_[7] = output_levels_[17] = volume(cymbal());
 		oscillator_.update_lfsr();
 
 		// High-hat.
-		output_levels_[0] = output_levels_[13] = VOLUME(high_hat());
+		output_levels_[0] = output_levels_[13] = volume(high_hat());
 		oscillator_.update_lfsr();
 
 		// Unutilised slots.
@@ -365,32 +369,35 @@ void OPLL::update_all_channels() {
 		output_levels_[6] = output_levels_[7] = output_levels_[8] =
 		output_levels_[12] = output_levels_[13] = output_levels_[14] = 0;
 
-		output_levels_[3] = VOLUME(melodic_output(0));
-		output_levels_[4] = VOLUME(melodic_output(1));
-		output_levels_[5] = VOLUME(melodic_output(2));
+		output_levels_[3] = volume(melodic_output(0));
+		output_levels_[4] = volume(melodic_output(1));
+		output_levels_[5] = volume(melodic_output(2));
 
-		output_levels_[9] = VOLUME(melodic_output(3));
-		output_levels_[10] = VOLUME(melodic_output(4));
-		output_levels_[11] = VOLUME(melodic_output(5));
+		output_levels_[9] = volume(melodic_output(3));
+		output_levels_[10] = volume(melodic_output(4));
+		output_levels_[11] = volume(melodic_output(5));
 
-		output_levels_[15] = VOLUME(melodic_output(6));
-		output_levels_[16] = VOLUME(melodic_output(7));
-		output_levels_[17] = VOLUME(melodic_output(8));
+		output_levels_[15] = volume(melodic_output(6));
+		output_levels_[16] = volume(melodic_output(7));
+		output_levels_[17] = volume(melodic_output(8));
 	}
 
-#undef VOLUME
-
 	// TODO: batch updates of the LFSR.
 }
 
-// TODO: verify attenuation scales pervasively below.
+namespace {
 
-#define ATTENUATION(x)	((x) << 7)
+// TODO: verify attenuation scales pervasively below.
+constexpr int attenuation(const int x) {
+	return x << 7;
+}
+
+}
 
 int OPLL::melodic_output(const int channel) {
 	// The modulator always updates after the carrier, oddly enough. So calculate actual output first, based on the modulator's last value.
 	auto carrier = WaveformGenerator<period_precision>::wave(channels_[channel].carrier_waveform, phase_generators_[channel].scaled_phase(), channels_[channel].modulator_output);
-	carrier += envelope_generators_[channel].attenuation() + ATTENUATION(channels_[channel].attenuation) + key_level_scalers_[channel].attenuation();
+	carrier += envelope_generators_[channel].attenuation() + attenuation(channels_[channel].attenuation) + key_level_scalers_[channel].attenuation();
 
 	// Get the modulator's new value.
 	auto modulation = WaveformGenerator<period_precision>::wave(channels_[channel].modulator_waveform, phase_generators_[channel + 9].phase());
@@ -409,7 +416,7 @@ int OPLL::bass_drum() const {
 	modulation += rhythm_envelope_generators_[RhythmIndices::BassModulator].attenuation();
 
 	auto carrier = WaveformGenerator<period_precision>::wave(Waveform::Sine, phase_generators_[6].scaled_phase(), modulation);
-	carrier += rhythm_envelope_generators_[RhythmIndices::BassCarrier].attenuation() + ATTENUATION(channels_[6].attenuation);
+	carrier += rhythm_envelope_generators_[RhythmIndices::BassCarrier].attenuation() + attenuation(channels_[6].attenuation);
 	return carrier.level();
 }
 
@@ -417,7 +424,7 @@ int OPLL::tom_tom() const {
 	// Use modulator 8 and the 'instrument' selection for channel 8 as an attenuation.
 	auto tom_tom = WaveformGenerator<period_precision>::wave(Waveform::Sine, phase_generators_[8 + 9].phase());
 	tom_tom += rhythm_envelope_generators_[RhythmIndices::TomTom].attenuation();
-	tom_tom += ATTENUATION(channels_[8].instrument);
+	tom_tom += attenuation(channels_[8].instrument);
 	return tom_tom.level();
 }
 
@@ -425,7 +432,7 @@ int OPLL::snare_drum() const {
 	// Use modulator 7 and the carrier attenuation level for channel 7.
 	LogSign snare = WaveformGenerator<period_precision>::snare(oscillator_, phase_generators_[7 + 9].phase());
 	snare += rhythm_envelope_generators_[RhythmIndices::Snare].attenuation();
-	snare += ATTENUATION(channels_[7].attenuation);
+	snare += attenuation(channels_[7].attenuation);
 	return snare.level();
 }
 
@@ -433,7 +440,7 @@ int OPLL::cymbal() const {
 	// Use modulator 7, carrier 8 and the attenuation level for channel 8.
 	LogSign cymbal = WaveformGenerator<period_precision>::cymbal(phase_generators_[8].phase(), phase_generators_[7 + 9].phase());
 	cymbal += rhythm_envelope_generators_[RhythmIndices::Cymbal].attenuation();
-	cymbal += ATTENUATION(channels_[8].attenuation);
+	cymbal += attenuation(channels_[8].attenuation);
 	return cymbal.level();
 }
 
@@ -441,8 +448,6 @@ int OPLL::high_hat() const {
 	// Use modulator 7, carrier 8 a and the 'instrument' selection for channel 7 as an attenuation.
 	LogSign high_hat = WaveformGenerator<period_precision>::high_hat(oscillator_, phase_generators_[8].phase(), phase_generators_[7 + 9].phase());
 	high_hat += rhythm_envelope_generators_[RhythmIndices::HighHat].attenuation();
-	high_hat += ATTENUATION(channels_[7].instrument);
+	high_hat += attenuation(channels_[7].instrument);
 	return high_hat.level();
 }
-
-#undef ATTENUATION

Components/RP5C01/RP5C01.cpp

@@ -47,7 +47,7 @@ void RP5C01::run_for(const HalfCycles cycles) {
 	// Update time within day.
 	seconds_ += elapsed_seconds;
 
-	constexpr int day_length = 60 * 60 * 24;
+	static constexpr int day_length = 60 * 60 * 24;
 	if(seconds_ < day_length) {
 		return;
 	}

Components/SAA5050/SAA5050.cpp

@@ -0,0 +1,351 @@
+//
+//  SAA5050.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 24/09/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#include "SAA5050.hpp"
+
+#include <algorithm>
+#include <cstdint>
+
+namespace {
+// SAA5050 font, padded out to one byte per row. The least-significant five bits of each byte
+// are the meaningful pixels for that row, with the LSB being on the right.
+constexpr uint8_t font[][10] = {
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, },	// Character 32.
+	{0x00, 0x04, 0x04, 0x04, 0x04, 0x04, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x0a, 0x0a, 0x0a, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x06, 0x09, 0x08, 0x1c, 0x08, 0x08, 0x1f, 0x00, 0x00, },
+	{0x00, 0x0e, 0x15, 0x14, 0x0e, 0x05, 0x15, 0x0e, 0x00, 0x00, },
+	{0x00, 0x18, 0x19, 0x02, 0x04, 0x08, 0x13, 0x03, 0x00, 0x00, },
+	{0x00, 0x08, 0x14, 0x14, 0x08, 0x15, 0x12, 0x0d, 0x00, 0x00, },
+	{0x00, 0x04, 0x04, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x02, 0x04, 0x08, 0x08, 0x08, 0x04, 0x02, 0x00, 0x00, },
+	{0x00, 0x08, 0x04, 0x02, 0x02, 0x02, 0x04, 0x08, 0x00, 0x00, },
+	{0x00, 0x04, 0x15, 0x0e, 0x04, 0x0e, 0x15, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x04, 0x04, 0x1f, 0x04, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x04, 0x08, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x0e, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x00, 0x00, 0x00, },
+	{0x00, 0x04, 0x0a, 0x11, 0x11, 0x11, 0x0a, 0x04, 0x00, 0x00, },
+	{0x00, 0x04, 0x0c, 0x04, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x01, 0x06, 0x08, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x1f, 0x01, 0x02, 0x06, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x02, 0x06, 0x0a, 0x12, 0x1f, 0x02, 0x02, 0x00, 0x00, },
+	{0x00, 0x1f, 0x10, 0x1e, 0x01, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x06, 0x08, 0x10, 0x1e, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1f, 0x01, 0x02, 0x04, 0x08, 0x08, 0x08, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x0e, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x0f, 0x01, 0x02, 0x0c, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x04, 0x04, 0x08, 0x00, },
+	{0x00, 0x02, 0x04, 0x08, 0x10, 0x08, 0x04, 0x02, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1f, 0x00, 0x1f, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x08, 0x04, 0x02, 0x01, 0x02, 0x04, 0x08, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x02, 0x04, 0x04, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x17, 0x15, 0x17, 0x10, 0x0e, 0x00, 0x00, },
+	{0x00, 0x04, 0x0a, 0x11, 0x11, 0x1f, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x1e, 0x11, 0x11, 0x1e, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x10, 0x10, 0x10, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x11, 0x11, 0x11, 0x1e, 0x00, 0x00, },
+	{0x00, 0x1f, 0x10, 0x10, 0x1e, 0x10, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x1f, 0x10, 0x10, 0x1e, 0x10, 0x10, 0x10, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x10, 0x10, 0x13, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x1f, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x0e, 0x04, 0x04, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x01, 0x01, 0x01, 0x01, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x11, 0x12, 0x14, 0x18, 0x14, 0x12, 0x11, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x11, 0x1b, 0x15, 0x15, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x19, 0x15, 0x13, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x11, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x1e, 0x10, 0x10, 0x10, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x11, 0x15, 0x12, 0x0d, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x1e, 0x14, 0x12, 0x11, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x10, 0x0e, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1f, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x0a, 0x0a, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x15, 0x15, 0x15, 0x0a, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x0a, 0x04, 0x0a, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x0a, 0x04, 0x04, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x1f, 0x01, 0x02, 0x04, 0x08, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x00, 0x04, 0x08, 0x1f, 0x08, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x10, 0x10, 0x16, 0x01, 0x02, 0x04, 0x07, },
+	{0x00, 0x00, 0x04, 0x02, 0x1f, 0x02, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x04, 0x0e, 0x15, 0x04, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x0a, 0x0a, 0x1f, 0x0a, 0x1f, 0x0a, 0x0a, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x1f, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0e, 0x01, 0x0f, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x1e, 0x11, 0x11, 0x11, 0x1e, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0f, 0x10, 0x10, 0x10, 0x0f, 0x00, 0x00, },
+	{0x00, 0x01, 0x01, 0x0f, 0x11, 0x11, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0e, 0x11, 0x1f, 0x10, 0x0e, 0x00, 0x00, },
+	{0x00, 0x02, 0x04, 0x04, 0x0e, 0x04, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0f, 0x11, 0x11, 0x11, 0x0f, 0x01, 0x0e, },
+	{0x00, 0x10, 0x10, 0x1e, 0x11, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x04, 0x00, 0x0c, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x04, 0x00, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x08, },
+	{0x00, 0x08, 0x08, 0x09, 0x0a, 0x0c, 0x0a, 0x09, 0x00, 0x00, },
+	{0x00, 0x0c, 0x04, 0x04, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1a, 0x15, 0x15, 0x15, 0x15, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1e, 0x11, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0e, 0x11, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1e, 0x11, 0x11, 0x11, 0x1e, 0x10, 0x10, },
+	{0x00, 0x00, 0x00, 0x0f, 0x11, 0x11, 0x11, 0x0f, 0x01, 0x01, },
+	{0x00, 0x00, 0x00, 0x0b, 0x0c, 0x08, 0x08, 0x08, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0f, 0x10, 0x0e, 0x01, 0x1e, 0x00, 0x00, },
+	{0x00, 0x04, 0x04, 0x0e, 0x04, 0x04, 0x04, 0x02, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x0a, 0x0a, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x15, 0x15, 0x0a, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x0a, 0x04, 0x0a, 0x11, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x0f, 0x01, 0x0e, },
+	{0x00, 0x00, 0x00, 0x1f, 0x02, 0x04, 0x08, 0x1f, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x10, 0x10, 0x11, 0x03, 0x05, 0x07, 0x01, },
+	{0x00, 0x0a, 0x0a, 0x0a, 0x0a, 0x0a, 0x0a, 0x0a, 0x00, 0x00, },
+	{0x00, 0x18, 0x04, 0x18, 0x04, 0x19, 0x03, 0x05, 0x07, 0x01, },
+	{0x00, 0x00, 0x04, 0x00, 0x1f, 0x00, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x00, 0x00, },
+};
+
+enum ControlCode: uint8_t {
+	RedAlpha = 0x01,
+	GreenAlpha = 0x02,
+	YellowAlpha = 0x03,
+	BlueAlpha = 0x04,
+	MagentaAlpha = 0x05,
+	CyanAlpha = 0x06,
+	WhiteAlpha = 0x07,
+
+	Flash = 0x08,
+	Steady = 0x09,
+
+	RedGraphics = 0x11,
+	GreenGraphics = 0x12,
+	YellowGraphics = 0x13,
+	BlueGraphics = 0x14,
+	MagentaGraphics = 0x15,
+	CyanGraphics = 0x16,
+	WhiteGraphics = 0x17,
+
+	Conceal = 0x18,
+
+	ContinuousGraphics = 0x19,
+	SeparatedGraphics = 0x1a,
+
+	NormalHeight = 0xc,
+	DoubleHeight = 0xd,
+
+	BlackBackground = 0x1c,
+	NewBackground = 0x1d,
+
+	HoldGraphics = 0x1e,
+	ReleaseGraphics = 0x1f,
+};}
+
+using namespace Mullard;
+
+void SAA5050Serialiser::begin_frame(const bool is_odd) {
+	line_ = -2;
+	row_ = 0;
+	odd_frame_ = is_odd;
+
+	row_has_double_height_ = false;
+	double_height_offset_ = 0;
+
+	++frame_counter_;
+}
+
+void SAA5050Serialiser::begin_line() {
+	line_ += 2;
+	if(line_ == 20) {
+		line_ = 0;
+		++row_;
+
+		if(row_has_double_height_) {
+			double_height_offset_ = (double_height_offset_ + 5) % 10;
+		}
+		row_has_double_height_ = false;
+	}
+
+	output_.reset();
+	has_output_ = false;
+
+	apply_control(ControlCode::WhiteAlpha);
+	apply_control(ControlCode::Steady);
+	apply_control(ControlCode::NormalHeight);
+	apply_control(ControlCode::ContinuousGraphics);
+	apply_control(ControlCode::BlackBackground);
+	apply_control(ControlCode::ReleaseGraphics);
+}
+
+bool SAA5050Serialiser::has_output() const {
+	return has_output_;
+}
+
+SAA5050Serialiser::Output SAA5050Serialiser::output() {
+	has_output_ = false;
+	return output_;
+}
+
+void SAA5050Serialiser::apply_control(const uint8_t value) {
+	const auto set_alpha = [&](const uint8_t colour) {
+		alpha_mode_ = true;
+		conceal_ = false;
+		output_.alpha = colour;
+		hold_graphics_ = false;
+	};
+
+	const auto set_graphics = [&](const uint8_t colour) {
+		alpha_mode_ = false;
+		conceal_ = false;
+		output_.alpha = colour;
+		hold_graphics_ = false;
+	};
+
+	switch(value) {
+		default: break;
+
+		case RedAlpha:				set_alpha(0b100);									break;
+		case GreenAlpha:			set_alpha(0b010);									break;
+		case YellowAlpha:			set_alpha(0b110);									break;
+		case BlueAlpha:				set_alpha(0b001);									break;
+		case MagentaAlpha:			set_alpha(0b101);									break;
+		case CyanAlpha:				set_alpha(0b011);									break;
+		case WhiteAlpha:			set_alpha(0b111);									break;
+
+		case Flash:					flash_ = true;										break;
+		case Steady:				flash_ = false;										break;
+
+		case RedGraphics:			set_graphics(0b100);								break;
+		case GreenGraphics:			set_graphics(0b010);								break;
+		case YellowGraphics:		set_graphics(0b110);								break;
+		case BlueGraphics:			set_graphics(0b001);								break;
+		case MagentaGraphics:		set_graphics(0b101);								break;
+		case CyanGraphics:			set_graphics(0b011);								break;
+		case WhiteGraphics:			set_graphics(0b111);								break;
+
+		case Conceal:				conceal_ = true;									break;
+
+		case ContinuousGraphics:	separated_graphics_ = false;						break;
+		case SeparatedGraphics:		separated_graphics_ = true;							break;
+
+		case NormalHeight:			double_height_ = false;								break;
+		case DoubleHeight:			double_height_ = row_has_double_height_ = true;		break;
+
+		case BlackBackground:		output_.background = 0;								break;
+		case NewBackground:			output_.background = output_.alpha;					break;
+
+		case HoldGraphics:			hold_graphics_ = true;								break;
+		case ReleaseGraphics:		hold_graphics_ = false; last_graphic_ = 32;			break;
+	}
+}
+
+void SAA5050Serialiser::set_reveal(const bool reveal) {
+	reveal_ = reveal;
+}
+
+void SAA5050Serialiser::add(const Numeric::SizedInt<7> c) {
+	has_output_ = true;
+	if(c.get() < 32) {
+		if(hold_graphics_) {
+			load_pixels(last_graphic_);
+		} else {
+			output_.reset();
+		}
+		apply_control(c.get());
+		return;
+	}
+	load_pixels(c.get());
+}
+
+void SAA5050Serialiser::load_pixels(const uint8_t c) {
+	if(flash_ && ((frame_counter_&31) > 23)) {	// Complete guess on the blink period here.
+		output_.reset();
+		return;
+	}
+
+	if(conceal_ && !reveal_) {
+		output_.reset();
+		return;
+	}
+
+	// Divert into graphics only if both the mode and the character code allows it.
+	if(!alpha_mode_ && (c & (1 << 5))) {
+		last_graphic_ = c;
+
+		// Graphics layout:
+		//
+		//	|----|----|
+		//	|    |    |
+		//	| b0 | b1 |
+		//	|    |    |
+		//	|----|----|
+		//	|    |    |
+		//	| b2 | b3 |
+		//	|    |    |
+		//	|----|----|
+		//	|    |    |
+		//	| b4 | b6 |
+		//	|    |    |
+		//	|----|----|
+
+		if(separated_graphics_ && (line_ == 6 || line_ == 12 || line_ == 18)) {
+			output_.reset();
+			return;
+		}
+
+		uint8_t pixels;
+		if(line_ < 6) {
+			pixels =
+				((c & 1) ? 0b111'000 : 0) |
+				((c & 2) ? 0b000'111 : 0);
+		} else if(line_ < 14) {
+			pixels =
+				((c & 4) ? 0b111'000 : 0) |
+				((c & 8) ? 0b000'111 : 0);
+		} else {
+			pixels =
+				((c & 16) ? 0b111'000 : 0) |
+				((c & 64) ? 0b000'111 : 0);
+		}
+
+		if(separated_graphics_) {
+			pixels &= 0b011'011;
+		}
+
+		output_.load(pixels);
+		return;
+	}
+
+	if(double_height_) {
+		const auto top_address = (line_ >> 2) + double_height_offset_;
+		const uint8_t top = font[c - 32][top_address];
+		const uint8_t bottom = font[c - 32][std::min(9, top_address + 1)];
+
+		if(line_ & 2) {
+			output_.load(bottom, top);
+		} else {
+			output_.load(top, bottom);
+		}
+	} else {
+		if(double_height_offset_) {
+			output_.reset();
+		} else {
+			const auto top_address = line_ >> 1;
+			const uint8_t top = font[c - 32][top_address];
+			const uint8_t bottom = font[c - 32][std::min(9, top_address + 1)];
+
+			if(odd_frame_) {
+				output_.load(bottom, top);
+			} else {
+				output_.load(top, bottom);
+			}
+		}
+	}
+}

Components/SAA5050/SAA5050.hpp

@@ -0,0 +1,100 @@
+//
+//  SAA5050.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 24/09/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include <cstdint>
+#include "Numeric/SizedInt.hpp"
+
+namespace Mullard {
+
+struct SAA5050Serialiser {
+public:
+	void begin_frame(bool is_odd);
+	void begin_line();
+
+	void add(Numeric::SizedInt<7>);
+
+	struct Output {
+		void reset() {
+			top_ = bottom_ = 0;
+		}
+		void load(const uint8_t top, const uint8_t bottom) {
+			top_ = top;
+			bottom_ = bottom;
+		}
+		void load(const uint8_t top) {
+			top_ = bottom_ = top;
+		}
+
+		// The low twelve bits of this word provide 1bpp pixels.
+		uint16_t pixels() const {
+			// Adapted from old ElectrEm source; my original provenance for this being the correct logic is unknown.
+			uint16_t wide =
+				((top_ & 0b000001) ? 0b0000'0000'0011 : 0) |
+				((top_ & 0b000010) ? 0b0000'0000'1100 : 0) |
+				((top_ & 0b000100) ? 0b0000'0011'0000 : 0) |
+				((top_ & 0b001000) ? 0b0000'1100'0000 : 0) |
+				((top_ & 0b010000) ? 0b0011'0000'0000 : 0) |
+				((top_ & 0b100000) ? 0b1100'0000'0000 : 0);
+
+			if(top_ != bottom_) {
+				if((top_ & 0b10000) && (bottom_ & 0b11000) == 0b01000) wide |= 0b0000'1000'0000;
+				if((top_ & 0b01000) && (bottom_ & 0b01100) == 0b00100) wide |= 0b0000'0010'0000;
+				if((top_ & 0b00100) && (bottom_ & 0b00110) == 0b00010) wide |= 0b0000'0000'1000;
+				if((top_ & 0b00010) && (bottom_ & 0b00011) == 0b00001) wide |= 0b0000'0000'0010;
+
+				if((top_ & 0b01000) && (bottom_ & 0b11000) == 0b10000) wide |= 0b0001'0000'0000;
+				if((top_ & 0b00100) && (bottom_ & 0b01100) == 0b01000) wide |= 0b0000'0100'0000;
+				if((top_ & 0b00010) && (bottom_ & 0b00110) == 0b00100) wide |= 0b0000'0001'0000;
+				if((top_ & 0b00001) && (bottom_ & 0b00011) == 0b00010) wide |= 0b0000'0000'0100;
+			}
+
+			return wide;
+		}
+
+		// Colours for foreground and background pixels.
+		uint8_t alpha;
+		uint8_t background;
+
+	private:
+		uint8_t top_, bottom_;
+	};
+	bool has_output() const;
+	Output output();
+
+	void set_reveal(bool);
+
+private:
+	Output output_;
+	bool has_output_ = false;
+
+	int row_, line_;
+	bool odd_frame_;
+
+	bool flash_ = false;
+	int frame_counter_ = 0;
+
+	bool reveal_ = false;
+	bool conceal_ = false;
+
+	bool alpha_mode_ = true;
+	bool separated_graphics_ = false;
+
+	bool double_height_ = false;
+	bool row_has_double_height_ = false;
+	int double_height_offset_ = 0;
+
+	bool hold_graphics_ = false;
+	uint8_t last_graphic_ = 0;
+
+	void load_pixels(const uint8_t);
+	void apply_control(const uint8_t);
+};
+
+}

Components/SID/SID.cpp

@@ -0,0 +1,433 @@
+//
+//  SID.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#include "SID.hpp"
+
+// Sources used:
+//
+//	(1) SID Article v0.2 at https://github.com/ImreOlajos/SID-Article
+//	(2) Technical SID Information/Software stuff at http://www.sidmusic.org/sid/sidtech2.html
+//	(3) SID 6581/8580 (Sound Interface Device) reference at https://oxyron.de/html/registers_sid.html
+
+using namespace MOS::SID;
+
+SID::SID(Concurrency::AsyncTaskQueue<false> &audio_queue) :
+	audio_queue_(audio_queue),
+	output_filter_(
+		SignalProcessing::BiquadFilter::Type::LowPass,
+		1000000.0f,
+		15000.0f
+	) {}
+
+// MARK: - Programmer interface.
+
+void SID::write(const Numeric::SizedInt<5> address, const uint8_t value) {
+	last_write_ = value;
+	audio_queue_.enqueue([=, this] {
+		const auto voice = [&]() -> Voice & {
+			return voices_[address.get() / 7];
+		};
+		const auto oscillator = [&]() -> Voice::Oscillator & {
+			return voice().oscillator;
+		};
+		const auto adsr = [&]() -> Voice::ADSR & {
+			return voice().adsr;
+		};
+
+		switch(address.get()) {
+			case 0x00:	case 0x07:	case 0x0e:
+				oscillator().pitch = (oscillator().pitch & 0xff'00'00) | uint32_t(value << 8);
+			break;
+			case 0x01:	case 0x08:	case 0x0f:
+				oscillator().pitch = (oscillator().pitch & 0x00'ff'00) | uint32_t(value << 16);
+			break;
+			case 0x02:	case 0x09:	case 0x10:
+				oscillator().pulse_width = (oscillator().pitch & 0xf0'00'00'00) | uint32_t(value << 20);
+			break;
+			case 0x03:	case 0x0a:	case 0x11:
+				// The top bit of the phase counter is inverted; since it'll be compared directly with the
+				// pulse width, invert that bit too.
+				oscillator().pulse_width =
+					(
+						(oscillator().pitch & 0x0f'f0'00'00) |
+						uint32_t(value << 28)
+					);
+			break;
+			case 0x04:	case 0x0b:	case 0x12:
+				voice().set_control(value);
+			break;
+			case 0x05:	case 0x0c:	case 0x13:
+				adsr().attack = value >> 4;
+				adsr().decay = value;
+				adsr().set_phase(adsr().phase);
+			break;
+			case 0x06:	case 0x0d:	case 0x14:
+				adsr().sustain = (value >> 4) | (value & 0xf0);
+				adsr().release = value;
+				adsr().set_phase(adsr().phase);
+			break;
+
+			case 0x15:
+				filter_cutoff_.load<0, 3>(value);
+				update_filter();
+			break;
+			case 0x16:
+				filter_cutoff_.load<3>(value);
+				update_filter();
+			break;
+			case 0x17:
+				filter_channels_ = value;
+				filter_resonance_ = value >> 4;
+				update_filter();
+			break;
+			case 0x18:
+				volume_ = value & 0x0f;
+				filter_mode_ = value >> 4;
+				voice3_disable_ = value & 0x80;
+				update_filter();
+			break;
+		}
+	});
+}
+
+void SID::set_potentometer_input(const int index, const uint8_t value) {
+	potentometers_[index] = value;
+}
+
+void SID::update_filter() {
+	using Type = SignalProcessing::BiquadFilter::Type;
+	Type type = Type::AllPass;
+
+	switch(filter_mode_.get()) {
+		case 0:
+			filter_ = SignalProcessing::BiquadFilter();
+		return;
+
+		case 1:
+		case 3: type = Type::LowPass;	break;
+
+		case 2: type = Type::BandPass;	break;
+		case 5: type = Type::Notch;		break;
+
+		case 4:
+		case 6: type = Type::HighPass;	break;
+
+		case 7: type = Type::AllPass;	break;
+	}
+
+	filter_.configure(
+		type,
+		1'000'000.0f,
+		30.0f + float(filter_cutoff_.get()) * 5.8f,
+		0.707f + float(filter_resonance_.get()) * 0.2862f,
+		6.0f,
+		true
+	);
+
+	// Filter cutoff: the data sheet provides that it is linear, and "approximate Cutoff Frequency
+	// ranges between 30Hz and 12KHz [with recommended externally-supplied capacitors]."
+	//
+	// It's an 11-bit number, so the above is "approximate"ly right.
+
+	// Resonance: a complete from-thin-air guess. The data sheet says merely:
+	//
+	//	"There are 16 Resonance settings ranging from about 0.707 (Critical Damping) for a count of 0
+	//	to a maximum for a count of 15"
+	//
+	// i.e. no information is given on the maximum. I've taken it to be 5-ish per commentary on more general sites
+	// that 5 is a typical ceiling for the resonance factor.
+}
+
+uint8_t SID::read(const Numeric::SizedInt<5> address) {
+	switch(address.get()) {
+		default:	return last_write_;
+
+		case 0x19:	return potentometers_[0];
+		case 0x1a:	return potentometers_[1];
+
+		case 0x1b:
+		case 0x1c:
+			// Ensure all channels are entirely up to date.
+			audio_queue_.spin_flush();
+			return (address == 0x1c) ? voices_[2].adsr.envelope : uint8_t(voices_[2].output(voices_[1]) >> 4);
+	}
+}
+
+// MARK: - Oscillators.
+
+void Voice::Oscillator::reset_phase() {
+	phase = PhaseReload;
+}
+
+bool Voice::Oscillator::did_raise_b23() const {
+	return previous_phase > phase;
+}
+
+bool Voice::Oscillator::did_raise_b19() const {
+	static constexpr int NoiseBit = 1 << (19 + 8);
+	return (previous_phase ^ phase) & phase & NoiseBit;
+}
+
+uint16_t Voice::Oscillator::sawtooth_output() const {
+	return (phase >> 20) ^ 0x800;
+}
+
+// MARK: - Noise generator.
+
+uint16_t Voice::NoiseGenerator::output() const {
+	// Uses bits: 20, 18, 14, 11, 9, 5, 2 and 0, plus four more zero bits.
+	const uint16_t output =
+		((noise >> 9) & 0b1000'0000'0000) |		// b20 -> b11
+		((noise >> 8) & 0b0100'0000'0000) |		// b18 -> b10
+		((noise >> 5) & 0b0010'0000'0000) |		// b14 -> b9
+		((noise >> 3) & 0b0001'0000'0000) |		// b11 -> b8
+		((noise >> 2) & 0b0000'1000'0000) |		// b9 -> b7
+		((noise << 1) & 0b0000'0100'0000) |		// b5 -> b6
+		((noise << 3) & 0b0000'0010'0000) |		// b2 -> b5
+		((noise << 4) & 0b0000'0001'0000);		// b0 -> b4
+
+	assert(output <= Voice::MaxWaveformValue);
+	return output;
+}
+
+void Voice::NoiseGenerator::update(const bool test) {
+	noise =
+		(noise << 1) |
+		(((noise >> 17) ^ ((noise >> 22) | test)) & 1);
+}
+
+// MARK: - ADSR.
+
+void Voice::ADSR::set_phase(const Phase new_phase) {
+	static constexpr uint16_t rate_prescaler[] = {
+		9, 32, 63, 95, 149, 220, 267, 313, 392, 977, 1954, 3126, 3907, 11720, 19532, 31251
+	};
+	static_assert(sizeof(rate_prescaler) / sizeof(*rate_prescaler) == 16);
+
+	phase = new_phase;
+	switch(phase) {
+		case Phase::Attack:			rate_counter_target = rate_prescaler[attack.get()]; break;
+		case Phase::DecayAndHold:	rate_counter_target = rate_prescaler[decay.get()]; break;
+		case Phase::Release:		rate_counter_target = rate_prescaler[release.get()]; break;
+	}
+}
+
+// MARK: - Voices.
+
+void Voice::set_control(const uint8_t new_control) {
+	const bool old_gate = gate();
+	control = new_control;
+	if(gate() && !old_gate) {
+		adsr.set_phase(ADSR::Phase::Attack);
+	} else if(!gate() && old_gate) {
+		adsr.set_phase(ADSR::Phase::Release);
+	}
+}
+
+bool Voice::noise() const		{ return control.bit<7>(); }
+bool Voice::pulse() const		{ return control.bit<6>(); }
+bool Voice::sawtooth() const	{ return control.bit<5>(); }
+bool Voice::triangle() const	{ return control.bit<4>(); }
+bool Voice::test() const		{ return control.bit<3>(); }
+bool Voice::ring_mod() const	{ return control.bit<2>(); }
+bool Voice::sync() const		{ return control.bit<1>(); }
+bool Voice::gate() const		{ return control.bit<0>(); }
+
+void Voice::update() {
+	// Oscillator.
+	oscillator.previous_phase = oscillator.phase;
+	if(test()) {
+		oscillator.phase = 0;
+	} else {
+		oscillator.phase += oscillator.pitch;
+
+		if(oscillator.did_raise_b19()) {
+			noise_generator.update(test());
+		}
+	}
+
+	// ADSR.
+
+	// First prescalar, which is a function of the programmer-set rate.
+	++ adsr.rate_counter;
+	if(adsr.rate_counter == adsr.rate_counter_target) {
+		adsr.rate_counter = 0;
+
+		// Second prescalar, which approximates an exponential.
+		static constexpr uint8_t exponential_prescaler[] = {
+			1,														// 0
+			30, 30, 30, 30, 30, 30,									// 1–6
+			16, 16, 16, 16, 16, 16, 16, 16,							// 7–14
+			8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,						// 15–26
+			4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+			4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,				// 27–54
+			2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+			2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+			2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,					// 55–94
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+			1, 1, 1, 1, 1, 1, 1,
+		};
+		static_assert(sizeof(exponential_prescaler) == 256);
+		static_assert(exponential_prescaler[0] == 1);
+		static_assert(exponential_prescaler[1] == 30);
+		static_assert(exponential_prescaler[6] == 30);
+		static_assert(exponential_prescaler[7] == 16);
+		static_assert(exponential_prescaler[14] == 16);
+		static_assert(exponential_prescaler[15] == 8);
+		static_assert(exponential_prescaler[26] == 8);
+		static_assert(exponential_prescaler[27] == 4);
+		static_assert(exponential_prescaler[54] == 4);
+		static_assert(exponential_prescaler[55] == 2);
+		static_assert(exponential_prescaler[94] == 2);
+		static_assert(exponential_prescaler[95] == 1);
+		static_assert(exponential_prescaler[255] == 1);
+
+		if(adsr.phase == ADSR::Phase::Attack) {
+			++adsr.envelope;
+			// TODO: what really resets the exponential counter? If anything?
+			adsr.exponential_counter = 0;
+
+			if(adsr.envelope == 0xff) {
+				adsr.set_phase(ADSR::Phase::DecayAndHold);
+			}
+		} else {
+			++adsr.exponential_counter;
+			if(adsr.exponential_counter == exponential_prescaler[adsr.envelope]) {
+				adsr.exponential_counter = 0;
+
+				if(adsr.envelope && (adsr.envelope != adsr.sustain || adsr.phase != ADSR::Phase::DecayAndHold)) {
+					--adsr.envelope;
+				}
+			}
+		}
+	}
+}
+
+void Voice::synchronise(const Voice &prior) {
+	// Only oscillator work to do here.
+	if(
+		sync() &&
+		prior.oscillator.did_raise_b23()
+	) {
+		oscillator.phase = Oscillator::PhaseReload;
+	}
+}
+
+uint16_t Voice::pulse_output() const {
+	return (
+		(oscillator.phase ^ 0x8000'0000) < oscillator.pulse_width
+	) ? 0 : MaxWaveformValue;
+}
+
+uint16_t Voice::triangle_output(const Voice &prior) const {
+	const uint16_t sawtooth = oscillator.sawtooth_output();
+	const uint16_t xor_mask1 = sawtooth;
+	const uint16_t xor_mask2 = ring_mod() ? prior.sawtooth() : 0;
+	const uint16_t xor_mask = ((xor_mask1 ^ xor_mask2) & 0x800) ? 0xfff : 0x000;
+	return ((sawtooth << 1) ^ xor_mask) & 0xfff;
+}
+
+uint16_t Voice::output(const Voice &prior) const {
+	// TODO: true composite waves.
+	//
+	// My current understanding on this: if multiple waveforms are enabled, the pull to zero beats the
+	// pull to one on any line where the two compete. But the twist is that the lines are not necessarily
+	// one per bit since they lead to a common ground. Ummm, I think.
+	//
+	// Anyway, first pass: logical AND. It's not right. It will temporarily do.
+
+	uint16_t output = MaxWaveformValue;
+
+	if(pulse())		output &= pulse_output();
+	if(sawtooth())	output &= oscillator.sawtooth_output();
+	if(triangle())	output &= triangle_output(prior);
+	if(noise())		output &= noise_generator.output();
+
+	return (output * adsr.envelope) / 255;
+}
+
+// MARK: - Wave generation
+
+void SID::set_sample_volume_range(const std::int16_t range) {
+	range_ = range;
+}
+
+bool SID::is_zero_level() const {
+	return false;
+}
+
+template <Outputs::Speaker::Action action>
+void SID::apply_samples(const std::size_t number_of_samples, Outputs::Speaker::MonoSample *const target) {
+	for(std::size_t c = 0; c < number_of_samples; c++) {
+		// Advance phase.
+		voices_[0].update();
+		voices_[1].update();
+		voices_[2].update();
+
+		// Apply hard synchronisations.
+		voices_[0].synchronise(voices_[2]);
+		voices_[1].synchronise(voices_[0]);
+		voices_[2].synchronise(voices_[1]);
+
+		// Construct filtered and unfiltered output.
+		const uint16_t outputs[3] = {
+			voices_[0].output(voices_[2]),
+			voices_[1].output(voices_[0]),
+			voices_[2].output(voices_[1]),
+		};
+
+		const uint16_t direct_sample =
+			(filter_channels_.bit<0>() ? 0 : outputs[0]) +
+			(filter_channels_.bit<1>() ? 0 : outputs[1]) +
+			(filter_channels_.bit<2>() || voice3_disable_ ? 0 : outputs[2]);
+
+		const int16_t filtered_sample =
+			filter_.apply(
+				(filter_channels_.bit<0>() ? outputs[0] : 0) +
+				(filter_channels_.bit<1>() ? outputs[1] : 0) +
+				(filter_channels_.bit<2>() ? outputs[2] : 0)
+			);
+
+		// Sum, apply volume and output.
+		const auto sample = output_filter_.apply(int16_t(
+			(
+				volume_ * (
+					direct_sample +
+					filtered_sample
+						- 227	// DC offset.
+				)
+				- 88732
+			) / 3
+		));
+		// Maximum range of above: 15 * (4095 * 3 - 227) = [-3405, 180870]
+		// So subtracting 88732 will move to the centre of the range, and 3 is the smallest
+		// integer that avoids clipping.
+
+		Outputs::Speaker::apply<action>(
+			target[c],
+			Outputs::Speaker::MonoSample((sample * range_) >> 16)
+		);
+	}
+}
+
+template void SID::apply_samples<Outputs::Speaker::Action::Mix>(
+	std::size_t, Outputs::Speaker::MonoSample *);
+template void SID::apply_samples<Outputs::Speaker::Action::Store>(
+	std::size_t, Outputs::Speaker::MonoSample *);
+template void SID::apply_samples<Outputs::Speaker::Action::Ignore>(
+	std::size_t, Outputs::Speaker::MonoSample *);

Components/SID/SID.hpp

@@ -0,0 +1,129 @@
+//
+//  SID.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Numeric/SizedInt.hpp"
+
+#include "Concurrency/AsyncTaskQueue.hpp"
+#include "Outputs/Speaker/Implementation/BufferSource.hpp"
+#include "SignalProcessing/BiquadFilter.hpp"
+
+namespace MOS::SID {
+
+struct Voice {
+	static constexpr uint16_t MaxWaveformValue = (1 << 12) - 1;
+
+	struct Oscillator {
+		// Programmer inputs.
+		uint32_t pitch = 0;
+		uint32_t pulse_width = 0;
+
+		// State.
+		//
+		// A real SID has a 24-bit phase counter and does various things when the top bit transitions from 0 to 1.
+		// This implementation maintains a 32-bit phase counter in which the low byte is unused and the top bit
+		// is inverted. That saves the cost of any masking and makes the 0 -> 1 transition test actually a 1 -> 0
+		// transition test, which can be phrased simply as after < before. Sadly overflow of signed integers is
+		// still undefined behaviour in C++ at the time of writing.
+		static constexpr uint32_t PhaseReload = 0x8000'0000;
+		uint32_t phase = PhaseReload;
+		uint32_t previous_phase = PhaseReload;
+
+		void reset_phase();
+		bool did_raise_b23() const;
+		bool did_raise_b19() const;
+		uint16_t sawtooth_output() const;
+	} oscillator;
+	struct ADSR {
+		// Programmer inputs.
+		Numeric::SizedInt<4> attack;
+		Numeric::SizedInt<4> decay;
+		Numeric::SizedInt<4> release;
+
+		Numeric::SizedInt<8> sustain;
+
+		// State.
+		enum class Phase {
+			Attack,
+			DecayAndHold,
+			Release,
+		} phase = Phase::Release;
+		Numeric::SizedInt<15> rate_counter;
+		Numeric::SizedInt<15> rate_counter_target;
+
+		uint8_t exponential_counter;
+		uint8_t envelope;
+
+		void set_phase(const Phase);
+	} adsr;
+	struct NoiseGenerator {
+		static constexpr uint32_t NoiseReload = 0x7'ffff;
+		uint32_t noise = NoiseReload;
+
+		uint16_t output() const;
+		void update(const bool test);
+	} noise_generator;
+
+	void set_control(const uint8_t);
+	void update();
+	void synchronise(const Voice &prior);
+	uint16_t output(const Voice &prior) const;
+
+private:
+	Numeric::SizedInt<8> control;
+	bool noise() const;
+	bool pulse() const;
+	bool sawtooth() const;
+	bool triangle() const;
+	bool test() const;
+	bool ring_mod() const;
+	bool sync() const;
+	bool gate() const;
+
+	uint16_t pulse_output() const;
+	uint16_t triangle_output(const Voice &prior) const;
+};
+
+class SID: public Outputs::Speaker::BufferSource<SID, false> {
+public:
+	SID(Concurrency::AsyncTaskQueue<false> &audio_queue);
+
+	void write(Numeric::SizedInt<5> address, uint8_t value);
+	uint8_t read(Numeric::SizedInt<5> address);
+	void set_potentometer_input(int index, uint8_t value);
+
+	// Outputs::Speaker::BufferSource.
+	template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t, Outputs::Speaker::MonoSample *);
+	bool is_zero_level() const;
+	void set_sample_volume_range(std::int16_t);
+
+private:
+	Concurrency::AsyncTaskQueue<false> &audio_queue_;
+	Voice voices_[3];
+
+	uint8_t last_write_;
+
+	int16_t range_ = 0;
+	uint8_t volume_ = 0;
+
+	SignalProcessing::BiquadFilter filter_;
+	Numeric::SizedInt<11> filter_cutoff_;
+	Numeric::SizedInt<4> filter_resonance_;
+	Numeric::SizedInt<4> filter_channels_;
+	Numeric::SizedInt<3> filter_mode_;
+	bool voice3_disable_;
+	void update_filter();
+
+	SignalProcessing::BiquadFilter output_filter_;
+
+	uint8_t potentometers_[2]{};
+};
+
+}

Components/Serial/Line.cpp

@@ -101,7 +101,7 @@ template <bool lsb_first, typename IntT> void Line<include_clock>::write_interna
 			bit = levels & 1;
 			levels >>= 1;
 		} else {
-			constexpr auto top_bit = IntT(0x80) << ((sizeof(IntT) - 1) * 8);
+			static constexpr auto top_bit = IntT(0x80) << ((sizeof(IntT) - 1) * 8);
 			bit = levels & top_bit;
 			levels <<= 1;
 		}

Components/Serial/Line.hpp

@@ -137,7 +137,6 @@ private:
 	Defines an RS-232-esque srial port.
 */
 class Port {
-	public:
 };
 
 }

Components/uPD7002/uPD7002.cpp

@@ -0,0 +1,85 @@
+//
+//  uPD7002.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 17/09/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#include "uPD7002.hpp"
+
+using namespace NEC;
+
+uPD7002::uPD7002(const HalfCycles clock_rate) {
+	// Per the BBC AUG: "8 bit conversions typically take 4 ms to complete whereas 10 bit
+	// conversions typically take 10 ms to complete".
+	fast_period_ = clock_rate / 250;
+	slow_period_ = clock_rate / 100;
+}
+
+void uPD7002::run_for(const HalfCycles count) {
+	if(!conversion_time_remaining_) {
+		return;
+	}
+
+	if(count >= conversion_time_remaining_) {
+		conversion_time_remaining_ = HalfCycles(0);
+		result_ = uint16_t(inputs_[channel_] * 65535.0f) & (high_precision_ ? 0xfff0 : 0xff00);
+		set_interrupt(true);
+		return;
+	}
+
+	conversion_time_remaining_ -= count;
+}
+
+bool uPD7002::interrupt() const {
+	return interrupt_;
+}
+
+void uPD7002::write(const uint16_t address, const uint8_t value) {
+	const auto local_address = address & 3;
+	if(!local_address) {
+		channel_ = value & 0b0000'0011;
+		spare_ = value & 0b0000'0100;
+		high_precision_ = value & 0b0000'1000;
+		conversion_time_remaining_ = high_precision_ ? slow_period_ : fast_period_;
+		set_interrupt(false);
+		return;
+	}
+}
+
+uint8_t uPD7002::read(const uint16_t address) {
+	switch(address & 3) {
+		default:
+		case 0:	return status();
+		case 1:
+			set_interrupt(false);
+		return uint8_t(result_ >> 8);
+		case 2:	return uint8_t(result_);
+		case 3:	return 0xff;
+	}
+}
+
+uint8_t uPD7002::status() const {
+	return
+		channel_ |
+		spare_ |
+		(high_precision_ ? 0x08 : 0) |
+		((result_ >> 14) & 0x30) |
+		(conversion_time_remaining_ > HalfCycles(0) ? 0x00 : 0x40) |
+		(interrupt_ ? 0x00 : 0x80);
+}
+
+void uPD7002::set_delegate(Delegate *const delegate) {
+	delegate_ = delegate;
+}
+
+void uPD7002::set_interrupt(const bool value) {
+	if(interrupt_ == value) return;
+	interrupt_ = value;
+	if(delegate_) delegate_->did_change_interrupt_status(*this);
+}
+
+void uPD7002::set_input(const int channel, const float value) {
+	inputs_[channel] = value;
+}

Components/uPD7002/uPD7002.hpp

@@ -0,0 +1,51 @@
+//
+//  uPD7002.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 17/09/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#include "ClockReceiver/ClockReceiver.hpp"
+
+namespace NEC {
+
+class uPD7002 {
+public:
+	/// Constructs a PD7002 that will receive @c run_for updates at the specified clock rate.
+	uPD7002(HalfCycles clock_rate);
+	void run_for(HalfCycles);
+
+	/// @returns The current state of the interrupt line.
+	bool interrupt() const;
+
+	/// Defines a mean for an observer to receive notifications upon updates to the interrupt line.
+	struct Delegate {
+	virtual void did_change_interrupt_status(uPD7002 &) = 0;
+	};
+	void set_delegate(Delegate *);
+
+	void write(uint16_t address, uint8_t value);
+	uint8_t read(uint16_t address);
+
+	/// Sets the floating point value, which should be in the range [0.0, 1.0], for the signal currently
+	/// being supplied to @c channel.
+	void set_input(int channel, float value);
+
+private:
+	float inputs_[4]{};
+	uint16_t result_ = 0;
+	bool interrupt_ = false;
+
+	uint8_t channel_ = 0, spare_ = 0;
+	bool high_precision_ = false;
+
+	HalfCycles conversion_time_remaining_{};
+	HalfCycles fast_period_, slow_period_;
+
+	uint8_t status() const;
+	void set_interrupt(bool);
+	Delegate *delegate_ = nullptr;
+};
+
+}

Concurrency/AsyncTaskQueue.hpp

@@ -28,7 +28,7 @@ template <typename Performer> struct TaskQueueStorage {
 
 protected:
 	void update() {
-		auto time_now = Time::nanos_now();
+		const auto time_now = Time::nanos_now();
 		performer.perform(time_now - last_fired_);
 		last_fired_ = time_now;
 	}
@@ -40,9 +40,12 @@ private:
 /// An implementation detail; provides a no-op implementation of time advances for TaskQueues without a Performer.
 template <> struct TaskQueueStorage<void> {
 	TaskQueueStorage() {}
+protected:
+	void update() {}
+};
 
-	protected:
-		void update() {}
+struct EnqueueDelegate {
+	virtual std::function<void(void)> prepare_enqueue() = 0;
 };
 
 /*!
@@ -64,12 +67,22 @@ template <> struct TaskQueueStorage<void> {
 	action occupies the asynchronous thread for long enough. So it is not true that @c perform will be
 	called once per action.
 */
-template <bool perform_automatically, bool start_immediately = true, typename Performer = void> class AsyncTaskQueue: public TaskQueueStorage<Performer> {
+template <
+	bool perform_automatically,
+	bool start_immediately = true,
+	bool use_enqueue_delegate = false,
+	typename Performer = void
+>
+class AsyncTaskQueue: public TaskQueueStorage<Performer> {
 public:
+	void set_enqueue_delegate(EnqueueDelegate *const delegate) {
+		enqueue_delegate_ = delegate;
+	}
+
 	template <typename... Args> AsyncTaskQueue(Args&&... args) :
 		TaskQueueStorage<Performer>(std::forward<Args>(args)...) {
 		if constexpr (start_immediately) {
-			start();
+			start_impl();
 		}
 	}
 
@@ -84,7 +97,10 @@ public:
 	/// on the same thread as the performer, after the performer has been updated
 	/// to 'now'.
 	void enqueue(const std::function<void(void)> &post_action) {
-		std::lock_guard guard(condition_mutex_);
+		const std::lock_guard guard(condition_mutex_);
+		if constexpr (use_enqueue_delegate) {
+			actions_.push_back(enqueue_delegate_->prepare_enqueue());
+		}
 		actions_.push_back(post_action);
 
 		if constexpr (perform_automatically) {
@@ -92,8 +108,15 @@ public:
 		}
 	}
 
+	/// @returns The number of items currently enqueued.
+	size_t size() {
+		const std::lock_guard guard(condition_mutex_);
+		return actions_.size();
+	}
+
 	/// Causes any enqueued actions that are not yet scheduled to be scheduled.
 	void perform() {
+		static_assert(!perform_automatically);
 		if(actions_.empty()) {
 			return;
 		}
@@ -106,7 +129,7 @@ public:
 	/// The queue cannot be restarted; this is a destructive action.
 	void stop() {
 		if(thread_.joinable()) {
-			should_quit_ = true;
+			should_quit_.store(true, std::memory_order_relaxed);
 			enqueue([] {});
 			if constexpr (!perform_automatically) {
 				perform();
@@ -119,36 +142,13 @@ public:
 	///
 	/// This is not guaranteed safely to restart a stopped queue.
 	void start() {
-		thread_ = std::thread{
-			[this] {
-				ActionVector actions;
-
-				// Continue until told to quit.
-				while(!should_quit_) {
-					// Wait for new actions to be signalled, and grab them.
-					std::unique_lock lock(condition_mutex_);
-					while(actions_.empty() && !should_quit_) {
-						condition_.wait(lock);
-					}
-					std::swap(actions, actions_);
-					lock.unlock();
-
-					// Update to now (which is possibly a no-op).
-					TaskQueueStorage<Performer>::update();
-
-					// Perform the actions and destroy them.
-					for(const auto &action: actions) {
-						action();
-					}
-					actions.clear();
-				}
-			}
-		};
+		static_assert(!start_immediately);
+		start_impl();
 	}
 
 	/// Schedules any remaining unscheduled work, then blocks synchronously
 	/// until all scheduled work has been performed.
-	void flush() {
+	void lock_flush() {
 		std::mutex flush_mutex;
 		std::condition_variable flush_condition;
 		bool has_run = false;
@@ -167,11 +167,58 @@ public:
 		flush_condition.wait(lock, [&has_run] { return has_run; });
 	}
 
+	/// Schedules any remaining unscheduled work, then spins
+	/// until all scheduled work has been performed, placing a memory barrier
+	/// in between.
+	void spin_flush() {
+		std::atomic<bool> has_run = false;
+
+		enqueue([&has_run] () {
+			has_run.store(true, std::memory_order::release);
+		});
+
+		if constexpr (!perform_automatically) {
+			perform();
+		}
+
+		while(!has_run.load(std::memory_order::acquire));
+	}
+
 	~AsyncTaskQueue() {
 		stop();
 	}
 
 private:
+	void start_impl() {
+		thread_ = std::thread{
+			[this] {
+				ActionVector actions;
+
+				// Continue until told to quit.
+				while(!should_quit_.load(std::memory_order_relaxed)) {
+					// Wait for new actions to be signalled, and grab them.
+					std::unique_lock lock(condition_mutex_);
+					condition_.wait(lock, [&] {
+						return !actions_.empty() || should_quit_.load(std::memory_order_relaxed);
+					});
+					std::swap(actions, actions_);
+					lock.unlock();
+
+					// Update to now (which is possibly a no-op).
+					TaskQueueStorage<Performer>::update();
+
+					// Perform the actions and destroy them.
+					for(const auto &action: actions) {
+						action();
+					}
+					actions.clear();
+				}
+			}
+		};
+	}
+
+	EnqueueDelegate *enqueue_delegate_ = nullptr;
+
 	// The list of actions waiting be performed. These will be elided,
 	// increasing their latency, if the emulation thread falls behind.
 	using ActionVector = std::vector<std::function<void(void)>>;

Configurable/StandardOptions.hpp

@@ -25,10 +25,12 @@ ReflectableEnum(Display,
 // ensure unified property naming.
 //===
 
-template <typename Owner> class DisplayOption {
+namespace Options {
+
+template <typename Owner> class Display {
 public:
 	Configurable::Display output;
-	DisplayOption(Configurable::Display output) : output(output) {}
+	Display(const Configurable::Display output) noexcept : output(output) {}
 
 protected:
 	void declare_display_option() {
@@ -37,26 +39,38 @@ protected:
 	}
 };
 
-template <typename Owner> class QuickloadOption {
+template <typename Owner> class QuickLoad {
 public:
-	bool quickload;
-	QuickloadOption(bool quickload) : quickload(quickload) {}
+	bool quick_load;
+	QuickLoad(const bool quick_load) noexcept : quick_load(quick_load) {}
 
 protected:
 	void declare_quickload_option() {
-		static_cast<Owner *>(this)->declare(&quickload, "quickload");
+		static_cast<Owner *>(this)->declare(&quick_load, "quickload");
 	}
 };
 
-template <typename Owner> class QuickbootOption {
+template <typename Owner> class QuickBoot {
 public:
-	bool quickboot;
-	QuickbootOption(bool quickboot) : quickboot(quickboot) {}
+	bool quick_boot;
+	QuickBoot(const bool quick_boot) noexcept : quick_boot(quick_boot) {}
 
 protected:
 	void declare_quickboot_option() {
-		static_cast<Owner *>(this)->declare(&quickboot, "quickboot");
+		static_cast<Owner *>(this)->declare(&quick_boot, "quickboot");
+	}
+};
+
+template <typename Owner> class DynamicCrop {
+public:
+	bool dynamic_crop;
+	DynamicCrop(const bool dynamic_crop) noexcept : dynamic_crop(dynamic_crop) {}
+
+protected:
+	void declare_dynamic_crop_option() {
+		static_cast<Owner *>(this)->declare(&dynamic_crop, "dynamiccrop");
 	}
 };
 
 }
+}

Inputs/Joystick.hpp

@@ -29,7 +29,7 @@ public:
 		/// Defines the broad type of the input.
 		enum Type {
 			// Half-axis inputs.
-			Up, Down, Left, Right,
+			Down, Up, Left, Right,
 			// Full-axis inputs.
 			Horizontal, Vertical,
 			// Fire buttons.
@@ -165,10 +165,11 @@ public:
 			const bool is_analogue_axis = input.is_analogue_axis();
 			if(is_digital_axis || is_analogue_axis) {
 				const size_t required_size = size_t(input.info.control.index+1);
-				if(stick_types_.size() < required_size) {
-					stick_types_.resize(required_size);
+				if(sticks_.size() < required_size) {
+					sticks_.resize(required_size);
 				}
-				stick_types_[size_t(input.info.control.index)] = is_digital_axis ? StickType::Digital : StickType::Analogue;
+				sticks_[size_t(input.info.control.index)].type =
+					is_digital_axis ? Stick::Type::Digital : Stick::Type::Analogue;
 			}
 		}
 	}
@@ -179,26 +180,50 @@ public:
 
 	void set_input(const Input &input, const bool is_active) final {
 		// If this is a digital setting to a digital property, just pass it along.
-		if(input.is_button() || stick_types_[input.info.control.index] == StickType::Digital) {
+		if(input.is_button() || sticks_[input.info.control.index].type == Stick::Type::Digital) {
 			did_set_input(input, is_active);
 			return;
 		}
 
-		// Otherwise this is logically to an analogue axis; for now just use some
-		// convenient hard-coded values. TODO: make these a function of time.
-		using Type = Joystick::Input::Type;
+		// Otherwise this is logically to an analogue axis; map appropriately.
+		// TODO: make these a function of time.
+		auto &stick = sticks_[input.info.control.index];
+		stick.apply_digital(input, is_active);
+		const auto analogue_value = [&](const int mask) {
+			switch(mask) {
+				default:	return 0.5f;
+				case 0b01:	return digital_minimum();
+				case 0b10:	return digital_maximum();
+			}
+		};
+
 		switch(input.type) {
-			default:			did_set_input(input, is_active ? 1.0f : 0.0f);													break;
-			case Type::Left:	did_set_input(Input(Type::Horizontal, input.info.control.index), is_active ? 0.1f : 0.5f);		break;
-			case Type::Right:	did_set_input(Input(Type::Horizontal, input.info.control.index), is_active ? 0.9f : 0.5f);		break;
-			case Type::Up:		did_set_input(Input(Type::Vertical, input.info.control.index), is_active ? 0.1f : 0.5f);		break;
-			case Type::Down:	did_set_input(Input(Type::Vertical, input.info.control.index), is_active ? 0.9f : 0.5f);		break;
+			using enum Joystick::Input::Type;
+
+			default:
+				did_set_input(input, is_active ? 1.0f : 0.0f);
+			break;
+
+			case Left:
+			case Right:
+				did_set_input(
+					Input(Horizontal, input.info.control.index),
+					analogue_value(stick.digital_mask(Horizontal))
+				);
+			break;
+			case Up:
+			case Down:
+				did_set_input(
+					Input(Vertical, input.info.control.index),
+					analogue_value(stick.digital_mask(Vertical))
+				);
+			break;
 		}
 	}
 
 	void set_input(const Input &input, const float value) final {
 		// If this is an analogue setting to an analogue property, just pass it along.
-		if(!input.is_button() && stick_types_[input.info.control.index] == StickType::Analogue) {
+		if(!input.is_button() && sticks_[input.info.control.index].type == Stick::Type::Analogue) {
 			did_set_input(input, value);
 			return;
 		}
@@ -206,7 +231,9 @@ public:
 		// Otherwise apply a threshold test to convert to digital, with remapping from axes to digital inputs.
 		using Type = Joystick::Input::Type;
 		switch(input.type) {
-			default:			did_set_input(input, value > 0.5f);											break;
+			default:
+				did_set_input(input, value > 0.5f);
+			break;
 			case Type::Horizontal:
 				did_set_input(Input(Type::Left, input.info.control.index), value <= 0.25f);
 				did_set_input(Input(Type::Right, input.info.control.index), value >= 0.75f);
@@ -221,15 +248,45 @@ public:
 protected:
 	virtual void did_set_input([[maybe_unused]] const Input &input, [[maybe_unused]] float value) {}
 	virtual void did_set_input([[maybe_unused]] const Input &input, [[maybe_unused]] bool value) {}
+	virtual float digital_minimum() const { return 0.1f; }
+	virtual float digital_maximum() const { return 0.9f; }
 
 private:
 	const std::vector<Input> inputs_;
 
-	enum class StickType {
-		Digital,
-		Analogue
+	struct Stick {
+		enum class Type {
+			Digital,
+			Analogue
+		} type;
+
+		void apply_digital(const Input &input, const bool is_active) {
+			const int mask = [&] {
+				switch(input.type) {
+					default: return 0;
+					case Input::Type::Up:		return 1 << 0;
+					case Input::Type::Down:		return 1 << 1;
+
+					case Input::Type::Left:		return 1 << 2;
+					case Input::Type::Right:	return 1 << 3;
+				}
+			} ();
+			if(is_active) {
+				digital_inputs_ |= mask;
+			} else {
+				digital_inputs_ &= ~mask;
+			}
+		}
+		int digital_mask(const Input::Type axis) const {
+			switch(axis) {
+				default: return 0;
+				case Input::Type::Horizontal:	return (digital_inputs_ >> 2) & 3;
+				case Input::Type::Vertical:		return (digital_inputs_ >> 0) & 3;
+			}
+		}
+		int digital_inputs_ = 0;
 	};
-	std::vector<StickType> stick_types_;
+	std::vector<Stick> sticks_;
 };
 
 }

Inputs/Keyboard.cpp

@@ -8,6 +8,7 @@
 
 #include "Keyboard.hpp"
 
+#include <algorithm>
 #include <cstddef>
 
 using namespace Inputs;
@@ -28,7 +29,7 @@ bool Keyboard::set_key_pressed(const Key key, const char, const bool is_pressed,
 	}
 	key_states_[key_offset] = is_pressed;
 
-	if(delegate_) return delegate_->keyboard_did_change_key(this, key, is_pressed);
+	if(delegate_) return delegate_->keyboard_did_change_key(*this, key, is_pressed);
 	return false;
 }
 
@@ -38,7 +39,7 @@ const std::set<Inputs::Keyboard::Key> &Keyboard::get_essential_modifiers() const
 
 void Keyboard::reset_all_keys() {
 	std::fill(key_states_.begin(), key_states_.end(), false);
-	if(delegate_) delegate_->reset_all_keys(this);
+	if(delegate_) delegate_->reset_all_keys(*this);
 }
 
 void Keyboard::set_delegate(Delegate *const delegate) {

Inputs/Keyboard.hpp

@@ -73,8 +73,8 @@ public:
 
 	// Delegate interface.
 	struct Delegate {
-		virtual bool keyboard_did_change_key(Keyboard *keyboard, Key key, bool is_pressed) = 0;
-		virtual void reset_all_keys(Keyboard *keyboard) = 0;
+		virtual bool keyboard_did_change_key(Keyboard &, Key, bool is_pressed) = 0;
+		virtual void reset_all_keys(Keyboard &) = 0;
 	};
 	void set_delegate(Delegate *);
 	bool get_key_state(Key) const;

Inputs/Mouse.hpp

@@ -15,30 +15,30 @@ namespace Inputs {
 	some quantity of buttons.
 */
 class Mouse {
-	public:
-		/*!
-			Indicates a movement of the mouse.
-		*/
-		virtual void move([[maybe_unused]] const int x, [[maybe_unused]] const int y) {}
+public:
+	/*!
+		Indicates a movement of the mouse.
+	*/
+	virtual void move([[maybe_unused]] const int x, [[maybe_unused]] const int y) {}
 
-		/*!
-			@returns the number of buttons on this mouse.
-		*/
-		virtual int get_number_of_buttons() const {
-			return 1;
-		}
+	/*!
+		@returns the number of buttons on this mouse.
+	*/
+	virtual int get_number_of_buttons() const {
+		return 1;
+	}
 
-		/*!
-			Indicates that button @c index is now either pressed or unpressed.
-			The intention is that @c index be semantic, not positional:
-			0 for the primary button, 1 for the secondary, 2 for the tertiary, etc.
-		*/
-		virtual void set_button_pressed([[maybe_unused]] const int index, [[maybe_unused]] const bool is_pressed) {}
+	/*!
+		Indicates that button @c index is now either pressed or unpressed.
+		The intention is that @c index be semantic, not positional:
+		0 for the primary button, 1 for the secondary, 2 for the tertiary, etc.
+	*/
+	virtual void set_button_pressed([[maybe_unused]] const int index, [[maybe_unused]] const bool is_pressed) {}
 
-		/*!
-			Releases all depressed buttons.
-		*/
-		virtual void reset_all_buttons() {}
+	/*!
+		Releases all depressed buttons.
+	*/
+	virtual void reset_all_buttons() {}
 };
 
 }

InstructionSets/6809/OperationMapper.hpp

@@ -79,23 +79,23 @@ template <int i, typename SchedulerT> void OperationMapper<Page::Page0>::dispatc
 	using AM = AddressingMode;
 	using O = Operation;
 
-	constexpr auto upper = (i >> 4) & 0xf;
-	constexpr auto lower = (i >> 0) & 0xf;
+	static constexpr auto upper = (i >> 4) & 0xf;
+	static constexpr auto lower = (i >> 0) & 0xf;
 
-	constexpr AddressingMode modes[] = {
+	static constexpr AddressingMode modes[] = {
 		AM::Immediate, AM::Direct, AM::Indexed, AM::Extended
 	};
-	constexpr AddressingMode mode = modes[(i >> 4) & 3];
+	static constexpr AddressingMode mode = modes[(i >> 4) & 3];
 
 	switch(upper) {
 		default: break;
 
 		case 0x1: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::Page1,	O::Page2,	O::NOP,		O::SYNC,	O::None,	O::None,	O::LBRA,	O::LBSR,
 				O::None,	O::DAA,		O::ORCC,	O::None,	O::ANDCC,	O::SEX,		O::EXG,		O::TFR,
 			};
-			constexpr AddressingMode modes[] = {
+			static constexpr AddressingMode modes[] = {
 				AM::Variant,	AM::Variant,	AM::Inherent,	AM::Inherent,
 				AM::Illegal,	AM::Illegal,	AM::Relative,	AM::Relative,
 				AM::Illegal,	AM::Inherent,	AM::Immediate,	AM::Illegal,
@@ -104,18 +104,18 @@ template <int i, typename SchedulerT> void OperationMapper<Page::Page0>::dispatc
 			s.template schedule<operations[lower], modes[lower]>();
 		} break;
 		case 0x2: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::BRA,		O::BRN,		O::BHI,		O::BLS,		O::BCC,		O::BCS,		O::BNE,		O::BEQ,
 				O::BVC,		O::BVS,		O::BPL,		O::BMI,		O::BGE,		O::BLT,		O::BGT,		O::BLE,
 			};
 			s.template schedule<operations[lower], AM::Relative>();
 		} break;
 		case 0x3: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::LEAX,	O::LEAY,	O::LEAS,	O::LEAU,	O::PSHS,	O::PULS,	O::PSHU,	O::PULU,
 				O::None,	O::RTS,		O::ABX,		O::RTI,		O::CWAI,	O::MUL,		O::RESET,	O::SWI,
 			};
-			constexpr auto op = operations[lower];
+			static constexpr auto op = operations[lower];
 			switch(lower) {
 				case 0x0:	case 0x1:	case 0x2:	case 0x3:
 					s.template schedule<op, AM::Indexed>();
@@ -132,31 +132,31 @@ template <int i, typename SchedulerT> void OperationMapper<Page::Page0>::dispatc
 			}
 		} break;
 		case 0x4: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::NEGA,	O::None,	O::None,	O::COMA,	O::LSRA,	O::None,	O::RORA,	O::ASRA,
 				O::LSLA,	O::ROLA,	O::DECA,	O::None,	O::INCA,	O::TSTA,	O::None,	O::CLRA,
 			};
-			constexpr auto op = operations[lower];
+			static constexpr auto op = operations[lower];
 			s.template schedule<op, op == O::None ? AM::Illegal : AM::Inherent>();
 		} break;
 		case 0x5: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::NEGB,	O::None,	O::None,	O::COMB,	O::LSRB,	O::None,	O::RORB,	O::ASRB,
 				O::LSLB,	O::ROLB,	O::DECB,	O::None,	O::INCB,	O::TSTB,	O::None,	O::CLRB,
 			};
-			constexpr auto op = operations[lower];
+			static constexpr auto op = operations[lower];
 			s.template schedule<op, op == O::None ? AM::Illegal : AM::Inherent>();
 		} break;
 		case 0x0: case 0x6:	case 0x7: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::NEG,		O::None,	O::None,	O::COM,		O::LSR,		O::None,	O::ROR,		O::ASR,
 				O::LSL,		O::ROL,		O::DEC,		O::None,	O::INC,		O::TST,		O::JMP,		O::CLR,
 			};
-			constexpr auto op = operations[lower];
+			static constexpr auto op = operations[lower];
 			s.template schedule<op, op == O::None ? AM::Illegal : upper == 0 ? AM::Direct : mode>();
 		} break;
 		case 0x8:	case 0x9:	case 0xa:	case 0xb: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::SUBA,	O::CMPA,	O::SBCA,	O::SUBD,	O::ANDA,	O::BITA,	O::LDA,		O::STA,
 				O::EORA,	O::ADCA,	O::ORA,		O::ADDA,	O::CMPX,	O::JSR,		O::LDX,		O::STX,
 			};
@@ -164,7 +164,7 @@ template <int i, typename SchedulerT> void OperationMapper<Page::Page0>::dispatc
 			else			s.template schedule<operations[lower], mode>();
 		} break;
 		case 0xc:	case 0xd:	case 0xe:	case 0xf: {
-			constexpr Operation operations[] = {
+			static constexpr Operation operations[] = {
 				O::SUBB,	O::CMPB,	O::SBCB,	O::ADDD,	O::ANDB,	O::BITB,	O::LDB,		O::STB,
 				O::EORB,	O::ADCB,	O::ORB,		O::ADDB,	O::LDD,		O::STD,		O::LDU,		O::STU,
 			};
@@ -178,13 +178,13 @@ template <int i, typename SchedulerT> void OperationMapper<Page::Page1>::dispatc
 	using AM = AddressingMode;
 	using O = Operation;
 
-	constexpr AddressingMode modes[] = {
+	static constexpr AddressingMode modes[] = {
 		AM::Immediate, AM::Direct, AM::Indexed, AM::Extended
 	};
-	constexpr auto mode = modes[(i >> 4) & 3];
+	static constexpr auto mode = modes[(i >> 4) & 3];
 
 	if constexpr (i >= 0x21 && i < 0x30) {
-		constexpr Operation operations[] = {
+		static constexpr Operation operations[] = {
 						O::LBRN,	O::LBHI,	O::LBLS,	O::LBCC,	O::LBCS,	O::LBNE,	O::LBEQ,
 			O::LBVC,	O::LBVS,	O::LBPL,	O::LBMI,	O::LBGE,	O::LBLT,	O::LBGT,	O::LBLE,
 		};
@@ -219,10 +219,10 @@ template <int i, typename SchedulerT> void OperationMapper<Page::Page2>::dispatc
 	using AM = AddressingMode;
 	using O = Operation;
 
-	constexpr AddressingMode modes[] = {
+	static constexpr AddressingMode modes[] = {
 		AM::Immediate, AM::Direct, AM::Indexed, AM::Extended
 	};
-	constexpr auto mode = modes[(i >> 4) & 3];
+	static constexpr auto mode = modes[(i >> 4) & 3];
 
 	switch(i) {
 		default:	s.template schedule<O::None, AM::Illegal>();	break;

InstructionSets/ARM/BarrelShifter.hpp

@@ -8,6 +8,8 @@
 
 #pragma once
 
+#include <bit>
+
 namespace InstructionSet::ARM {
 
 enum class ShiftType {
@@ -99,14 +101,12 @@ void shift(uint32_t &source, uint32_t amount, const typename Carry<set_carry>::t
 			amount &= 31;
 			if(amount) {
 				if constexpr (set_carry) carry = source & (1 << (amount - 1));
-				source = (source >> amount) | (source << (32 - amount));
+				source = std::rotr(source, int(amount));
 			} else {
 				if constexpr (set_carry) carry = source & 0x8000'0000;
 			}
 		} break;
 
-		// TODO: upon adoption of C++20, use std::rotr.
-
 		default: break;
 	}
 }

InstructionSets/ARM/Disassembler.hpp

@@ -172,7 +172,7 @@ struct Disassembler {
 	}
 
 	template <Flags f> void perform(const DataProcessing fields) {
-		constexpr DataProcessingFlags flags(f);
+		static constexpr DataProcessingFlags flags(f);
 
 		instruction_.operand1.type = Operand::Type::Register;
 		instruction_.operand1.value = fields.operand1();
@@ -215,7 +215,7 @@ struct Disassembler {
 
 	template <Flags> void perform(Multiply) {}
 	template <Flags f> void perform(const SingleDataTransfer fields) {
-		constexpr SingleDataTransferFlags flags(f);
+		static constexpr SingleDataTransferFlags flags(f);
 		instruction_.operation =
 			(flags.operation() == SingleDataTransferFlags::Operation::STR) ?
 				Instruction::Operation::STR : Instruction::Operation::LDR;
@@ -227,7 +227,7 @@ struct Disassembler {
 		instruction_.operand1.value = fields.base();
 	}
 	template <Flags f> void perform(const BlockDataTransfer fields) {
-		constexpr BlockDataTransferFlags flags(f);
+		static constexpr BlockDataTransferFlags flags(f);
 		instruction_.operation =
 			(flags.operation() == BlockDataTransferFlags::Operation::STM) ?
 				Instruction::Operation::STM : Instruction::Operation::LDM;
@@ -239,7 +239,7 @@ struct Disassembler {
 		instruction_.operand1.value = fields.register_list();
 	}
 	template <Flags f> void perform(const Branch fields) {
-		constexpr BranchFlags flags(f);
+		static constexpr BranchFlags flags(f);
 		instruction_.operation =
 			(flags.operation() == BranchFlags::Operation::BL) ?
 				Instruction::Operation::BL : Instruction::Operation::B;
@@ -247,7 +247,7 @@ struct Disassembler {
 		instruction_.operand1.value = fields.offset();
 	}
 	template <Flags f> void perform(CoprocessorRegisterTransfer) {
-		constexpr CoprocessorRegisterTransferFlags flags(f);
+		static constexpr CoprocessorRegisterTransferFlags flags(f);
 		instruction_.operation =
 			(flags.operation() == CoprocessorRegisterTransferFlags::Operation::MRC) ?
 				Instruction::Operation::MRC : Instruction::Operation::MCR;

InstructionSets/ARM/Executor.hpp

@@ -63,7 +63,7 @@ struct Executor {
 		return condition == Condition::AL ? true : registers_.test(condition);
 	}
 
-	template <bool allow_register, bool set_carry, typename FieldsT>
+	template <bool set_carry, typename FieldsT>
 	uint32_t decode_shift(const FieldsT fields, uint32_t &rotate_carry, const uint32_t pc_offset) {
 		// "When R15 appears in the Rm position it will give the value of the PC together
 		// with the PSR flags to the barrel shifter. ...
@@ -78,8 +78,7 @@ struct Executor {
 			operand2 = registers_[fields.operand2()];
 		}
 
-		// TODO: in C++20, a quick `if constexpr (requires` can eliminate the `allow_register` parameter.
-		if constexpr (allow_register) {
+		if constexpr (requires {fields.shift_count_is_register();}) {
 			if(fields.shift_count_is_register()) {
 				uint32_t shift_amount;
 
@@ -106,7 +105,7 @@ struct Executor {
 	}
 
 	template <Flags f> void perform(const DataProcessing fields) {
-		constexpr DataProcessingFlags flags(f);
+		static constexpr DataProcessingFlags flags(f);
 		const bool shift_by_register = !flags.operand2_is_immediate() && fields.shift_count_is_register();
 
 		// Write a raw result into the PC proxy if the target is R15; it'll be stored properly later.
@@ -128,14 +127,14 @@ struct Executor {
 		uint32_t rotate_carry = registers_.c();
 
 		// Populate carry from the shift only if it'll be used.
-		constexpr bool shift_sets_carry = is_logical(flags.operation()) && flags.set_condition_codes();
+		static constexpr bool shift_sets_carry = is_logical(flags.operation()) && flags.set_condition_codes();
 
 		// Get operand 2.
 		if constexpr (flags.operand2_is_immediate()) {
 			operand2 = fields.immediate();
 			shift<ShiftType::RotateRight, shift_sets_carry, false>(operand2, fields.rotate(), rotate_carry);
 		} else {
-			operand2 = decode_shift<true, shift_sets_carry>(fields, rotate_carry, shift_by_register ? 8 : 4);
+			operand2 = decode_shift<shift_sets_carry>(fields, rotate_carry, shift_by_register ? 8 : 4);
 		}
 
 		uint32_t conditions = 0;
@@ -231,7 +230,7 @@ struct Executor {
 	}
 
 	template <Flags f> void perform(const Multiply fields) {
-		constexpr MultiplyFlags flags(f);
+		static constexpr MultiplyFlags flags(f);
 
 		// R15 rules:
 		//
@@ -258,7 +257,7 @@ struct Executor {
 	}
 
 	template <Flags f> void perform(const Branch branch) {
-		constexpr BranchFlags flags(f);
+		static constexpr BranchFlags flags(f);
 
 		if constexpr (flags.operation() == BranchFlags::Operation::BL) {
 			registers_[14] = registers_.pc_status(0);
@@ -267,7 +266,7 @@ struct Executor {
 	}
 
 	template <Flags f> void perform(const SingleDataTransfer transfer) {
-		constexpr SingleDataTransferFlags flags(f);
+		static constexpr SingleDataTransferFlags flags(f);
 
 		// Calculate offset.
 		uint32_t offset;
@@ -276,7 +275,7 @@ struct Executor {
 			// the register specified shift amounts are not available
 			// in this instruction class.
 			uint32_t carry = registers_.c();
-			offset = decode_shift<false, false>(transfer, carry, 4);
+			offset = decode_shift<false>(transfer, carry, 4);
 		} else {
 			offset = transfer.immediate();
 		}
@@ -392,8 +391,8 @@ struct Executor {
 		}
 	}
 	template <Flags f> void perform(const BlockDataTransfer transfer) {
-		constexpr BlockDataTransferFlags flags(f);
-		constexpr bool is_ldm = flags.operation() == BlockDataTransferFlags::Operation::LDM;
+		static constexpr BlockDataTransferFlags flags(f);
+		static constexpr bool is_ldm = flags.operation() == BlockDataTransferFlags::Operation::LDM;
 
 		// Ensure that *base points to the base register if it can be written back;
 		// also set address to the base.

InstructionSets/ARM/OperationMapper.hpp

@@ -293,18 +293,7 @@ struct BlockDataTransfer: public WithShiftControlBits {
 	uint32_t base() const				{	return (opcode_ >> 16) & 0xf;			}
 
 	/// A bitfield indicating which registers to load or store.
-	uint16_t register_list() const		{	return static_cast<uint16_t>(opcode_);	}
-	uint32_t popcount() const {
-		const uint16_t list = register_list();
-
-		// TODO: just use std::popcount when adopting C++20.
-		uint32_t total = ((list & 0xaaaa) >> 1) + (list & 0x5555);
-		total = ((total & 0xcccc) >> 2) + (total & 0x3333);
-		total = ((total & 0xf0f0) >> 4) + (total & 0x0f0f);
-		total = ((total & 0xff00) >> 8) + (total & 0x00ff);
-
-		return total;
-	}
+	uint16_t register_list() const		{	return static_cast<uint16_t>(opcode_);				}
 };
 
 //

InstructionSets/M50740/Decoder.cpp

@@ -17,7 +17,8 @@ Instruction Decoder::instrucion_for_opcode(const uint8_t opcode) {
 	switch(opcode) {
 		default:	return Instruction(opcode);
 
-#define Map(opcode, operation, addressing_mode)	case opcode: return Instruction(Operation::operation, AddressingMode::addressing_mode, opcode);
+#define Map(opcode, operation, addressing_mode)	\
+	case opcode: return Instruction(Operation::operation, AddressingMode::addressing_mode, opcode);
 
 	/* 0x00 – 0x0f */
 		Map(0x00, BRK, Implied);					Map(0x01, ORA, XIndirect);

InstructionSets/M50740/Executor.cpp

@@ -18,8 +18,8 @@
 using namespace InstructionSet::M50740;
 
 namespace {
-	constexpr int port_remap[] = {0, 1, 2, 0, 3};
-	Log::Logger<Log::Source::M50740> logger;
+constexpr int port_remap[] = {0, 1, 2, 0, 3};
+using Logger = Log::Logger<Log::Source::M50740>;
 }
 
 Executor::Executor(PortHandler &port_handler) : port_handler_(port_handler) {
@@ -82,13 +82,13 @@ uint8_t Executor::read(uint16_t address) {
 	port_handler_.run_ports_for(cycles_since_port_handler_.flush<Cycles>());
 	switch(address) {
 		default:
-			logger.error().append("Unrecognised read from %02x", address);
+			Logger::error().append("Unrecognised read from %02x", address);
 		return 0xff;
 
 		// "Port R"; sixteen four-bit ports
 		case 0xd0: case 0xd1: case 0xd2: case 0xd3: case 0xd4: case 0xd5: case 0xd6: case 0xd7:
 		case 0xd8: case 0xd9: case 0xda: case 0xdb: case 0xdc: case 0xdd: case 0xde: case 0xdf:
-			logger.error().append("Unimplemented Port R read from %04x", address);
+			Logger::error().append("Unimplemented Port R read from %04x", address);
 		return 0x00;
 
 		// Ports P0–P3.
@@ -133,7 +133,7 @@ void Executor::write(uint16_t address, const uint8_t value) {
 
 	// ROM 'writes' are almost as easy (albeit unexpected).
 	if(address >= 0x100) {
-		logger.info().append("Attempted ROM write of %02x to %04x", value, address);
+		Logger::info().append("Attempted ROM write of %02x to %04x", value, address);
 		return;
 	}
 
@@ -142,13 +142,13 @@ void Executor::write(uint16_t address, const uint8_t value) {
 
 	switch(address) {
 		default:
-			logger.error().append("Unrecognised write of %02x to %04x", value, address);
+			Logger::error().append("Unrecognised write of %02x to %04x", value, address);
 		break;
 
 		// "Port R"; sixteen four-bit ports
 		case 0xd0: case 0xd1: case 0xd2: case 0xd3: case 0xd4: case 0xd5: case 0xd6: case 0xd7:
 		case 0xd8: case 0xd9: case 0xda: case 0xdb: case 0xdc: case 0xdd: case 0xde: case 0xdf:
-			logger.error().append("Unimplemented Port R write of %02x to %04x", value, address);
+			Logger::error().append("Unimplemented Port R write of %02x to %04x", value, address);
 		break;
 
 		// Ports P0–P3.
@@ -241,7 +241,7 @@ template <Operation operation, AddressingMode addressing_mode> void Executor::pe
 		case Operation::ADC:	case Operation::AND:	case Operation::CMP:	case Operation::EOR:
 		case Operation::LDA:	case Operation::ORA:	case Operation::SBC:
 		{
-			constexpr int t_lengths[] = {
+			static constexpr int t_lengths[] = {
 				0,
 				operation == Operation::LDA ? 2 : (operation == Operation::CMP ? 1 : 3)
 			};
@@ -444,7 +444,7 @@ template <Operation operation, AddressingMode addressing_mode> void Executor::pe
 					case Operation::BBS0:	case Operation::BBS1:	case Operation::BBS2:	case Operation::BBS3:
 					case Operation::BBS4:	case Operation::BBS5:	case Operation::BBS6:	case Operation::BBS7: {
 						if constexpr (operation >= Operation::BBS0 && operation <= Operation::BBS7) {
-							constexpr uint8_t mask = 1 << (int(operation) - int(Operation::BBS0));
+							static constexpr uint8_t mask = 1 << (int(operation) - int(Operation::BBS0));
 							if(value & mask) {
 								set_program_counter(uint16_t(address));
 								subtract_duration(2);
@@ -454,7 +454,7 @@ template <Operation operation, AddressingMode addressing_mode> void Executor::pe
 					case Operation::BBC0:	case Operation::BBC1:	case Operation::BBC2:	case Operation::BBC3:
 					case Operation::BBC4:	case Operation::BBC5:	case Operation::BBC6:	case Operation::BBC7: {
 						if constexpr (operation >= Operation::BBC0 && operation <= Operation::BBC7) {
-							constexpr uint8_t mask = 1 << (int(operation) - int(Operation::BBC0));
+							static constexpr uint8_t mask = 1 << (int(operation) - int(Operation::BBC0));
 							if(!(value & mask)) {
 								set_program_counter(uint16_t(address));
 								subtract_duration(2);
@@ -792,7 +792,7 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
 		*/
 
 		default:
-			logger.error().append("Unimplemented operation: %d", operation);
+			Logger::error().append("Unimplemented operation: %d", operation);
 			assert(false);
 	}
 }
@@ -805,8 +805,9 @@ inline void Executor::subtract_duration(const int duration) {
 	cycles_since_port_handler_ += Cycles(duration);
 
 	// Update timer 1 and 2 prescaler.
-	constexpr int t12_divider = 4;		// A divide by 4 has already been applied before counting instruction lengths; therefore
-										// this additional divide by 4 produces the correct net divide by 16.
+	static constexpr int t12_divider = 4;	// A divide by 4 has already been applied before counting instruction
+											// lengths; therefore this additional divide by 4 produces the correct net
+											// divide by 16.
 
 	timer_divider_ += duration;
 	const int clock_ticks = timer_divider_ / t12_divider;
@@ -835,13 +836,13 @@ inline void Executor::subtract_duration(const int duration) {
 			}
 		} break;
 		case 0x04:
-			logger.error().append("TODO: Timer X; Pulse output mode");
+			Logger::error().append("TODO: Timer X; Pulse output mode");
 		break;
 		case 0x08:
-			logger.error().append("TODO: Timer X; Event counter mode");
+			Logger::error().append("TODO: Timer X; Event counter mode");
 		break;
 		case 0x0c:
-			logger.error().append("TODO: Timer X; Pulse width measurement mode");
+			Logger::error().append("TODO: Timer X; Pulse width measurement mode");
 		break;
 	}
 }

InstructionSets/M68k/Implementation/ExecutorImplementation.hpp

@@ -202,7 +202,7 @@ template <typename IntT> IntT Executor<model, BusHandler>::State::read_pc() {
 template <Model model, typename BusHandler>
 uint32_t Executor<model, BusHandler>::State::index_8bitdisplacement(uint32_t base) {
 	// Determine whether full extension addressing modes are supported.
-	constexpr bool supports_full_extensions = model >= Model::M68020;
+	static constexpr bool supports_full_extensions = model >= Model::M68020;
 
 	// Get the [first] extension word.
 	const auto extension = read_pc<uint16_t>();

InstructionSets/M68k/Implementation/InstructionOperandFlags.hpp

@@ -14,6 +14,7 @@ template <Model model, Operation t_operation> constexpr uint8_t operand_flags(co
 	switch((t_operation != Operation::Undefined) ? t_operation : r_operation) {
 		default:
 			assert(false);
+			[[fallthrough]];
 
 		//
 		//	No operands are fetched or stored.

InstructionSets/M68k/Implementation/PerformImplementation.hpp

@@ -12,6 +12,7 @@
 #include "InstructionSets/M68k/ExceptionVectors.hpp"
 
 #include <algorithm>
+#include <bit>
 #include <cassert>
 #include <cmath>
 
@@ -33,7 +34,7 @@ static void add_sub(const IntT source, IntT &destination, Status &status) {
 	static_assert(!std::numeric_limits<IntT>::is_signed);
 
 	static_assert(operation == Numeric::Operation::Add || operation == Numeric::Operation::Subtract);
-	constexpr bool is_add = operation == Numeric::Operation::Add;
+	static constexpr bool is_add = operation == Numeric::Operation::Add;
 	IntT result = is_add ?
 		destination + source :
 		destination - source;
@@ -312,7 +313,7 @@ void shift(const uint32_t source, IntT &destination, Status &status, FlowControl
 		operation == Operation::LSRb || operation == Operation::LSRw || operation == Operation::LSRl
 	);
 
-	constexpr auto size = Numeric::bit_size<IntT>();
+	static constexpr auto size = Numeric::bit_size<IntT>();
 	const auto shift = shift_count<IntT>(uint8_t(source), flow_controller);
 
 	if(!shift) {
@@ -407,7 +408,7 @@ void rotate(const uint32_t source, IntT &destination, Status &status, FlowContro
 		operation == Operation::RORb || operation == Operation::RORw || operation == Operation::RORl
 	);
 
-	constexpr auto size = Numeric::bit_size<IntT>();
+	static constexpr auto size = Numeric::bit_size<IntT>();
 	auto shift = shift_count<IntT>(uint8_t(source), flow_controller);
 
 	if(!shift) {
@@ -417,21 +418,11 @@ void rotate(const uint32_t source, IntT &destination, Status &status, FlowContro
 
 		switch(operation) {
 			case Operation::ROLb:	case Operation::ROLw:	case Operation::ROLl:
-				if(shift) {
-					destination = IntT(
-						(destination << shift) |
-						(destination >> (size - shift))
-					);
-				}
+				destination = std::rotl<IntT>(destination, shift);
 				status.carry_flag = Status::FlagT(destination & 1);
 			break;
 			case Operation::RORb:	case Operation::RORw:	case Operation::RORl:
-				if(shift) {
-					destination = IntT(
-						(destination >> shift) |
-						(destination << (size - shift))
-					);
-				}
+				destination = std::rotr<IntT>(destination, shift);
 				status.carry_flag = Status::FlagT(destination & Numeric::top_bit<IntT>());
 			break;
 		}
@@ -449,7 +440,7 @@ void rox(const uint32_t source, IntT &destination, Status &status, FlowControlle
 		operation == Operation::ROXRb || operation == Operation::ROXRw || operation == Operation::ROXRl
 	);
 
-	constexpr auto size = Numeric::bit_size<IntT>();
+	static constexpr auto size = Numeric::bit_size<IntT>();
 	auto shift = shift_count<IntT>(uint8_t(source), flow_controller) % (size + 1);
 
 	if(!shift) {

InstructionSets/M68k/Instruction.cpp

@@ -14,8 +14,6 @@ using namespace InstructionSet::M68k;
 
 std::string Preinstruction::operand_description(const int index, const int opcode) const {
 	switch(mode(index)) {
-		default:	assert(false);
-
 		case AddressingMode::None:
 			return "";
 
@@ -54,7 +52,12 @@ std::string Preinstruction::operand_description(const int index, const int opcod
 				return "Q";
 			}
 			return std::to_string(int(quick(uint16_t(opcode), operation)));
+
+		// TODO: 68020+ modes.
+		default: break;
 	}
+	assert(false);
+	return "[TODO]";
 }
 
 namespace {

InstructionSets/PowerPC/Instruction.hpp

@@ -1500,7 +1500,7 @@ struct Instruction {
 
 	/// A 24-bit signed number; provided as already sign extended.
 	int32_t li() const {
-		constexpr uint32_t extensions[2] = {
+		static constexpr uint32_t extensions[2] = {
 			0x0000'0000,
 			0xfc00'0000
 		};

InstructionSets/x86/AccessType.hpp

@@ -8,6 +8,8 @@
 
 #pragma once
 
+#include <type_traits>
+
 namespace InstructionSet::x86 {
 
 /// Explains the type of access that `perform` intends to perform; is provided as a template parameter to whatever
@@ -43,25 +45,41 @@ constexpr bool is_writeable(const AccessType type) {
 	return type == AccessType::ReadModifyWrite || type == AccessType::Write;
 }
 
+// Allow only 8-, 16- and 32-bit unsigned int accesses.
+template <typename IntT>
+concept is_x86_data_type
+	= std::is_same_v<IntT, uint8_t> || std::is_same_v<IntT, uint16_t> || std::is_same_v<IntT, uint32_t>;
+
 template <typename IntT, AccessType type> struct Accessor;
 
 // Reads: return a value directly.
-template <typename IntT> struct Accessor<IntT, AccessType::Read> { using type = const IntT; };
-template <typename IntT> struct Accessor<IntT, AccessType::PreauthorisedRead> { using type = const IntT; };
+template <typename IntT>
+requires is_x86_data_type<IntT>
+struct Accessor<IntT, AccessType::Read> { using type = IntT; };
+
+template <typename IntT>
+requires is_x86_data_type<IntT>
+struct Accessor<IntT, AccessType::PreauthorisedRead> { using type = IntT; };
 
 // Writes: return a custom type that can be written but not read.
 template <typename IntT>
+requires is_x86_data_type<IntT>
 class Writeable {
 public:
-	Writeable(IntT &target) : target_(target) {}
-	IntT operator=(IntT value) { return target_ = value; }
+	constexpr Writeable(IntT &target) noexcept : target_(target) {}
+	IntT operator=(const IntT value) { return target_ = value; }
 private:
 	IntT &target_;
 };
-template <typename IntT> struct Accessor<IntT, AccessType::Write> { using type = Writeable<IntT>; };
+
+template <typename IntT>
+requires is_x86_data_type<IntT>
+struct Accessor<IntT, AccessType::Write> { using type = Writeable<IntT>; };
 
 // Read-modify-writes: return a reference.
-template <typename IntT> struct Accessor<IntT, AccessType::ReadModifyWrite> { using type = IntT &; };
+template <typename IntT>
+requires is_x86_data_type<IntT>
+struct Accessor<IntT, AccessType::ReadModifyWrite> { using type = IntT &; };
 
 // Shorthands; assumed that preauthorised reads have the same return type as reads.
 template<typename IntT> using read_t = typename Accessor<IntT, AccessType::Read>::type;

InstructionSets/x86/Decoder.cpp

@@ -30,6 +30,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 	// without any loss of context. This reduces the risk of the decoder tricking a caller into
 	// an infinite loop.
 	static constexpr int max_instruction_length = model >= Model::i80386 ? 15 : (model == Model::i80286 ? 10 : 65536);
+	static constexpr bool is_32bit = instruction_type(model) == InstructionType::Bits32;
 	const uint8_t *const end = source + std::min(length, size_t(max_instruction_length - consumed_));
 
 	// MARK: - Prefixes (if present) and the opcode.
@@ -194,6 +195,8 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 					displacement(Operation::JP, DataSize::Byte);
 				} else {
 					immediate(Operation::PUSH, DataSize::Byte);
+					operation_size_ = data_size_;
+					sign_extend_operand_ = true;
 				}
 			break;
 			case 0x6b:
@@ -688,7 +691,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 			};
 			displacement_size_ = sizes[mod];
 
-			if(is_32bit(model) && address_size_ == AddressSize::b32) {
+			if(is_32bit && address_size_ == AddressSize::b32) {
 				// 32-bit decoding: the range of potential indirections is expanded,
 				// and may segue into obtaining a SIB.
 				sib_ = ScaleIndexBase(0, Source::None, reg_table[rm]);
@@ -734,9 +737,8 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 
 				switch(reg) {
 					default:
-						// case 1 is treated as another form of TEST on the 8086.
-						// (and, I guess, the 80186?)
-						if constexpr (model >= Model::i80286) {
+						// case 1 is treated as another form of TEST through to at least the 80286.
+						if constexpr (model >= Model::i80386) {
 							return undefined();
 						}
 						[[fallthrough]];
@@ -763,7 +765,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 
 				// The 16-bit chips have four segment registers;
 				// the 80386 onwards has six.
-				if constexpr (is_32bit(model)) {
+				if constexpr (is_32bit) {
 					if(masked_reg > 5) {
 						return undefined();
 					}
@@ -790,15 +792,27 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 			case ModRegRMFormat::MemRegROL_to_SAR:
 				destination_ = memreg;
 
+				// TODO: is this true? It appears empirically to be so from the PC AT BIOS, but find a source.
+				if(operand_size_ != DataSize::None) {
+					operand_size_ = DataSize::Byte;
+				}
+
 				switch(reg) {
 					default:
-						if constexpr (model == Model::i8086) {
-							if(source_ == Source::eCX) {
-								set(Operation::SETMOC);
-							} else {
-								set(Operation::SETMO);
-							}
-						} else {
+						switch(model) {
+							case Model::i8086:
+								if(source_ == Source::eCX) {
+									set(Operation::SETMOC);
+								} else {
+									set(Operation::SETMO);
+								}
+							break;
+
+							case Model::i80286:
+								set(Operation::SAL);
+							break;
+
+							default:
 							return undefined();
 						}
 					break;
@@ -858,6 +872,13 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 				source_ = Source::Immediate;
 				destination_ = memreg;
 				operand_size_ = operation_size_;
+
+				// This form requires that the reg field be blank
+				if constexpr (model >= Model::i80286) {
+					if(reg != 0) {
+						return undefined();
+					}
+				}
 			break;
 
 			case ModRegRMFormat::MemRegADD_to_CMP:
@@ -888,7 +909,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 				destination_ = source_ = memreg;
 
 				switch(reg) {
-					default: 	return undefined();
+					default:	return undefined();
 
 					case 0:		set(Operation::SLDT);	break;
 					case 1:		set(Operation::STR);	break;
@@ -903,7 +924,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 				destination_ = source_ = memreg;
 
 				switch(reg) {
-					default: 	return undefined();
+					default:	return undefined();
 
 					case 0:		set(Operation::SGDT);	break;
 					case 1:		set(Operation::SIDT);	break;
@@ -943,7 +964,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 
 	// MARK: - ScaleIndexBase
 
-	if constexpr (is_32bit(model)) {
+	if constexpr (is_32bit) {
 		if(phase_ == Phase::ScaleIndexBase && source != end) {
 			sib_ = *source;
 			++source;
@@ -1010,8 +1031,13 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 				}
 			}
 		} else {
-			// Provide a genuine measure of further bytes required.
-			return std::make_pair(-(outstanding_bytes - bytes_to_consume), InstructionT());
+			// Provide a genuine measure of further bytes required, or post a bad instruction
+			// if the length limit has been breached.
+			if(consumed_ != max_instruction_length) {
+				return std::make_pair(-(outstanding_bytes - bytes_to_consume), InstructionT());
+			} else {
+				return overlong();
+			}
 		}
 	}
 
@@ -1030,6 +1056,18 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 		// operations would unlock an extra bit of storage for a net gain of 239 extra operation types and thereby
 		// alleviating any concerns over whether there'll be space to handle MMX, floating point extensions, etc.
 
+		if constexpr (model >= Model::i80286) {
+			if(operation_ == Operation::BOUND && !is_address(source_)) {
+				return undefined();
+			}
+		}
+		if(
+			(operation_ == Operation::JMPfar || operation_ == Operation::CALLfar) &&
+			destination_ < Source::DirectAddress
+		) {
+			return undefined();
+		}
+
 		const auto result = std::make_pair(
 			consumed_,
 			InstructionT(
@@ -1051,14 +1089,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 
 	// Check for a too-long instruction.
 	if(consumed_ == max_instruction_length) {
-		std::pair<int, InstructionT> result;
-		if(max_instruction_length == 65536) {
-			result = std::make_pair(consumed_, InstructionT(Operation::NOP));
-		} else {
-			result = std::make_pair(consumed_, InstructionT());
-		}
-		reset_parsing();
-		return result;
+		return overlong();
 	}
 
 	// i.e. not done yet.
@@ -1066,7 +1097,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(
 }
 
 template <Model model> void Decoder<model>::set_32bit_protected_mode(bool enabled) {
-	if constexpr (!is_32bit(model)) {
+	if constexpr (instruction_type(model) == InstructionType::Bits16) {
 		assert(!enabled);
 		return;
 	}

InstructionSets/x86/Decoder.hpp

@@ -23,7 +23,7 @@ namespace InstructionSet::x86 {
 */
 template <Model model> class Decoder {
 public:
-	using InstructionT = Instruction<is_32bit(model)>;
+	using InstructionT = Instruction<instruction_type(model)>;
 
 	/*!
 		@returns an @c Instruction plus a size; a positive size indicates successful decoding of
@@ -349,6 +349,7 @@ private:
 		phase_ = Phase::DisplacementOrOperand;
 		displacement_size_ = DataSize::Word;
 		operand_size_ = DataSize::Byte;
+		operation_size_ = DataSize::Byte;
 	}
 
 	/// Sets up the operation size, oncoming phase and modregrm format for a member of the shift group (i.e. 'group 2').
@@ -367,6 +368,16 @@ private:
 		reset_parsing();
 		return result;
 	}
+
+	std::pair<int, typename Decoder<model>::InstructionT> overlong() {
+		const auto consumed = consumed_;
+		reset_parsing();
+		if(consumed == 65536) {
+			return std::make_pair(consumed, InstructionT(Operation::NOP));
+		} else {
+			return std::make_pair(consumed, InstructionT(ExceptionCode()));
+		}
+	}
 };
 
 extern template class InstructionSet::x86::Decoder<InstructionSet::x86::Model::i8086>;

InstructionSets/x86/Descriptors.hpp

@@ -0,0 +1,356 @@
+//
+//  Descriptors.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 19/03/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Exceptions.hpp"
+#include "Instruction.hpp"
+//#include "Perform.hpp"
+
+#include <cassert>
+#include <concepts>
+
+namespace InstructionSet::x86 {
+
+enum class DescriptorTable {
+	Global, Local, Interrupt,
+};
+
+struct DescriptorTablePointer {
+	uint16_t limit;
+	uint32_t base;
+};
+
+struct DescriptorBounds {
+	uint32_t begin, end;
+	auto operator <=>(const DescriptorBounds &) const = default;
+};
+
+enum class DescriptorType {
+	Code, Data, Stack,
+	CallGate, TaskGate, InterruptGate, TrapGate,
+	AvailableTaskStateSegment, LDT, BusyTaskStateSegment,
+	Invalid,
+};
+
+constexpr bool is_data_or_code(const DescriptorType type) {
+	return type <= DescriptorType::Stack;
+}
+
+enum DescriptorTypeFlag: uint8_t {
+	Accessed	= 1 << 0,
+	Busy		= 1 << 1,
+};
+
+struct DescriptorDescription {
+	DescriptorType type = DescriptorType::Invalid;
+	bool readable = false;
+	bool writeable = false;
+	bool conforming = false;
+	bool is32bit = false;
+};
+
+struct SegmentDescriptor {
+	SegmentDescriptor() = default;
+
+	/// Creates a new descriptor with four 16-bit from a descriptor table.
+	SegmentDescriptor(
+		const uint16_t segment,
+		const bool local,
+		const uint16_t descriptor[4]
+	) noexcept : segment_(segment), local_(local) {
+		base_ = uint32_t(descriptor[1] | ((descriptor[2] & 0xff) << 16));
+		type_ = descriptor[2] >> 8;
+
+		offset_ = descriptor[0];
+		if(description().type != DescriptorType::Stack) {
+			bounds_ = DescriptorBounds{ 0, offset_ };
+		} else {
+			if(offset_ != std::numeric_limits<uint32_t>::max()) {
+				bounds_ = DescriptorBounds{ uint32_t(offset_ + 1), std::numeric_limits<uint32_t>::max() };
+			} else {
+				// This descriptor is impossible to satisfy for reasons that aren't
+				// properly expressed if the lower bound is incremented, so make it
+				// impossible to satisfy in a more prosaic sense.
+				bounds_ = DescriptorBounds{ 1, 0 };
+			}
+		}
+	}
+
+	/// Rewrites this descriptor as a real-mode segment.
+	void set_segment(const uint16_t segment) {
+		segment_ = segment;
+		base_ = uint32_t(segment) << 4;
+		bounds_ = DescriptorBounds{ 0x0000, 0xffff };
+		offset_ = 0;
+		type_ = 0b1'00'1'001'0;		// Present, privilege level 0, expand-up writeable data, unaccessed.
+	}
+
+	uint16_t segment() const {
+		return segment_;
+	}
+
+	/// @returns The linear address for offest @c address within the segment described by this descriptor.
+	uint32_t to_linear(const uint32_t address) const {
+		return base_ + address;
+	}
+
+	void throw_gpf() const {
+		throw Exception::exception<Vector::GeneralProtectionFault>(
+			ExceptionCode(
+				segment_,
+				local_,
+				false,
+				false
+			)
+		);
+	}
+
+	template <AccessType type, typename AddressT>
+	requires std::same_as<AddressT, uint16_t> || std::same_as<AddressT, uint32_t>
+	void authorise(const AddressT begin, const AddressT end) const {
+		// Test for bounds; end && end < begin captures instances where end is
+		// both out of bounds and beyond the range of AddressT.
+		if(begin < bounds_.begin || end > bounds_.end || (end && end < begin)) {
+			throw_gpf();
+		}
+
+		// Tested at loading (?): present(), privilege_level().
+		const auto desc = description();
+		if(type == AccessType::Read && !desc.readable) {
+			throw_gpf();
+		}
+
+		if(type == AccessType::Write && !desc.writeable) {
+			throw_gpf();
+		}
+	}
+
+	void validate_as(const Source segment) const {
+		const auto desc = description();
+		switch(segment) {
+			case Source::DS:
+			case Source::ES:
+				if(!desc.readable) {
+					printf("TODO: throw for unreadable DS or ES source.\n");
+					assert(false);
+				}
+			break;
+
+			case Source::SS:
+				if(!desc.writeable) {
+					printf("TODO: throw for unwriteable SS target.\n");
+					assert(false);
+				}
+			break;
+
+			default: break;
+		}
+
+		// TODO: is this descriptor privilege within reach?
+		// TODO: is this an empty descriptor*? If so: exception!
+	}
+
+	// TODO: validators for:
+	//	INT
+	//	IRET
+	//	JMP
+	//	RET
+	//
+	// Verify also: MOV, POP, both of which can mutate DS/ES, SS, etc.
+
+	void validate_call(
+		const std::function<void(const SegmentDescriptor &)> &call_callback
+	) const {
+		const auto desc = description();
+		switch(desc.type) {
+			case DescriptorType::Code:
+				if(desc.conforming) {
+					// TODO:
+					// DPL must be :5 CPL else #GP (code segment selector)
+				} else {
+
+				}
+
+				call_callback(*this);
+			break;
+
+			case DescriptorType::CallGate:
+				assert(false);
+			break;
+
+			case DescriptorType::AvailableTaskStateSegment:
+				assert(false);
+			break;
+
+			default:
+				throw_gpf();
+			break;
+		}
+	}
+
+	/// @returns The base of this segment descriptor.
+	uint32_t base() const {		return base_;	}
+
+	/// @returns The offset of this segment descriptor.
+	uint32_t offset() const {	return offset_;	}
+
+	/// @returns The bounds of this segment descriptor; will be either [0, limit] or [limit, INT_MAX] depending on descriptor type.
+	/// Accesses must be `>= bounds().begin` and `<= bounds().end`.
+	DescriptorBounds bounds() const {	return bounds_;	}
+
+	bool present() const			{	return type_ & 0x80;		}
+	int privilege_level() const		{	return (type_ >> 5) & 3;	}
+	uint8_t access_rights() const	{	return uint8_t(type_);		}
+
+	DescriptorDescription description() const {
+		using Type = DescriptorType;
+		switch(type_ & 0b11111) {
+			default:
+			case 0b00000:    return { .type = Type::Invalid };
+			case 0b00001:    return { .type = Type::AvailableTaskStateSegment, .is32bit = false };
+			case 0b00010:    return { .type = Type::LDT };
+			case 0b00011:    return { .type = Type::BusyTaskStateSegment, .is32bit = false };
+
+			case 0b00100:    return { .type = Type::CallGate, .is32bit = false };
+			case 0b00101:    return { .type = Type::TaskGate };
+			case 0b00110:    return { .type = Type::InterruptGate, .is32bit = false };
+			case 0b00111:    return { .type = Type::TrapGate, .is32bit = false };
+
+			case 0b01000:    return { .type = Type::Invalid };
+			case 0b01001:    return { .type = Type::AvailableTaskStateSegment, .is32bit = true };
+			case 0b01010:    return { .type = Type::Invalid };
+			case 0b01011:    return { .type = Type::BusyTaskStateSegment, .is32bit = true };
+
+			case 0b01100:    return { .type = Type::CallGate, .is32bit = true };
+			case 0b01101:    return { .type = Type::Invalid };
+			case 0b01110:    return { .type = Type::InterruptGate, .is32bit = true };
+			case 0b01111:    return { .type = Type::TrapGate, .is32bit = true };
+
+			// b0 is the accessed flag for non-system descriptors; it doesn't affect the type.
+			case 0b10000:
+			case 0b10001:    return { .type = Type::Data, .readable = true, .writeable = false };
+			case 0b10010:
+			case 0b10011:    return { .type = Type::Data, .readable = true, .writeable = true };
+			case 0b10100:
+			case 0b10101:    return { .type = Type::Stack, .readable = true, .writeable = false };
+			case 0b10110:
+			case 0b10111:    return { .type = Type::Stack, .readable = true, .writeable = true };
+
+			case 0b11000:
+			case 0b11001:    return { .type = Type::Code, .readable = false, .writeable = false, .conforming = false };
+			case 0b11010:
+			case 0b11011:    return { .type = Type::Code, .readable = true, .writeable = false, .conforming = false };
+			case 0b11100:
+			case 0b11101:    return { .type = Type::Code, .readable = false, .writeable = false, .conforming = true };
+			case 0b11110:
+			case 0b11111:    return { .type = Type::Code, .readable = true, .writeable = false, .conforming = true };
+		}
+	}
+
+	auto operator <=> (const SegmentDescriptor &) const = default;
+
+private:
+	uint32_t base_;
+	uint32_t offset_;
+	DescriptorBounds bounds_;
+	uint8_t type_;
+	uint16_t segment_;
+	bool local_;
+};
+
+struct InterruptDescriptor {
+	InterruptDescriptor(const uint16_t, bool, const uint16_t descriptor[4]) noexcept :
+		segment_(descriptor[1]),
+		offset_(uint32_t(descriptor[0] | (descriptor[3] << 16))),
+		flags_(descriptor[2] >> 8) {}
+
+	uint16_t segment() const { return segment_; }
+	uint32_t offset() const { return offset_; }
+	bool present() const { return flags_ & 0x80; }
+	uint8_t priority() const { return (flags_ >> 5) & 3; }
+
+	enum class Type {
+		Task = 0x5,
+		Interrupt16 = 0x6,	Trap16 = 0x7,
+		Interrupt32 = 0xe,	Trap32 = 0xf,
+	};
+	Type type() const {
+		return Type(flags_ & 0xf);
+	}
+
+private:
+	uint16_t segment_;
+	uint32_t offset_;
+	uint8_t flags_;
+};
+
+
+template <typename SegmentT>
+struct SegmentRegisterSet {
+	SegmentT &operator[](const Source segment) {
+		return values_[index_of(segment)];
+	}
+
+	const SegmentT &operator[](const Source segment) const {
+		return values_[index_of(segment)];
+	}
+
+	auto operator <=>(const SegmentRegisterSet &rhs) const = default;
+
+private:
+	std::array<SegmentT, 6> values_{};
+	static constexpr size_t index_of(const Source segment) {
+		assert(is_segment_register(segment));
+		return size_t(segment) - size_t(Source::ES);
+	}
+};
+
+template <typename DescriptorT, typename LinearMemoryT>
+//requires is_linear_memory<LinearMemoryT>
+DescriptorT descriptor_at(
+	LinearMemoryT &memory,
+	const DescriptorTablePointer table,
+	const uint16_t offset,
+	const bool local
+) {
+	if(offset > table.limit - 8) {
+		printf("TODO: descriptor table overrun exception.\n");
+		assert(false);
+	}
+	const auto address = table.base + offset;
+
+	using AccessType = InstructionSet::x86::AccessType;
+	const uint32_t table_end = table.base + table.limit;
+	const uint16_t entry[] = {
+		memory.template access<uint16_t, AccessType::Read>(address, table_end),
+		memory.template access<uint16_t, AccessType::Read>(address + 2, table_end),
+		memory.template access<uint16_t, AccessType::Read>(address + 4, table_end),
+		memory.template access<uint16_t, AccessType::Read>(address + 6, table_end)
+	};
+
+	return DescriptorT(uint16_t(offset) & ~7, local, entry);
+}
+
+template <typename DescriptorT, typename LinearMemoryT>
+//requires is_linear_memory<LinearMemoryT>
+void set_descriptor_type_flag(
+	LinearMemoryT &memory,
+	const DescriptorTablePointer table,
+	const DescriptorT &descriptor,
+	const DescriptorTypeFlag flag
+) {
+	const auto address = table.base + (descriptor.segment() & ~7);
+	const uint32_t table_end = table.base + table.limit;
+
+	auto type = memory.template access<uint16_t, AccessType::PreauthorisedRead>(address + 5, table_end);
+	type |= flag;
+	memory.template access<uint16_t, AccessType::Write>(address + 5, table_end) = type;
+}
+
+}

InstructionSets/x86/Exceptions.hpp

@@ -0,0 +1,168 @@
+//
+//  Interrupts.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 06/10/2023.
+//  Copyright © 2023 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include <cassert>
+#include <cstdint>
+
+namespace InstructionSet::x86 {
+
+enum class Vector: uint8_t {
+	//
+	// Present on all devices.
+	//
+	DivideError					= 0,
+	SingleStep					= 1,
+	NMI							= 2,
+	Breakpoint					= 3,
+	Overflow					= 4,
+	BoundRangeExceeded			= 5,
+
+	//
+	// Added by the 80286.
+	//
+	InvalidOpcode				= 6,
+	DeviceNotAvailable			= 7,
+	DoubleFault					= 8,
+	CoprocessorSegmentOverrun	= 9,
+	InvalidTSS					= 10,
+	SegmentNotPresent			= 11,
+	StackSegmentFault			= 12,
+	GeneralProtectionFault		= 13,
+	FloatingPointException		= 16,
+
+	//
+	// Added by the 80286.
+	//
+	PageFault					= 14,
+	AlignmentCheck				= 17,
+	MachineCheck				= 18,
+};
+
+constexpr bool has_error_code(const Vector vector) {
+	switch(vector) {
+		using enum Vector;
+
+		case DivideError:
+		case SingleStep:
+		case NMI:
+		case Breakpoint:
+		case Overflow:
+		case BoundRangeExceeded:
+		case InvalidOpcode:
+		case DeviceNotAvailable:
+		case CoprocessorSegmentOverrun:
+		case FloatingPointException:
+			return false;
+
+		case DoubleFault:
+		case InvalidTSS:
+		case SegmentNotPresent:
+		case StackSegmentFault:
+		case GeneralProtectionFault:
+			return true;
+
+		default:	// 386 exceptions; I don't know yet.
+		break;
+	}
+	assert(false);
+	return false;
+}
+
+constexpr bool posts_next_ip(const Vector vector) {
+	switch(vector) {
+		using enum Vector;
+
+		default:
+			return false;
+
+		case SingleStep:
+		case Breakpoint:
+		case Overflow:
+			return true;
+	}
+}
+
+struct ExceptionCode {
+	ExceptionCode() = default;
+	ExceptionCode(
+		const uint16_t index,
+		const bool is_local,
+		const bool is_interrupt,
+		const bool was_external) noexcept :
+			value_(
+				index |
+				(is_local ? 0x4 : 0x0) |
+				(is_interrupt ? 0x2 : 0x0) |
+				(was_external ? 0x1 : 0x0)
+			) {}
+
+		// i.e.:
+		//	b3–b15: IDT/GDT/LDT entry
+		//	b2: 1 => in LDT; 0 => in GDT;
+		//	b1: 1 => in IDT, ignore b2; 0 => use b2;
+		//	b0:
+		//		1 => trigger was external to program code;
+		//		0 => trigger was caused by the instruction described by the CS:IP that is on the stack.
+
+	ExceptionCode(const uint16_t value) :
+		value_(value) {}
+
+	operator uint16_t() const {
+		return value_;
+	}
+
+	static ExceptionCode zero() {
+		return ExceptionCode();
+	}
+
+private:
+	uint16_t value_ = 0;
+};
+
+struct Exception {
+	ExceptionCode code{};			// Exception code to push to the stack if this is an internal
+									// exception that provides a code and post_ip_as_code is `false`.
+	uint8_t vector{};				// Will be equal to value of a `Vector` enum if internal.
+
+	enum class CodeType: uint8_t {
+		Internal,
+		External,
+	};
+	CodeType code_type = CodeType::Internal;
+
+	/// Generates an internal exception with no error code.
+	template <Vector cause>
+	requires (!has_error_code(cause))
+	static constexpr Exception exception() {
+		return Exception(uint8_t(cause));
+	}
+
+	/// Generates an internal exception with a specified error code.
+	template <Vector cause>
+	requires (has_error_code(cause))
+	static constexpr Exception exception(const ExceptionCode code) {
+		return Exception(uint8_t(cause), code);
+	}
+
+	/// Generates an externally-motivated exception (i.e. an interrupt).
+	static constexpr Exception interrupt(const uint8_t vector) {
+		return Exception(vector, CodeType::External);
+	}
+
+private:
+	constexpr Exception(const uint8_t vector) noexcept : vector(vector) {}
+	constexpr Exception(const uint8_t vector, const ExceptionCode code) noexcept : code(code), vector(vector){}
+	constexpr Exception(const uint8_t vector, const CodeType code_type) noexcept :
+		vector(vector), code_type(code_type) {}
+};
+
+static_assert(sizeof(Exception) <= 4);
+
+}

InstructionSets/x86/Flags.hpp

@@ -9,6 +9,7 @@
 #pragma once
 
 #include "Numeric/Carry.hpp"
+#include "AccessType.hpp"
 
 namespace InstructionSet::x86 {
 
@@ -80,6 +81,18 @@ class Flags {
 public:
 	using FlagT = uint32_t;
 
+	Flags(const Model model) {
+		switch(model) {
+			case Model::i8086:
+			case Model::i80186:
+				forced_set_ = 0xf002;
+			break;
+			default:
+				forced_set_ = 0x0002;
+			break;
+		}
+	}
+
 	// Flag getters.
 	template <Flag flag_v> bool flag() const {
 		switch(flag_v) {
@@ -121,7 +134,9 @@ public:
 	/// • Flag::Interrupt: sets interrupt if @c value is non-zero;
 	/// • Flag::Trap: sets interrupt if @c value is non-zero;
 	/// • Flag::Direction: sets direction if @c value is non-zero.
-	template <typename IntT, Flag... flags> void set_from(const IntT value) {
+	template <typename IntT, Flag... flags>
+	requires is_x86_data_type<IntT>
+	void set_from(const IntT value) {
 		for(const auto flag: {flags...}) {
 			switch(flag) {
 				default: break;
@@ -141,7 +156,9 @@ public:
 		set_from<FlagT, flags...>(value);
 	}
 
-	template <typename IntT> IntT carry_bit() const { return carry_ ? 1 : 0; }
+	template <typename IntT>
+	requires is_x86_data_type<IntT>
+	IntT carry_bit() const { return carry_ ? 1 : 0; }
 	bool not_parity_bit() const {
 		// x86 parity always considers the lowest 8-bits only.
 		auto result = static_cast<uint8_t>(parity_);
@@ -151,7 +168,9 @@ public:
 		return result & 1;
 	}
 
-	template <typename IntT> IntT direction() const { return static_cast<IntT>(direction_); }
+	template <typename IntT>
+	requires is_x86_data_type<IntT>
+	IntT direction() const { return static_cast<IntT>(direction_); }
 
 	// Complete value get and set.
 	void set(uint16_t value) {
@@ -170,7 +189,7 @@ public:
 
 	uint16_t get() const {
 		return
-			0xf002 |
+			forced_set_ |
 
 			(flag<Flag::Carry>() ? FlagValue::Carry : 0) |
 			(flag<Flag::AuxiliaryCarry>() ? FlagValue::AuxiliaryCarry : 0) |
@@ -209,22 +228,25 @@ public:
 
 private:
 	// Non-zero => set; zero => unset.
-	uint32_t carry_;
-	uint32_t auxiliary_carry_;
-	uint32_t sign_;
-	uint32_t overflow_;
-	uint32_t trap_;
-	uint32_t interrupt_;
+	uint32_t carry_{};
+	uint32_t auxiliary_carry_{};
+	uint32_t sign_{};
+	uint32_t overflow_{};
+	uint32_t trap_{};
+	uint32_t interrupt_{};
 
 	// +1 = direction flag not set;
 	// -1 = direction flag set.
-	int32_t direction_;
+	int32_t direction_{};
 
 	// Zero => set; non-zero => unset.
-	uint32_t zero_;
+	uint32_t zero_{};
 
 	// Odd number of bits => set; even => unset.
-	uint32_t parity_;
+	uint32_t parity_{};
+
+	// Model specific stuff: bits that are always set, regardless of other state.
+	uint16_t forced_set_{};
 };
 
 }

InstructionSets/x86/Implementation/Arithmetic.hpp

@@ -9,7 +9,7 @@
 #pragma once
 
 #include "InstructionSets/x86/AccessType.hpp"
-#include "InstructionSets/x86/Interrupts.hpp"
+#include "InstructionSets/x86/Exceptions.hpp"
 #include "InstructionSets/x86/Perform.hpp"
 
 #include "Numeric/Carry.hpp"
@@ -92,11 +92,11 @@ void test(
 	/*
 		The OF and CF flags are cleared to 0.
 		The SF, ZF, and PF flags are set according to the result (see the “Operation” section above).
-		The state of the AF flag is undefined.
+		The state of the AF flag is formally undefined but known to be reset.
 	*/
 	const IntT result = destination & source;
 
-	context.flags.template set_from<Flag::Carry, Flag::Overflow>(0);
+	context.flags.template set_from<Flag::Carry, Flag::Overflow, Flag::AuxiliaryCarry>(0);
 	context.flags.template set_from<IntT, Flag::Zero, Flag::Sign, Flag::ParityOdd>(result);
 }
 
@@ -128,7 +128,7 @@ void mul(
 }
 
 template <typename IntT, typename ContextT>
-void imul(
+void imul_double(
 	modify_t<IntT> destination_high,
 	modify_t<IntT> destination_low,
 	read_t<IntT> source,
@@ -167,6 +167,36 @@ void imul(
 	context.flags.template set_from<Flag::Overflow, Flag::Carry>(destination_high != sign_extension);
 }
 
+template <typename IntT, typename ContextT>
+void imul_single(
+	write_t<IntT> destination,
+	read_t<IntT> source1,
+	read_t<IntT> source2,
+	ContextT &context
+) {
+	using sIntT = typename std::make_signed<IntT>::type;
+	const auto top_part = IntT((sIntT(source1) * sIntT(source2)) >> (8 * sizeof(IntT)));
+	const auto result = IntT(sIntT(source1) * sIntT(source2));
+	destination = result;
+
+	const auto sign_extension = (result & Numeric::top_bit<IntT>()) ? IntT(~0) : 0;
+	context.flags.template set_from<Flag::Overflow, Flag::Carry>(top_part != sign_extension);
+}
+
+template <typename ContextT>
+void divide_error(ContextT &context) {
+	// 8086-style: just segue directly to the interrupt.
+	//
+	// 80286-style: throw the divide error, allowing the caller to insert
+	// additional context (primarily: IP of this instruction, not the next).
+	static constexpr auto exception = Exception::exception<Vector::DivideError>();
+	if constexpr (uses_8086_exceptions(ContextT::model)) {
+		interrupt(exception, context);
+	} else {
+		throw exception;
+	}
+}
+
 template <typename IntT, typename ContextT>
 void div(
 	modify_t<IntT> destination_high,
@@ -212,16 +242,14 @@ void div(
 		The CF, OF, SF, ZF, AF, and PF flags are undefined.
 	*/
 	if(!source) {
-		interrupt(Interrupt::DivideError, context);
-		return;
+		return divide_error(context);
 	}
 
 	// TEMPORARY HACK. Will not work with DWords.
 	const uint32_t dividend = uint32_t((destination_high << (8 * sizeof(IntT))) + destination_low);
 	const auto result = dividend / source;
 	if(IntT(result) != result) {
-		interrupt(Interrupt::DivideError, context);
-		return;
+		return divide_error(context);
 	}
 
 	destination_low = IntT(result);
@@ -262,7 +290,7 @@ void idiv(
 					FI;
 				ELSE (* quadword/doubleword operation *)
 					temp ← EDX:EAX / SRC; (* signed division *)
-					IF (temp > 7FFFFFFFH) OR (temp < 80000000H) 	(* if a positive result is greater than 7FFFFFFFH
+					IF (temp > 7FFFFFFFH) OR (temp < 80000000H)		(* if a positive result is greater than 7FFFFFFFH
 																	or a negative result is less than 80000000H *)
 						THEN #DE; (* divide error *) ;
 						ELSE
@@ -276,8 +304,7 @@ void idiv(
 		The CF, OF, SF, ZF, AF, and PF flags are undefined.
 	*/
 	if(!source) {
-		interrupt(Interrupt::DivideError, context);
-		return;
+		return divide_error(context);
 	}
 
 	// TEMPORARY HACK. Will not work with DWords.
@@ -292,8 +319,7 @@ void idiv(
 	}
 
 	if(sIntT(result) != result) {
-		interrupt(Interrupt::DivideError, context);
-		return;
+		return divide_error(context);
 	}
 
 	destination_low = IntT(result);

InstructionSets/x86/Implementation/BCD.hpp

@@ -22,10 +22,18 @@ void aaas(
 ) {
 	if((ax.halves.low & 0x0f) > 9 || context.flags.template flag<Flag::AuxiliaryCarry>()) {
 		if constexpr (add) {
-			ax.halves.low += 6;
+			if constexpr (ContextT::model <= Model::i80186) {
+				ax.halves.low += 6;
+			} else {
+				ax.full += 6;
+			}
 			++ax.halves.high;
 		} else {
-			ax.halves.low -= 6;
+			if constexpr (ContextT::model <= Model::i80186) {
+				ax.halves.low -= 6;
+			} else {
+				ax.full -= 6;
+			}
 			--ax.halves.high;
 		}
 		context.flags.template set_from<Flag::Carry, Flag::AuxiliaryCarry>(1);
@@ -75,8 +83,13 @@ void aam(
 		If ... an immediate value of 0 is used, it will cause a #DE (divide error) exception.
 	*/
 	if(!imm) {
-		interrupt(Interrupt::DivideError, context);
-		return;
+		static constexpr auto exception = Exception::exception<Vector::DivideError>();
+		if constexpr (uses_8086_exceptions(ContextT::model)) {
+			interrupt(exception, context);
+			return;
+		} else {
+			throw exception;
+		}
 	}
 
 	ax.halves.high = ax.halves.low / imm;
@@ -91,18 +104,27 @@ void daas(
 	ContextT &context
 ) {
 	bool top_exceeded_threshold;
-	if constexpr (ContextT::model == Model::i8086) {
+	static constexpr bool is_8086 = ContextT::model == Model::i8086;
+	if constexpr (is_8086) {
 		top_exceeded_threshold = al > (context.flags.template flag<Flag::AuxiliaryCarry>() ? 0x9f : 0x99);
 	} else {
 		top_exceeded_threshold = al > 0x99;
 	}
 
+	const auto initial_cf = context.flags.template flag<Flag::Carry>();
 	if((al & 0x0f) > 0x09 || context.flags.template flag<Flag::AuxiliaryCarry>()) {
-		if constexpr (add) al += 0x06; else al -= 0x06;
+		const auto prior_al = al;
+		if constexpr (add) {
+			al += 0x06;
+			if(!is_8086 && al < prior_al) context.flags.template set_from<Flag::Carry>(1);
+		} else {
+			al -= 0x06;
+			if(!is_8086 && al > prior_al) context.flags.template set_from<Flag::Carry>(1);
+		}
 		context.flags.template set_from<Flag::AuxiliaryCarry>(1);
 	}
 
-	if(top_exceeded_threshold || context.flags.template flag<Flag::Carry>()) {
+	if(top_exceeded_threshold || initial_cf) {
 		if constexpr (add) al += 0x60; else al -= 0x60;
 		context.flags.template set_from<Flag::Carry>(1);
 	}

InstructionSets/x86/Implementation/FlowControl.hpp

@@ -10,6 +10,7 @@
 
 #include "Resolver.hpp"
 #include "Stack.hpp"
+#include "InstructionSets/x86/TaskStateSegment.hpp"
 #include "InstructionSets/x86/AccessType.hpp"
 
 #include <type_traits>
@@ -105,59 +106,73 @@ void jump_absolute(
 	context.flow_controller.template jump<uint16_t>(target);
 }
 
-template <typename AddressT, typename InstructionT, typename ContextT>
+template <typename AddressT, typename ContextT>
 void call_far(
-	InstructionT &instruction,
+	const uint16_t segment,
+	const AddressT offset,
 	ContextT &context
 ) {
-	// TODO: eliminate 16-bit assumption below.
-	const Source source_segment = instruction.data_segment();
-	context.memory.preauthorise_stack_write(sizeof(uint16_t) * 2);
+	context.segments.preauthorise_call(
+		Source::CS,
+		offset,
+		[&] {
+			context.memory.preauthorise_stack_write(sizeof(uint16_t) * 2, sizeof(uint16_t));
+			push<uint16_t, true>(context.registers.cs(), context);
+			push<uint16_t, true>(context.registers.ip(), context);
+			context.flow_controller.template jump<AddressT>(segment, offset);
+		},
+		[&] (const SegmentDescriptor &descriptor) {
+			(void)descriptor;
+			printf("TODO: protected mode far call");
+		}
+	);
+}
 
-	uint16_t source_address;
+template <typename AddressT, InstructionType type, typename ContextT>
+void call_far(
+	const Instruction<type> &instruction,
+	ContextT &context
+) {
+	const Source source_segment = instruction.data_segment();
+
+	AddressT source_address;
 	const auto pointer = instruction.destination();
 	switch(pointer.source()) {
 		default:
 		case Source::Immediate:
-			push<uint16_t, true>(context.registers.cs(), context);
-			push<uint16_t, true>(context.registers.ip(), context);
-			context.flow_controller.template jump<uint16_t>(instruction.segment(), instruction.offset());
+			call_far(instruction.segment(), instruction.offset(), context);
 		return;
 
 		case Source::Indirect:
 			source_address = uint16_t(
-				address<Source::Indirect, uint16_t, AccessType::Read>(instruction, pointer, context)
+				address<Source::Indirect, AddressT, AccessType::Read>(instruction, pointer, context)
 			);
 		break;
 		case Source::IndirectNoBase:
 			source_address = uint16_t(
-				address<Source::IndirectNoBase, uint16_t, AccessType::Read>(instruction, pointer, context)
+				address<Source::IndirectNoBase, AddressT, AccessType::Read>(instruction, pointer, context)
 			);
 		break;
 		case Source::DirectAddress:
 			source_address = uint16_t(
-				address<Source::DirectAddress, uint16_t, AccessType::Read>(instruction, pointer, context)
+				address<Source::DirectAddress, AddressT, AccessType::Read>(instruction, pointer, context)
 			);
 		break;
 	}
 
-	context.memory.preauthorise_read(source_segment, source_address, sizeof(uint16_t) * 2);
+//	context.memory.preauthorise_read(source_segment, source_address, sizeof(uint16_t) + sizeof(AddressT));
 	const auto offset =
-		context.memory.template access<uint16_t, AccessType::PreauthorisedRead>(source_segment, source_address);
+		context.memory.template access<AddressT, AccessType::Read>(source_segment, source_address);
 	source_address += 2;
 	const auto segment =
-		context.memory.template access<uint16_t, AccessType::PreauthorisedRead>(source_segment, source_address);
+		context.memory.template access<uint16_t, AccessType::Read>(source_segment, source_address);
 
-	// At least on an 8086, the stack writes occur after the target address read.
-	push<uint16_t, true>(context.registers.cs(), context);
-	push<uint16_t, true>(context.registers.ip(), context);
-
-	context.flow_controller.template jump<AddressT>(segment, offset);
+	call_far(segment, offset, context);
 }
 
-template <typename InstructionT, typename ContextT>
+template <InstructionType type, typename ContextT>
 void jump_far(
-	InstructionT &instruction,
+	const Instruction<type> &instruction,
 	ContextT &context
 ) {
 	// TODO: eliminate 16-bit assumption below.
@@ -187,13 +202,13 @@ void jump_far(
 	}
 
 	const Source source_segment = instruction.data_segment();
-	context.memory.preauthorise_read(source_segment, source_address, sizeof(uint16_t) * 2);
+//	context.memory.preauthorise_read(source_segment, source_address, sizeof(uint16_t) * 2);
 
 	const auto offset =
-		context.memory.template access<uint16_t, AccessType::PreauthorisedRead>(source_segment, source_address);
+		context.memory.template access<uint16_t, AccessType::Read>(source_segment, source_address);
 	source_address += 2;
 	const auto segment =
-		context.memory.template access<uint16_t, AccessType::PreauthorisedRead>(source_segment, source_address);
+		context.memory.template access<uint16_t, AccessType::Read>(source_segment, source_address);
 	context.flow_controller.template jump<uint16_t>(segment, offset);
 }
 
@@ -202,7 +217,7 @@ void iret(
 	ContextT &context
 ) {
 	// TODO: all modes other than 16-bit real mode.
-	context.memory.preauthorise_stack_read(sizeof(uint16_t) * 3);
+	context.memory.preauthorise_stack_read(sizeof(uint16_t) * 3, sizeof(uint16_t));
 	const auto ip = pop<uint16_t, true>(context);
 	const auto cs = pop<uint16_t, true>(context);
 	context.flags.set(pop<uint16_t, true>(context));
@@ -224,7 +239,7 @@ void ret_far(
 	const InstructionT instruction,
 	ContextT &context
 ) {
-	context.memory.preauthorise_stack_read(sizeof(uint16_t) * 2);
+	context.memory.preauthorise_stack_read(sizeof(uint16_t) * 2, sizeof(uint16_t));
 	const auto ip = pop<uint16_t, true>(context);
 	const auto cs = pop<uint16_t, true>(context);
 	context.registers.sp() += instruction.operand();
@@ -236,28 +251,37 @@ void into(
 	ContextT &context
 ) {
 	if(context.flags.template flag<Flag::Overflow>()) {
-		interrupt(Interrupt::Overflow, context);
+		static constexpr auto exception = Exception::exception<Vector::Overflow>();
+		if constexpr (uses_8086_exceptions(ContextT::model)) {
+			interrupt(exception, context);
+		} else {
+			throw exception;
+		}
 	}
 }
 
 template <typename IntT, typename AddressT, typename InstructionT, typename ContextT>
 void bound(
 	const InstructionT &instruction,
-	read_t<AddressT> destination,
+	read_t<IntT> destination,
 	read_t<AddressT> source,
 	ContextT &context
 ) {
 	using sIntT = typename std::make_signed<IntT>::type;
 
 	const auto source_segment = instruction.data_segment();
-	context.memory.preauthorise_read(source_segment, source, 2*sizeof(IntT));
 	const auto lower_bound =
-		sIntT(context.memory.template access<IntT, AccessType::PreauthorisedRead>(source_segment, source));
+		sIntT(context.memory.template access<IntT, AccessType::Read>(source_segment, source));
 	const auto upper_bound =
-		sIntT(context.memory.template access<IntT, AccessType::PreauthorisedRead>(source_segment, IntT(source + 2)));
+		sIntT(context.memory.template access<IntT, AccessType::Read>(source_segment, IntT(source + 2)));
 
 	if(sIntT(destination) < lower_bound || sIntT(destination) > upper_bound) {
-		interrupt(Interrupt::BoundRangeExceeded, context);
+		static constexpr auto exception = Exception::exception<Vector::BoundRangeExceeded>();
+		if constexpr (uses_8086_exceptions(ContextT::model)) {
+			interrupt(exception, context);
+		} else {
+			throw exception;
+		}
 	}
 }