Merge pull request #1643 from TomHarte/EXOSDirect

Enterprise: support .BAS and .COM and corresponding host filing system access.

Analyser/Static/Acorn/Target.hpp

@@ -44,6 +44,7 @@ struct BBCMicroTarget: public ::Analyser::Static::Target, public Reflection::Str
 	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;
@@ -56,6 +57,7 @@ private:
 		DeclareField(has_1770dfs);
 		DeclareField(has_adfs);
 		DeclareField(has_sideways_ram);
+		DeclareField(has_beebsid);
 		AnnounceEnum(TubeProcessor);
 		DeclareField(tube_processor);
 	}

Analyser/Static/Enterprise/StaticAnalyser.cpp

@@ -33,7 +33,7 @@ Analyser::Static::TargetList Analyser::Static::Enterprise::GetTargets(
 	bool
 ) {
 	// This analyser can comprehend disks only.
-	if(media.disks.empty()) return {};
+	if(media.disks.empty() && media.file_bundles.empty()) return {};
 
 	// Otherwise, assume a return will happen.
 	Analyser::Static::TargetList targets;
@@ -86,7 +86,36 @@ Analyser::Static::TargetList Analyser::Static::Enterprise::GetTargets(
 		}
 	}
 
-	targets.push_back(std::unique_ptr<Analyser::Static::Target>(target));
+	if(!media.file_bundles.empty()) {
+		auto &bundle = *media.file_bundles.front();
+		const auto key = bundle.key_file();
+
+		if(key.has_value()) {
+			auto file = bundle.open(*key, Storage::FileMode::Read);
+
+			enum class FileType: uint16_t {
+				COM = 0x0500,
+				BAS = 0x0400,
+			};
+
+			// Check for a .COM by inspecting the header.
+			const auto type = FileType(file.get_le<uint16_t>());
+			const uint16_t size = file.get_le<uint16_t>();
+			// There are then 12 bytes of 0 padding that could be tested for.
+
+			if((type != FileType::COM && type != FileType::BAS) || size > file.stats().st_size - 16) {
+				target->media.file_bundles.clear();
+			} else {
+				target->loading_command = "run \"file:\"\n";
+			}
+		}
+
+		// TODO: look for a key file, similar logic to above.
+	}
+
+	if(!target->media.empty()) {
+		targets.push_back(std::unique_ptr<Analyser::Static::Target>(target));
+	}
 
 	return targets;
 }

Analyser/Static/StaticAnalyser.cpp

@@ -63,6 +63,9 @@
 #include "Storage/Disk/DiskImage/Formats/STX.hpp"
 #include "Storage/Disk/DiskImage/Formats/WOZ.hpp"
 
+// File Bundles.
+#include "Storage/FileBundle/FileBundle.hpp"
+
 // Mass Storage Devices (i.e. usually, hard disks)
 #include "Storage/MassStorage/Formats/DAT.hpp"
 #include "Storage/MassStorage/Formats/DSK.hpp"
@@ -123,6 +126,8 @@ public:
 			media.cartridges.push_back(instance);
 		} else if constexpr (std::is_base_of_v<Storage::MassStorage::MassStorageDevice, InstanceT>) {
 			media.mass_storage_devices.push_back(instance);
+		} else if constexpr (std::is_base_of_v<Storage::FileBundle::FileBundle, InstanceT>) {
+			media.file_bundles.push_back(instance);
 		} else {
 			static_assert(always_false_v<InstanceT>, "Unexpected type encountered.");
 		}
@@ -208,13 +213,14 @@ 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<FileBundle::LocalFSFileBundle>(TargetPlatform::Enterprise, "bas");
 	accumulator.try_standard<Cartridge::BinaryDump>(TargetPlatform::AllCartridge, "bin");
 
 	accumulator.try_standard<Tape::CAS>(TargetPlatform::MSX, "cas");
 	accumulator.try_standard<Tape::TZX>(TargetPlatform::AmstradCPC, "cdt");
 	accumulator.try_standard<Cartridge::BinaryDump>(TargetPlatform::Coleco, "col");
+	accumulator.try_standard<FileBundle::LocalFSFileBundle>(TargetPlatform::Enterprise, "com");
 	accumulator.try_standard<Tape::CSW>(TargetPlatform::AllTape, "csw");
 
 	accumulator.try_standard<Disk::DiskImageHolder<Disk::D64>>(TargetPlatform::Commodore8bit, "d64");
@@ -257,6 +263,7 @@ static Media GetMediaAndPlatforms(const std::string &file_name, TargetPlatform::
 		TargetPlatform::Amiga | TargetPlatform::AtariST | TargetPlatform::AmstradCPC | TargetPlatform::ZXSpectrum,
 		"ipf");
 
+	accumulator.try_standard<Disk::DiskImageHolder<Disk::JFD>>(TargetPlatform::Archimedes, "jfd");
 	accumulator.try_standard<Disk::DiskImageHolder<Disk::MSA>>(TargetPlatform::AtariST, "msa");
 	accumulator.try_standard<Cartridge::BinaryDump>(TargetPlatform::MSX, "mx2");
 	accumulator.try_standard<Disk::DiskImageHolder<Disk::NIB>>(TargetPlatform::DiskII, "nib");

Analyser/Static/StaticAnalyser.hpp

@@ -12,6 +12,7 @@
 
 #include "Storage/Cartridge/Cartridge.hpp"
 #include "Storage/Disk/Disk.hpp"
+#include "Storage/FileBundle/FileBundle.hpp"
 #include "Storage/MassStorage/MassStorageDevice.hpp"
 #include "Storage/Tape/Tape.hpp"
 #include "Storage/TargetPlatforms.hpp"
@@ -33,9 +34,15 @@ struct Media {
 	std::vector<std::shared_ptr<Storage::Tape::Tape>> tapes;
 	std::vector<std::shared_ptr<Storage::Cartridge::Cartridge>> cartridges;
 	std::vector<std::shared_ptr<Storage::MassStorage::MassStorageDevice>> mass_storage_devices;
+	std::vector<std::shared_ptr<Storage::FileBundle::FileBundle>> file_bundles;
 
 	bool empty() const {
-		return disks.empty() && tapes.empty() && cartridges.empty() && mass_storage_devices.empty();
+		return
+			disks.empty() &&
+			tapes.empty() &&
+			cartridges.empty() &&
+			mass_storage_devices.empty() &&
+			file_bundles.empty();
 	}
 
 	Media &operator +=(const Media &rhs) {
@@ -47,6 +54,7 @@ struct Media {
 		append(tapes, rhs.tapes);
 		append(cartridges, rhs.cartridges);
 		append(mass_storage_devices, rhs.mass_storage_devices);
+		append(file_bundles, rhs.file_bundles);
 
 		return *this;
 	}

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

@@ -562,7 +562,7 @@ void WD1770::posit_event(const int new_event_type) {
 		}
 
 		set_data_mode(DataMode::Writing);
-		begin_writing(false);
+		begin_writing(false, false);
 		for(int c = 0; c < (get_is_double_density() ? 12 : 6); c++) {
 			write_byte(0);
 		}
@@ -755,7 +755,7 @@ void WD1770::posit_event(const int new_event_type) {
 		}
 
 		WAIT_FOR_EVENT(Event1770::IndexHoleTarget);
-		begin_writing(true);
+		begin_writing(true, false);
 		index_hole_count_ = 0;
 
 	write_track_write_loop:

Components/6560/6560.cpp

@@ -15,7 +15,6 @@ using namespace MOS::MOS6560;
 AudioGenerator::AudioGenerator(Concurrency::AsyncTaskQueue<false> &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_;
@@ -148,7 +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

@@ -75,7 +75,7 @@ public:
 	}
 
 	~MOS6560() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_clock_rate(const double clock_rate) {

Components/8272/i8272.cpp

@@ -487,7 +487,7 @@ void i8272::posit_event(const int event_type) {
 
 		write_data_found_header:
 			WAIT_FOR_BYTES(get_is_double_density() ? 22 : 11);
-			begin_writing(true);
+			begin_writing(true, false);
 
 			write_id_data_joiner(command_.command() == Command::WriteDeletedData, true);
 
@@ -603,7 +603,7 @@ void i8272::posit_event(const int event_type) {
 			// Wait for the index hole.
 			WAIT_FOR_EVENT(Event::IndexHole);
 			index_hole_count_ = 0;
-			begin_writing(true);
+			begin_writing(true, false);
 
 			// Write start-of-track.
 			write_start_of_track();

Components/DiskII/DiskII.cpp

@@ -296,8 +296,9 @@ int DiskII::read_address(int address) {
 			inputs_ &= ~input_mode;
 		break;
 		case 0xf:
-			if(!(inputs_ & input_mode))
-				drives_[active_drive_].begin_writing(Storage::Time(1, int(clock_rate_)), false);
+			if(!(inputs_ & input_mode)) {
+				drives_[active_drive_].begin_writing(Storage::Time(1, int(clock_rate_)), false, false);
+			}
 			inputs_ |= input_mode;
 		break;
 	}

Components/DiskII/IWM.cpp

@@ -346,7 +346,9 @@ void IWM::select_shift_mode() {
 
 	// If writing mode just began, set the drive into write mode and cue up the first output byte.
 	if(old_shift_mode != ShiftMode::Writing && shift_mode_ == ShiftMode::Writing) {
-		if(drives_[active_drive_]) drives_[active_drive_]->begin_writing(Storage::Time(1, clock_rate_ / bit_length_.as_integral()), false);
+		if(drives_[active_drive_]) {
+			drives_[active_drive_]->begin_writing(Storage::Time(1, clock_rate_ / bit_length_.as_integral()), false, false);
+		}
 		shift_register_ = next_output_;
 		write_handshake_ |= 0x80 | 0x40;
 		output_bits_remaining_ = 8;

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]{};
+};
+
+}

Concurrency/AsyncTaskQueue.hpp

@@ -97,6 +97,12 @@ 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);
@@ -131,7 +137,7 @@ public:
 
 	/// 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;
@@ -150,6 +156,23 @@ 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();
 	}

Machines/Acorn/BBCMicro/BBCMicro.cpp

@@ -24,6 +24,7 @@
 #include "Components/6522/6522.hpp"
 #include "Components/6845/CRTC6845.hpp"
 #include "Components/6850/6850.hpp"
+#include "Components/SID/SID.hpp"
 #include "Components/SAA5050/SAA5050.hpp"
 #include "Components/SN76489/SN76489.hpp"
 #include "Components/uPD7002/uPD7002.hpp"
@@ -35,6 +36,7 @@
 #include "Outputs/Log.hpp"
 
 #include "Outputs/CRT/CRT.hpp"
+#include "Outputs/Speaker/Implementation/CompoundSource.hpp"
 #include "Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
 #include "Concurrency/AsyncTaskQueue.hpp"
 
@@ -107,22 +109,48 @@ private:
 /*!
 	Combines an SN76489 with an appropriate asynchronous queue and filtering speaker.
 */
+
+// TODO: generalise the below and clean up across the project.
+template <bool has_beebsid>
 struct Audio {
+private:
+	using CompoundSource = Outputs::Speaker::CompoundSource<TI::SN76489, MOS::SID::SID>;
+	using Source = std::conditional_t<has_beebsid, CompoundSource, TI::SN76489>;
+	using Speaker = Outputs::Speaker::PullLowpass<Source>;
+
+	Source &speaker_source() {
+		if constexpr (has_beebsid) {
+			return compound_;
+		} else {
+			return sn76489_;
+		}
+	}
+
+public:
 	Audio() :
-		sn76489_(TI::SN76489::Personality::SN76489, audio_queue_, 2),
-		speaker_(sn76489_)
+		sn76489_(TI::SN76489::Personality::SN76489, audio_queue_, 4),
+		sid_(audio_queue_),
+		compound_(sn76489_, sid_),
+		speaker_(speaker_source())
 	{
-		// Combined with the additional divider specified above, implies this chip is clocked at 4Mhz.
-		speaker_.set_input_rate(2'000'000.0f);
+		// Combined with the additional divider specified above, implies the SN76489 is clocked at 4Mhz.
+		speaker_.set_input_rate(1'000'000.0f);
 	}
 
 	~Audio() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
-	TI::SN76489 *operator ->() {
-		speaker_.run_for(audio_queue_, time_since_update_.flush<Cycles>());
-		return &sn76489_;
+	template <typename TargetT>
+	TargetT &get() {
+		post_time();
+
+		if constexpr (std::is_same_v<TargetT, TI::SN76489>) {
+			return sn76489_;
+		}
+		if constexpr (std::is_same_v<TargetT, MOS::SID::SID>) {
+			return sid_;
+		}
 	}
 
 	void operator +=(const Cycles duration) {
@@ -130,7 +158,7 @@ struct Audio {
 	}
 
 	void flush() {
-		speaker_.run_for(audio_queue_, time_since_update_.flush<Cycles>());
+		post_time();
 		audio_queue_.perform();
 	}
 
@@ -138,10 +166,20 @@ struct Audio {
 		return &speaker_;
 	}
 
+	size_t queue_size() {
+		return audio_queue_.size();
+	}
+
 private:
+	void post_time() {
+		speaker_.run_for(audio_queue_, time_since_update_.divide(Cycles(2)));
+	}
+
 	Concurrency::AsyncTaskQueue<false> audio_queue_;
 	TI::SN76489 sn76489_;
-	Outputs::Speaker::PullLowpass<TI::SN76489> speaker_;
+	MOS::SID::SID sid_;
+	CompoundSource compound_;
+	Outputs::Speaker::PullLowpass<Source> speaker_;
 	Cycles time_since_update_;
 };
 
@@ -174,19 +212,20 @@ protected:
 /*!
 	Models the system VIA, which connects to the SN76489 and the keyboard.
 */
-struct SystemVIAPortHandler;
-using SystemVIA = MOS::MOS6522::MOS6522<SystemVIAPortHandler>;
-
-struct SystemVIAPortHandler: public MOS::MOS6522::IRQDelegatePortHandler {
-	struct Delegate {
-		virtual void strobe_lightpen() = 0;
-	};
+struct VSyncReceiver {
+	virtual void set_vsync(bool) = 0;
+};
+struct SystemVIADelegate {
+	virtual void strobe_lightpen() = 0;
+};
 
+template <typename AudioT>
+struct SystemVIAPortHandler: public MOS::MOS6522::IRQDelegatePortHandler, public VSyncReceiver {
 	SystemVIAPortHandler(
-		Audio &audio,
+		AudioT &audio,
 		VideoBaseAddress &video_base,
-		SystemVIA &via,
-		Delegate &delegate,
+		MOS::MOS6522::MOS6522<SystemVIAPortHandler<AudioT>> &via,
+		SystemVIADelegate &delegate,
 		const std::vector<std::unique_ptr<Inputs::Joystick>> &joysticks,
 		const bool run_disk
 	) :
@@ -221,7 +260,7 @@ struct SystemVIAPortHandler: public MOS::MOS6522::IRQDelegatePortHandler {
 
 		// Check for a strobe on the audio output.
 		if((old_latch^latch_) & old_latch & LatchFlags::WriteToSN76489) {
-			audio_->write(port_a_output_);
+			audio_.template get<TI::SN76489>().write(port_a_output_);
 		}
 
 		// Pass on the video wraparound/base.
@@ -335,10 +374,10 @@ private:
 	uint8_t port_a_output_ = 0;
 	bool previous_cb2_ = false;
 
-	Audio &audio_;
+	AudioT &audio_;
 	VideoBaseAddress &video_base_;
 
-	SystemVIA &via_;
+	MOS::MOS6522::MOS6522<SystemVIAPortHandler<AudioT>> &via_;
 
 	// MARK: - Keyboard state and helpers.
 
@@ -369,7 +408,7 @@ private:
 				}
 		} ()).to_ulong() & 0xfe;	// Discard the first row.
 
-		via_.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::Two>(state);
+		via_.template set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::Two>(state);
 	}
 
 	static inline const std::string caps_led = "CAPS";
@@ -379,7 +418,11 @@ private:
 	Activity::Observer *activity_observer_ = nullptr;
 
 	const std::vector<std::unique_ptr<Inputs::Joystick>> &joysticks_;
-	Delegate &delegate_;
+	SystemVIADelegate &delegate_;
+
+	void set_vsync(const bool vsync) override {
+		via_.template set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(vsync);
+	}
 };
 
 // MARK: - CRTC output.
@@ -389,10 +432,10 @@ private:
 */
 class CRTCBusHandler: public VideoBaseAddress {
 public:
-	CRTCBusHandler(const uint8_t *const ram, SystemVIA &system_via) :
+	CRTCBusHandler(const uint8_t *const ram, VSyncReceiver &vsync_receiver) :
 		crt_(1024, 1, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red1Green1Blue1),
 		ram_(ram),
-		system_via_(system_via)
+		vsync_receiver_(vsync_receiver)
 	{}
 
 	void set_dynamic_framing(const bool enable) {
@@ -440,7 +483,10 @@ public:
 		static_assert(!(PixelAllocationUnit % 16));
 		static_assert(!(PixelAllocationUnit % 12));
 
-		system_via_.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(state.vsync);
+		if(state.vsync != vsync_) {
+			vsync_receiver_.set_vsync(state.vsync);
+			vsync_ = state.vsync;
+		}
 
 		// Count cycles since horizontal sync to insert a colour burst.
 		// TODO: this is copy/pasted from the CPC. How does the BBC do it?
@@ -675,7 +721,8 @@ private:
 	}
 
 	const uint8_t *const ram_ = nullptr;
-	SystemVIA &system_via_;
+	VSyncReceiver &vsync_receiver_;
+	bool vsync_ = false;
 
 	Mullard::SAA5050Serialiser saa5050_serialiser_;
 };
@@ -705,7 +752,7 @@ struct Tube<HostT, TubeProcessor::None> {
 
 // MARK: - ConcreteMachine.
 
-template <TubeProcessor tube_processor, bool has_1770>
+template <TubeProcessor tube_processor, bool has_1770, bool has_beebsid>
 class ConcreteMachine:
 	public Activity::Source,
 	public Configurable::Device,
@@ -718,7 +765,7 @@ class ConcreteMachine:
 	public MachineTypes::TimedMachine,
 	public MOS::MOS6522::IRQDelegatePortHandler::Delegate,
 	public NEC::uPD7002::Delegate,
-	public SystemVIAPortHandler::Delegate,
+	public SystemVIADelegate,
 	public Utility::TypeRecipient<CharacterMapper>,
 	public WD::WD1770::Delegate
 {
@@ -731,7 +778,7 @@ public:
 		system_via_port_handler_(audio_, crtc_bus_handler_, system_via_, *this, joysticks_, target.should_shift_restart),
 		user_via_(user_via_port_handler_),
 		system_via_(system_via_port_handler_),
-		crtc_bus_handler_(ram_.data(), system_via_),
+		crtc_bus_handler_(ram_.data(), system_via_port_handler_),
 		crtc_(crtc_bus_handler_),
 		acia_(HalfCycles(2'000'000)), // TODO: look up real ACIA clock rate.
 		adc_(HalfCycles(2'000'000)),
@@ -990,6 +1037,12 @@ public:
 						}
 					break;
 				}
+			} else if(has_beebsid && address >= 0xfc20 && address < 0xfc40) {
+				if constexpr (is_read(operation)) {
+					value = audio_.template get<MOS::SID::SID>().read(+address);
+				} else {
+					audio_.template get<MOS::SID::SID>().write(+address, value);
+				}
 			} else {
 				Logger::error()
 					.append("Unhandled IO %s at %04x", is_read(operation) ? "read" : "write", address)
@@ -1045,8 +1098,7 @@ private:
 		return crtc_bus_handler_.get_scaled_scan_status();
 	}
 
-
-	// MARK: - SystemVIAPortHandler::Delegate.
+	// MARK: - SystemVIADelegate.
 	void strobe_lightpen() override {
 		crtc_.trigger_light_pen();
 	}
@@ -1129,7 +1181,10 @@ private:
 	}
 
 	void flush_output(const int outputs) final {
-		if(outputs & Output::Audio) {
+		// TODO: I think there's an infrastructural bug here on macOS; if the audio output has stalled out,
+		// the outer wrapper won't ask for an audio flush, which means the queue will never try to start,
+		// and the audio queue will just fill indefinitely. Could this be the mythical 'leak'?
+		if(outputs & Output::Audio || audio_.queue_size() > 200) {
 			audio_.flush();
 		}
 	}
@@ -1141,7 +1196,7 @@ private:
 
 	// MARK: - uPD7002::Delegate.
 	void did_change_interrupt_status(NEC::uPD7002 &) override {
-		system_via_.set_control_line_input<MOS::MOS6522::Port::B, MOS::MOS6522::Line::One>(adc_.interrupt());
+		system_via_.template set_control_line_input<MOS::MOS6522::Port::B, MOS::MOS6522::Line::One>(adc_.interrupt());
 	}
 
 	// MARK: - MediaTarget.
@@ -1200,9 +1255,9 @@ private:
 	CPU::MOS6502Mk2::Processor<CPU::MOS6502Mk2::Model::M6502, M6502Traits> m6502_;
 
 	UserVIAPortHandler user_via_port_handler_;
-	SystemVIAPortHandler system_via_port_handler_;
+	SystemVIAPortHandler<Audio<has_beebsid>> system_via_port_handler_;
 	UserVIA user_via_;
-	SystemVIA system_via_;
+	MOS::MOS6522::MOS6522<SystemVIAPortHandler<Audio<has_beebsid>>> system_via_;
 
 	void update_irq_line() {
 		const bool tube_irq =
@@ -1221,7 +1276,7 @@ private:
 		);
 	}
 
-	Audio audio_;
+	Audio<has_beebsid> audio_;
 
 	CRTCBusHandler crtc_bus_handler_;
 	CRTC crtc_;
@@ -1275,12 +1330,21 @@ using namespace BBCMicro;
 namespace {
 using Target = Analyser::Static::Acorn::BBCMicroTarget;
 
+template <Target::TubeProcessor processor, bool has_1770>
+std::unique_ptr<Machine> machine(const Target &target, const ROMMachine::ROMFetcher &rom_fetcher) {
+	if(target.has_beebsid) {
+		return std::make_unique<BBCMicro::ConcreteMachine<processor, has_1770, true>>(target, rom_fetcher);
+	} else {
+		return std::make_unique<BBCMicro::ConcreteMachine<processor, has_1770, false>>(target, rom_fetcher);
+	}
+}
+
 template <Target::TubeProcessor processor>
 std::unique_ptr<Machine> machine(const Target &target, const ROMMachine::ROMFetcher &rom_fetcher) {
 	if(target.has_1770dfs || target.has_adfs) {
-		return std::make_unique<BBCMicro::ConcreteMachine<processor, true>>(target, rom_fetcher);
+		return machine<processor, true>(target, rom_fetcher);
 	} else {
-		return std::make_unique<BBCMicro::ConcreteMachine<processor, false>>(target, rom_fetcher);
+		return machine<processor, false>(target, rom_fetcher);
 	}
 }
 }

Machines/Acorn/Electron/Electron.cpp

@@ -143,7 +143,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_key_state(uint16_t key, bool isPressed) final {

Machines/AmstradCPC/AmstradCPC.cpp

@@ -127,7 +127,7 @@ public:
 	}
 
 	~AYDeferrer() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	/// Adds @c half_cycles half cycles to the amount of time that has passed.

Machines/Apple/AppleII/AppleII.cpp

@@ -678,7 +678,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_scan_target(Outputs::Display::ScanTarget *scan_target) final {

Machines/Apple/AppleIIgs/AppleIIgs.cpp

@@ -210,7 +210,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void run_for(const Cycles cycles) override {

Machines/Apple/Macintosh/Macintosh.cpp

@@ -172,7 +172,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_.queue.flush();
+		audio_.queue.lock_flush();
 	}
 
 	void set_scan_target(Outputs::Display::ScanTarget *scan_target) final {

Machines/Atari/2600/Bus.hpp

@@ -26,7 +26,7 @@ public:
 		speaker_(tia_sound_) {}
 
 	virtual ~Bus() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	virtual void run_for(const Cycles cycles) = 0;

Machines/Atari/ST/AtariST.cpp

@@ -144,7 +144,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	// MARK: CRTMachine::Machine

Machines/ColecoVision/ColecoVision.cpp

@@ -168,7 +168,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	const std::vector<std::unique_ptr<Inputs::Joystick>> &get_joysticks() final {

Machines/Commodore/1540/Implementation/C1540.cpp

@@ -17,7 +17,10 @@
 using namespace Commodore::C1540;
 
 namespace {
-ROM::Name rom_name(Personality personality) {
+
+// MARK: - Construction, including ROM requests.
+
+ROM::Name rom_name(const Personality personality) {
 	switch(personality) {
 		default:
 		case Personality::C1540:	return ROM::Name::Commodore1540;
@@ -26,11 +29,11 @@ ROM::Name rom_name(Personality personality) {
 }
 }
 
-ROM::Request Machine::rom_request(Personality personality) {
+ROM::Request Machine::rom_request(const Personality personality) {
 	return ROM::Request(rom_name(personality));
 }
 
-MachineBase::MachineBase(Personality personality, const ROM::Map &roms) :
+MachineBase::MachineBase(const Personality personality, const ROM::Map &roms) :
 		Storage::Disk::Controller(1000000),
 		m6502_(*this),
 		drive_VIA_(drive_VIA_port_handler_),
@@ -58,14 +61,13 @@ MachineBase::MachineBase(Personality personality, const ROM::Map &roms) :
 	std::memcpy(rom_, rom->second.data(), std::min(sizeof(rom_), rom->second.size()));
 }
 
-Machine::Machine(Personality personality, const ROM::Map &roms) :
+Machine::Machine(const Personality personality, const ROM::Map &roms) :
 	MachineBase(personality, roms) {}
 
-void Machine::set_serial_bus(Commodore::Serial::Bus &serial_bus) {
-	Commodore::Serial::attach(serial_port_, serial_bus);
-}
+// MARK: - 6502 bus.
 
-Cycles MachineBase::perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) {
+template <CPU::MOS6502Mk2::BusOperation operation, typename AddressT>
+Cycles MachineBase::perform(const AddressT address, CPU::MOS6502Mk2::data_t<operation> value) {
 	/*
 		Memory map (given that I'm unsure yet on any potential mirroring):
 
@@ -75,24 +77,28 @@ Cycles MachineBase::perform_bus_operation(CPU::MOS6502::BusOperation operation,
 			0xc000-0xffff	ROM
 	*/
 	if(address < 0x800) {
-		if(is_read(operation))
-			*value = ram_[address];
+		if constexpr (is_read(operation))
+			value = ram_[address];
 		else
-			ram_[address] = *value;
+			ram_[address] = value;
 	} else if(address >= 0xc000) {
-		if(is_read(operation)) {
-			*value = rom_[address & 0x3fff];
+		if constexpr (is_read(operation)) {
+			value = rom_[address & 0x3fff];
 		}
 	} else if(address >= 0x1800 && address <= 0x180f) {
-		if(is_read(operation))
-			*value = serial_port_VIA_.read(address);
+		if constexpr (is_read(operation))
+			value = serial_port_VIA_.read(address);
 		else
-			serial_port_VIA_.write(address, *value);
+			serial_port_VIA_.write(address, value);
 	} else if(address >= 0x1c00 && address <= 0x1c0f) {
-		if(is_read(operation))
-			*value = drive_VIA_.read(address);
+		if constexpr (is_read(operation))
+			value = drive_VIA_.read(address);
 		else
-			drive_VIA_.write(address, *value);
+			drive_VIA_.write(address, value);
+	} else {
+		if constexpr (is_read(operation)) {
+			value = 0xff;
+		}
 	}
 
 	serial_port_VIA_.run_for(Cycles(1));
@@ -101,34 +107,39 @@ Cycles MachineBase::perform_bus_operation(CPU::MOS6502::BusOperation operation,
 	return Cycles(1);
 }
 
-void Machine::set_disk(std::shared_ptr<Storage::Disk::Disk> disk) {
-	get_drive().set_disk(disk);
-}
-
 void Machine::run_for(const Cycles cycles) {
 	m6502_.run_for(cycles);
-
-	const bool drive_motor = drive_VIA_port_handler_.get_motor_enabled();
-	get_drive().set_motor_on(drive_motor);
-	if(drive_motor)
+	if(get_drive().get_motor_on()) {
 		Storage::Disk::Controller::run_for(cycles);
+	}
 }
 
-void MachineBase::set_activity_observer(Activity::Observer *observer) {
+// MARK: - External attachments.
+
+void Machine::set_serial_bus(Commodore::Serial::Bus &serial_bus) {
+	Commodore::Serial::attach(serial_port_, serial_bus);
+}
+
+void Machine::set_disk(std::shared_ptr<Storage::Disk::Disk> disk) {
+	get_drive().set_disk(disk);
+	drive_VIA_port_handler_.set_is_read_only(disk->is_read_only());
+}
+
+void MachineBase::set_activity_observer(Activity::Observer *const observer) {
 	drive_VIA_.bus_handler().set_activity_observer(observer);
 	get_drive().set_activity_observer(observer, "Drive", false);
 }
 
-// MARK: - 6522 delegate
+// MARK: - 6522 delegate.
 
 void MachineBase::mos6522_did_change_interrupt_status(void *) {
 	// both VIAs are connected to the IRQ line
-	m6502_.set_irq_line(serial_port_VIA_.get_interrupt_line() || drive_VIA_.get_interrupt_line());
+	m6502_.set<CPU::MOS6502Mk2::Line::IRQ>(serial_port_VIA_.get_interrupt_line() || drive_VIA_.get_interrupt_line());
 }
 
-// MARK: - Disk drive
+// MARK: - Disk drive.
 
-void MachineBase::process_input_bit(int value) {
+void MachineBase::process_input_bit(const int value) {
 	shift_register_ = (shift_register_ << 1) | value;
 	if((shift_register_ & 0x3ff) == 0x3ff) {
 		drive_VIA_port_handler_.set_sync_detected(true);
@@ -136,18 +147,40 @@ void MachineBase::process_input_bit(int value) {
 	} else {
 		drive_VIA_port_handler_.set_sync_detected(false);
 	}
-	bit_window_offset_++;
+
+	++bit_window_offset_;
 	if(bit_window_offset_ == 8) {
 		drive_VIA_port_handler_.set_data_input(uint8_t(shift_register_));
 		bit_window_offset_ = 0;
-		if(drive_VIA_port_handler_.get_should_set_overflow()) {
-			m6502_.set_overflow_line(true);
+		if(set_cpu_overflow_) {
+			m6502_.set<CPU::MOS6502Mk2::Line::Overflow>(true);
 		}
+	} else {
+		m6502_.set<CPU::MOS6502Mk2::Line::Overflow>(false);
 	}
-	else m6502_.set_overflow_line(false);
 }
 
-// the 1540 does not recognise index holes
+void MachineBase::is_writing_final_bit() {
+	if(set_cpu_overflow_) {
+		m6502_.set<CPU::MOS6502Mk2::Line::Overflow>(true);
+	}
+}
+
+void MachineBase::process_write_completed() {
+	m6502_.set<CPU::MOS6502Mk2::Line::Overflow>(false);
+	serialise_shift_output();
+}
+
+void MachineBase::serialise_shift_output() {
+	auto &drive = get_drive();
+	uint8_t value = port_a_output_;
+	for(int c = 0; c < 8; c++) {
+		drive.write_bit(value & 0x80);
+		value <<= 1;
+	}
+}
+
+// The 1540 does not recognise index holes.
 void MachineBase::process_index_hole()	{}
 
 // MARK: - Drive VIA delegate
@@ -160,11 +193,36 @@ void MachineBase::drive_via_did_set_data_density(DriveVIA &, const int density)
 	set_expected_bit_length(Storage::Encodings::CommodoreGCR::length_of_a_bit_in_time_zone(unsigned(density)));
 }
 
+void MachineBase::drive_via_did_set_drive_motor(DriveVIA &, const bool enabled) {
+	get_drive().set_motor_on(enabled);
+}
+
+void MachineBase::drive_via_did_set_write_mode(DriveVIA &, const bool enabled) {
+	if(enabled) {
+		begin_writing(false, true);
+	} else {
+		end_writing();
+	}
+}
+
+void MachineBase::drive_via_set_to_shifter_output(DriveVIA &, const uint8_t value) {
+	port_a_output_ = value;
+}
+
+void MachineBase::drive_via_should_set_cpu_overflow(DriveVIA &, const bool overflow) {
+	set_cpu_overflow_ = overflow;
+	if(!overflow) {
+		m6502_.set<CPU::MOS6502Mk2::Line::Overflow>(false);
+	}
+}
+
 // MARK: - SerialPortVIA
 
 template <MOS::MOS6522::Port port>
 uint8_t SerialPortVIA::get_port_input() const {
-	if(port) return port_b_;
+	if(port) {
+		return port_b_;
+	}
 	return 0xff;
 }
 
@@ -184,13 +242,17 @@ void SerialPortVIA::set_serial_line_state(
 	const bool value,
 	MOS::MOS6522::MOS6522<SerialPortVIA> &via
 ) {
+	const auto set = [&](const uint8_t mask) {
+		port_b_ = (port_b_ & ~mask) | (value ? 0x00 : mask);
+	};
+
 	switch(line) {
 		default: break;
-		case ::Commodore::Serial::Line::Data:		port_b_ = (port_b_ & ~0x01) | (value ? 0x00 : 0x01);		break;
-		case ::Commodore::Serial::Line::Clock:		port_b_ = (port_b_ & ~0x04) | (value ? 0x00 : 0x04);		break;
+		case ::Commodore::Serial::Line::Data:		set(0x01);		break;
+		case ::Commodore::Serial::Line::Clock:		set(0x04);		break;
 		case ::Commodore::Serial::Line::Attention:
+			set(0x80);
 			attention_level_input_ = !value;
-			port_b_ = (port_b_ & ~0x80) | (value ? 0x00 : 0x80);
 			via.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(!value);
 			update_data_line();
 		break;
@@ -202,14 +264,17 @@ void SerialPortVIA::set_serial_port(Commodore::Serial::Port &port) {
 }
 
 void SerialPortVIA::update_data_line() {
-	// "ATN (Attention) is an input on pin 3 of P2 and P3 that is sensed at PB7 and CA1 of UC3 after being inverted by UA1"
-	serial_port_->set_output(::Commodore::Serial::Line::Data,
-		Serial::LineLevel(!data_level_output_ && (attention_level_input_ != attention_acknowledge_level_)));
+	// "ATN (Attention) is an input on pin 3 of P2 and P3 that
+	// is sensed at PB7 and CA1 of UC3 after being inverted by UA1"
+	serial_port_->set_output(
+		::Commodore::Serial::Line::Data,
+		Serial::LineLevel(!data_level_output_ && (attention_level_input_ != attention_acknowledge_level_))
+	);
 }
 
 // MARK: - DriveVIA
 
-void DriveVIA::set_delegate(Delegate *delegate) {
+void DriveVIA::set_delegate(Delegate *const delegate) {
 	delegate_ = delegate;
 }
 
@@ -220,56 +285,80 @@ uint8_t DriveVIA::get_port_input() const {
 }
 
 void DriveVIA::set_sync_detected(const bool sync_detected) {
-	port_b_ = (port_b_ & 0x7f) | (sync_detected ? 0x00 : 0x80);
+	port_b_ = (port_b_ & ~0x80) | (sync_detected ? 0x00 : 0x80);
 }
 
-void DriveVIA::set_data_input(uint8_t value) {
+void DriveVIA::set_is_read_only(const bool is_read_only) {
+	port_b_ = (port_b_ & ~0x10) | (is_read_only ? 0x00 : 0x10);
+}
+
+void DriveVIA::set_data_input(const uint8_t value) {
 	port_a_ = value;
 }
 
-bool DriveVIA::get_should_set_overflow() {
-	return should_set_overflow_;
-}
-
-bool DriveVIA::get_motor_enabled() {
-	return drive_motor_;
-}
-
 template <MOS::MOS6522::Port port, MOS::MOS6522::Line line>
 void DriveVIA::set_control_line_output(const bool value) {
 	if(port == MOS::MOS6522::Port::A && line == MOS::MOS6522::Line::Two) {
-		should_set_overflow_ = value;
+		if(set_cpu_overflow_ != value) {
+			set_cpu_overflow_ = value;
+			if(delegate_) {
+				delegate_->drive_via_should_set_cpu_overflow(*this, set_cpu_overflow_);
+			}
+		}
 	}
-}
 
-template <MOS::MOS6522::Port port>
-void DriveVIA::set_port_output(const uint8_t value, uint8_t) {
-	if(port) {
-		if(previous_port_b_output_ != value) {
-			// Record drive motor state.
-			drive_motor_ = value&4;
-
-			// Check for a head step.
-			const int step_difference = ((value&3) - (previous_port_b_output_&3))&3;
-			if(step_difference) {
-				if(delegate_) delegate_->drive_via_did_step_head(*this, (step_difference == 1) ? 1 : -1);
+	if(port == MOS::MOS6522::Port::B && line == MOS::MOS6522::Line::Two) {
+		const bool new_write_mode = !value;
+		if(new_write_mode != write_mode_) {
+			write_mode_ = new_write_mode;
+			if(delegate_) {
+				delegate_->drive_via_did_set_write_mode(*this, write_mode_);
 			}
-
-			// Check for a change in density.
-			const int density_difference = (previous_port_b_output_^value) & (3 << 5);
-			if(density_difference && delegate_) {
-				delegate_->drive_via_did_set_data_density(*this, (value >> 5)&3);
-			}
-
-			// Post the LED status.
-			if(observer_) observer_->set_led_status("Drive", value&8);
-
-			previous_port_b_output_ = value;
 		}
 	}
 }
 
-void DriveVIA::set_activity_observer(Activity::Observer *observer) {
+template <>
+void DriveVIA::set_port_output<MOS::MOS6522::Port::B>(const uint8_t value, uint8_t) {
+	if(previous_port_b_output_ != value) {
+		// Record drive motor state.
+		const bool new_drive_motor = value & 4;
+		if(new_drive_motor != drive_motor_) {
+			drive_motor_ = new_drive_motor;
+			if(delegate_) {
+				delegate_->drive_via_did_set_drive_motor(*this, drive_motor_);
+			}
+		}
+
+		// Check for a head step.
+		const int step_difference = ((value&3) - (previous_port_b_output_&3))&3;
+		if(step_difference && delegate_) {
+			delegate_->drive_via_did_step_head(*this, (step_difference == 1) ? 1 : -1);
+		}
+
+		// Check for a change in density.
+		const int density_difference = (previous_port_b_output_^value) & (3 << 5);
+		if(density_difference && delegate_) {
+			delegate_->drive_via_did_set_data_density(*this, (value >> 5)&3);
+		}
+
+		// Post the LED status.
+		if(observer_) {
+			observer_->set_led_status("Drive", value&8);
+		}
+
+		previous_port_b_output_ = value;
+	}
+}
+
+template <>
+void DriveVIA::set_port_output<MOS::MOS6522::Port::A>(const uint8_t value, uint8_t) {
+	if(delegate_) {
+		delegate_->drive_via_set_to_shifter_output(*this, value);
+	}
+}
+
+void DriveVIA::set_activity_observer(Activity::Observer *const observer) {
 	observer_ = observer;
 	if(observer) {
 		observer->register_led("Drive");
@@ -277,9 +366,9 @@ void DriveVIA::set_activity_observer(Activity::Observer *observer) {
 	}
 }
 
-// MARK: - SerialPort
+// MARK: - SerialPort.
 
-void SerialPort::set_input(Serial::Line line, Serial::LineLevel level) {
+void SerialPort::set_input(const Serial::Line line, const Serial::LineLevel level) {
 	serial_port_via_->set_serial_line_state(line, bool(level), *via_);
 }
 

Machines/Commodore/1540/Implementation/C1540Base.hpp

@@ -8,7 +8,7 @@
 
 #pragma once
 
-#include "Processors/6502/6502.hpp"
+#include "Processors/6502Mk2/6502Mk2.hpp"
 #include "Components/6522/6522.hpp"
 
 #include "Machines/Commodore/SerialBus.hpp"
@@ -65,21 +65,27 @@ private:
 	It is wired up such that Port B contains:
 		Bits 0/1:	head step direction
 		Bit 2:		motor control
-		Bit 3:		LED control (TODO)
+		Bit 3:		LED control
 		Bit 4:		write protect photocell status (TODO)
 		Bits 5/6:	read/write density
 		Bit 7:		0 if sync marks are currently being detected, 1 otherwise.
 
 	... and Port A contains the byte most recently read from the disk or the byte next to write to the disk, depending on data direction.
 
-	It is implied that CA2 might be used to set processor overflow, CA1 a strobe for data input, and one of the CBs being definitive on
-	whether the disk head is being told to read or write, but it's unclear and I've yet to investigate. So, TODO.
+	Elsewhere:
+	* CA2 might is used to set processor overflow;
+	* CA1 a strobe for data input; and
+	* CB2 indicates read/write mode; 1 = read, 0 = write.
 */
 class DriveVIA: public MOS::MOS6522::IRQDelegatePortHandler {
 public:
 	struct Delegate {
 		virtual void drive_via_did_step_head(DriveVIA &, int direction) = 0;
 		virtual void drive_via_did_set_data_density(DriveVIA &, int density) = 0;
+		virtual void drive_via_did_set_drive_motor(DriveVIA &, bool enabled) = 0;
+		virtual void drive_via_did_set_write_mode(DriveVIA &, bool write) = 0;
+		virtual void drive_via_should_set_cpu_overflow(DriveVIA &, bool overflow) = 0;
+		virtual void drive_via_set_to_shifter_output(DriveVIA &, uint8_t) = 0;
 	};
 	void set_delegate(Delegate *);
 
@@ -88,8 +94,7 @@ public:
 
 	void set_sync_detected(bool);
 	void set_data_input(uint8_t);
-	bool get_should_set_overflow();
-	bool get_motor_enabled();
+	void set_is_read_only(bool);
 
 	template <MOS::MOS6522::Port, MOS::MOS6522::Line>
 	void set_control_line_output(bool value);
@@ -101,8 +106,11 @@ public:
 
 private:
 	uint8_t port_b_ = 0xff, port_a_ = 0xff;
-	bool should_set_overflow_ = false;
+
+	bool set_cpu_overflow_ = false;
 	bool drive_motor_ = false;
+	bool write_mode_ = false;
+
 	uint8_t previous_port_b_output_ = 0;
 	Delegate *delegate_ = nullptr;
 	Activity::Observer *observer_ = nullptr;
@@ -122,7 +130,6 @@ private:
 };
 
 class MachineBase:
-	public CPU::MOS6502::BusHandler,
 	public MOS::MOS6522::IRQDelegatePortHandler::Delegate,
 	public DriveVIA::Delegate,
 	public Storage::Disk::Controller {
@@ -134,17 +141,27 @@ public:
 	void set_activity_observer(Activity::Observer *);
 
 	// to satisfy CPU::MOS6502::Processor
-	Cycles perform_bus_operation(CPU::MOS6502::BusOperation, uint16_t address, uint8_t *value);
+	template <CPU::MOS6502Mk2::BusOperation operation, typename AddressT>
+	Cycles perform(const AddressT, CPU::MOS6502Mk2::data_t<operation>);
 
 protected:
 	// to satisfy MOS::MOS6522::Delegate
 	void mos6522_did_change_interrupt_status(void *mos6522) override;
 
 	// to satisfy DriveVIA::Delegate
-	void drive_via_did_step_head(DriveVIA &, int direction) override;
-	void drive_via_did_set_data_density(DriveVIA &, int density) override;
+	void drive_via_did_step_head(DriveVIA &, int) override;
+	void drive_via_did_set_data_density(DriveVIA &, int) override;
+	void drive_via_did_set_drive_motor(DriveVIA &, bool) override;
+	void drive_via_did_set_write_mode(DriveVIA &, bool) override;
+	void drive_via_should_set_cpu_overflow(DriveVIA &, bool) override;
+	void drive_via_set_to_shifter_output(DriveVIA &, uint8_t) override;
 
-	CPU::MOS6502::Processor<CPU::MOS6502::Personality::P6502, MachineBase, false> m6502_;
+	struct M6502Traits {
+		static constexpr auto uses_ready_line = false;
+		static constexpr auto pause_precision = CPU::MOS6502Mk2::PausePrecision::AnyCycle;
+		using BusHandlerT = MachineBase;
+	};
+	CPU::MOS6502Mk2::Processor<CPU::MOS6502Mk2::Model::M6502, M6502Traits> m6502_;
 
 	uint8_t ram_[0x800];
 	uint8_t rom_[0x4000];
@@ -156,9 +173,15 @@ protected:
 	MOS::MOS6522::MOS6522<DriveVIA> drive_VIA_;
 	MOS::MOS6522::MOS6522<SerialPortVIA> serial_port_VIA_;
 
+	bool set_cpu_overflow_ = false;
 	int shift_register_ = 0, bit_window_offset_;
 	void process_input_bit(int value) override;
 	void process_index_hole() override;
+	void process_write_completed() override;
+	void is_writing_final_bit() override;
+
+	uint8_t port_a_output_ = 0xff;
+	void serialise_shift_output();
 };
 
 }

Machines/Commodore/Plus4/Plus4.cpp

@@ -16,7 +16,7 @@
 
 #include "Machines/MachineTypes.hpp"
 #include "Machines/Utility/MemoryFuzzer.hpp"
-#include "Processors/6502/6502.hpp"
+#include "Processors/6502Mk2/6502Mk2.hpp"
 #include "Analyser/Static/Commodore/Target.hpp"
 #include "Outputs/Log.hpp"
 #include "Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
@@ -236,20 +236,17 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	// HACK. NOCOMMIT.
 //	int pulse_num_ = 0;
 
-	Cycles perform_bus_operation(
-		const CPU::MOS6502::BusOperation operation,
-		const uint16_t address,
-		uint8_t *const value
-	) {
+	template <CPU::MOS6502Mk2::BusOperation operation, typename AddressT>
+	Cycles perform(const AddressT address, CPU::MOS6502Mk2::data_t<operation> value) {
 		// Determine from the TED video subsystem the length of this clock cycle as perceived by the 6502,
 		// relative to the master clock.
-		const auto length = video_.cycle_length(operation == CPU::MOS6502::BusOperation::Ready);
+		const auto length = video_.cycle_length(operation == CPU::MOS6502Mk2::BusOperation::Ready);
 
 		// Update other subsystems.
 		advance_timers_and_tape(length);
@@ -265,7 +262,7 @@ public:
 			time_since_audio_update_ += length;
 		}
 
-		if(operation == CPU::MOS6502::BusOperation::Ready) {
+		if(operation == CPU::MOS6502Mk2::BusOperation::Ready) {
 			return length;
 		}
 
@@ -282,17 +279,17 @@ public:
 			//	b1 = serial clock out and cassette write;
 			//	b0 = serial data out.
 
-			if(is_read(operation)) {
+			if constexpr (is_read(operation)) {
 				if(!address) {
-					*value = io_direction_;
+					value = io_direction_;
 				} else {
-					*value = io_input();
+					value = io_input();
 				}
 			} else {
 				if(!address) {
-					io_direction_ = *value;
+					io_direction_ = value;
 				} else {
-					io_output_ = *value;
+					io_output_ = value;
 				}
 
 				const auto output = io_output_ | ~io_direction_;
@@ -323,36 +320,36 @@ public:
 //				);
 //			}
 
-			if(
-				use_fast_tape_hack_ &&
-				operation == CPU::MOS6502Esque::BusOperation::ReadOpcode &&
-				(
-					(use_hle && address == 0xe5fd) ||
-					address == 0xe68b ||
-					address == 0xe68d
-				)
-			) {
-//				++pulse_num_;
-				if(use_hle) {
-					read_dipole();
-				}
+			if constexpr (is_read(operation)) {
+				if(
+					use_fast_tape_hack_ &&
+					operation == CPU::MOS6502Mk2::BusOperation::ReadOpcode &&
+					(
+						(use_hle && address == 0xe5fd) ||
+						address == 0xe68b ||
+						address == 0xe68d
+					)
+				) {
+	//				++pulse_num_;
+					if(use_hle) {
+						read_dipole();
+					}
 
-//				using Flag = CPU::MOS6502::Flag;
-//				using Register = CPU::MOS6502::Register;
-//				const auto flags = m6502_.value_of(Register::Flags);
-//				printf("to %lld: %c%c%c\n",
-//					tape_player_->serialiser()->offset(),
-//					flags & Flag::Sign ? 'n' : '-',
-//					flags & Flag::Overflow ? 'v' : '-',
-//					flags & Flag::Carry ? 'c' : '-'
-//				);
-				*value = 0x60;
-			} else {
-				if(is_read(operation)) {
-					*value = map_.read(address);
+	//				using Flag = CPU::MOS6502::Flag;
+	//				using Register = CPU::MOS6502::Register;
+	//				const auto flags = m6502_.value_of(Register::Flags);
+	//				printf("to %lld: %c%c%c\n",
+	//					tape_player_->serialiser()->offset(),
+	//					flags & Flag::Sign ? 'n' : '-',
+	//					flags & Flag::Overflow ? 'v' : '-',
+	//					flags & Flag::Carry ? 'c' : '-'
+	//				);
+					value = 0x60;
 				} else {
-					map_.write(address) = *value;
+					value = map_.read(address);
 				}
+			} else {
+				map_.write(address) = value;
 			}
 
 
@@ -393,12 +390,12 @@ public:
 //					ram_[0x90] = 0;
 //					ram_[0x93] = 0;
 //
-//					*value = 0x0c;	// NOP abs.
+//					value = 0x0c;	// NOP abs.
 //				}
 //			}
 		} else if(address < 0xff00) {
 			// Miscellaneous hardware. All TODO.
-			if(is_read(operation)) {
+			if constexpr (is_read(operation)) {
 				switch(address & 0xfff0) {
 					case 0xfd10:
 						// 6529 parallel port, about which I know only what I've found in kernel ROM disassemblies.
@@ -406,7 +403,7 @@ public:
 						// If play button is not currently pressed and this read is immediately followed by
 						// an AND 4, press it. The kernel will deal with motor control subsequently.
 						if(!play_button_) {
-							const uint16_t pc = m6502_.value_of(CPU::MOS6502::Register::ProgramCounter);
+							const uint16_t pc = m6502_.registers().pc.full;
 							const uint8_t next[] = {
 								map_.read(pc+0),
 								map_.read(pc+1),
@@ -422,22 +419,23 @@ public:
 							}
 						}
 
-						*value = 0xff ^ (play_button_ ? 0x4 :0x0);
+						value = 0xff ^ (play_button_ ? 0x4 :0x0);
 					break;
 
 					case 0xfdd0:
 					case 0xfdf0:
-						*value = uint8_t(address >> 8);
+						value = uint8_t(address >> 8);
 					break;
 
 					default:
+						value = 0xff;
 						Logger::info().append("TODO: read @ %04x", address);
 					break;
 				}
 			} else {
 				switch(address & 0xfff0) {
 					case 0xfd30:
-						keyboard_mask_ = *value;
+						keyboard_mask_ = value;
 					break;
 
 					case 0xfdd0: {
@@ -447,28 +445,28 @@ public:
 					} break;
 
 					default:
-						Logger::info().append("TODO: write of %02x @ %04x", *value, address);
+						Logger::info().append("TODO: write of %02x @ %04x", value, address);
 					break;
 				}
 			}
 		} else {
-			const auto pc = m6502_.value_of(CPU::MOS6502::Register::ProgramCounter);
+			const auto pc = m6502_.registers().pc.full;
 			const bool is_from_rom =
 				(rom_is_paged_ && pc >= 0x8000) ||
 				(pc >= 0x400 && pc < 0x500) ||
 				(pc >= 0x700 && pc < 0x800);
 			bool is_hit = true;
 
-			if(is_read(operation)) {
+			if constexpr (is_read(operation)) {
 				switch(address) {
-					case 0xff00:	*value = timers_.read<0>();		break;
-					case 0xff01:	*value = timers_.read<1>();		break;
-					case 0xff02:	*value = timers_.read<2>();		break;
-					case 0xff03:	*value = timers_.read<3>();		break;
-					case 0xff04:	*value = timers_.read<4>();		break;
-					case 0xff05:	*value = timers_.read<5>();		break;
-					case 0xff06:	*value = video_.read<0xff06>();	break;
-					case 0xff07:	*value = video_.read<0xff07>();	break;
+					case 0xff00:	value = timers_.read<0>();		break;
+					case 0xff01:	value = timers_.read<1>();		break;
+					case 0xff02:	value = timers_.read<2>();		break;
+					case 0xff03:	value = timers_.read<3>();		break;
+					case 0xff04:	value = timers_.read<4>();		break;
+					case 0xff05:	value = timers_.read<5>();		break;
+					case 0xff06:	value = video_.read<0xff06>();	break;
+					case 0xff07:	value = video_.read<0xff07>();	break;
 					case 0xff08: {
 						const uint8_t keyboard_input =
 							~(
@@ -487,127 +485,128 @@ public:
 							((joystick_mask_ & 0x02) ? 0xff : (joystick(0).mask() | 0x40)) &
 							((joystick_mask_ & 0x04) ? 0xff : (joystick(1).mask() | 0x80));
 
-						*value = keyboard_input & joystick_mask;
+						value = keyboard_input & joystick_mask;
 					} break;
-					case 0xff09:	*value = interrupts_.status();	break;
+					case 0xff09:	value = interrupts_.status();	break;
 					case 0xff0a:
-						*value = interrupts_.mask() | video_.read<0xff0a>() | 0xa0;
+						value = interrupts_.mask() | video_.read<0xff0a>() | 0xa0;
 					break;
-					case 0xff0b:	*value = video_.read<0xff0b>();	break;
-					case 0xff0c:	*value = video_.read<0xff0c>();	break;
-					case 0xff0d:	*value = video_.read<0xff0d>();	break;
-					case 0xff0e:	*value = ff0e_;					break;
-					case 0xff0f:	*value = ff0f_;					break;
-					case 0xff10:	*value = ff10_ | 0xfc;			break;
-					case 0xff11:	*value = ff11_;					break;
-					case 0xff12:	*value = ff12_ | 0xc0;			break;
-					case 0xff13:	*value = ff13_ | (rom_is_paged_ ? 1 : 0);	break;
-					case 0xff14:	*value = video_.read<0xff14>();	break;
-					case 0xff15:	*value = video_.read<0xff15>();	break;
-					case 0xff16:	*value = video_.read<0xff16>();	break;
-					case 0xff17:	*value = video_.read<0xff17>();	break;
-					case 0xff18:	*value = video_.read<0xff18>();	break;
-					case 0xff19:	*value = video_.read<0xff19>();	break;
-					case 0xff1a:	*value = video_.read<0xff1a>();	break;
-					case 0xff1b:	*value = video_.read<0xff1b>();	break;
-					case 0xff1c:	*value = video_.read<0xff1c>();	break;
-					case 0xff1d:	*value = video_.read<0xff1d>();	break;
-					case 0xff1e:	*value = video_.read<0xff1e>();	break;
-					case 0xff1f:	*value = video_.read<0xff1f>();	break;
+					case 0xff0b:	value = video_.read<0xff0b>();	break;
+					case 0xff0c:	value = video_.read<0xff0c>();	break;
+					case 0xff0d:	value = video_.read<0xff0d>();	break;
+					case 0xff0e:	value = ff0e_;					break;
+					case 0xff0f:	value = ff0f_;					break;
+					case 0xff10:	value = ff10_ | 0xfc;			break;
+					case 0xff11:	value = ff11_;					break;
+					case 0xff12:	value = ff12_ | 0xc0;			break;
+					case 0xff13:	value = ff13_ | (rom_is_paged_ ? 1 : 0);	break;
+					case 0xff14:	value = video_.read<0xff14>();	break;
+					case 0xff15:	value = video_.read<0xff15>();	break;
+					case 0xff16:	value = video_.read<0xff16>();	break;
+					case 0xff17:	value = video_.read<0xff17>();	break;
+					case 0xff18:	value = video_.read<0xff18>();	break;
+					case 0xff19:	value = video_.read<0xff19>();	break;
+					case 0xff1a:	value = video_.read<0xff1a>();	break;
+					case 0xff1b:	value = video_.read<0xff1b>();	break;
+					case 0xff1c:	value = video_.read<0xff1c>();	break;
+					case 0xff1d:	value = video_.read<0xff1d>();	break;
+					case 0xff1e:	value = video_.read<0xff1e>();	break;
+					case 0xff1f:	value = video_.read<0xff1f>();	break;
 
-					case 0xff3e:	*value = 0;						break;
-					case 0xff3f:	*value = 0;						break;
+					case 0xff3e:	value = 0;						break;
+					case 0xff3f:	value = 0;						break;
 
 					default:
 						Logger::info().append("TODO: TED read at %04x", address);
+						value = 0xff;
 						is_hit = false;
 				}
 			} else {
 				switch(address) {
-					case 0xff00:	timers_.write<0>(*value);		break;
-					case 0xff01:	timers_.write<1>(*value);		break;
-					case 0xff02:	timers_.write<2>(*value);		break;
-					case 0xff03:	timers_.write<3>(*value);		break;
-					case 0xff04:	timers_.write<4>(*value);		break;
-					case 0xff05:	timers_.write<5>(*value);		break;
-					case 0xff06:	video_.write<0xff06>(*value);	break;
+					case 0xff00:	timers_.write<0>(value);		break;
+					case 0xff01:	timers_.write<1>(value);		break;
+					case 0xff02:	timers_.write<2>(value);		break;
+					case 0xff03:	timers_.write<3>(value);		break;
+					case 0xff04:	timers_.write<4>(value);		break;
+					case 0xff05:	timers_.write<5>(value);		break;
+					case 0xff06:	video_.write<0xff06>(value);	break;
 					case 0xff07:
-						video_.write<0xff07>(*value);
+						video_.write<0xff07>(value);
 						update_audio();
-						audio_.set_divider(*value);
+						audio_.set_divider(value);
 					break;
 					case 0xff08:
 						// Observation here: the kernel posts a 0 to this
 						// address upon completing each keyboard scan cycle,
 						// once per frame.
-						if(typer_ && !*value) {
+						if(typer_ && !value) {
 							if(!typer_->type_next_character()) {
 								clear_all_keys();
 								typer_.reset();
 							}
 						}
 
-						joystick_mask_ = *value;
+						joystick_mask_ = value;
 					break;
 					case 0xff09:
-						interrupts_.set_status(*value);
+						interrupts_.set_status(value);
 					break;
 					case 0xff0a:
-						interrupts_.set_mask(*value);
-						video_.write<0xff0a>(*value);
+						interrupts_.set_mask(value);
+						video_.write<0xff0a>(value);
 					break;
-					case 0xff0b:	video_.write<0xff0b>(*value);	break;
-					case 0xff0c:	video_.write<0xff0c>(*value);	break;
-					case 0xff0d:	video_.write<0xff0d>(*value);	break;
+					case 0xff0b:	video_.write<0xff0b>(value);	break;
+					case 0xff0c:	video_.write<0xff0c>(value);	break;
+					case 0xff0d:	video_.write<0xff0d>(value);	break;
 					case 0xff0e:
-						ff0e_ = *value;
+						ff0e_ = value;
 						update_audio();
-						audio_.set_frequency_low<0>(*value);
+						audio_.set_frequency_low<0>(value);
 					break;
 					case 0xff0f:
-						ff0f_ = *value;
+						ff0f_ = value;
 						update_audio();
-						audio_.set_frequency_low<1>(*value);
+						audio_.set_frequency_low<1>(value);
 					break;
 					case 0xff10:
-						ff10_ = *value;
+						ff10_ = value;
 						update_audio();
-						audio_.set_frequency_high<1>(*value);
+						audio_.set_frequency_high<1>(value);
 					break;
 					case 0xff11:
-						ff11_ = *value;
+						ff11_ = value;
 						update_audio();
-						audio_.set_control(*value);
+						audio_.set_control(value);
 					break;
 					case 0xff12:
-						ff12_ = *value & 0x3f;
-						video_.write<0xff12>(*value);
+						ff12_ = value & 0x3f;
+						video_.write<0xff12>(value);
 
-						if((*value & 4)) {
+						if((value & 4)) {
 							page_video_rom();
 						} else {
 							page_video_ram();
 						}
 
 						update_audio();
-						audio_.set_frequency_high<0>(*value);
+						audio_.set_frequency_high<0>(value);
 					break;
 					case 0xff13:
-						ff13_ = *value & 0xfe;
-						video_.write<0xff13>(*value);
+						ff13_ = value & 0xfe;
+						video_.write<0xff13>(value);
 					break;
-					case 0xff14:	video_.write<0xff14>(*value);	break;
-					case 0xff15:	video_.write<0xff15>(*value);	break;
-					case 0xff16:	video_.write<0xff16>(*value);	break;
-					case 0xff17:	video_.write<0xff17>(*value);	break;
-					case 0xff18:	video_.write<0xff18>(*value);	break;
-					case 0xff19:	video_.write<0xff19>(*value);	break;
-					case 0xff1a:	video_.write<0xff1a>(*value);	break;
-					case 0xff1b:	video_.write<0xff1b>(*value);	break;
-					case 0xff1c:	video_.write<0xff1c>(*value);	break;
-					case 0xff1d:	video_.write<0xff1d>(*value);	break;
-					case 0xff1e:	video_.write<0xff1e>(*value);	break;
-					case 0xff1f:	video_.write<0xff1f>(*value);	break;
+					case 0xff14:	video_.write<0xff14>(value);	break;
+					case 0xff15:	video_.write<0xff15>(value);	break;
+					case 0xff16:	video_.write<0xff16>(value);	break;
+					case 0xff17:	video_.write<0xff17>(value);	break;
+					case 0xff18:	video_.write<0xff18>(value);	break;
+					case 0xff19:	video_.write<0xff19>(value);	break;
+					case 0xff1a:	video_.write<0xff1a>(value);	break;
+					case 0xff1b:	video_.write<0xff1b>(value);	break;
+					case 0xff1c:	video_.write<0xff1c>(value);	break;
+					case 0xff1d:	video_.write<0xff1d>(value);	break;
+					case 0xff1e:	video_.write<0xff1e>(value);	break;
+					case 0xff1f:	video_.write<0xff1f>(value);	break;
 
 					case 0xff3e:	page_cpu_rom();					break;
 					case 0xff3f:	page_cpu_ram();					break;
@@ -626,8 +625,12 @@ public:
 	}
 
 private:
-	using Processor = CPU::MOS6502::Processor<CPU::MOS6502::Personality::P6502, ConcreteMachine, true>;
-	Processor m6502_;
+	struct M6502Traits {
+		static constexpr auto uses_ready_line = true;
+		static constexpr auto pause_precision = CPU::MOS6502Mk2::PausePrecision::BetweenInstructions;
+		using BusHandlerT = ConcreteMachine;
+	};
+	CPU::MOS6502Mk2::Processor<CPU::MOS6502Mk2::Model::M6502, M6502Traits> m6502_;
 
 	Outputs::Speaker::Speaker *get_speaker() override {
 		return &speaker_;
@@ -637,11 +640,11 @@ private:
 		if(c1541_) c1541_->set_activity_observer(observer);
 	}
 
-	void set_irq_line(bool active) override {
-		m6502_.set_irq_line(active);
+	void set_irq_line(const bool active) override {
+		m6502_.template set<CPU::MOS6502Mk2::Line::IRQ>(active);
 	}
-	void set_ready_line(bool active) override {
-		m6502_.set_ready_line(active);
+	void set_ready_line(const bool active) override {
+		m6502_.template set<CPU::MOS6502Mk2::Line::Ready>(active);
 	}
 
 	void page_video_rom() {
@@ -788,26 +791,19 @@ private:
 	// TODO: substantially simplify the below; at the minute it's a
 	// literal transcription of the original as a simple first step.
 	void read_dipole() {
-		using Register = CPU::MOS6502::Register;
-		using Flag = CPU::MOS6502::Flag;
+		using Flag = CPU::MOS6502Mk2::Flag;
 
 		//
 		// Get registers now and ensure they'll be written back at function exit.
 		//
-		CPU::MOS6502Esque::LazyFlags flags(uint8_t(m6502_.value_of(Register::Flags)));
-		uint8_t x, y, a;
-		uint8_t s = uint8_t(m6502_.value_of(Register::StackPointer));
+		auto registers = m6502_.registers();
 		struct ScopeGuard {
 			ScopeGuard(std::function<void(void)> at_exit) : at_exit_(at_exit) {}
 			~ScopeGuard() {	at_exit_();	}
 		private:
 			std::function<void(void)> at_exit_;
-		} registers([&] {
-			m6502_.set_value_of(Register::Flags, flags.get());
-			m6502_.set_value_of(Register::A, a);
-			m6502_.set_value_of(Register::X, x);
-			m6502_.set_value_of(Register::Y, y);
-			m6502_.set_value_of(Register::StackPointer, s);
+		} store_registers([&] {
+			m6502_.set_registers(registers);
 		});
 
 		//
@@ -822,38 +818,38 @@ private:
 		// 6502 pseudo-ops.
 		//
 		const auto ldabs = [&] (uint8_t &target, const uint16_t address) {
-			flags.set_nz(target = map_.read(address));
+			registers.flags.set_per<Flag::NegativeZero>(target = map_.read(address));
 		};
 		const auto ldimm = [&] (uint8_t &target, const uint8_t value) {
-			flags.set_nz(target = value);
+			registers.flags.set_per<Flag::NegativeZero>(target = value);
 		};
 		const auto pha = [&] () {
-			map_.write(0x100 + s) = a;
-			--s;
+			map_.write(0x100 + registers.s) = registers.a;
+			--registers.s;
 		};
 		const auto pla = [&] () {
-			++s;
-			a = map_.read(0x100 + s);
+			++registers.s;
+			registers.a = map_.read(0x100 + registers.s);
 		};
 		const auto bit = [&] (const uint8_t value) {
-			flags.zero_result = a & value;
-			flags.negative_result = value;
-			flags.overflow = value & CPU::MOS6502Esque::Flag::Overflow;
+			registers.flags.set_per<Flag::Zero>(registers.a & value);
+			registers.flags.set_per<Flag::Negative>(value);
+			registers.flags.set_per<Flag::Overflow>(value);
 		};
 		const auto cmp = [&] (const uint8_t value) {
-			const uint16_t temp16 = a - value;
-			flags.set_nz(uint8_t(temp16));
-			flags.carry = ((~temp16) >> 8)&1;
+			const uint16_t temp16 = registers.a - value;
+			registers.flags.set_per<Flag::NegativeZero>(uint8_t(temp16));
+			registers.flags.set_per<Flag::Carry>(((~temp16) >> 8)&1);
 		};
 		const auto andimm = [&] (const uint8_t value) {
-			a &= value;
-			flags.set_nz(a);
+			registers.a &= value;
+			registers.flags.set_per<Flag::NegativeZero>(registers.a);
 		};
 		const auto ne = [&]() -> bool {
-			return flags.zero_result;
+			return !registers.flags.get<Flag::Zero>();
 		};
 		const auto eq = [&]() -> bool {
-			return !flags.zero_result;
+			return registers.flags.get<Flag::Zero>();
 		};
 
 		//
@@ -862,7 +858,7 @@ private:
 		const auto dipok = [&] {
 			//       clc             	; everything's fine
 			//       rts
-			flags.carry = 0;
+			registers.flags.set_per<Flag::Carry>(0);
 		};
 		const auto rshort = [&] {
 			//       bit  tshrtd     	; got a short
@@ -878,7 +874,7 @@ private:
 		const auto rderr1 = [&] {
 			//       sec             	; i'm confused
 			//       rts
-			flags.carry = Flag::Carry;
+			registers.flags.set_per<Flag::Carry>(Flag::Carry);
 		};
 
 		//
@@ -891,8 +887,8 @@ private:
 		//rddipl
 		//       ldx  dsamp1     	; setup x,y with 1st sample point
 		//       ldy  dsamp1+1
-		ldabs(x, dsamp1);
-		ldabs(y, dsamp1 + 1);
+		ldabs(registers.x, dsamp1);
+		ldabs(registers.y, dsamp1 + 1);
 		advance_cycles(8);
 
 		//badeg1
@@ -901,9 +897,9 @@ private:
 			//       pha
 			//       lda  dsamp2
 			//       pha
-			ldabs(a, dsamp2 + 1);
+			ldabs(registers.a, dsamp2 + 1);
 			pha();
-			ldabs(a, dsamp2);
+			ldabs(registers.a, dsamp2);
 			pha();
 			advance_cycles(14);
 
@@ -911,7 +907,7 @@ private:
 			//rwtl   			; wait till rd line is high
 			//       bit  port	[= $0001]
 			//       beq  rwtl       	; !ls!
-			ldimm(a, 0x10);
+			ldimm(registers.a, 0x10);
 			advance_cycles(2);
 			do {
 				bit(io_input());
@@ -933,8 +929,8 @@ private:
 
 			//       stx  timr2l
 			//       sty  timr2h
-			timers_.write<2>(x);
-			timers_.write<3>(y);
+			timers_.write<2>(registers.x);
+			timers_.write<3>(registers.y);
 			advance_cycles(8);
 
 
@@ -945,9 +941,9 @@ private:
 			//       pla
 			//       sta  timr3h     	;go! ...tb
 			pla();
-			timers_.write<4>(a);
+			timers_.write<4>(registers.a);
 			pla();
-			timers_.write<5>(a);
+			timers_.write<5>(registers.a);
 			advance_cycles(14);
 
 
@@ -955,8 +951,8 @@ private:
 			//
 			//       lda  #$50       	; clr ta,tb
 			//       sta  tedirq
-			ldimm(a, 0x50);
-			interrupts_.set_status(a);
+			ldimm(registers.a, 0x50);
+			interrupts_.set_status(registers.a);
 			advance_cycles(6);
 
 
@@ -969,7 +965,7 @@ private:
 			//       and  #$10       	; a look at that edge again
 			//       bne  badeg1     	; woa! got a bad edge trigger  !ls!
 			do {
-				ldimm(a, io_input());
+				ldimm(registers.a, io_input());
 				cmp(io_input());
 				if(advance_cycles(9)) {
 					return;
@@ -992,7 +988,7 @@ private:
 
 		//       lda  #$10
 		//wata   			; wait for ta to timeout
-		ldimm(a, 0x10);
+		ldimm(registers.a, 0x10);
 		advance_cycles(3);
 		do {
 			//       bit  port       	; kuldge, kludge, kludge !!! <<><>>
@@ -1020,7 +1016,7 @@ private:
 		do {
 			//       lda  port
 			//       cmp  port
-			ldimm(a, io_input());
+			ldimm(registers.a, io_input());
 			cmp(io_input());
 
 			if(advance_cycles(9)) {
@@ -1048,7 +1044,7 @@ private:
 		//
 		//; wait for tb to timeout
 		//; now do the dipole sample #2
-		ldimm(a, 0x40);
+		ldimm(registers.a, 0x40);
 		advance_cycles(3);
 		do {
 			bit(interrupts_.status());
@@ -1063,7 +1059,7 @@ private:
 		//       cmp  port
 		//       bne  casdb3
 		do {
-			ldimm(a, io_input());
+			ldimm(registers.a, io_input());
 			cmp(io_input());
 			if(advance_cycles(9)) {
 				return;
@@ -1084,10 +1080,10 @@ private:
 		//       sta  timr2l
 		//       lda  zcell+1
 		//       sta  timr2h
-		ldabs(a, zcell);
-		timers_.write<2>(a);
-		ldabs(a, zcell + 1);
-		timers_.write<3>(y);
+		ldabs(registers.a, zcell);
+		timers_.write<2>(registers.a);
+		ldabs(registers.a, zcell + 1);
+		timers_.write<3>(registers.y);
 		advance_cycles(16);
 
 
@@ -1096,9 +1092,9 @@ private:
 		//       lda  #$10
 		//       sta  tedirq	; verify +180 half of word dipole
 		//       lda  #$10
-		ldimm(a, 0x10);
-		interrupts_.set_status(a);
-		ldimm(a, 0x10);
+		ldimm(registers.a, 0x10);
+		interrupts_.set_status(registers.a);
+		ldimm(registers.a, 0x10);
 		advance_cycles(8);
 
 		//wata2
@@ -1116,7 +1112,7 @@ private:
 		//       cmp  port
 		//       bne  casdb4
 		do {
-			ldimm(a, io_input());
+			ldimm(registers.a, io_input());
 			cmp(io_input());
 			if(advance_cycles(9)) {
 				return;

Machines/Commodore/Vic-20/Vic20.cpp

@@ -13,7 +13,7 @@
 #include "Activity/Source.hpp"
 #include "Machines/MachineTypes.hpp"
 
-#include "Processors/6502/6502.hpp"
+#include "Processors/6502Mk2/6502Mk2.hpp"
 #include "Components/6560/6560.hpp"
 #include "Components/6522/6522.hpp"
 
@@ -72,26 +72,30 @@ public:
 		// Port A provides information about the presence or absence of a tape, and parts of
 		// the joystick and serial port state, both of which have been statefully collected
 		// into port_a_.
-		if(!port) {
+		if constexpr (port == MOS::MOS6522::Port::A) {
 			return port_a_ | (tape_->has_tape() ? 0x00 : 0x40);
 		}
 		return 0xff;
 	}
 
 	/// Receives announcements of control line output change from the 6522.
-	template <MOS::MOS6522::Port port, MOS::MOS6522::Line line> void set_control_line_output(const bool value) {
-		// The CA2 output is used to control the tape motor.
-		if(port == MOS::MOS6522::Port::A && line == MOS::MOS6522::Line::Two) {
+	template <MOS::MOS6522::Port port, MOS::MOS6522::Line line>
+	void set_control_line_output(const bool value) {
+		// CA2: control the tape motor.
+		if constexpr (port == MOS::MOS6522::Port::A && line == MOS::MOS6522::Line::Two) {
 			tape_->set_motor_control(!value);
 		}
 	}
 
 	/// Receives announcements of changes in the serial bus connected to the serial port and propagates them into Port A.
-	void set_serial_line_state(Commodore::Serial::Line line, const bool value) {
+	void set_serial_line_state(const Commodore::Serial::Line line, const bool value) {
+		const auto set = [&](const uint8_t bit) {
+			port_a_ = (port_a_ & ~bit) | (value ? bit : 0x00);
+		};
 		switch(line) {
 			default: break;
-			case ::Commodore::Serial::Line::Data: port_a_ = (port_a_ & ~0x02) | (value ? 0x02 : 0x00);	break;
-			case ::Commodore::Serial::Line::Clock: port_a_ = (port_a_ & ~0x01) | (value ? 0x01 : 0x00);	break;
+			case ::Commodore::Serial::Line::Data: 	set(0x02);	break;
+			case ::Commodore::Serial::Line::Clock: 	set(0x01);	break;
 		}
 	}
 
@@ -146,7 +150,7 @@ public:
 
 	/// Sets all keys as unpressed.
 	void clear_all_keys() {
-		memset(columns_, 0xff, sizeof(columns_));
+		std::fill(std::begin(columns_), std::end(columns_), 0xff);
 	}
 
 	/// Called by the 6522 to get input. Reads the keyboard on Port A, returns a small amount of joystick state on Port B.
@@ -230,8 +234,6 @@ struct Vic6560BusHandler {
 	// It is assumed that these pointers have been filled in by the machine.
 	const uint8_t *video_memory_map[16]{};	// Segments video memory into 1kb portions.
 	const uint8_t *colour_memory{};			// Colour memory must be contiguous.
-
-	// TODO: make the above const.
 };
 
 /*!
@@ -280,7 +282,6 @@ class ConcreteMachine:
 	public MachineTypes::MappedKeyboardMachine,
 	public MachineTypes::JoystickMachine,
 	public Configurable::Device,
-	public CPU::MOS6502::BusHandler,
 	public MOS::MOS6522::IRQDelegatePortHandler::Delegate,
 	public Utility::TypeRecipient<CharacterMapper>,
 	public Storage::Tape::BinaryTapePlayer::Delegate,
@@ -455,54 +456,50 @@ public:
 	}
 
 	void set_key_state(const uint16_t key, const bool is_pressed) final {
-		if(key < 0xfff0) {
+		const auto apply_shifted = [&](const uint16_t key) {
+			keyboard_via_port_handler_.set_key_state(KeyLShift, is_pressed);
 			keyboard_via_port_handler_.set_key_state(key, is_pressed);
-		} else {
-			switch(key) {
-				case KeyRestore:
-					user_port_via_.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(!is_pressed);
-				break;
-#define ShiftedMap(source, target)	\
-				case source:	\
-					keyboard_via_port_handler_.set_key_state(KeyLShift, is_pressed);	\
-					keyboard_via_port_handler_.set_key_state(target, is_pressed);	\
-				break;
+		};
 
-				ShiftedMap(KeyUp, KeyDown);
-				ShiftedMap(KeyLeft, KeyRight);
-				ShiftedMap(KeyF2, KeyF1);
-				ShiftedMap(KeyF4, KeyF3);
-				ShiftedMap(KeyF6, KeyF5);
-				ShiftedMap(KeyF8, KeyF7);
-#undef ShiftedMap
-			}
+		switch(key) {
+			default:
+				keyboard_via_port_handler_.set_key_state(key, is_pressed);
+			break;
+			case KeyRestore:
+				user_port_via_.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(!is_pressed);
+			break;
+			case KeyUp:		apply_shifted(KeyDown);		break;
+			case KeyLeft:	apply_shifted(KeyRight);	break;
+			case KeyF2:		apply_shifted(KeyF1);		break;
+			case KeyF4:		apply_shifted(KeyF3);		break;
+			case KeyF6:		apply_shifted(KeyF5);		break;
+			case KeyF8:		apply_shifted(KeyF7);		break;
 		}
 	}
 
 	void clear_all_keys() final {
 		keyboard_via_port_handler_.clear_all_keys();
+		set_key_state(KeyRestore, false);
 	}
 
 	const std::vector<std::unique_ptr<Inputs::Joystick>> &get_joysticks() final {
 		return joysticks_;
 	}
 
-	// to satisfy CPU::MOS6502::Processor
-	forceinline Cycles perform_bus_operation(
-		const CPU::MOS6502::BusOperation operation,
-		const uint16_t address,
-		uint8_t *const value
-	) {
+	template <CPU::MOS6502Mk2::BusOperation operation, typename AddressT>
+	Cycles perform(const AddressT address, CPU::MOS6502Mk2::data_t<operation> value) {
 		// Tun the phase-1 part of this cycle, in which the VIC accesses memory.
 		cycles_since_mos6560_update_++;
 
 		// Run the phase-2 part of the cycle, which is whatever the 6502 said it should be.
-		const bool is_from_rom = m6502_.value_of(CPU::MOS6502::Register::ProgramCounter) > 0x8000;
-		if(is_read(operation)) {
+		const auto is_from_rom = [&]() {
+			return m6502_.registers().pc.full > 0x8000;
+		};
+		if constexpr (is_read(operation)) {
 			const auto page = processor_read_memory_map_[address >> 10];
 			uint8_t result;
 			if(!page) {
-				if(!is_from_rom) confidence_.add_miss();
+				if(!is_from_rom()) confidence_.add_miss();
 				result = 0xff;
 			} else {
 				result = processor_read_memory_map_[address >> 10][address & 0x3ff];
@@ -515,7 +512,7 @@ public:
 				if(address & 0x10) result &= user_port_via_.read(address);
 				if(address & 0x20) result &= keyboard_via_.read(address);
 
-				if(!is_from_rom) {
+				if(!is_from_rom()) {
 					if((address & 0x100) && !(address & 0x30)) {
 						confidence_.add_miss();
 					} else {
@@ -523,10 +520,10 @@ public:
 					}
 				}
 			}
-			*value = result;
+			value = result;
 
 			// Consider applying the fast tape hack.
-			if(use_fast_tape_hack_ && operation == CPU::MOS6502::BusOperation::ReadOpcode) {
+			if(use_fast_tape_hack_ && operation == CPU::MOS6502Mk2::BusOperation::ReadOpcode) {
 				if(address == 0xf7b2) {
 					// Address 0xf7b2 contains a JSR to 0xf8c0 ('RDTPBLKS') that will fill the tape buffer with the
 					// next header. Skip that via a three-byte NOP and fill in the next header programmatically.
@@ -551,10 +548,10 @@ public:
 					ram_[0x90] = 0;
 					ram_[0x93] = 0;
 
-					*value = 0x0c;	// i.e. NOP abs, to swallow the entire JSR
+					value = 0x0c;	// i.e. NOP abs, to swallow the entire JSR
 				} else if(address == 0xf90b) {
-					const auto x = uint8_t(m6502_.value_of(CPU::MOS6502::Register::X));
-					if(x == 0xe) {
+					auto registers = m6502_.registers();
+					if(registers.x == 0xe) {
 						Storage::Tape::Commodore::Parser parser(TargetPlatform::Vic20);
 						const auto tape_position = tape_->serialiser()->offset();
 						const std::unique_ptr<Storage::Tape::Commodore::Data> data = parser.get_next_data(*tape_->serialiser());
@@ -576,14 +573,13 @@ public:
 
 							// set tape status, carry and flag
 							ram_[0x90] |= 0x40;
-							uint8_t	flags = uint8_t(m6502_.value_of(CPU::MOS6502::Register::Flags));
-							flags &= ~uint8_t((CPU::MOS6502::Flag::Carry | CPU::MOS6502::Flag::Interrupt));
-							m6502_.set_value_of(CPU::MOS6502::Register::Flags, flags);
+							registers.flags.set_per<CPU::MOS6502Mk2::Flag::Carry>(0);
+							registers.flags.set_per<CPU::MOS6502Mk2::Flag::Interrupt>(0);
 
 							// to ensure that execution proceeds to 0xfccf, pretend a NOP was here and
 							// ensure that the PC leaps to 0xfccf
-							m6502_.set_value_of(CPU::MOS6502::Register::ProgramCounter, 0xfccf);
-							*value = 0xea;	// i.e. NOP implied
+							registers.pc.full = 0xfccf;
+							value = 0xea;	// i.e. NOP implied
 							hold_tape_ = true;
 							Logger::info().append("Found data");
 						} else {
@@ -592,27 +588,28 @@ public:
 							Logger::info().append("Didn't find data");
 						}
 					}
+					m6502_.set_registers(registers);
 				}
 			}
 		} else {
 			uint8_t *const ram = processor_write_memory_map_[address >> 10];
 			if(ram) {
 				update_video();
-				ram[address & 0x3ff] = *value;
+				ram[address & 0x3ff] = value;
 			}
 			// Anything between 0x9000 and 0x9400 is the IO area.
 			if((address&0xfc00) == 0x9000) {
 				// The VIC is selected by bit 8 = 0
 				if(!(address&0x100)) {
 					update_video();
-					mos6560_.write(address, *value);
+					mos6560_.write(address, value);
 				}
 				// The first VIA is selected by bit 4 = 1.
-				if(address & 0x10) user_port_via_.write(address, *value);
+				if(address & 0x10) user_port_via_.write(address, value);
 				// The second VIA is selected by bit 5 = 1.
-				if(address & 0x20) keyboard_via_.write(address, *value);
+				if(address & 0x20) keyboard_via_.write(address, value);
 
-				if(!is_from_rom) {
+				if(!is_from_rom()) {
 					if((address & 0x100) && !(address & 0x30)) {
 						confidence_.add_miss();
 					} else {
@@ -620,13 +617,13 @@ public:
 					}
 				}
 			} else if(!ram) {
-				if(!is_from_rom) confidence_.add_miss();
+				if(!is_from_rom()) confidence_.add_miss();
 			}
 		}
 
 		user_port_via_.run_for(Cycles(1));
 		keyboard_via_.run_for(Cycles(1));
-		if(typer_ && address == 0xeb1e && operation == CPU::MOS6502::BusOperation::ReadOpcode) {
+		if(typer_ && address == 0xeb1e && operation == CPU::MOS6502Mk2::BusOperation::ReadOpcode) {
 			if(!typer_->type_next_character()) {
 				clear_all_keys();
 				typer_.reset();
@@ -672,8 +669,8 @@ public:
 	}
 
 	void mos6522_did_change_interrupt_status(void *) final {
-		m6502_.set_nmi_line(user_port_via_.get_interrupt_line());
-		m6502_.set_irq_line(keyboard_via_.get_interrupt_line());
+		m6502_.template set<CPU::MOS6502Mk2::Line::NMI>(user_port_via_.get_interrupt_line());
+		m6502_.template set<CPU::MOS6502Mk2::Line::IRQ>(keyboard_via_.get_interrupt_line());
 	}
 
 	void type_string(const std::string &string) final {
@@ -718,10 +715,16 @@ public:
 	}
 
 private:
+	struct M6502Traits {
+		static constexpr auto uses_ready_line = false;
+		static constexpr auto pause_precision = CPU::MOS6502Mk2::PausePrecision::BetweenInstructions;
+		using BusHandlerT = ConcreteMachine;
+	};
+	CPU::MOS6502Mk2::Processor<CPU::MOS6502Mk2::Model::M6502, M6502Traits> m6502_;
+
 	void update_video() {
 		mos6560_.run_for(cycles_since_mos6560_update_.flush<Cycles>());
 	}
-	CPU::MOS6502::Processor<CPU::MOS6502::Personality::P6502, ConcreteMachine, false> m6502_;
 
 	std::vector<uint8_t> character_rom_;
 	std::vector<uint8_t> basic_rom_;
@@ -745,12 +748,22 @@ private:
 			++address;
 		}
 	}
-	void write_to_map(const uint8_t **const map, const uint8_t *area, uint16_t address, size_t length) {
+	void write_to_map(
+		const uint8_t **const map,
+		const uint8_t *const area,
+		const uint16_t address,
+		const size_t length
+	) {
 		write_to_map([&](const uint16_t address, const size_t offset) {
 			map[address] = &area[offset];
 		}, address, length);
 	}
-	void write_to_map(uint8_t **const map, uint8_t *area, uint16_t address, size_t length) {
+	void write_to_map(
+		uint8_t **const map,
+		uint8_t *const area,
+		const uint16_t address,
+		const size_t length
+	) {
 		write_to_map([&](const uint16_t address, const size_t offset) {
 			map[address] = &area[offset];
 		}, address, length);

Machines/Enterprise/EXOSCodes.hpp

@@ -0,0 +1,159 @@
+//
+//  EXOSCodes.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 20/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+// Various EXOS codes, transcribed from	EXOS20_technical_information.pdf via archive.org,
+// which appears to be a compilation of original documentation so page numbers below
+// refer to the page within the PDF. Numbers printed on the in-document pages are inconsistent.
+
+namespace Enterprise::EXOS {
+
+// Page 67.
+enum class Function: uint8_t {
+	ResetSystem = 0,				// RESET
+	OpenChannel = 1,				// OPEN
+	CreateChannel = 2,				// CREAT
+	CloseChannel = 3,				// CLOSE
+	DestroyChannel = 4,				// DEST
+	ReadCharacter = 5,				// RDCH
+	ReadBlock = 6,					// RDBLK
+	WriteCharacter = 7,				// WRCH
+	WriteBlock = 8,					// WRBLK
+	ReadChannelStatus = 9,			// RSTAT
+	SetChannelStatus = 10,			// SSTAT
+	SpecialFunction = 11,			// SFUNC
+
+	SetReadToggleEXOSVariable = 16,	// EVAR
+	CaptureChannel = 17,			// CAPT
+	RedirectChannel = 18,			// REDIR
+	SetDefaultDevice = 19,			// DDEV
+	ReturnSystemStatus = 20,		// SYSS
+	LinkDevices = 21,				// LINK
+	ReadEXOSBoundary = 22,			// READB
+	SetUSERBoundary = 23,			// SETB,
+	AllocateSegment = 24,			// ALLOC,
+	FreeSegment = 25,				// FREE
+	LocateROMs = 26,				// ROMS
+	AllocateChannelBuffer = 27,		// BUFF
+	ReturnErrorMessage = 28,		// ERRMSG
+};
+
+// Page 25.
+enum class DeviceDescriptorFunction: uint8_t {
+	//
+	// Codes are the same as `Function` in the range 1–11.
+	//
+	Interrupt = 0,
+	Initialise = 12,
+	BufferMoved = 13,
+};
+
+enum class Error: uint8_t {
+	NoError = 0x00,
+
+	//
+	// General Kernel Errors.
+	//
+	InvalidFunctionCode = 0xff,				// IFUNC
+	FunctionCallNotAllowed = 0xfe,			// ILLFN
+	InvalidString = 0xfd,					// INAME
+	InsufficientStack = 0xfc,				// STACK
+	ChannelIllegalOrDoesNotExist = 0xfb,	// ICHAN
+	DeviceDoesNotExist = 0xfa,				// NODEV
+	ChannelAlreadyExists = 0xf9,			// CHANX
+	NoAllocateBufferCallMade = 0xf8,		// NOBUF
+	InsufficientRAMForBuffer = 0xf7,		// NORAM
+	InsufficientVideoRAM = 0xf6,			// NOVID
+	NoFreeSegments = 0xf5,					// NOSEG
+	InvalidSegment = 0xf4,					// ISEG
+	InvalidUserBoundary = 0xf3,				// IBOUND
+	InvalidEXOSVariableNumber = 0xf2,		// IVAR
+	InvalidDesviceDescriptorType = 0xf1,	// IDESC
+	UnrecognisedCommandString = 0xf0,		// NOSTR
+	InvalidFileHeader = 0xef,				// ASCII
+	UnknownModuleType = 0xee,				// ITYPE
+	InvalidRelocatableModule = 0xed,		// IREL
+	NoModule = 0xec,						// NOMOD
+	InvalidTimeOrDateValue,					// ITIME
+
+	//
+	// General Device Errors.
+	//
+	InvalidSpecialFunctionCode = 0xea,		// ISPEC
+	AttemptToOpenSecondChannel = 0xe9,		// 2NDCH
+	InvalidUnitNumber = 0xe8,				// IUNIT
+	FunctionNotSupported = 0xe7,			// NOFN
+	InvalidEscapeSequence = 0xe6,			// ESC
+	StopKeyPressed = 0xe5,					// STOP
+	EndOfFileMetInRead = 0xe4,				// EOF
+	ProtectionViolation = 0xe3,				// PROT
+
+	//
+	// Device-Specific Errors.
+	//
+//	FileDoesNotExist = 0xea,				// NOFIL
+//	FileAlreadyExists = 0xe9,				// EXFIL
+//	FileAlreadyOpen = 0xe8,					// FOPEN
+//	FileIsTooBig = 0xe6,					// FSIZE
+//	InvalidFilePointerValue = 0xe5,			// FPTR
+//
+//	//
+//	// Keyboard errors.
+//	//
+//	InvalidFunctionKeyNumber = 0xe3,		// KFKEY
+//	RunOutOfFunctionKeySpace = 0xe2,		// KFSPC
+//
+//	//
+//	// Sound errors.
+//	//
+//	EnvelopeInvalidOrTooBig = 0xe1,				// SENV
+//	NotEnoughRoomToDefineEnvelope = 0xe0,		// SENDBF
+//	EnvelopeStorageRequestedTooSmall = 0xdf,	// SENFLO
+//	SoundQueueFull = 0xde,						// SQFUL
+//
+//	//
+//	// Video errors.
+//	//
+//	InvalidRowNumberToScroll = 0xdd,			// VROW
+//	AttemptToMoveCursorOffPage = 0xdc,			// VCURS
+//	InvalidColourPassedToINKOrPAPER = 0xdb,		// VCOLR
+//	InvalidXOrYSizeToOPEN = 0xda,				// VSIZE
+//	InvalidVideoModeToOPEN = 0xd9,				// VMODE
+//	BadParameterToDISPLAY = 0xdb,				// VDISP, and officially 'naff' rather than 'bad'
+//	NotEnoughRowsInPageToDISPLAY = 0xd7,		// VDSP2
+//	AttemptToMoveBeamOffPage = 0xd6,			// VBEAM
+//	LineStyleTooBig = 0xd5,						// VLSTY
+//	LineModeTooBig = 0xd4,						// VLMOD
+//	CantDisplayCharacterOrGraphic = 0xd3,		// VCHAR
+//
+//	//
+//	// Serial errors.
+//	//
+//	InvalidBaudRate = 0xd2,						// BAUD
+//
+//	//
+//	// Editor errors.
+//	//
+//	InvalidVideoPageForOPEN = 0xd1,				// EVID
+//	TroubleInCommunicatingWithKeyboard = 0xd0,	// EKEY
+//	InvalidCoordinatesForPosition = 0xcf,		// ECURS
+//
+//	//
+//	// Cassette errors.
+//	//
+//	CRCErrorFromCassetteDriver = 0xce,			// CCRC
+//
+//	//
+//	// Network errors
+//	//
+//	SerialDeviceOpenCannotUseNetwork = 0xcd,	// SEROP
+//	ADDR_NETNotSetUp = 0xcc,					// NOADR
+};
+
+}

Machines/Enterprise/Enterprise.cpp

@@ -10,6 +10,7 @@
 
 #include "Dave.hpp"
 #include "EXDos.hpp"
+#include "HostFSHandler.hpp"
 #include "Keyboard.hpp"
 #include "Nick.hpp"
 
@@ -23,6 +24,8 @@
 #include "Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
 #include "Processors/Z80/Z80.hpp"
 
+#include <unordered_set>
+
 namespace {
 using Logger = Log::Logger<Log::Source::Enterprise>;
 }
@@ -72,6 +75,7 @@ template <bool has_disk_controller, bool is_6mhz> class ConcreteMachine:
 	public Activity::Source,
 	public Configurable::Device,
 	public CPU::Z80::BusHandler,
+	public HostFSHandler::MemoryAccessor,
 	public Machine,
 	public MachineTypes::AudioProducer,
 	public MachineTypes::MappedKeyboardMachine,
@@ -104,7 +108,8 @@ public:
 		z80_(*this),
 		nick_(ram_.end() - 65536),
 		dave_audio_(audio_queue_),
-		speaker_(dave_audio_) {
+		speaker_(dave_audio_),
+		host_fs_(*this) {
 
 		// Request a clock of 4Mhz; this'll be mapped upwards for Nick and downwards for Dave elsewhere.
 		set_clock_rate(clock_rate);
@@ -228,6 +233,14 @@ public:
 			memcpy(exdos_rom_.data(), exdos->second.data(), std::min(exdos_rom_.size(), exdos->second.size()));
 		}
 
+		// Possibly install the host FS ROM.
+		host_fs_rom_.fill(0xff);
+		if(!target.media.file_bundles.empty()) {
+			const auto rom = host_fs_.rom();
+			std::copy(rom.begin(), rom.end(), host_fs_rom_.begin());
+			find_host_fs_hooks();
+		}
+
 		// Seed key state.
 		clear_all_keys();
 
@@ -257,7 +270,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	// MARK: - Z80::BusHandler.
@@ -539,8 +552,40 @@ public:
 				}
 			break;
 
-			case PartialMachineCycle::Read:
 			case PartialMachineCycle::ReadOpcode:
+				{
+					static bool print_opcode = false;
+					if(print_opcode) {
+						printf("%04x: %02x\n", address, read_pointers_[address >> 14][address]);
+					}
+				}
+
+				// Potential segue for the host FS. I'm relying on branch prediction to
+				// avoid this cost almost always.
+				if(test_host_fs_traps_ && (address >> 14) == 3) [[unlikely]] {
+					const auto is_trap = host_fs_traps_.contains(address);
+
+					if(is_trap) {
+						using Register = CPU::Z80::Register;
+
+						uint8_t a = uint8_t(z80_.value_of(Register::A));
+						uint16_t bc = z80_.value_of(Register::BC);
+						uint16_t de = z80_.value_of(Register::DE);
+
+						// Grab function code from where the PC actually is, and return a NOP
+						host_fs_.perform(read_pointers_[address >> 14][address], a, bc, de);
+						*cycle.value = 0x00;	// i.e. NOP.
+
+						z80_.set_value_of(Register::A, a);
+						z80_.set_value_of(Register::BC, bc);
+						z80_.set_value_of(Register::DE, de);
+
+						break;
+					}
+				}
+				[[fallthrough]];
+
+			case PartialMachineCycle::Read:
 				if(read_pointers_[address >> 14]) {
 					*cycle.value = read_pointers_[address >> 14][address];
 				} else {
@@ -570,13 +615,23 @@ public:
 
 private:
 	// MARK: - Memory layout
+
 	std::array<uint8_t, 256 * 1024> ram_{};
 	std::array<uint8_t, 64 * 1024> exos_;
 	std::array<uint8_t, 16 * 1024> basic_;
 	std::array<uint8_t, 16 * 1024> exdos_rom_;
 	std::array<uint8_t, 32 * 1024> epdos_rom_;
+	std::array<uint8_t, 16 * 1024> host_fs_rom_;
 	const uint8_t min_ram_slot_;
 
+	uint8_t *ram_segment(const uint8_t page) {
+		if(page < min_ram_slot_) return nullptr;
+		const auto ram_floor = (0x100 << 14) - ram_.size();
+			// Each segment is 2^14 bytes long and there are 256 of them. So the Enterprise has a 22-bit address space.
+			// RAM is at the end of that range; `ram_floor` is the 22-bit address at which RAM starts.
+		return &ram_[size_t((page << 14)) - ram_floor];
+	}
+
 	const uint8_t *read_pointers_[4] = {nullptr, nullptr, nullptr, nullptr};
 	uint8_t *write_pointers_[4] = {nullptr, nullptr, nullptr, nullptr};
 	uint8_t pages_[4] = {0x80, 0x80, 0x80, 0x80};
@@ -595,20 +650,29 @@ private:
 	template <size_t slot> void page(const uint8_t offset) {
 		pages_[slot] = offset;
 
+		if constexpr (slot == 3) {
+			test_host_fs_traps_ = false;
+		}
+
 		if(page_rom<slot>(offset, 0, exos_)) return;
 		if(page_rom<slot>(offset, 16, basic_)) return;
 		if(page_rom<slot>(offset, 32, exdos_rom_)) return;
 		if(page_rom<slot>(offset, 48, epdos_rom_)) return;
+		if(page_rom<slot>(offset, 64, host_fs_rom_)) {
+			if constexpr (slot == 3) {
+				test_host_fs_traps_ = true;
+			}
+			return;
+		}
 
 		// Of whatever size of RAM I've declared above, use only the final portion.
 		// This correlated with Nick always having been handed the final 64kb and,
 		// at least while the RAM is the first thing declared above, does a little
 		// to benefit data locality. Albeit not in a useful sense.
 		if(offset >= min_ram_slot_) {
-			const auto ram_floor = 4194304 - ram_.size();
-			const size_t address = offset * 0x4000 - ram_floor;
 			is_video_[slot] = offset >= 0xfc;	// TODO: this hard-codes a 64kb video assumption.
-			page<slot>(&ram_[address], &ram_[address]);
+			auto pointer = ram_segment(offset);
+			page<slot>(pointer, pointer);
 			return;
 		}
 
@@ -621,7 +685,6 @@ private:
 	}
 
 	// MARK: - Memory Timing
-
 	// The wait mode affects all memory accesses _outside of the video area_.
 	enum class WaitMode {
 		None,
@@ -631,6 +694,7 @@ private:
 	bool is_video_[4]{};
 
 	// MARK: - ScanProducer
+
 	void set_scan_target(Outputs::Display::ScanTarget *const scan_target) override {
 		nick_.last_valid()->set_scan_target(scan_target);
 	}
@@ -706,11 +770,14 @@ private:
 			}
 		}
 
+		if(!media.file_bundles.empty()) {
+			host_fs_.set_file_bundle(media.file_bundles.front());
+		}
+
 		return true;
 	}
 
 	// MARK: - Interrupts
-
 	uint8_t interrupt_mask_ = 0x00, interrupt_state_ = 0x00;
 	void set_interrupts(const uint8_t mask, const HalfCycles offset = HalfCycles(0)) {
 		interrupt_state_ |= uint8_t(mask);
@@ -742,9 +809,69 @@ private:
 	}
 
 	// MARK: - EXDos card.
+
 	EXDos exdos_;
 
+	// MARK: - Host FS.
+
+	HostFSHandler host_fs_;
+	std::unordered_set<uint16_t> host_fs_traps_;
+	bool test_host_fs_traps_ = false;
+
+	uint8_t hostfs_read(const uint16_t address) override {
+		if(read_pointers_[address >> 14]) {
+			return read_pointers_[address >> 14][address];
+		} else {
+			return 0xff;
+		}
+	}
+
+	uint8_t &user_ram(const uint16_t address) {
+		// "User" accesses go to to wherever the user last had paged;
+		// per 5.4 System Segment Usage those pages are stored in memory from
+		// 0xbffc, so grab from there.
+		const auto page_id = address >> 14;
+		const uint8_t page = read_pointers_[0xbffc >> 14] ? read_pointers_[0xbffc >> 14][0xbffc + page_id] : 0xff;
+		const auto offset = address & 0x3fff;
+		return ram_segment(page)[offset];
+	}
+
+	uint8_t hostfs_user_read(const uint16_t address) override {
+		return user_ram(address);
+	}
+
+	void hostfs_user_write(const uint16_t address, const uint8_t value) override {
+		user_ram(address) = value;
+	}
+
+	void find_host_fs_hooks() {
+		static constexpr uint8_t syscall[] = {
+			0xed, 0xfe, 0xfe
+		};
+
+		auto begin = host_fs_rom_.begin();
+		while(true) {
+			begin = std::search(
+				begin, host_fs_rom_.end(),
+				std::begin(syscall), std::end(syscall)
+			);
+
+			if(begin == host_fs_rom_.end()) {
+				break;
+			}
+
+			const auto offset = begin - host_fs_rom_.begin() + 0xc000;	// ROM will be paged in slot 3, i.e. at $c000.
+			host_fs_traps_.insert(uint16_t(offset));
+
+			// Move function code up to where this trap was, and NOP out the tail.
+			begin[0] = begin[3];
+			begin[1] = begin[2] = begin[3] = 0x00;
+			begin += 4;
+		}
+	}
+
 	// MARK: - Activity Source
+
 	void set_activity_observer([[maybe_unused]] Activity::Observer *const observer) final {
 		if constexpr (has_disk_controller) {
 			exdos_.set_activity_observer(observer);
@@ -752,6 +879,7 @@ private:
 	}
 
 	// MARK: - Configuration options.
+
 	std::unique_ptr<Reflection::Struct> get_options() const final {
 		auto options = std::make_unique<Options>(Configurable::OptionsType::UserFriendly);
 		options->output = get_video_signal_configurable();

Machines/Enterprise/HostFS/compile.sh

@@ -0,0 +1 @@
+pyz80.py --obj=hostfs.rom hostfs.z80s && xxd -i hostfs.rom

Machines/Enterprise/HostFS/hostfs.z80s

@@ -0,0 +1,215 @@
+;
+; Designed for assembly with pyz80, https://github.com/simonowen/pyz80/
+; E.g. pyz80 --obj=hostfs.rom hostfs.z80s
+;
+
+;
+; Sources:
+;
+;	http://ep.homeserver.hu/Dokumentacio/Konyvek/EXOS_2.1_technikal_information/exos/kernel/Ch9.html
+;		on signature, device chain pointer and ROM entry point
+;
+;	http://ep.homeserver.hu/Dokumentacio/Konyvek/EXOS_2.1_technikal_information/exos/kernel/Ch6.html
+;		on the device chain
+;
+
+
+	;
+	; This code adapts the same mechanism for a host call as that used by EP128Emu's FILE IO ROM.
+	; My original thinking was that one could be substituted for the other to permit comparative testing.
+	; EP128 has a couple of emulator-specific call codes that I don't implement though, and otherwise
+	; doesn't seem to work in this emulator. And likely the converse holds.
+	;
+	hostfscall: macro
+		db 0xed, 0xfe, 0xfe
+		db \0
+	endm
+
+	exoscall: macro
+		rst 0x30
+		db \0
+	endm
+
+	org 0xc000
+
+	dm "EXOS_ROM"		; Standard ROM signature.
+
+	; Pointer to the included device chain, which should be valid when this
+	; ROM is paged at $4000, though when executed from it'll be at $c000.
+	dw 0x4000 + (device_chain & 0x3fff)
+
+	; ROM entry point; handle nothing.
+	ret
+
+	dw 0		; XX_NEXT_LOW/HI:	Pointer to start of next device. There is no next device.
+	dw 0xfffe	; XX_RAM_LOW/HI:	[(Amount of host RAM used) + 2] negatived.
+	
+device_chain_type:
+	db 0		; DD_TYPE:			Type, which must be 0.
+	db 0		; DD_IRQFLAG:		No interrupts required.
+	db 0		; DD_FLAGS:			Not a video device.
+
+	dw 0x4000 + (dispatch & 0x3fff)
+	db 0		; DD_TAB_LOW/HI/SEG:	
+
+	db 0		; DD_UNIT_COUNT:	?
+device_name:
+	db 4
+	dm "FILE"	; DD_NAME
+
+device_chain:
+	dw  device_chain - device_chain_type
+
+dispatch:
+	@dispatch: EQU FOR 14
+		dw	call{@dispatch}
+	NEXT @dispatch
+
+;
+; Interrupt.
+;
+; The device chain indicates that this ROM doesn't receive interrupts. So no need to escalate.
+;
+call0:
+	ret
+
+;
+; Open channel.
+;
+; EXOS requires the programmer manually to call its function 27 to allocate a channel buffer if
+; it otherwise expects to succeed. So some handling is most easily done within the client machine.
+;
+call1:
+	ld b, a			; Backup the channel number
+	hostfscall 1
+	call allocate_exos_buffer
+	ret z			; Exit on success.
+
+	; Otherwise, close the file and return the EXOS error.
+	ld c, a
+	ld a, b
+	hostfscall 3
+	ld a, c
+	ret
+
+;
+; Create channel.
+;
+call2:
+	ld b, a
+	hostfscall 2
+	call allocate_exos_buffer
+	ret z			; Exit on success.
+
+	; Otherwise, erase the newly-created file and return the EXOS error.
+	ld c, a
+	ld a, b
+	hostfscall 4
+	ld a, c
+	ret
+
+;
+; Close channel.
+;
+call3:
+	hostfscall 3
+	ret
+
+;
+; Destroy channel.
+;
+call4:
+	hostfscall 4
+	ret
+
+;
+; Read character.
+;
+call5:
+	hostfscall 5
+	ret
+
+;
+; Read block.
+;
+call6:
+	hostfscall 6
+	ret
+
+;
+; Write character.
+;
+call7:
+	hostfscall 7
+	ret
+
+;
+; Write block.
+;
+call8:
+	hostfscall 8
+	ret
+
+;
+; Read channel status.
+;
+call9:
+	hostfscall 9
+	ret
+
+;
+; Set channel status.
+;
+call10:
+	hostfscall 10
+	ret
+
+;
+; Special function.
+;
+call11:
+	hostfscall 11
+	ret
+
+;
+; Initialise.
+;
+call12:
+	hostfscall 12
+
+	;
+	; Set this as the default filing system.
+	; Disk dives do this, it's not unprecedented.
+	;
+	ld de, device_name
+	ld c, 1
+	exoscall 19
+	ret
+
+;
+; Buffer moved.
+;
+call13:
+	hostfscall 13
+	ret
+
+;
+; Attempts to allocate EXOS storage for a channel.
+; Returns Z set for success, clear for failure.
+;
+allocate_exos_buffer:
+	; Exit immediately if that call already failed.
+	and a
+	ret nz
+
+	; Restore the channel number and otherwise configure to allocate a buffer.
+	push bc
+	ld a, b
+	ld bc, 0
+	ld de, 1
+	exoscall 27
+
+	; If there's no error from that, exit.
+	pop bc
+	and a
+	ret

Machines/Enterprise/HostFSHandler.cpp

@@ -0,0 +1,262 @@
+//
+//  HostFSHandler.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 20/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#include "HostFSHandler.hpp"
+#include "EXOSCodes.hpp"
+
+using namespace Enterprise;
+
+HostFSHandler::HostFSHandler(MemoryAccessor &accessor) : accessor_(accessor) {}
+
+void HostFSHandler::perform(const uint8_t function, uint8_t &a, uint16_t &bc, uint16_t &de) {
+	const auto set_error = [&](const EXOS::Error error) {
+		a = uint8_t(error);
+	};
+	const auto set_b = [&](const uint8_t ch) {
+		bc = uint16_t((bc & 0xffff) | (ch << 8));
+	};
+	const auto set_c = [&](const uint8_t ch) {
+		bc = (bc & 0xff00) | (ch);
+	};
+	const auto b = [&]() -> uint8_t {
+		return bc >> 8;
+	};
+	const auto read_name = [&]() {
+		// Get name.
+		uint8_t length = accessor_.hostfs_read(de++);
+		std::string name;
+		while(length--) {
+			name.push_back(char(accessor_.hostfs_read(de++)));
+		}
+
+		// Use the key file if no name is specified.
+		if(name.empty()) {
+			if(const auto key_file = bundle_->key_file(); key_file.has_value()) {
+				name = *key_file;
+			}
+		}
+
+		return name;
+	};
+
+	//
+	// Functions that don't require an existing channel.
+	//
+	switch(function) {
+		default: break;
+
+		case uint8_t(EXOS::DeviceDescriptorFunction::Initialise):
+			channels_.clear();
+			set_error(EXOS::Error::NoError);
+		return;
+
+		case uint8_t(EXOS::DeviceDescriptorFunction::Interrupt):
+		case uint8_t(EXOS::DeviceDescriptorFunction::BufferMoved):
+			set_error(EXOS::Error::NoError);
+		return;
+
+		// Page 54.
+		// Emprically: C contains the unit number.
+		case uint8_t(EXOS::Function::OpenChannel): {
+			if(a == 255) {
+				set_error(EXOS::Error::ChannelIllegalOrDoesNotExist);
+				break;
+			}
+			const auto name = read_name();
+
+			try {
+				channels_.emplace(a, bundle_->open(name, Storage::FileMode::ReadWrite));
+				set_error(EXOS::Error::NoError);
+			} catch(Storage::FileHolder::Error) {
+				try {
+					channels_.emplace(a, bundle_->open(name, Storage::FileMode::Read));
+					set_error(EXOS::Error::NoError);
+				} catch(Storage::FileHolder::Error) {
+//					set_error(EXOS::Error::FileDoesNotExist);
+					set_error(EXOS::Error::ProtectionViolation);
+				}
+			}
+		}
+		return;
+
+		// Page 54.
+		case uint8_t(EXOS::Function::CreateChannel): {
+			if(a == 255) {
+				set_error(EXOS::Error::ChannelIllegalOrDoesNotExist);
+				break;
+			}
+			const auto name = read_name();
+
+			try {
+				channels_.emplace(a, bundle_->open(name, Storage::FileMode::Rewrite));
+				set_error(EXOS::Error::NoError);
+			} catch(Storage::FileHolder::Error) {
+//				set_error(EXOS::Error::FileAlreadyExists);
+				set_error(EXOS::Error::ProtectionViolation);
+			}
+		} return;
+
+		case uint8_t(EXOS::Function::SpecialFunction):
+			// Not supported;
+			set_error(EXOS::Error::InvalidSpecialFunctionCode);
+		return;
+	}
+
+	//
+	// Functions from here require a channel already open.
+	//
+	const auto channel = channels_.find(a);
+	if(channel == channels_.end()) {
+		set_error(EXOS::Error::ChannelIllegalOrDoesNotExist);
+		return;
+	}
+	auto &file = channel->second;
+
+	switch(function) {
+		default:
+			printf("UNIMPLEMENTED function %d with A:%02x BC:%04x DE:%04x\n", function, a, bc, de);
+		break;
+
+		// Page 54.
+		case uint8_t(EXOS::Function::CloseChannel):
+			set_error(EXOS::Error::NoError);
+			channels_.erase(channel);
+		break;
+
+		// Page 54.
+		case uint8_t(EXOS::Function::DestroyChannel): {
+			const auto name = file.name();
+			channels_.erase(channel);
+			if(bundle_->erase(name)) {
+				set_error(EXOS::Error::NoError);
+			} else {
+				set_error(EXOS::Error::ProtectionViolation);
+			}
+		} break;
+
+		// Page 55.
+		case uint8_t(EXOS::Function::ReadCharacter): {
+			const auto next = file.get();
+			if(file.eof()) {
+				set_error(EXOS::Error::EndOfFileMetInRead);
+			} else {
+				set_b(next);
+				set_error(EXOS::Error::NoError);
+			}
+		} break;
+
+		// Page 55.
+		case uint8_t(EXOS::Function::WriteCharacter): {
+			if(file.put(b())) {
+				set_error(EXOS::Error::NoError);
+			} else {
+				set_error(EXOS::Error::EndOfFileMetInRead);
+			}
+		} break;
+
+		// Page 55.
+		case uint8_t(EXOS::Function::ReadBlock): {
+			set_error(EXOS::Error::NoError);
+			while(bc) {
+				const auto next = file.get();
+				if(channel->second.eof()) {
+					set_error(EXOS::Error::EndOfFileMetInRead);
+					break;
+				}
+
+				accessor_.hostfs_user_write(de++, next);
+				--bc;
+			}
+		} break;
+
+		// Page 56.
+		case uint8_t(EXOS::Function::WriteBlock): {
+			set_error(EXOS::Error::NoError);
+			while(bc) {
+				const auto next = accessor_.hostfs_user_read(de);
+				if(!file.put(next)) {
+					set_error(EXOS::Error::EndOfFileMetInRead);
+					break;
+				}
+
+				++de;
+				--bc;
+			}
+		} break;
+
+		// Page 56.
+		case uint8_t(EXOS::Function::ReadChannelStatus):
+			a = file.eof() ? 0xff : 0x00;
+		break;
+
+		// Page 56.
+		case uint8_t(EXOS::Function::SetChannelStatus): {
+			if(bc & 4) {
+				// Protection byte is not supported.
+				set_error(EXOS::Error::FunctionNotSupported);
+				break;
+			}
+
+			if(bc & 1) {	// User is requesting a seek.
+				auto pointer = de;
+				uint32_t file_pointer;
+				file_pointer = accessor_.hostfs_user_read(pointer++);
+				file_pointer |= uint32_t(accessor_.hostfs_user_read(pointer++) << 8);
+				file_pointer |= uint32_t(accessor_.hostfs_user_read(pointer++) << 16);
+				file_pointer |= uint32_t(accessor_.hostfs_user_read(pointer++) << 24);
+
+				if(!file.seek(file_pointer, Storage::Whence::SET)) {
+					set_error(EXOS::Error::EndOfFileMetInRead);
+					break;
+				}
+			}
+
+			// Fill in both position and length.
+			set_c(3);
+			const uint32_t file_pointer = uint32_t(file.tell());
+			const uint32_t file_length = uint32_t(file.stats().st_size);
+
+			auto pointer = de;
+			const auto write = [&](const uint32_t source) {
+				accessor_.hostfs_user_write(pointer++, uint8_t(source >> 0));
+				accessor_.hostfs_user_write(pointer++, uint8_t(source >> 8));
+				accessor_.hostfs_user_write(pointer++, uint8_t(source >> 16));
+				accessor_.hostfs_user_write(pointer++, uint8_t(source >> 24));
+			};
+			write(file_pointer);
+			write(file_length);
+
+			set_error(EXOS::Error::NoError);
+		} break;
+	}
+}
+
+void HostFSHandler::set_file_bundle(std::shared_ptr<Storage::FileBundle::FileBundle> bundle) {
+	bundle_ = bundle;
+}
+
+std::vector<uint8_t> HostFSHandler::rom() {
+	// Assembled and transcribed from hostfs.z80.
+	return std::vector<uint8_t>{
+		0x45, 0x58, 0x4f, 0x53, 0x5f, 0x52, 0x4f, 0x4d, 0x1b, 0x40, 0xc9, 0x00,
+		0x00, 0xfe, 0xff, 0x00, 0x00, 0x00, 0x1d, 0x40, 0x00, 0x00, 0x04, 0x46,
+		0x49, 0x4c, 0x45, 0x0c, 0x00, 0x39, 0xc0, 0x3a, 0xc0, 0x4b, 0xc0, 0x5c,
+		0xc0, 0x61, 0xc0, 0x66, 0xc0, 0x6b, 0xc0, 0x70, 0xc0, 0x75, 0xc0, 0x7a,
+		0xc0, 0x7f, 0xc0, 0x84, 0xc0, 0x89, 0xc0, 0x95, 0xc0, 0xc9, 0x47, 0xed,
+		0xfe, 0xfe, 0x01, 0xcd, 0x9a, 0xc0, 0xc8, 0x4f, 0x78, 0xed, 0xfe, 0xfe,
+		0x03, 0x79, 0xc9, 0x47, 0xed, 0xfe, 0xfe, 0x02, 0xcd, 0x9a, 0xc0, 0xc8,
+		0x4f, 0x78, 0xed, 0xfe, 0xfe, 0x04, 0x79, 0xc9, 0xed, 0xfe, 0xfe, 0x03,
+		0xc9, 0xed, 0xfe, 0xfe, 0x04, 0xc9, 0xed, 0xfe, 0xfe, 0x05, 0xc9, 0xed,
+		0xfe, 0xfe, 0x06, 0xc9, 0xed, 0xfe, 0xfe, 0x07, 0xc9, 0xed, 0xfe, 0xfe,
+		0x08, 0xc9, 0xed, 0xfe, 0xfe, 0x09, 0xc9, 0xed, 0xfe, 0xfe, 0x0a, 0xc9,
+		0xed, 0xfe, 0xfe, 0x0b, 0xc9, 0xed, 0xfe, 0xfe, 0x0c, 0x11, 0x16, 0xc0,
+		0x0e, 0x01, 0xf7, 0x13, 0xc9, 0xed, 0xfe, 0xfe, 0x0d, 0xc9, 0xa7, 0xc0,
+		0xc5, 0x78, 0x01, 0x00, 0x00, 0x11, 0x01, 0x00, 0xf7, 0x1b, 0xc1, 0xa7,
+		0xc9
+	};
+}

Machines/Enterprise/HostFSHandler.hpp

@@ -0,0 +1,52 @@
+//
+//  HostFSHandler.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 20/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Storage/FileBundle/FileBundle.hpp"
+
+#include <cstdint>
+#include <memory>
+#include <unordered_map>
+#include <vector>
+
+namespace Enterprise {
+
+struct HostFSHandler {
+	struct MemoryAccessor {
+		// Accessors that read from however the Z80's 64kb is currently laid out.
+		virtual uint8_t hostfs_read(uint16_t) = 0;
+//		virtual void hostfs_write(uint16_t, uint8_t) = 0;
+
+		// Accessors that read from 'user' address space, i.e. the 64kb Z80 address space as currently
+		// mapped according to the user's preference.
+		virtual uint8_t hostfs_user_read(uint16_t) = 0;
+		virtual void hostfs_user_write(uint16_t, uint8_t) = 0;
+	};
+
+	HostFSHandler(MemoryAccessor &);
+
+	/// Perform the internally-defined @c function given other provided state.
+	/// These function calls mostly align with those in EXOSCodes.hpp
+	void perform(uint8_t function, uint8_t &a, uint16_t &bc, uint16_t &de);
+
+	/// Sets the bundle of files on which this handler should operate.
+	void set_file_bundle(std::shared_ptr<Storage::FileBundle::FileBundle> bundle);
+
+	/// @returns A suitable in-client filing system ROM.
+	std::vector<uint8_t> rom();
+
+private:
+	MemoryAccessor &accessor_;
+	std::shared_ptr<Storage::FileBundle::FileBundle> bundle_;
+
+	using ChannelHandler = uint8_t;
+	std::unordered_map<ChannelHandler, Storage::FileHolder> channels_;
+};
+
+};

Machines/MSX/MSX.cpp

@@ -360,7 +360,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		speaker_.audio_queue.flush();
+		speaker_.audio_queue.lock_flush();
 	}
 
 	void set_scan_target(Outputs::Display::ScanTarget *scan_target) final {

Machines/MasterSystem/MasterSystem.cpp

@@ -178,7 +178,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	ChangeEffect effect_for_file_did_change(const std::string &) const final {

Machines/Oric/Oric.cpp

@@ -406,7 +406,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_key_state(uint16_t key, bool is_pressed) final {

Machines/PCCompatible/PCCompatible.cpp

@@ -817,7 +817,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		speaker_.queue.flush();
+		speaker_.queue.lock_flush();
 	}
 
 	// MARK: - TimedMachine.

Machines/Sinclair/ZX8081/ZX8081.cpp

@@ -114,7 +114,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	forceinline HalfCycles perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {

Machines/Sinclair/ZXSpectrum/ZXSpectrum.cpp

@@ -213,7 +213,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	static constexpr unsigned int clock_rate() {

Numeric/SizedInt.hpp

@@ -24,8 +24,9 @@ struct SizedInt {
 	constexpr SizedInt(const IntT start_value) noexcept : counter_(start_value & Mask) {}
 	SizedInt() = default;
 
+	template <int begin = 0>
 	IntT get() const {
-		return counter_;
+		return counter_ >> begin;
 	}
 
 	SizedInt operator +(const SizedInt offset) const {	return SizedInt<bits>(counter_ + offset.counter_); }

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -753,6 +753,10 @@
 		4B92E26B234AE35100CD6D1B /* MFP68901.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B92E268234AE35000CD6D1B /* MFP68901.cpp */; };
 		4B92EACA1B7C112B00246143 /* 6502TimingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4B92EAC91B7C112B00246143 /* 6502TimingTests.swift */; };
 		4B9378E422A199C600973513 /* Audio.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B9378E222A199C600973513 /* Audio.cpp */; };
+		4B96DECC2EBEE7D100505298 /* SID.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B96DECA2EBEE7D100505298 /* SID.cpp */; };
+		4B96DECD2EBEE7D100505298 /* SID.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B96DECA2EBEE7D100505298 /* SID.cpp */; };
+		4B96DECE2EBEE7D100505298 /* SID.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B96DECA2EBEE7D100505298 /* SID.cpp */; };
+		4B96DED32EC3ECDA00505298 /* SIDTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4B96DED22EC3ECDA00505298 /* SIDTests.mm */; };
 		4B96F7CE263E33B10092AEE1 /* DSK.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B96F7CC263E33B10092AEE1 /* DSK.cpp */; };
 		4B96F7CF263E33B10092AEE1 /* DSK.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B96F7CC263E33B10092AEE1 /* DSK.cpp */; };
 		4B98A05E1FFAD3F600ADF63B /* CSROMFetcher.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4B98A05D1FFAD3F600ADF63B /* CSROMFetcher.mm */; };
@@ -1144,6 +1148,12 @@
 		4BCE0060227D39AB000CA200 /* Video.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCE005E227D39AB000CA200 /* Video.cpp */; };
 		4BCE1DF125D4C3FA00AE7A2B /* Bus.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCE1DEF25D4C3FA00AE7A2B /* Bus.cpp */; };
 		4BCE1DF225D4C3FA00AE7A2B /* Bus.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCE1DEF25D4C3FA00AE7A2B /* Bus.cpp */; };
+		4BCF1ACF2ECE759000109999 /* FileBundle.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCF1ACD2ECE759000109999 /* FileBundle.cpp */; };
+		4BCF1AD02ECE759000109999 /* FileBundle.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCF1ACD2ECE759000109999 /* FileBundle.cpp */; };
+		4BCF1AD12ECE759000109999 /* FileBundle.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCF1ACD2ECE759000109999 /* FileBundle.cpp */; };
+		4BCF1AD52ECF884100109999 /* HostFSHandler.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCF1AD42ECF884100109999 /* HostFSHandler.cpp */; };
+		4BCF1AD62ECF884100109999 /* HostFSHandler.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCF1AD42ECF884100109999 /* HostFSHandler.cpp */; };
+		4BCF1AD72ECF884100109999 /* HostFSHandler.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCF1AD42ECF884100109999 /* HostFSHandler.cpp */; };
 		4BCF1FA41DADC3DD0039D2E7 /* Oric.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCF1FA21DADC3DD0039D2E7 /* Oric.cpp */; };
 		4BD0FBC3233706A200148981 /* CSApplication.m in Sources */ = {isa = PBXBuildFile; fileRef = 4BD0FBC2233706A200148981 /* CSApplication.m */; };
 		4BD191F52191180E0042E144 /* ScanTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD191F22191180E0042E144 /* ScanTarget.cpp */; };
@@ -1952,6 +1962,10 @@
 		4B95FA9C1F11893B0008E395 /* ZX8081Controller.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ZX8081Controller.swift; sourceTree = "<group>"; };
 		4B961408222760E0001A7BF2 /* Screenshot.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Screenshot.hpp; sourceTree = "<group>"; };
 		4B96DEC32EBEA88C00505298 /* TubeProcessor.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = TubeProcessor.hpp; sourceTree = "<group>"; };
+		4B96DEC92EBEE7D100505298 /* SID.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = SID.hpp; sourceTree = "<group>"; };
+		4B96DECA2EBEE7D100505298 /* SID.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = SID.cpp; sourceTree = "<group>"; };
+		4B96DED22EC3ECDA00505298 /* SIDTests.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = SIDTests.mm; sourceTree = "<group>"; };
+		4B96DED42EC53BC300505298 /* BiquadFilter.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = BiquadFilter.hpp; sourceTree = "<group>"; };
 		4B96F7CB263E30B00092AEE1 /* RawSectorDump.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = RawSectorDump.hpp; sourceTree = "<group>"; };
 		4B96F7CC263E33B10092AEE1 /* DSK.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = DSK.cpp; sourceTree = "<group>"; };
 		4B96F7CD263E33B10092AEE1 /* DSK.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = DSK.hpp; sourceTree = "<group>"; };
@@ -2417,6 +2431,11 @@
 		4BCE005F227D39AB000CA200 /* Video.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Video.hpp; sourceTree = "<group>"; };
 		4BCE1DEF25D4C3FA00AE7A2B /* Bus.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Bus.cpp; sourceTree = "<group>"; };
 		4BCE1DF025D4C3FA00AE7A2B /* Bus.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Bus.hpp; sourceTree = "<group>"; };
+		4BCF1ACC2ECE759000109999 /* FileBundle.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = FileBundle.hpp; sourceTree = "<group>"; };
+		4BCF1ACD2ECE759000109999 /* FileBundle.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = FileBundle.cpp; sourceTree = "<group>"; };
+		4BCF1AD22ECF743500109999 /* EXOSCodes.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = EXOSCodes.hpp; sourceTree = "<group>"; };
+		4BCF1AD32ECF884100109999 /* HostFSHandler.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = HostFSHandler.hpp; sourceTree = "<group>"; };
+		4BCF1AD42ECF884100109999 /* HostFSHandler.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = HostFSHandler.cpp; sourceTree = "<group>"; };
 		4BCF1FA21DADC3DD0039D2E7 /* Oric.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Oric.cpp; sourceTree = "<group>"; };
 		4BCF1FA31DADC3DD0039D2E7 /* Oric.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Oric.hpp; sourceTree = "<group>"; };
 		4BD060A51FE49D3C006E14BE /* Speaker.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Speaker.hpp; sourceTree = "<group>"; };
@@ -2692,11 +2711,14 @@
 				4BFEA2ED2682A7B900EBF94C /* Dave.cpp */,
 				4B051CA12676F52200CA44E8 /* Enterprise.cpp */,
 				4B051CB42680158600CA44E8 /* EXDos.cpp */,
+				4BCF1AD42ECF884100109999 /* HostFSHandler.cpp */,
 				4B051CAE267C1CA200CA44E8 /* Keyboard.cpp */,
 				4B051CAA26783E2000CA44E8 /* Nick.cpp */,
 				4BFEA2EE2682A7B900EBF94C /* Dave.hpp */,
 				4B051CA02676F52200CA44E8 /* Enterprise.hpp */,
 				4B051CB52680158600CA44E8 /* EXDos.hpp */,
+				4BCF1AD22ECF743500109999 /* EXOSCodes.hpp */,
+				4BCF1AD32ECF884100109999 /* HostFSHandler.hpp */,
 				4B051CAF267C1CA200CA44E8 /* Keyboard.hpp */,
 				4B051CAB26783E2000CA44E8 /* Nick.hpp */,
 			);
@@ -3017,6 +3039,7 @@
 				4BC76E671C98E31700E6EF73 /* FIRFilter.cpp */,
 				4BC76E681C98E31700E6EF73 /* FIRFilter.hpp */,
 				4B24095A1C45DF85004DA684 /* Stepper.hpp */,
+				4B96DED42EC53BC300505298 /* BiquadFilter.hpp */,
 			);
 			name = SignalProcessing;
 			path = ../../SignalProcessing;
@@ -3578,6 +3601,7 @@
 				4BEE0A691D72496600532C7B /* Cartridge */,
 				4B8805F81DCFF6CD003085B1 /* Data */,
 				4BAB62AA1D3272D200DF5BA0 /* Disk */,
+				4BCF1ACE2ECE759000109999 /* FileBundle */,
 				4B6AAEA1230E3E1D0078E864 /* MassStorage */,
 				4B8DD3832634D37E00B3C866 /* State */,
 				4B69FB3A1C4D908A00B5F0AA /* Tape */,
@@ -4354,6 +4378,15 @@
 			path = 68901;
 			sourceTree = "<group>";
 		};
+		4B96DECB2EBEE7D100505298 /* SID */ = {
+			isa = PBXGroup;
+			children = (
+				4B96DEC92EBEE7D100505298 /* SID.hpp */,
+				4B96DECA2EBEE7D100505298 /* SID.cpp */,
+			);
+			path = SID;
+			sourceTree = "<group>";
+		};
 		4B9F11C72272375400701480 /* QL Startup */ = {
 			isa = PBXGroup;
 			children = (
@@ -4872,6 +4905,7 @@
 				4BD4A8CF1E077FD20020D856 /* PCMTrackTests.mm */,
 				4B3F76B825A1635300178AEC /* PowerPCDecoderTests.mm */,
 				4BE76CF822641ED300ACD6FA /* QLTests.mm */,
+				4B96DED22EC3ECDA00505298 /* SIDTests.mm */,
 				4B8DD3672633B2D400B3C866 /* SpectrumVideoContentionTests.mm */,
 				4B2AF8681E513FC20027EE29 /* TIATests.mm */,
 				4B1D08051E0F7A1100763741 /* TimeTests.mm */,
@@ -5168,6 +5202,7 @@
 				4BF0BC6E2973318E00CCA2B5 /* RP5C01 */,
 				4B8855A42E84D51B00E251DD /* SAA5050 */,
 				4B0ACBFF237756EC008902D0 /* Serial */,
+				4B96DECB2EBEE7D100505298 /* SID */,
 				4BB0A6582044FD3000FB3688 /* SN76489 */,
 				4B47F3B42E7B9A14005D4DEC /* uPD7002 */,
 			);
@@ -5269,6 +5304,15 @@
 			path = ADB;
 			sourceTree = "<group>";
 		};
+		4BCF1ACE2ECE759000109999 /* FileBundle */ = {
+			isa = PBXGroup;
+			children = (
+				4BCF1ACC2ECE759000109999 /* FileBundle.hpp */,
+				4BCF1ACD2ECE759000109999 /* FileBundle.cpp */,
+			);
+			path = FileBundle;
+			sourceTree = "<group>";
+		};
 		4BCF1FA51DADC3E10039D2E7 /* Oric */ = {
 			isa = PBXGroup;
 			children = (
@@ -6163,6 +6207,7 @@
 				4B894521201967B4007DE474 /* StaticAnalyser.cpp in Sources */,
 				4B47F3B62E7BAB94005D4DEC /* uPD7002.cpp in Sources */,
 				4B8318B522D3E548006DB630 /* Macintosh.cpp in Sources */,
+				4B96DECD2EBEE7D100505298 /* SID.cpp in Sources */,
 				4B8DF4FA254E36AE00F3433C /* Video.cpp in Sources */,
 				4B7BA03123C2B19C00B98D9E /* Jasmin.cpp in Sources */,
 				4B7F188F2154825E00388727 /* MasterSystem.cpp in Sources */,
@@ -6176,6 +6221,7 @@
 				4B65086122F4CFE0009C1100 /* Keyboard.cpp in Sources */,
 				4BBB70A9202014E2002FE009 /* MultiProducer.cpp in Sources */,
 				4B2E86BF25D74F160024F1E9 /* Mouse.cpp in Sources */,
+				4BCF1AD12ECE759000109999 /* FileBundle.cpp in Sources */,
 				4B6ED2F1208E2F8A0047B343 /* WOZ.cpp in Sources */,
 				4B5D5C9825F56FC7001B4623 /* Spectrum.cpp in Sources */,
 				4B7C681727517A59001671EC /* Sprites.cpp in Sources */,
@@ -6318,6 +6364,7 @@
 				4B055AC41FAE9AE80060FFFF /* Keyboard.cpp in Sources */,
 				4B8DF506254E3C9D00F3433C /* ADB.cpp in Sources */,
 				4B055A941FAE85B50060FFFF /* CommodoreROM.cpp in Sources */,
+				4BCF1AD72ECF884100109999 /* HostFSHandler.cpp in Sources */,
 				4BBB70A5202011C2002FE009 /* MultiMediaTarget.cpp in Sources */,
 				4B8318BC22D3E588006DB630 /* DisplayMetrics.cpp in Sources */,
 				4BEDA40E25B2844B000C2DBD /* Decoder.cpp in Sources */,
@@ -6411,6 +6458,7 @@
 				4B1082C42C1F5E7D00B07C5D /* CSL.cpp in Sources */,
 				4B0ACC3023775819008902D0 /* TIASound.cpp in Sources */,
 				4B7136861F78724F008B8ED9 /* Encoder.cpp in Sources */,
+				4BCF1AD62ECF884100109999 /* HostFSHandler.cpp in Sources */,
 				4B0E04EA1FC9E5DA00F43484 /* CAS.cpp in Sources */,
 				4B7A90ED20410A85008514A2 /* StaticAnalyser.cpp in Sources */,
 				4B58601E1F806AB200AEE2E3 /* MFMSectorDump.cpp in Sources */,
@@ -6476,6 +6524,7 @@
 				4BEDA3BF25B25563000C2DBD /* Decoder.cpp in Sources */,
 				4B051C95266EF50200CA44E8 /* AppleIIController.swift in Sources */,
 				4B4DC82B1D2C27A4003C5BF8 /* SerialBus.cpp in Sources */,
+				4BCF1ACF2ECE759000109999 /* FileBundle.cpp in Sources */,
 				4BE8EB6625C750B50040BC40 /* DAT.cpp in Sources */,
 				4BBFFEE61F7B27F1005F3FEB /* TrackSerialiser.cpp in Sources */,
 				4B8855A52E84D51B00E251DD /* SAA5050.cpp in Sources */,
@@ -6557,6 +6606,7 @@
 				4BC080D026A257A200D03FD8 /* StaticAnalyser.cpp in Sources */,
 				4B4DC8211D2C2425003C5BF8 /* Vic20.cpp in Sources */,
 				4B71368E1F788112008B8ED9 /* Parser.cpp in Sources */,
+				4B96DECC2EBEE7D100505298 /* SID.cpp in Sources */,
 				4B12C0ED1FCFA98D005BFD93 /* Keyboard.cpp in Sources */,
 				4BA0F68E1EEA0E8400E9489E /* ZX8081.cpp in Sources */,
 				429B13602B1F7BDA006BB4CB /* StaticAnalyser.cpp in Sources */,
@@ -6683,6 +6733,7 @@
 				4B06AAF82C6460760034D014 /* IntelligentKeyboard.cpp in Sources */,
 				4B7752B628217EE70073E2C5 /* DSK.cpp in Sources */,
 				4B06AAD12C645F130034D014 /* 1770.cpp in Sources */,
+				4B96DECE2EBEE7D100505298 /* SID.cpp in Sources */,
 				4B778F2523A5EDF40000D260 /* Encoder.cpp in Sources */,
 				4B778F4223A5F1A70000D260 /* MemoryFuzzer.cpp in Sources */,
 				4B778F0123A5EBA00000D260 /* MacintoshIMG.cpp in Sources */,
@@ -6778,6 +6829,7 @@
 				4B778F4623A5F1D80000D260 /* StaticAnalyser.cpp in Sources */,
 				4B778F1323A5EC890000D260 /* Z80Base.cpp in Sources */,
 				4B778F2923A5EF030000D260 /* CommodoreROM.cpp in Sources */,
+				4B96DED32EC3ECDA00505298 /* SIDTests.mm in Sources */,
 				4B06AADC2C645F720034D014 /* BD500.cpp in Sources */,
 				4B778F4823A5F1E70000D260 /* StaticAnalyser.cpp in Sources */,
 				4B92EACA1B7C112B00246143 /* 6502TimingTests.swift in Sources */,
@@ -6833,8 +6885,10 @@
 				4B778F4023A5F1910000D260 /* z8530.cpp in Sources */,
 				4B778EFD23A5EB8E0000D260 /* AppleDSK.cpp in Sources */,
 				4B7752B728217EF40073E2C5 /* Chipset.cpp in Sources */,
+				4BCF1AD02ECE759000109999 /* FileBundle.cpp in Sources */,
 				4B06AAF72C64606E0034D014 /* DiskII.cpp in Sources */,
 				4B778EFB23A5EB7E0000D260 /* HFE.cpp in Sources */,
+				4BCF1AD52ECF884100109999 /* HostFSHandler.cpp in Sources */,
 				4BC751B21D157E61006C31D9 /* 6522Tests.swift in Sources */,
 				4B0DA67D282DCDF300C12F17 /* Instruction.cpp in Sources */,
 				4B06AAE12C645F8B0034D014 /* Video.cpp in Sources */,

OSBindings/Mac/Clock Signal/Info.plist

@@ -807,6 +807,29 @@
 			<key>NSDocumentClass</key>
 			<string>$(PRODUCT_MODULE_NAME).MachineDocument</string>
 		</dict>
+		<dict>
+			<key>CFBundleTypeExtensions</key>
+			<array>
+				<string>com</string>
+				<string>bas</string>
+			</array>
+			<key>CFBundleTypeIconFile</key>
+			<string></string>
+			<key>CFBundleTypeName</key>
+			<string>Enterprise Executable</string>
+			<key>CFBundleTypeOSTypes</key>
+			<array>
+				<string>????</string>
+			</array>
+			<key>CFBundleTypeRole</key>
+			<string>Viewer</string>
+			<key>LSHandlerRank</key>
+			<string>Owner</string>
+			<key>LSTypeIsPackage</key>
+			<false/>
+			<key>NSDocumentClass</key>
+			<string>$(PRODUCT_MODULE_NAME).MachineDocument</string>
+		</dict>
 	</array>
 	<key>CFBundleExecutable</key>
 	<string>$(EXECUTABLE_NAME)</string>

OSBindings/Mac/Clock Signal/MachinePicker/Base.lproj/MachinePicker.xib

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="24128" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="24412" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
     <dependencies>
         <deployment identifier="macosx"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="24128"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="24412"/>
         <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
     </dependencies>
     <objects>

OSBindings/Qt/clksignal.pro

@@ -76,6 +76,7 @@ SOURCES += \
 	$$SRC/Components/KonamiSCC/*.cpp \
 	$$SRC/Components/OPx/*.cpp \
 	$$SRC/Components/RP5C01/*.cpp \
+	$$SRC/Components/SID/*.cpp \
 	$$SRC/Components/SAA5050/*.cpp \
 	$$SRC/Components/Serial/*.cpp \
 	$$SRC/Components/SN76489/*.cpp \
@@ -145,6 +146,7 @@ SOURCES += \
 	$$SRC/Storage/Disk/Encodings/MFM/*.cpp \
 	$$SRC/Storage/Disk/Parsers/*.cpp \
 	$$SRC/Storage/Disk/Track/*.cpp \
+	$$SRC/Storage/FileBundle/*.cpp \
 	$$SRC/Storage/MassStorage/*.cpp \
 	$$SRC/Storage/MassStorage/Encodings/*.cpp \
 	$$SRC/Storage/MassStorage/Formats/*.cpp \
@@ -213,6 +215,7 @@ HEADERS += \
 	$$SRC/Components/OPx/*.hpp \
 	$$SRC/Components/OPx/Implementation/*.hpp \
 	$$SRC/Components/RP5C01/*.hpp \
+	$$SRC/Components/SID/*.hpp \
 	$$SRC/Components/SAA5050/*.hpp \
 	$$SRC/Components/Serial/*.hpp \
 	$$SRC/Components/SN76489/*.hpp \
@@ -301,6 +304,7 @@ HEADERS += \
 	$$SRC/Storage/Disk/Encodings/MFM/*.hpp \
 	$$SRC/Storage/Disk/Parsers/*.hpp \
 	$$SRC/Storage/Disk/Track/*.hpp \
+	$$SRC/Storage/FileBundle/*.hpp \
 	$$SRC/Storage/MassStorage/*.hpp \
 	$$SRC/Storage/MassStorage/Encodings/*.hpp \
 	$$SRC/Storage/MassStorage/Formats/*.hpp \

OSBindings/SDL/SConstruct

@@ -61,6 +61,7 @@ SOURCES += glob.glob('../../Components/KonamiSCC/*.cpp')
 SOURCES += glob.glob('../../Components/OPx/*.cpp')
 SOURCES += glob.glob('../../Components/RP5C01/*.cpp')
 SOURCES += glob.glob('../../Components/SAA5050/*.cpp')
+SOURCES += glob.glob('../../Components/SID/*.cpp')
 SOURCES += glob.glob('../../Components/SN76489/*.cpp')
 SOURCES += glob.glob('../../Components/Serial/*.cpp')
 SOURCES += glob.glob('../../Components/uPD7002/*.cpp')
@@ -133,6 +134,7 @@ SOURCES += glob.glob('../../Storage/Disk/Encodings/MFM/*.cpp')
 SOURCES += glob.glob('../../Storage/Disk/Parsers/*.cpp')
 SOURCES += glob.glob('../../Storage/Disk/Track/*.cpp')
 SOURCES += glob.glob('../../Storage/Disk/Data/*.cpp')
+SOURCES += glob.glob('../../Storage/FileBundle/*.cpp')
 SOURCES += glob.glob('../../Storage/MassStorage/*.cpp')
 SOURCES += glob.glob('../../Storage/MassStorage/Encodings/*.cpp')
 SOURCES += glob.glob('../../Storage/MassStorage/Formats/*.cpp')

Processors/6502Mk2/6502Mk2.hpp

@@ -66,6 +66,7 @@ enum class Line {
 	PowerOn,
 	Overflow,
 	NMI,
+	Ready,
 };
 
 // MARK: - Address bus.
@@ -185,14 +186,24 @@ public:
 					(inputs_.interrupt_requests & Inputs::InterruptRequest::PowerOn);
 			break;
 
-			// Level triggered.
+			// Level triggered interrupts.
 			case Line::Reset:		level_sample(Inputs::InterruptRequest::Reset);						break;
 			case Line::IRQ:			level_sample(Inputs::InterruptRequest::IRQ);						break;
 
-			// Edge triggered.
-			case Line::Overflow:	edge_sample(Inputs::InterruptRequest::Reset, inputs_.overflow);		break;
+			// Edge triggered interrupts.
 			case Line::NMI:			edge_sample(Inputs::InterruptRequest::NMI, inputs_.nmi);			break;
 
+			// Leval-capturing state.
+			case Line::Ready:		inputs_.ready = value;												break;
+
+			// Edge-triggered state.
+			case Line::Overflow:
+				if(!inputs_.overflow && value) {
+					registers_.flags.set_per<Flag::Overflow>(Flag::Overflow);
+				}
+				inputs_.overflow = value;
+			break;
+
 			default:
 				__builtin_unreachable();
 		}

SignalProcessing/BiquadFilter.hpp

@@ -0,0 +1,214 @@
+//
+//  BiquadFilter.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 12/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include <cassert>
+#include <cmath>
+#include <numbers>
+
+namespace SignalProcessing {
+
+/*!
+	A biquad[ratic] filter approximates the real analogue thing in taking a 1d PCM signal and applying a
+	filter to it as a function of the current input plus the two most-recent inputs plus the two most-recent outputs.
+
+	So both IIR and three-tap FIR filters are degenerate cases of the biquad.
+
+	It is used quite often in real designs, hence an implementation of this filter specifically.
+
+	... and the below is largely textbook; I can't claim any great knowledge. I am especially indebted to
+	the W3C Group's audio EQ cookbook at https://www.w3.org/TR/audio-eq-cookbook/ .
+*/
+class BiquadFilter {
+public:
+	enum class Type {
+		LowPass,
+		HighPass,
+		BandPass,
+		Notch,
+		AllPass,
+		Peaking,
+		LowShelf,
+		HighShelf
+	};
+
+	// Default construction: a filter that produces _nothing_.
+	BiquadFilter() {}
+
+	BiquadFilter(
+		const Type type,
+		const float sample_rate,
+		const float frequency,
+		const float resonance = 0.707f,
+		const float gain = 8,
+		const bool normalise = true
+	) {
+		configure(type, sample_rate, frequency, resonance, gain, normalise);
+	}
+
+	void configure(
+		const Type type,
+		const float sample_rate,
+		const float frequency,
+		const float resonance = 0.707f,
+		const float gain = 8,
+		const bool normalise = true
+	) {
+		const float w0 = 2.0f * std::numbers::pi_v<float> * frequency / sample_rate;
+		const float alpha = std::sin(w0) / (2.0f * resonance);
+		const float cos_w0 = std::cos(w0);
+
+		float coefficients[5];
+		float magnitude = 1.0f;
+		switch(type) {
+			case Type::LowPass:
+				coefficients[0] = (1.0f - cos_w0) / 2.0f;
+				coefficients[1] = 1.0f - cos_w0;
+				coefficients[2] = (1.0f - cos_w0) / 2.0f;
+				magnitude = 1.0f + alpha;
+				coefficients[3] = -2.0f * cos_w0;
+				coefficients[4] = 1.0f - alpha;
+			break;
+
+			case Type::HighPass:
+				coefficients[0] = (1.0f - cos_w0) / 2.0f;
+				coefficients[1] = -(1.0f + cos_w0);
+				coefficients[2] = (1.0f - cos_w0) / 2.0f;
+				magnitude = 1.0f + alpha;
+				coefficients[3] = -2.0f * cos_w0;
+				coefficients[4] = 1.0f - alpha;
+			break;
+
+			case Type::BandPass:
+				coefficients[0] = alpha;
+				coefficients[1] = 0.0f;
+				coefficients[2] = -alpha;
+				magnitude = 1.0f + alpha;
+				coefficients[3] = -2.0f * cos_w0;
+				coefficients[0] = 1.0f - alpha;
+			break;
+
+			case Type::Notch:
+				coefficients[0] = 1.0f;
+				coefficients[1] = -2.0f * cos_w0;
+				coefficients[2] = 1.0f;
+				magnitude = 1.0f + alpha;
+				coefficients[3] = -2.0f * cos_w0;
+				coefficients[4] = 1.0f - alpha;
+			break;
+
+			case Type::AllPass:
+				coefficients[0] = 1.0f - alpha;
+				coefficients[1] = -2.0f * cos_w0;
+				coefficients[2] = 1.0f + alpha;
+				magnitude = 1.0f + alpha;
+				coefficients[3] = -2.0f * cos_w0;
+				coefficients[4] = 1.0f - alpha;
+			break;
+
+			case Type::Peaking: {
+				const float a = std::pow(10.0f, gain / 40.0f);
+
+				coefficients[0] = 1.0f + (alpha * a);
+				coefficients[1] = -2.0f * cos_w0;
+				coefficients[2] = 1.0f - (alpha * a);
+				magnitude = 1.0f + (alpha / a);
+				coefficients[3] = -2.0f * cos_w0;
+				coefficients[4] = 1.0f - (alpha / a);
+			} break;
+
+			case Type::LowShelf: {
+				const float a_ls = std::pow(10.0f, gain / 40.0f);
+				const float sqrt_a = std::sqrt(a_ls);
+				const float alpha_ls =
+					std::sin(w0) / 2.0f * std::sqrt((a_ls + 1.0f / a_ls) * (1.0f / resonance - 1.0f) + 2.0f);
+
+				coefficients[0] = a_ls * ((a_ls + 1.0f) - (a_ls - 1.0f) * cos_w0 + 2.0f * sqrt_a * alpha_ls);
+				coefficients[1] = 2.0f * a_ls * ((a_ls - 1.0f) - (a_ls + 1.0f) * cos_w0);
+				coefficients[2] = a_ls * ((a_ls + 1.0f) - (a_ls - 1.0f) * cos_w0 - 2.0f * sqrt_a * alpha_ls);
+				magnitude = (a_ls + 1.0f) + (a_ls - 1.0f) * cos_w0 + 2.0f * sqrt_a * alpha_ls;
+				coefficients[3] = -2.0f * ((a_ls - 1) + (a_ls + 1) * cos_w0);
+				coefficients[4] = (a_ls + 1.0f) + (a_ls - 1.0f) * cos_w0 - 2.0f * sqrt_a * alpha_ls;
+			} break;
+
+			case Type::HighShelf: {
+				const float a_hs = std::pow(10.0f, gain / 40.0f);
+				const float sqrt_a_hs = std::sqrt(a_hs);
+				const float alpha_hs =
+					std::sin(w0) / 2.0f * std::sqrt((a_hs + 1.0f / a_hs) * (1.0f / resonance - 1.0f) + 2.0f);
+
+				coefficients[0] = a_hs * ((a_hs + 1.0f) + (a_hs - 1.0f) * cos_w0 + 2.0f * sqrt_a_hs * alpha_hs);
+				coefficients[1] = -2.0f * a_hs * ((a_hs - 1.0f) + (a_hs + 1.0f) * cos_w0);
+				coefficients[2] = a_hs * ((a_hs + 1.0f) + (a_hs - 1.0f) * cos_w0 - 2.0f * sqrt_a_hs * alpha_hs);
+				magnitude = (a_hs + 1.0f) - (a_hs - 1.0f) * cos_w0 + 2.0f * sqrt_a_hs * alpha_hs;
+				coefficients[3] = 2.0f * ((a_hs - 1.0f) - (a_hs + 1.0f) * cos_w0);
+				coefficients[4] = (a_hs + 1.0f) - (a_hs - 1.0f) * cos_w0 - 2.0f * sqrt_a_hs * alpha_hs;
+			} break;
+		}
+
+		if(normalise) {
+			for(int c = 0; c < 5; c++) {
+				coefficients[c] /= magnitude;
+			}
+		}
+		for(int c = 0; c < 5; c++) {
+#ifdef FIXED
+			coefficients_[c] = FixedType(coefficients[c] * FixedMultiplier);
+#else
+			coefficients_[c] = coefficients[c];
+#endif
+		}
+	}
+
+	int16_t apply(const int16_t input) {
+#ifdef FIXED
+		const auto applied =
+			coefficients_[0] * input +
+			coefficients_[1] * inputs_[0] +
+			coefficients_[2] * inputs_[1] -
+			coefficients_[3] * outputs_[0] -
+			coefficients_[4] * outputs_[1];
+
+		const auto output = int16_t(applied >> FixedShift);
+#else
+		const float output =
+			coefficients_[0] * float(input) +
+			coefficients_[1] * inputs_[0] +
+			coefficients_[2] * inputs_[1] -
+			coefficients_[3] * outputs_[0] -
+			coefficients_[4] * outputs_[1];
+#endif
+
+		inputs_[1] = inputs_[0];
+		inputs_[0] = input;
+		outputs_[1] = outputs_[0];
+		outputs_[0] = output;
+
+		return int16_t(output);
+	}
+
+private:
+#ifdef FIXED
+	int16_t inputs_[2]{};
+	int16_t outputs_[2]{};
+
+	using FixedType = int64_t;
+	static constexpr int FixedShift = 48;
+	static constexpr auto FixedMultiplier = static_cast<float>(int64_t(1) << FixedShift);
+	FixedType coefficients_[5]{};
+#else
+	float inputs_[2]{};
+	float outputs_[2]{};
+	float coefficients_[5]{};
+#endif
+		// Coefficients indices versus common textbook terms:
+		//	0 = b0; 1 = b1; 2 = b2; 3 = a1; 4 = a2
+};
+
+}

Storage/Disk/Controller/DiskController.cpp

@@ -71,9 +71,13 @@ void Controller::process_write_completed() {
 	// Provided for subclasses to override.
 }
 
+void Controller::is_writing_final_bit() {
+	// Provided for subclasses to override.
+}
+
 // MARK: - PLL control and delegate
 
-void Controller::set_expected_bit_length(Time bit_length) {
+void Controller::set_expected_bit_length(const Time bit_length) {
 	bit_length_ = bit_length;
 	bit_length_.simplify();
 
@@ -86,6 +90,10 @@ void Controller::set_expected_bit_length(Time bit_length) {
 	pll_.set_clocks_per_bit(clocks_per_bit);
 }
 
+Storage::Time Controller::expected_bit_length() {
+	return bit_length_;
+}
+
 void Controller::digital_phase_locked_loop_output_bit(int value) {
 	if(is_reading_) process_input_bit(value);
 }
@@ -124,9 +132,9 @@ void Controller::set_drive(int index_mask) {
 	}
 }
 
-void Controller::begin_writing(bool clamp_to_index_hole) {
+void Controller::begin_writing(const bool clamp_to_index_hole, const bool synthesise_initial_writing_events) {
 	is_reading_ = false;
-	get_drive().begin_writing(bit_length_, clamp_to_index_hole);
+	get_drive().begin_writing(bit_length_, clamp_to_index_hole, synthesise_initial_writing_events);
 }
 
 void Controller::end_writing() {

Storage/Disk/Controller/DiskController.hpp

@@ -40,6 +40,7 @@ protected:
 		Communicates to the PLL the expected length of a bit as a fraction of a second.
 	*/
 	void set_expected_bit_length(Time bit_length);
+	Time expected_bit_length();
 
 	/*!
 		Advances the drive by @c number_of_cycles cycles.
@@ -85,10 +86,16 @@ protected:
 
 	/*!
 		Should be implemented by subclasses if they implement writing; communicates that
-		all bits supplied to write_bit have now been written.
+		all bits supplied to `write_bit` have now been written.
 	*/
 	virtual void process_write_completed() override;
 
+	/*!
+		Can be implemented by subclasses that perform writing; indicates that the final
+		bit previously provided to the drive has started its output.
+	*/
+	virtual void is_writing_final_bit() override;
+
 	/*!
 		Puts the controller and the drive returned by get_drive() into write mode, supplying to
 		the drive the current bit length.
@@ -99,7 +106,7 @@ protected:
 		@param clamp_to_index_hole If @c true then writing will automatically be truncated by
 		the index hole. Writing will continue over the index hole otherwise.
 	*/
-	void begin_writing(bool clamp_to_index_hole);
+	void begin_writing(bool clamp_to_index_hole, bool synthesise_initial_writing_events);
 
 	/*!
 		Puts the drive returned by get_drive() out of write mode, and marks the controller

Storage/Disk/DiskImage/DiskImageImplementation.hpp

@@ -75,7 +75,7 @@ Track *DiskImageHolder<T>::track_at_position(Track::Address address) const {
 
 template <typename T>
 DiskImageHolder<T>::~DiskImageHolder() {
-	if(update_queue_) update_queue_->flush();
+	if(update_queue_) update_queue_->lock_flush();
 }
 
 template <typename T>

Storage/Disk/DiskImage/Formats/D64.cpp

@@ -10,10 +10,13 @@
 
 #include <algorithm>
 #include <cstring>
+#include <set>
 #include <sys/stat.h>
 
 #include "Storage/Disk/Track/PCMTrack.hpp"
 #include "Storage/Disk/Encodings/CommodoreGCR.hpp"
+#include "Storage/Disk/Track/TrackSerialiser.hpp"
+#include "Numeric/SizedInt.hpp"
 
 using namespace Storage::Disk;
 
@@ -38,23 +41,42 @@ HeadPosition D64::maximum_head_position() const {
 	return HeadPosition(number_of_tracks_);
 }
 
-std::unique_ptr<Track> D64::track_at_position(const Track::Address address) const {
-	// Figure out where this track starts on the disk.
+bool D64::is_read_only() const {
+	return file_.is_known_read_only();
+}
+
+bool D64::represents(const std::string &name) const {
+	return name == file_.name();
+}
+
+D64::TrackExtent D64::track_extent(const Track::Address address) const {
+	static constexpr int tracks_in_zone[] = {17, 7, 6, 10};
+	static constexpr int sectors_by_zone[] = {21, 19, 18, 17};
+
 	int offset_to_track = 0;
 	int tracks_to_traverse = address.position.as_int();
-
-	int zone_sizes[] = {17, 7, 6, 10};
-	int sectors_by_zone[] = {21, 19, 18, 17};
 	int zone = 0;
 	for(int current_zone = 0; current_zone < 4; current_zone++) {
-		int tracks_in_this_zone = std::min(tracks_to_traverse, zone_sizes[current_zone]);
-		offset_to_track += tracks_in_this_zone * sectors_by_zone[current_zone];
-		tracks_to_traverse -= tracks_in_this_zone;
-		if(tracks_in_this_zone == zone_sizes[current_zone]) zone++;
+		const int tracks = std::min(tracks_to_traverse, tracks_in_zone[current_zone]);
+		offset_to_track += tracks * sectors_by_zone[current_zone];
+		tracks_to_traverse -= tracks;
+		if(tracks == tracks_in_zone[current_zone]) {
+			++zone;
+		}
 	}
 
+	return TrackExtent {
+		.file_offset = offset_to_track * 256,
+		.zone = zone,
+		.number_of_sectors = sectors_by_zone[zone]
+	};
+}
+
+std::unique_ptr<Track> D64::track_at_position(const Track::Address address) const {
 	// Seek to start of data.
-	file_.seek(offset_to_track * 256, Whence::SET);
+	const auto extent = track_extent(address);
+	std::lock_guard lock_guard(file_.file_access_mutex());
+	file_.seek(extent.file_offset, Whence::SET);
 
 	// Build up a PCM sampling of the GCR version of this track.
 
@@ -78,17 +100,17 @@ std::unique_ptr<Track> D64::track_at_position(const Track::Address address) cons
 	//
 	// = 349 GCR bytes per sector
 
-	std::size_t track_bytes = 349 * size_t(sectors_by_zone[zone]);
+	std::size_t track_bytes = 349 * size_t(extent.number_of_sectors);
 	std::vector<uint8_t> data(track_bytes);
 
-	for(int sector = 0; sector < sectors_by_zone[zone]; sector++) {
-		uint8_t *sector_data = &data[size_t(sector) * 349];
+	for(int sector = 0; sector < extent.number_of_sectors; sector++) {
+		uint8_t *const sector_data = &data[size_t(sector) * 349];
 		sector_data[0] = sector_data[1] = sector_data[2] = 0xff;
 
-		uint8_t sector_number = uint8_t(sector);						// Sectors count from 0.
-		uint8_t track_number = uint8_t(address.position.as_int() + 1);	// Tracks count from 1.
+		const uint8_t sector_number = uint8_t(sector);							// Sectors count from 0.
+		const uint8_t track_number = uint8_t(address.position.as_int() + 1);	// Tracks count from 1.
 		uint8_t checksum = uint8_t(sector_number ^ track_number ^ disk_id_ ^ (disk_id_ >> 8));
-		uint8_t header_start[4] = {
+		const uint8_t header_start[4] = {
 			0x08, checksum, sector_number, track_number
 		};
 		Encodings::CommodoreGCR::encode_block(&sector_data[3], header_start);
@@ -99,7 +121,7 @@ std::unique_ptr<Track> D64::track_at_position(const Track::Address address) cons
 		Encodings::CommodoreGCR::encode_block(&sector_data[8], header_end);
 
 		// Pad out post-header parts.
-		uint8_t zeros[4] = {0, 0, 0, 0};
+		static constexpr uint8_t zeros[4] = {0, 0, 0, 0};
 		Encodings::CommodoreGCR::encode_block(&sector_data[13], zeros);
 		sector_data[18] = 0x52;
 		sector_data[19] = 0x94;
@@ -111,14 +133,15 @@ std::unique_ptr<Track> D64::track_at_position(const Track::Address address) cons
 
 		// Compute the latest checksum.
 		checksum = 0;
-		for(int c = 0; c < 256; c++)
+		for(int c = 0; c < 256; c++) {
 			checksum ^= source_data[c];
+		}
 
 		// Put in another sync.
 		sector_data[21] = sector_data[22] = sector_data[23] = 0xff;
 
 		// Now start writing in the actual data.
-		uint8_t start_of_data[4] = {
+		const uint8_t start_of_data[4] = {
 			0x07, source_data[0], source_data[1], source_data[2]
 		};
 		Encodings::CommodoreGCR::encode_block(&sector_data[24], start_of_data);
@@ -129,7 +152,7 @@ std::unique_ptr<Track> D64::track_at_position(const Track::Address address) cons
 			target_data_offset += 5;
 			source_data_offset += 4;
 		}
-		uint8_t end_of_data[4] = {
+		const uint8_t end_of_data[4] = {
 			source_data[255], checksum, 0, 0
 		};
 		Encodings::CommodoreGCR::encode_block(&sector_data[target_data_offset], end_of_data);
@@ -138,6 +161,103 @@ std::unique_ptr<Track> D64::track_at_position(const Track::Address address) cons
 	return std::make_unique<PCMTrack>(PCMSegment(data));
 }
 
-bool D64::represents(const std::string &name) const {
-	return name == file_.name();
+void D64::set_tracks(const std::map<Track::Address, std::unique_ptr<Track>> &tracks) {
+	for(const auto &[address, track]: tracks) {
+		const auto extent = track_extent(address);
+		std::map<int, std::vector<uint8_t>> decoded;
+
+		// Get bit stream.
+		const auto serialisation =
+			Storage::Disk::track_serialisation(
+				*track,
+				Time(1, extent.number_of_sectors * 349 * 8)	// This is relative to a normalised world where
+															// 1 unit of time = 1 track. So don't use
+															// length_of_a_bit_in_time_zone, which is relative to
+															// a wall clock.
+			);
+
+		// Decode sectors.
+		Numeric::SizedInt<10> shifter = 0;
+		int repeats = 2;
+		auto bit = serialisation.data.begin();
+		bool is_ended = false;
+		const auto shift = [&] {
+			shifter = uint16_t((shifter.get() << 1) | *bit);
+			++bit;
+
+			if(bit == serialisation.data.end()) {
+				bit = serialisation.data.begin();
+				--repeats;
+				is_ended |= !repeats;
+			}
+		};
+		const auto byte = [&] {
+			for(int c = 0; c < 9; c++) {
+				shift();
+			}
+			const auto result = Encodings::CommodoreGCR::decoding_from_dectet(shifter.get());
+			shift();
+			return uint8_t(result);
+		};
+		const auto block_type = [&] {
+			// Find synchronisation, then get first dectet after that.
+			while(!is_ended && shifter.get() != 0b11111'11111) {
+				shift();
+			}
+			while(!is_ended && shifter.get() == 0b11111'11111) {
+				shift();
+			}
+
+			// Type should be 8 for a header, 7 for some data.
+			return byte();
+		};
+
+		while(!is_ended && decoded.size() != size_t(extent.number_of_sectors)) {
+			// Find a header.
+			const auto header_start = block_type();
+			if(header_start != 0x8) {
+				continue;
+			}
+			const auto checksum = byte();
+			const auto sector_id = byte();
+			const auto track_id = byte();
+			const auto disk_id1 = byte();
+			const auto disk_id2 = byte();
+
+			if(checksum != (sector_id ^ track_id ^ disk_id1 ^ disk_id2)) {
+				continue;
+			}
+			if(sector_id >= extent.number_of_sectors) {
+				continue;
+			}
+
+			// Skip to data.
+			const auto data_start = block_type();
+			if(data_start != 0x7) {
+				continue;
+			}
+
+			// Copy into place if not yet present.
+			uint8_t data_checksum = 0;
+			std::vector<uint8_t> sector_contents(256);
+			for(size_t c = 0; c < 256; c++) {
+				const uint8_t next = byte();
+				data_checksum ^= next;
+				sector_contents[c] = next;
+			}
+
+			if(byte() != data_checksum) {
+				continue;
+			}
+			decoded.emplace(sector_id, std::move(sector_contents));
+		}
+
+		// Write.
+		std::lock_guard lock_guard(file_.file_access_mutex());
+		for(auto &[sector, contents]: decoded) {
+			file_.seek(extent.file_offset + sector * 256, Whence::SET);
+			file_.write(contents);
+		}
+	}
 }
+

Storage/Disk/DiskImage/Formats/D64.hpp

@@ -28,12 +28,21 @@ public:
 
 	HeadPosition maximum_head_position() const;
 	std::unique_ptr<Track> track_at_position(Track::Address) const;
+	bool is_read_only() const;
+	void set_tracks(const std::map<Track::Address, std::unique_ptr<Track>> &);
 	bool represents(const std::string &) const;
 
 private:
 	mutable Storage::FileHolder file_;
 	int number_of_tracks_;
 	uint16_t disk_id_;
+
+	struct TrackExtent {
+		long file_offset;
+		int zone;
+		int number_of_sectors;
+	};
+	TrackExtent track_extent(Track::Address) const;
 };
 
 }

Storage/Disk/Drive.cpp

@@ -16,13 +16,19 @@
 
 using namespace Storage::Disk;
 
-Drive::Drive(int input_clock_rate, int revolutions_per_minute, int number_of_heads, ReadyType rdy_type):
+Drive::Drive(
+	const int input_clock_rate,
+	const int revolutions_per_minute,
+	const int number_of_heads,
+	const ReadyType rdy_type
+) :
 	Storage::TimedEventLoop(input_clock_rate),
 	available_heads_(number_of_heads),
 	ready_type_(rdy_type) {
 	set_rotation_speed(revolutions_per_minute);
 
-	const auto seed = std::default_random_engine::result_type(std::chrono::system_clock::now().time_since_epoch().count());
+	const auto seed =
+		std::default_random_engine::result_type(std::chrono::system_clock::now().time_since_epoch().count());
 	std::default_random_engine randomiser(seed);
 
 	// Get at least 64 bits of random information; rounding is likey to give this a slight bias.
@@ -34,16 +40,21 @@ Drive::Drive(int input_clock_rate, int revolutions_per_minute, int number_of_hea
 	}
 }
 
-Drive::Drive(int input_clock_rate, int number_of_heads, ReadyType rdy_type) : Drive(input_clock_rate, 300, number_of_heads, rdy_type) {}
+Drive::Drive(
+	const int input_clock_rate,
+	const int number_of_heads,
+	const ReadyType rdy_type
+) : Drive(input_clock_rate, 300, number_of_heads, rdy_type) {}
 
-void Drive::set_rotation_speed(float revolutions_per_minute) {
+void Drive::set_rotation_speed(const float revolutions_per_minute) {
 	// Rationalise the supplied speed so that cycles_per_revolution_ is exact.
 	cycles_per_revolution_ = int(0.5f + float(get_input_clock_rate()) * 60.0f / revolutions_per_minute);
 
 	// From there derive the appropriate rotational multiplier and possibly update the
 	// count of cycles since the index hole proportionally.
 	const float new_rotational_multiplier = float(cycles_per_revolution_) / float(get_input_clock_rate());
-	cycles_since_index_hole_ = Cycles::IntType(float(cycles_since_index_hole_) * new_rotational_multiplier / rotational_multiplier_);
+	cycles_since_index_hole_ =
+		Cycles::IntType(float(cycles_since_index_hole_) * new_rotational_multiplier / rotational_multiplier_);
 	rotational_multiplier_ = new_rotational_multiplier;
 	cycles_since_index_hole_ %= cycles_per_revolution_;
 }
@@ -75,14 +86,16 @@ bool Drive::has_disk() const {
 }
 
 ClockingHint::Preference Drive::preferred_clocking() const {
-	return (!has_disk_ || (time_until_motor_transition == Cycles(0) && !disk_is_rotating_)) ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
+	return (
+		!has_disk_ || (time_until_motor_transition == Cycles(0) && !disk_is_rotating_)
+	) ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
 }
 
 bool Drive::get_is_track_zero() const {
 	return head_position_ == HeadPosition(0);
 }
 
-void Drive::step(HeadPosition offset) {
+void Drive::step(const HeadPosition offset) {
 	if(offset == HeadPosition(0)) {
 		return;
 	}
@@ -109,7 +122,7 @@ void Drive::step(HeadPosition offset) {
 	did_step(head_position_);
 }
 
-Track *Drive::step_to(HeadPosition offset) {
+Track *Drive::step_to(const HeadPosition offset) {
 	HeadPosition old_head_position = head_position_;
 	head_position_ = std::max(offset, HeadPosition(0));
 
@@ -160,7 +173,7 @@ bool Drive::get_is_ready() const {
 	return is_ready_;
 }
 
-void Drive::set_motor_on(bool motor_is_on) {
+void Drive::set_motor_on(const bool motor_is_on) {
 	// Do nothing if the input hasn't changed.
 	if(motor_input_is_on_ == motor_is_on) return;
 	motor_input_is_on_ = motor_is_on;
@@ -195,7 +208,7 @@ bool Drive::get_index_pulse() const {
 	return index_pulse_remaining_ > Cycles(0);
 }
 
-void Drive::set_event_delegate(Storage::Disk::Drive::EventDelegate *delegate) {
+void Drive::set_event_delegate(Storage::Disk::Drive::EventDelegate *const delegate) {
 	event_delegate_ = delegate;
 }
 
@@ -237,13 +250,21 @@ void Drive::run_for(const Cycles cycles) {
 					if(cycles_until_bits_written_ > zero) {
 						Storage::Time cycles_to_run_for_time(static_cast<int>(cycles_to_run_for));
 						if(cycles_until_bits_written_ <= cycles_to_run_for_time) {
-							if(event_delegate_) event_delegate_->process_write_completed();
-							if(cycles_until_bits_written_ <= cycles_to_run_for_time)
-								cycles_until_bits_written_.set_zero();
-							else
-								cycles_until_bits_written_ -= cycles_to_run_for_time;
+							cycles_until_bits_written_.set_zero();
+							if(event_delegate_) {
+								event_delegate_->process_write_completed();
+							}
 						} else {
+							const auto previous_cycles = cycles_until_bits_written_;
 							cycles_until_bits_written_ -= cycles_to_run_for_time;
+
+							if(
+								previous_cycles >= cycles_per_bit_ &&
+								cycles_until_bits_written_ < cycles_per_bit_ &&
+								event_delegate_
+							) {
+								event_delegate_->is_writing_final_bit();
+							}
 						}
 					}
 				}
@@ -257,7 +278,7 @@ void Drive::run_for(const Cycles cycles) {
 
 // MARK: - Track timed event loop
 
-void Drive::get_next_event(float duration_already_passed) {
+void Drive::get_next_event(const float duration_already_passed) {
 	/*
 		Quick word on random-bit generation logic below; it seeks to obey the following logic:
 		if there is a gap of 15µs between recorded bits, start generating flux transitions
@@ -387,7 +408,11 @@ void Drive::invalidate_track() {
 
 // MARK: - Writing
 
-void Drive::begin_writing(Time bit_length, bool clamp_to_index_hole) {
+void Drive::begin_writing(
+	const Time bit_length,
+	const bool clamp_to_index_hole,
+	const bool synthesise_initial_writing_events
+) {
 	// Do nothing if already writing.
 	// TODO: cope properly if there's no disk to write to.
 	if(!is_reading_ || !disk_) return;
@@ -407,10 +432,15 @@ void Drive::begin_writing(Time bit_length, bool clamp_to_index_hole) {
 	write_segment_.length_of_a_bit = bit_length / Time(rotational_multiplier_);
 	write_segment_.data.clear();
 
+	cycles_until_bits_written_.set_zero();
 	write_start_time_ = Time(get_time_into_track());
+	if(synthesise_initial_writing_events) {
+		write_start_time_ += bit_length;
+		cycles_until_bits_written_ += cycles_per_bit_;
+	}
 }
 
-void Drive::write_bit(bool value) {
+void Drive::write_bit(const bool value) {
 	write_segment_.data.push_back(value);
 	cycles_until_bits_written_ += cycles_per_bit_;
 }
@@ -444,7 +474,7 @@ bool Drive::is_writing() const {
 	return !is_reading_;
 }
 
-void Drive::set_disk_is_rotating(bool is_rotating) {
+void Drive::set_disk_is_rotating(const bool is_rotating) {
 	disk_is_rotating_ = is_rotating;
 
 	if(observer_) {
@@ -464,7 +494,11 @@ void Drive::set_disk_is_rotating(bool is_rotating) {
 	update_clocking_observer();
 }
 
-void Drive::set_activity_observer(Activity::Observer *observer, const std::string &name, bool add_motor_led) {
+void Drive::set_activity_observer(
+	Activity::Observer *const observer,
+	const std::string &name,
+	const bool add_motor_led
+) {
 	observer_ = observer;
 	announce_motor_led_ = add_motor_led;
 	if(observer) {

Storage/Disk/Drive.hpp

@@ -36,13 +36,7 @@ public:
 	Drive(int input_clock_rate, int number_of_heads, ReadyType rdy_type = ReadyType::ShugartRDY);
 	virtual ~Drive();
 
-	// TODO: Disallow copying.
-	//
-	// GCC 10 has an issue with the way the DiskII constructs its drive array if these are both
-	// deleted, despite not using the copy constructor.
-	//
-	// This seems to be fixed in GCC 11, so reenable this delete when possible.
-//		Drive(const Drive &) = delete;
+	Drive(const Drive &) = delete;
 	void operator=(const Drive &) = delete;
 
 	/*!
@@ -74,7 +68,7 @@ public:
 	/*!
 		Sets the current read head.
 	*/
-	void set_head(int head);
+	void set_head(int);
 
 	/*!
 		Gets the head count for this disk.
@@ -114,13 +108,16 @@ public:
 
 		@param clamp_to_index_hole If @c true then writing will automatically be truncated by
 		the index hole. Writing will continue over the index hole otherwise.
+
+		@param synthesise_initial_writing_events if @c true then an  @c is_writing_final_bit() /
+		@c process_write_completed() pair will follow without any data having been written.
 	*/
-	void begin_writing(Time bit_length, bool clamp_to_index_hole);
+	void begin_writing(Time bit_length, bool clamp_to_index_hole, bool synthesise_initial_writing_events);
 
 	/*!
 		Writes the bit @c value as the next in the PCM stream initiated by @c begin_writing.
 	*/
-	void write_bit(bool value);
+	void write_bit(bool);
 
 	/*!
 		Ends write mode, switching back to read mode. The drive will stop overwriting events.
@@ -149,7 +146,7 @@ public:
 	*/
 	struct EventDelegate {
 		/// Informs the delegate that @c event has been reached.
-		virtual void process_event(const Event &event) = 0;
+		virtual void process_event(const Event &) = 0;
 
 		/*!
 			If the drive is in write mode, announces that all queued bits have now been written.
@@ -157,8 +154,13 @@ public:
 		*/
 		virtual void process_write_completed() {}
 
+		/*!
+			When in write mode, indicates that output of the final bit has begun.
+		*/
+		virtual void is_writing_final_bit() {}
+
 		/// Informs the delegate of the passing of @c cycles.
-		virtual void advance([[maybe_unused]] Cycles cycles) {}
+		virtual void advance(Cycles) {}
 	};
 
 	/// Sets the current event delegate.

Storage/Disk/Encodings/CommodoreGCR.cpp

@@ -12,7 +12,8 @@
 using namespace Storage;
 
 Time Storage::Encodings::CommodoreGCR::length_of_a_bit_in_time_zone(const unsigned int time_zone) {
-	// the speed zone divides a 4Mhz clock by 13, 14, 15 or 16, with higher-numbered zones being faster (i.e. each bit taking less time)
+	// The speed zone divides a 4Mhz clock by 13, 14, 15 or 16, with higher-numbered zones being
+	// faster (i.e. each bit taking less time).
 	return Time(16 - time_zone, 4000000u);
 }
 

Storage/Disk/Track/Track.hpp

@@ -64,7 +64,7 @@ public:
 		HeadPosition position;
 
 		constexpr auto operator <=>(const Address&) const = default;
-		constexpr Address(int head, HeadPosition position) : head(head), position(position) {}
+		constexpr Address(const int head, const HeadPosition position) noexcept : head(head), position(position) {}
 	};
 
 	/*!

Storage/Disk/Track/TrackSerialiser.cpp

@@ -12,7 +12,7 @@
 
 // TODO: if this is a PCMTrack with only one segment and that segment's bit rate is within tolerance,
 // just return a copy of that segment.
-Storage::Disk::PCMSegment Storage::Disk::track_serialisation(const Track &track, Time length_of_a_bit) {
+Storage::Disk::PCMSegment Storage::Disk::track_serialisation(const Track &track, const Time length_of_a_bit) {
 	unsigned int history_size = 16;
 	std::unique_ptr<Track> track_copy(track.clone());
 

Storage/FileBundle/FileBundle.cpp

@@ -0,0 +1,35 @@
+//
+//  FileBundle.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 19/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#include "FileBundle.hpp"
+
+#include <cstdio>
+
+using namespace Storage::FileBundle;
+
+LocalFSFileBundle::LocalFSFileBundle(const std::string &to_contain) {
+	const auto last_separator = to_contain.find_last_of("/\\");
+	if(last_separator == std::string::npos) {
+		key_file_ = to_contain;
+	} else {
+		base_path_ = to_contain.substr(0, last_separator + 1);
+		key_file_ = to_contain.substr(last_separator + 1);
+	}
+}
+
+std::optional<std::string> LocalFSFileBundle::key_file() {
+	return key_file_;
+}
+
+Storage::FileHolder LocalFSFileBundle::open(const std::string &name, const Storage::FileMode mode) {
+	return Storage::FileHolder(base_path_ + name, mode);
+}
+
+bool LocalFSFileBundle::erase(const std::string &name) {
+	return !remove((base_path_ + name).c_str());
+}

Storage/FileBundle/FileBundle.hpp

@@ -0,0 +1,44 @@
+//
+//  FileBundle.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 19/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Storage/FileHolder.hpp"
+#include <optional>
+#include <string>
+
+namespace Storage::FileBundle {
+
+/*!
+	A File Bundle is a collection of individual files, abstracted from whatever media they might
+	be one.
+
+	Initial motivation is allowing some machines direct local filesystem access. An attempt has
+	been made to draft this in such a way as to allow it to do things like expose ZIP files as
+	bundles in the future.
+*/
+struct FileBundle {
+	virtual std::optional<std::string> key_file() = 0;
+	virtual FileHolder open(const std::string &, FileMode) = 0;
+	virtual bool erase(const std::string &) = 0;
+};
+
+
+struct LocalFSFileBundle: public FileBundle {
+	LocalFSFileBundle(const std::string &to_contain);
+
+	std::optional<std::string> key_file() override;
+	FileHolder open(const std::string &, FileMode) override;
+	bool erase(const std::string &) override;
+
+private:
+	std::string key_file_;
+	std::string base_path_;
+};
+
+};

Storage/FileHolder.cpp

@@ -13,6 +13,12 @@
 
 using namespace Storage;
 
+FileHolder::FileHolder(FileHolder &&rhs) {
+	file_ = rhs.file_;
+	rhs.file_ = nullptr;
+	// TODO: this leaves the RHS in an invalid state, which isn't appropriate for move semantics.
+}
+
 FileHolder::~FileHolder() {
 	if(file_) std::fclose(file_);
 }
@@ -45,8 +51,8 @@ uint8_t FileHolder::get() {
 	return uint8_t(std::fgetc(file_));
 }
 
-void FileHolder::put(const uint8_t value) {
-	std::fputc(value, file_);
+bool FileHolder::put(const uint8_t value) {
+	return std::fputc(value, file_) == value;
 }
 
 void FileHolder::putn(std::size_t repeats, const uint8_t value) {
@@ -71,9 +77,9 @@ std::size_t FileHolder::write(const uint8_t *buffer, const std::size_t size) {
 	return std::fwrite(buffer, 1, size, file_);
 }
 
-void FileHolder::seek(const long offset, const Whence whence) {
-	[[maybe_unused]] const auto result = std::fseek(file_, offset, int(whence));
-	assert(!result);
+bool FileHolder::seek(const long offset, const Whence whence) {
+	const auto result = std::fseek(file_, offset, int(whence));
+	return !result;
 }
 
 long FileHolder::tell() const {

Storage/FileHolder.hpp

@@ -56,9 +56,10 @@ public:
 			Rewrite		opens the file for rewriting; none of the original content is preserved; whatever
 						the caller outputs will replace the existing file.
 
-		@throws ErrorCantOpen if the file cannot be opened.
+		@throws Error::CantOpen if the file cannot be opened.
 	*/
 	FileHolder(const std::string &file_name, FileMode ideal_mode = FileMode::ReadWrite);
+	FileHolder(FileHolder &&);
 
 	/*!
 		Writes @c value using successive @c puts, in little endian order.
@@ -116,8 +117,11 @@ public:
 	/*! Reads a single byte from @c file. */
 	uint8_t get();
 
-	/*! Writes a single byte from @c file. */
-	void put(uint8_t);
+	/*!
+		Writes a single byte from @c file.
+		@returns @c true on success; @c false on failure.
+	*/
+	bool put(uint8_t);
 
 	/*! Writes @c value a total of @c repeats times. */
 	void putn(std::size_t repeats, uint8_t value);
@@ -140,7 +144,7 @@ public:
 	std::size_t write(const uint8_t *, std::size_t);
 
 	/*! Moves @c bytes from the anchor indicated by @c whence: SEEK_SET, SEEK_CUR or SEEK_END. */
-	void seek(long offset, Whence);
+	bool seek(long offset, Whence);
 
 	/*! @returns The current cursor position within this file. */
 	long tell() const;

Storage/Tape/Tape.cpp

@@ -94,7 +94,7 @@ void TapePlayer::set_tape(std::shared_ptr<Storage::Tape::Tape> tape, TargetPlatf
 }
 
 bool TapePlayer::is_at_end() const {
-	return serialiser_->is_at_end();
+	return !serialiser_ || serialiser_->is_at_end();
 }
 
 TapeSerialiser *TapePlayer::serialiser() {

cmake/CLK_SOURCES.cmake

@@ -59,6 +59,7 @@ set(CLK_SOURCES
 	Components/OPx/OPLL.cpp
 	Components/RP5C01/RP5C01.cpp
 	Components/SAA5050/SAA5050.cpp
+	Components/SID/SID.cpp
 	Components/SN76489/SN76489.cpp
 	Components/Serial/Line.cpp
 	Components/uPD7002/uPD7002.cpp
@@ -129,6 +130,7 @@ set(CLK_SOURCES
 	Machines/Enterprise/Dave.cpp
 	Machines/Enterprise/EXDos.cpp
 	Machines/Enterprise/Enterprise.cpp
+	Machines/Enterprise/HostFSHandler.cpp
 	Machines/Enterprise/Keyboard.cpp
 	Machines/Enterprise/Nick.cpp
 	Machines/KeyboardMachine.cpp
@@ -223,6 +225,7 @@ set(CLK_SOURCES
 	Storage/Disk/Track/PCMTrack.cpp
 	Storage/Disk/Track/TrackSerialiser.cpp
 	Storage/Disk/Track/UnformattedTrack.cpp
+	Storage/FileBundle/FileBundle.cpp
 	Storage/FileHolder.cpp
 	Storage/MassStorage/Encodings/MacintoshVolume.cpp
 	Storage/MassStorage/Formats/DAT.cpp