CLK/Machines/PCCompatible/PCCompatible.cpp

//
//  PCCompatible.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 15/11/2023.
//  Copyright © 2023 Thomas Harte. All rights reserved.
//

#include "PCCompatible.hpp"

#include "KeyboardMapper.hpp"
#include "PIC.hpp"
#include "PIT.hpp"
#include "DMA.hpp"
#include "Memory.hpp"

#include "../../InstructionSets/x86/Decoder.hpp"
#include "../../InstructionSets/x86/Flags.hpp"
#include "../../InstructionSets/x86/Instruction.hpp"
#include "../../InstructionSets/x86/Perform.hpp"

#include "../../Components/6845/CRTC6845.hpp"
#include "../../Components/8255/i8255.hpp"
#include "../../Components/8272/CommandDecoder.hpp"
#include "../../Components/8272/Results.hpp"
#include "../../Components/8272/Status.hpp"
#include "../../Components/AudioToggle/AudioToggle.hpp"

#include "../../Numeric/RegisterSizes.hpp"

#include "../../Outputs/CRT/CRT.hpp"
#include "../../Outputs/Speaker/Implementation/LowpassSpeaker.hpp"

#include "../../Storage/Disk/Track/TrackSerialiser.hpp"
#include "../../Storage/Disk/Encodings/MFM/Constants.hpp"
#include "../../Storage/Disk/Encodings/MFM/SegmentParser.hpp"

#include "../AudioProducer.hpp"
#include "../KeyboardMachine.hpp"
#include "../MediaTarget.hpp"
#include "../ScanProducer.hpp"
#include "../TimedMachine.hpp"

#include <array>
#include <iostream>

namespace PCCompatible {

//bool log = false;
//std::string previous;

class FloppyController {
	public:
		FloppyController(PIC &pic, DMA &dma) : pic_(pic), dma_(dma) {
			// Default: one floppy drive only.
			drives_[0].exists = true;
			drives_[1].exists = false;
			drives_[2].exists = false;
			drives_[3].exists = false;
		}

		void set_digital_output(uint8_t control) {
//			printf("FDC DOR: %02x\n", control);

			// b7, b6, b5, b4: enable motor for drive 4, 3, 2, 1;
			// b3: 1 => enable DMA; 0 => disable;
			// b2: 1 => enable FDC; 0 => hold at reset;
			// b1, b0: drive select (usurps FDC?)

			drives_[0].motor = control & 0x10;
			drives_[1].motor = control & 0x20;
			drives_[2].motor = control & 0x40;
			drives_[3].motor = control & 0x80;

			if(observer_) {
				for(int c = 0; c < 4; c++) {
					if(drives_[c].exists) observer_->set_led_status(drive_name(c), drives_[c].motor);
				}
			}

			enable_dma_ = control & 0x08;

			const bool hold_reset = !(control & 0x04);
			if(!hold_reset && hold_reset_) {
				// TODO: add a delay mechanism.
				reset();
			}
			hold_reset_ = hold_reset;
			if(hold_reset_) {
				pic_.apply_edge<6>(false);
			}
		}

		uint8_t status() const {
//			printf("FDC: read status %02x\n", status_.main());
			return status_.main();
		}

		void write(uint8_t value) {
			decoder_.push_back(value);

			if(decoder_.has_command()) {
				using Command = Intel::i8272::Command;
				switch(decoder_.command()) {
					default:
						printf("TODO: implement FDC command %d\n", uint8_t(decoder_.command()));
					break;

					case Command::ReadData: {
						printf("FDC: Read from drive %d / head %d / track %d of head %d / track %d / sector %d\n",
							decoder_.target().drive,
							decoder_.target().head,
							drives_[decoder_.target().drive].track,
							decoder_.geometry().head,
							decoder_.geometry().cylinder,
							decoder_.geometry().sector);

						status_.begin(decoder_);

						// Search for a matching sector.
						auto target = decoder_.geometry();
						bool complete = false;
						while(!complete) {
							bool found_sector = false;

							for(auto &pair: drives_[decoder_.target().drive].sectors(decoder_.target().head)) {
								if(
									(pair.second.address.track == target.cylinder) &&
									(pair.second.address.sector == target.sector) &&
									(pair.second.address.side == target.head) &&
									(pair.second.size == target.size)
								) {
									found_sector = true;
									bool wrote_in_full = true;

									for(int c = 0; c < 128 << target.size; c++) {
										const auto access_result = dma_.write(2, pair.second.samples[0].data()[c]);
										switch(access_result) {
											default: break;
											case AccessResult::NotAccepted:
												wrote_in_full = false;
											break;
											case AccessResult::AcceptedWithEOP:
												complete = true;
											break;
										}
										if(access_result != AccessResult::Accepted) {
											break;
										}
									}

									if(!wrote_in_full) {
										status_.set(Intel::i8272::Status1::OverRun);
										status_.set(Intel::i8272::Status0::AbnormalTermination);
										break;
									}

									++target.sector;	// TODO: multitrack?

									break;
								}
							}

							if(!found_sector) {
								status_.set(Intel::i8272::Status1::EndOfCylinder);
								status_.set(Intel::i8272::Status0::AbnormalTermination);
								break;
							}
						}

						results_.serialise(
							status_,
							decoder_.geometry().cylinder,
							decoder_.geometry().head,
							decoder_.geometry().sector,
							decoder_.geometry().size);

						// TODO: what if head has changed?
						drives_[decoder_.target().drive].status = decoder_.drive_head();
						drives_[decoder_.target().drive].raised_interrupt = true;
						pic_.apply_edge<6>(true);
					} break;

					case Command::Recalibrate:
						printf("FDC: Recalibrate\n");
						drives_[decoder_.target().drive].track = 0;

						drives_[decoder_.target().drive].raised_interrupt = true;
						drives_[decoder_.target().drive].status = decoder_.target().drive | uint8_t(Intel::i8272::Status0::SeekEnded);
						pic_.apply_edge<6>(true);
					break;
					case Command::Seek:
						printf("FDC: Seek %d:%d to %d\n", decoder_.target().drive, decoder_.target().head, decoder_.seek_target());
						drives_[decoder_.target().drive].track = decoder_.seek_target();

						drives_[decoder_.target().drive].raised_interrupt = true;
						drives_[decoder_.target().drive].status = decoder_.drive_head() | uint8_t(Intel::i8272::Status0::SeekEnded);
						pic_.apply_edge<6>(true);
					break;

					case Command::SenseInterruptStatus: {
						printf("FDC: SenseInterruptStatus\n");

						int c = 0;
						for(; c < 4; c++) {
							if(drives_[c].raised_interrupt) {
								drives_[c].raised_interrupt = false;
								status_.set_status0(drives_[c].status);
								results_.serialise(status_, drives_[0].track);
							}
						}

						bool any_remaining_interrupts = false;
						for(; c < 4; c++) {
							any_remaining_interrupts |= drives_[c].raised_interrupt;
						}
						if(!any_remaining_interrupts) {
							pic_.apply_edge<6>(false);
						}
					} break;
					case Command::Specify:
						printf("FDC: Specify\n");
						specify_specs_ = decoder_.specify_specs();
					break;
//					case Command::SenseDriveStatus: {
//					} break;

					case Command::Invalid:
						printf("FDC: Invalid\n");
						results_.serialise_none();
					break;
				}

				decoder_.clear();

				// If there are any results to provide, set data direction and data ready.
				if(!results_.empty()) {
					using MainStatus = Intel::i8272::MainStatus;
					status_.set(MainStatus::DataIsToProcessor, true);
					status_.set(MainStatus::DataReady, true);
					status_.set(MainStatus::CommandInProgress, true);
				}
			}
		}

		uint8_t read() {
			using MainStatus = Intel::i8272::MainStatus;
			if(status_.get(MainStatus::DataIsToProcessor)) {
				const uint8_t result = results_.next();
				if(results_.empty()) {
					status_.set(MainStatus::DataIsToProcessor, false);
					status_.set(MainStatus::CommandInProgress, false);
				}
//				printf("FDC read: %02x\n", result);
				return result;
			}

			printf("FDC read?\n");
			return 0x80;
		}

		void set_activity_observer(Activity::Observer *observer) {
			observer_ = observer;
			for(int c = 0; c < 4; c++) {
				if(drives_[c].exists) {
					observer_->register_led(drive_name(c), 0);
				}
			}
		}

		void set_disk(std::shared_ptr<Storage::Disk::Disk> disk, int drive) {
//			if(drives_[drive].has_disk()) {
//				// TODO: drive should only transition to unready if it was ready in the first place.
//				drives_[drive].status = uint8_t(Intel::i8272::Status0::BecameNotReady);
//				drives_[drive].raised_interrupt = true;
//				pic_.apply_edge<6>(true);
//			}
			drives_[drive].set_disk(disk);
		}

	private:
		void reset() {
			printf("FDC reset\n");
			decoder_.clear();
			status_.reset();

			// Necessary to pass GlaBIOS' POST test, but: why?
			//
			// Cf. INT_13_0_2 and the CMP	AL, 11000000B following a CALL	FDC_WAIT_SENSE.
			for(int c = 0; c < 4; c++) {
				drives_[c].raised_interrupt = true;
				drives_[c].status = uint8_t(Intel::i8272::Status0::BecameNotReady);
			}
			pic_.apply_edge<6>(true);

			using MainStatus = Intel::i8272::MainStatus;
			status_.set(MainStatus::DataReady, true);
			status_.set(MainStatus::DataIsToProcessor, false);
		}

		PIC &pic_;
		DMA &dma_;

		bool hold_reset_ = false;
		bool enable_dma_ = false;

		Intel::i8272::CommandDecoder decoder_;
		Intel::i8272::Status status_;
		Intel::i8272::Results results_;

		Intel::i8272::CommandDecoder::SpecifySpecs specify_specs_;
		struct DriveStatus {
			public:
				bool raised_interrupt = false;
				uint8_t status = 0;
				uint8_t track = 0;
				bool motor = false;
				bool exists = true;

				bool has_disk() const {
					return bool(disk);
				}

				void set_disk(std::shared_ptr<Storage::Disk::Disk> image) {
					disk = image;
					cached.clear();
				}

				Storage::Encodings::MFM::SectorMap &sectors(bool side) {
					if(cached.track == track && cached.side == side) {
						return cached.sectors;
					}

					cached.track = track;
					cached.side = side;
					cached.sectors.clear();

					if(!disk) {
						return cached.sectors;
					}

					auto raw_track = disk->get_track_at_position(
						Storage::Disk::Track::Address(
							side,
							Storage::Disk::HeadPosition(track)
						)
					);
					if(!raw_track) {
						return cached.sectors;
					}

					const bool is_double_density = true;	// TODO: use MFM flag here.
					auto serialisation = Storage::Disk::track_serialisation(
						*raw_track,
						is_double_density ? Storage::Encodings::MFM::MFMBitLength : Storage::Encodings::MFM::FMBitLength
					);
					cached.sectors = Storage::Encodings::MFM::sectors_from_segment(std::move(serialisation), is_double_density);
					return cached.sectors;
				}

			private:
				struct {
					uint8_t track = 0xff;
					bool side;
					Storage::Encodings::MFM::SectorMap sectors;

					void clear() {
						track = 0xff;
						sectors.clear();
					}
				} cached;
				std::shared_ptr<Storage::Disk::Disk> disk;

		} drives_[4];

		static std::string drive_name(int c) {
			char name[3] = "A";
			name[0] += c;
			return std::string("Drive ") + name;
		}

		Activity::Observer *observer_ = nullptr;
};

class KeyboardController {
	public:
		KeyboardController(PIC &pic) : pic_(pic) {}

		// KB Status Port 61h high bits:
		//; 01 - normal operation. wait for keypress, when one comes in,
		//;		force data line low (forcing keyboard to buffer additional
		//;		keypresses) and raise IRQ1 high
		//; 11 - stop forcing data line low. lower IRQ1 and don't raise it again.
		//;		drop all incoming keypresses on the floor.
		//; 10 - lower IRQ1 and force clock line low, resetting keyboard
		//; 00 - force clock line low, resetting keyboard, but on a 01->00 transition,
		//;		IRQ1 would remain high
		void set_mode(uint8_t mode) {
			mode_ = Mode(mode);
			switch(mode_) {
				case Mode::NormalOperation: 	break;
				case Mode::NoIRQsIgnoreInput:
					pic_.apply_edge<1>(false);
				break;
				case Mode::ClearIRQReset:
					pic_.apply_edge<1>(false);
					[[fallthrough]];
				case Mode::Reset:
					reset_delay_ = 5;	// Arbitrarily.
				break;
			}
		}

		void run_for(Cycles cycles) {
			if(reset_delay_ <= 0) {
				return;
			}
			reset_delay_ -= cycles.as<int>();
			if(reset_delay_ <= 0) {
				input_.clear();
				post(0xaa);
			}
		}

		uint8_t read() {
			pic_.apply_edge<1>(false);
			if(input_.empty()) {
				return 0;
			}

			const uint8_t key = input_.front();
			input_.erase(input_.begin());
			if(!input_.empty()) {
				pic_.apply_edge<1>(true);
			}
			return key;
		}

		void post(uint8_t value) {
			if(mode_ == Mode::NoIRQsIgnoreInput) {
				return;
			}
			input_.push_back(value);
			pic_.apply_edge<1>(true);
		}

	private:
		enum class Mode {
			NormalOperation = 0b01,
			NoIRQsIgnoreInput = 0b11,
			ClearIRQReset = 0b10,
			Reset = 0b00,
		} mode_;

		std::vector<uint8_t> input_;
		PIC &pic_;

		int reset_delay_ = 0;
};

class MDA {
	public:
		MDA() : crtc_(Motorola::CRTC::Personality::HD6845S, outputter_) {}

		void set_source(const uint8_t *ram, std::vector<uint8_t> font) {
			outputter_.ram = ram;
			outputter_.font = font;
		}

		void run_for(Cycles cycles) {
			// I _think_ the MDA's CRTC is clocked at 14/9ths the PIT clock.
			// Do that conversion here.
			full_clock_ += 14 * cycles.as<int>();
			crtc_.run_for(Cycles(full_clock_ / 9));
			full_clock_ %= 9;
		}

		template <int address>
		void write(uint8_t value) {
			if constexpr (address & 0x8) {
				outputter_.set_control(value);
			} else {
				if constexpr (address & 0x1) {
					crtc_.set_register(value);
				} else {
					crtc_.select_register(value);
				}
			}
		}

		template <int address>
		uint8_t read() {
			if constexpr (address & 0x8) {
				return outputter_.control();
			} else {
				return crtc_.get_register();
			}
		}

		// MARK: - Call-ins for ScanProducer.

		void set_scan_target(Outputs::Display::ScanTarget *scan_target) {
			outputter_.crt.set_scan_target(scan_target);
		}

		Outputs::Display::ScanStatus get_scaled_scan_status() const {
			return outputter_.crt.get_scaled_scan_status() * 9.0f / 14.0f;
		}

	private:
		struct CRTCOutputter {
			CRTCOutputter() :
				crt(882, 9, 382, 3, Outputs::Display::InputDataType::Red2Green2Blue2)
				// TODO: really this should be a Luminance8 and set an appropriate modal tint colour;
				// consider whether that's worth building into the scan target.
			{
//				crt.set_visible_area(Outputs::Display::Rect(0.1072f, 0.1f, 0.842105263157895f, 0.842105263157895f));
				crt.set_display_type(Outputs::Display::DisplayType::RGB);
			}

			void set_control(uint8_t control) {
				// b0: 'high resolution' (probably breaks if not 1)
				// b3: video enable
				// b5: enable blink
				control_ = control;
			}

			uint8_t control() {
				return control_;
			}

			void perform_bus_cycle_phase1(const Motorola::CRTC::BusState &state) {
				// Determine new output state.
				const OutputState new_state =
					(state.hsync | state.vsync) ? OutputState::Sync :
						((state.display_enable && control_&0x08) ? OutputState::Pixels : OutputState::Border);

				// Upon either a state change or just having accumulated too much local time...
				if(new_state != output_state || count > 882) {
					// (1) flush preexisting state.
					if(count) {
						switch(output_state) {
							case OutputState::Sync:		crt.output_sync(count);		break;
							case OutputState::Border: 	crt.output_blank(count);	break;
							case OutputState::Pixels:
								crt.output_data(count);
								pixels = pixel_pointer = nullptr;
							break;
						}
					}

					// (2) adopt new state.
					output_state = new_state;
					count = 0;
				}

				// Collect pixels if applicable.
				if(output_state == OutputState::Pixels) {
					if(!pixels) {
						pixel_pointer = pixels = crt.begin_data(DefaultAllocationSize);

						// Flush any period where pixels weren't recorded due to back pressure.
						if(pixels && count) {
							crt.output_blank(count);
							count = 0;
						}
					}

					if(pixels) {
						static constexpr uint8_t high_intensity = 0x0d;
						static constexpr uint8_t low_intensity = 0x09;
						static constexpr uint8_t off = 0x00;

						if(state.cursor) {
							pixel_pointer[0] =	pixel_pointer[1] =	pixel_pointer[2] =	pixel_pointer[3] =
							pixel_pointer[4] =	pixel_pointer[5] =	pixel_pointer[6] =	pixel_pointer[7] =
							pixel_pointer[8] =	low_intensity;
						} else {
							const uint8_t attributes = ram[((state.refresh_address << 1) + 1) & 0xfff];
							const uint8_t glyph = ram[((state.refresh_address << 1) + 0) & 0xfff];
							uint8_t row = font[(glyph * 14) + state.row_address];

							const uint8_t intensity = (attributes & 0x08) ? high_intensity : low_intensity;
							uint8_t blank = off;

							// Handle irregular attributes.
							// Cf. http://www.seasip.info/VintagePC/mda.html#memmap
							switch(attributes) {
								case 0x00:	case 0x08:	case 0x80:	case 0x88:
									row = 0;
								break;
								case 0x70:	case 0x78:	case 0xf0:	case 0xf8:
									row ^= 0xff;
									blank = intensity;
								break;
							}

							// Apply blink if enabled.
							if((control_ & 0x20) && (attributes & 0x80) && (state.field_count & 16)) {
								row ^= 0xff;
								blank = (blank == off) ? intensity : off;
							}

							if(((attributes & 7) == 1) && state.row_address == 13) {
								// Draw as underline.
								std::fill(pixel_pointer, pixel_pointer + 9, intensity);
							} else {
								// Draw according to ROM contents, possibly duplicating final column.
								pixel_pointer[0] = (row & 0x80) ? intensity : off;
								pixel_pointer[1] = (row & 0x40) ? intensity : off;
								pixel_pointer[2] = (row & 0x20) ? intensity : off;
								pixel_pointer[3] = (row & 0x10) ? intensity : off;
								pixel_pointer[4] = (row & 0x08) ? intensity : off;
								pixel_pointer[5] = (row & 0x04) ? intensity : off;
								pixel_pointer[6] = (row & 0x02) ? intensity : off;
								pixel_pointer[7] = (row & 0x01) ? intensity : off;
								pixel_pointer[8] = (glyph >= 0xc0 && glyph < 0xe0) ? pixel_pointer[7] : blank;
							}
						}
						pixel_pointer += 9;
					}
				}

				// Advance.
				count += 9;

				// Output pixel row prematurely if storage is exhausted.
				if(output_state == OutputState::Pixels && pixel_pointer == pixels + DefaultAllocationSize) {
					crt.output_data(count);
					count = 0;

					pixels = pixel_pointer = nullptr;
				}
			}
			void perform_bus_cycle_phase2(const Motorola::CRTC::BusState &) {}

			Outputs::CRT::CRT crt;

			enum class OutputState {
				Sync, Pixels, Border
			} output_state = OutputState::Sync;
			int count = 0;

			uint8_t *pixels = nullptr;
			uint8_t *pixel_pointer = nullptr;
			static constexpr size_t DefaultAllocationSize = 720;

			const uint8_t *ram = nullptr;
			std::vector<uint8_t> font;

			uint8_t control_ = 0;
		} outputter_;
		Motorola::CRTC::CRTC6845<CRTCOutputter, Motorola::CRTC::CursorType::MDA> crtc_;

		int full_clock_;
};

struct PCSpeaker {
	PCSpeaker() :
		toggle(queue),
		speaker(toggle) {}

	void update() {
		speaker.run_for(queue, cycles_since_update);
		cycles_since_update = 0;
	}

	void set_pit(bool pit_input) {
		pit_input_ = pit_input;
		set_level();
	}

	void set_control(bool pit_mask, bool level) {
		pit_mask_ = pit_mask;
		level_ = level;
		set_level();
	}

	void set_level() {
		// TODO: I think pit_mask_ actually acts as the gate input to the PIT.
		const bool new_output = (!pit_mask_ | pit_input_) & level_;

		if(new_output != output_) {
			update();
			toggle.set_output(new_output);
			output_ = new_output;
		}
	}

	Concurrency::AsyncTaskQueue<false> queue;
	Audio::Toggle toggle;
	Outputs::Speaker::PullLowpass<Audio::Toggle> speaker;
	Cycles cycles_since_update = 0;

	bool pit_input_ = false;
	bool pit_mask_ = false;
	bool level_ = false;
	bool output_ = false;
};

class PITObserver {
	public:
		PITObserver(PIC &pic, PCSpeaker &speaker) : pic_(pic), speaker_(speaker) {}

		template <int channel>
		void update_output(bool new_level) {
			switch(channel) {
				default: break;
				case 0: pic_.apply_edge<0>(new_level);	break;
				case 2: speaker_.set_pit(new_level);	break;
			}
		}

	private:
		PIC &pic_;
		PCSpeaker &speaker_;

	// TODO:
	//
	//	channel 0 is connected to IRQ 0;
	//	channel 1 is used for DRAM refresh (presumably connected to DMA?);
	//	channel 2 is gated by a PPI output and feeds into the speaker.
};
using PIT = i8253<false, PITObserver>;

class i8255PortHandler : public Intel::i8255::PortHandler {
	// Likely to be helpful: https://github.com/tmk/tmk_keyboard/wiki/IBM-PC-XT-Keyboard-Protocol
	public:
		i8255PortHandler(PCSpeaker &speaker, KeyboardController &keyboard) :
			speaker_(speaker), keyboard_(keyboard) {}

		void set_value(int port, uint8_t value) {
			switch(port) {
				case 1:
					// b7: 0 => enable keyboard read (and IRQ); 1 => don't;
					// b6: 0 => hold keyboard clock low; 1 => don't;
					// b5: 1 => disable IO check; 0 => don't;
					// b4: 1 => disable memory parity check; 0 => don't;
					// b3: [5150] cassette motor control; [5160] high or low switches select;
					// b2: [5150] high or low switches select; [5160] 1 => disable turbo mode;
					// b1, b0: speaker control.
					enable_keyboard_ = !(value & 0x80);
					keyboard_.set_mode(value >> 6);

					high_switches_ = value & 0x08;
					speaker_.set_control(value & 0x01, value & 0x02);
				break;
			}
//			printf("PPI: %02x to %d\n", value, port);
		}

		uint8_t get_value(int port) {
			switch(port) {
				case 0:
//					printf("PPI: from keyboard\n");
					return enable_keyboard_ ? keyboard_.read() : 0b0011'1101;
						// Guesses that switches is high and low combined as below.

				case 2:
					// Common:
					//
					// b7: 1 => memory parity error; 0 => none;
					// b6: 1 => IO channel error; 0 => none;
					// b5: timer 2 output;	[TODO]
					// b4: cassette data input; [TODO]
					return
						high_switches_ ?
							// b3, b2: drive count; 00 = 1, 01 = 2, etc
							// b1, b0: video mode (00 = ROM; 01 = CGA40; 10 = CGA80; 11 = MDA)
							0b0000'0011
						:
							// b3, b2: RAM on motherboard (64 * bit pattern)
							// b1: 1 => FPU present; 0 => absent;
							// b0: 1 => floppy drive present; 0 => absent.
							0b0000'1101;
			}
			return 0;
		};

	private:
		bool high_switches_ = false;
		PCSpeaker &speaker_;
		KeyboardController &keyboard_;

		bool enable_keyboard_ = false;
};
using PPI = Intel::i8255::i8255<i8255PortHandler>;

class IO {
	public:
		IO(PIT &pit, DMA &dma, PPI &ppi, PIC &pic, MDA &mda, FloppyController &fdc) :
			pit_(pit), dma_(dma), ppi_(ppi), pic_(pic), mda_(mda), fdc_(fdc) {}

		template <typename IntT> void out(uint16_t port, IntT value) {
			switch(port) {
				default:
					if constexpr (std::is_same_v<IntT, uint8_t>) {
						printf("Unhandled out: %02x to %04x\n", value, port);
					} else {
						printf("Unhandled out: %04x to %04x\n", value, port);
					}
				break;

				// On the XT the NMI can be masked by setting bit 7 on I/O port 0xA0.
				case 0x00a0:
					printf("TODO: NMIs %s\n", (value & 0x80) ? "masked" : "unmasked");
				break;

				case 0x0000:	dma_.controller.write<0>(uint8_t(value));				break;
				case 0x0001:	dma_.controller.write<1>(uint8_t(value));				break;
				case 0x0002:	dma_.controller.write<2>(uint8_t(value));				break;
				case 0x0003:	dma_.controller.write<3>(uint8_t(value));				break;
				case 0x0004:	dma_.controller.write<4>(uint8_t(value));				break;
				case 0x0005:	dma_.controller.write<5>(uint8_t(value));				break;
				case 0x0006:	dma_.controller.write<6>(uint8_t(value));				break;
				case 0x0007:	dma_.controller.write<7>(uint8_t(value));				break;
				case 0x0008:	dma_.controller.set_command(uint8_t(value));			break;
				case 0x0009:	dma_.controller.set_reset_request(uint8_t(value));		break;
				case 0x000a:	dma_.controller.set_reset_mask(uint8_t(value));			break;
				case 0x000b:	dma_.controller.set_mode(uint8_t(value));				break;
				case 0x000c:	dma_.controller.flip_flop_reset();						break;
				case 0x000d:	dma_.controller.master_reset();							break;
				case 0x000e:	dma_.controller.mask_reset();							break;
				case 0x000f:	dma_.controller.set_mask(uint8_t(value));				break;

				case 0x0020:	pic_.write<0>(uint8_t(value));	break;
				case 0x0021:	pic_.write<1>(uint8_t(value));	break;

				case 0x0040:	pit_.write<0>(uint8_t(value));	break;
				case 0x0041:	pit_.write<1>(uint8_t(value));	break;
				case 0x0042:	pit_.write<2>(uint8_t(value));	break;
				case 0x0043:	pit_.set_mode(uint8_t(value));	break;

				case 0x0060:	case 0x0061:	case 0x0062:	case 0x0063:
				case 0x0064:	case 0x0065:	case 0x0066:	case 0x0067:
				case 0x0068:	case 0x0069:	case 0x006a:	case 0x006b:
				case 0x006c:	case 0x006d:	case 0x006e:	case 0x006f:
					ppi_.write(port, uint8_t(value));
				break;

				case 0x0080:	dma_.pages.set_page<0>(uint8_t(value));	break;
				case 0x0081:	dma_.pages.set_page<1>(uint8_t(value));	break;
				case 0x0082:	dma_.pages.set_page<2>(uint8_t(value));	break;
				case 0x0083:	dma_.pages.set_page<3>(uint8_t(value));	break;
				case 0x0084:	dma_.pages.set_page<4>(uint8_t(value));	break;
				case 0x0085:	dma_.pages.set_page<5>(uint8_t(value));	break;
				case 0x0086:	dma_.pages.set_page<6>(uint8_t(value));	break;
				case 0x0087:	dma_.pages.set_page<7>(uint8_t(value));	break;

				case 0x03b0:	case 0x03b2:	case 0x03b4:	case 0x03b6:
					if constexpr (std::is_same_v<IntT, uint16_t>) {
						mda_.write<0>(uint8_t(value));
						mda_.write<1>(uint8_t(value >> 8));
					} else {
						mda_.write<0>(value);
					}
				break;

				case 0x03b1:	case 0x03b3:	case 0x03b5:	case 0x03b7:
					if constexpr (std::is_same_v<IntT, uint16_t>) {
						mda_.write<1>(uint8_t(value));
						mda_.write<0>(uint8_t(value >> 8));
					} else {
						mda_.write<1>(value);
					}
				break;

				case 0x03b8:
					mda_.write<8>(uint8_t(value));
				break;

				case 0x03d0:	case 0x03d1:	case 0x03d2:	case 0x03d3:
				case 0x03d4:	case 0x03d5:	case 0x03d6:	case 0x03d7:
				case 0x03d8:	case 0x03d9:	case 0x03da:	case 0x03db:
				case 0x03dc:	case 0x03dd:	case 0x03de:	case 0x03df:
					// Ignore CGA accesses.
				break;

				case 0x03f2:
					fdc_.set_digital_output(uint8_t(value));
				break;
				case 0x03f4:
					printf("TODO: FDC write of %02x at %04x\n", value, port);
				break;
				case 0x03f5:
					fdc_.write(uint8_t(value));
				break;

				case 0x0278:	case 0x0279:	case 0x027a:
				case 0x0378:	case 0x0379:	case 0x037a:
				case 0x03bc:	case 0x03bd:	case 0x03be:
					// Ignore parallel port accesses.
				break;

				case 0x02e8:	case 0x02e9:	case 0x02ea:	case 0x02eb:
				case 0x02ec:	case 0x02ed:	case 0x02ee:	case 0x02ef:
				case 0x02f8:	case 0x02f9:	case 0x02fa:	case 0x02fb:
				case 0x02fc:	case 0x02fd:	case 0x02fe:	case 0x02ff:
				case 0x03e8:	case 0x03e9:	case 0x03ea:	case 0x03eb:
				case 0x03ec:	case 0x03ed:	case 0x03ee:	case 0x03ef:
				case 0x03f8:	case 0x03f9:	case 0x03fa:	case 0x03fb:
				case 0x03fc:	case 0x03fd:	case 0x03fe:	case 0x03ff:
					// Ignore serial port accesses.
				break;
			}
		}
		template <typename IntT> IntT in([[maybe_unused]] uint16_t port) {
			switch(port) {
				default:
					printf("Unhandled in: %04x\n", port);
				break;

				case 0x0000:	return dma_.controller.template read<0>();
				case 0x0001:	return dma_.controller.template read<1>();
				case 0x0002:	return dma_.controller.template read<2>();
				case 0x0003:	return dma_.controller.template read<3>();
				case 0x0004:	return dma_.controller.template read<4>();
				case 0x0005:	return dma_.controller.template read<5>();
				case 0x0006:	return dma_.controller.template read<6>();
				case 0x0007:	return dma_.controller.template read<7>();

				case 0x0008:	return dma_.controller.status();

				case 0x0009:
				case 0x000a:	case 0x000b:
				case 0x000c:	case 0x000f:
					printf("TODO: DMA read from %04x\n", port);
				break;

				case 0x0020:	return pic_.read<0>();
				case 0x0021:	return pic_.read<1>();

				case 0x0040:	return pit_.read<0>();
				case 0x0041:	return pit_.read<1>();
				case 0x0042:	return pit_.read<2>();

				case 0x0060:	case 0x0061:	case 0x0062:	case 0x0063:
				case 0x0064:	case 0x0065:	case 0x0066:	case 0x0067:
				case 0x0068:	case 0x0069:	case 0x006a:	case 0x006b:
				case 0x006c:	case 0x006d:	case 0x006e:	case 0x006f:
				return ppi_.read(port);

				case 0x0080:	return dma_.pages.page<0>();
				case 0x0081:	return dma_.pages.page<1>();
				case 0x0082:	return dma_.pages.page<2>();
				case 0x0083:	return dma_.pages.page<3>();
				case 0x0084:	return dma_.pages.page<4>();
				case 0x0085:	return dma_.pages.page<5>();
				case 0x0086:	return dma_.pages.page<6>();
				case 0x0087:	return dma_.pages.page<7>();

				case 0x0201:	break;		// Ignore game port.

				case 0x0278:	case 0x0279:	case 0x027a:
				case 0x0378:	case 0x0379:	case 0x037a:
				case 0x03bc:	case 0x03bd:	case 0x03be:
					// Ignore parallel port accesses.
				break;

				case 0x03f4:	return fdc_.status();
				case 0x03f5:	return fdc_.read();

				case 0x03b8:	return mda_.read<8>();

				case 0x02e8:	case 0x02e9:	case 0x02ea:	case 0x02eb:
				case 0x02ec:	case 0x02ed:	case 0x02ee:	case 0x02ef:
				case 0x02f8:	case 0x02f9:	case 0x02fa:	case 0x02fb:
				case 0x02fc:	case 0x02fd:	case 0x02fe:	case 0x02ff:
				case 0x03e8:	case 0x03e9:	case 0x03ea:	case 0x03eb:
				case 0x03ec:	case 0x03ed:	case 0x03ee:	case 0x03ef:
				case 0x03f8:	case 0x03f9:	case 0x03fa:	case 0x03fb:
				case 0x03fc:	case 0x03fd:	case 0x03fe:	case 0x03ff:
					// Ignore serial port accesses.
				break;
			}
			return IntT(~0);
		}

	private:
		PIT &pit_;
		DMA &dma_;
		PPI &ppi_;
		PIC &pic_;
		MDA &mda_;
		FloppyController &fdc_;
};

class FlowController {
	public:
		FlowController(Registers &registers, Segments &segments) :
			registers_(registers), segments_(segments) {}

		// Requirements for perform.
		void jump(uint16_t address) {
			registers_.ip() = address;
		}

		void jump(uint16_t segment, uint16_t address) {
			registers_.cs() = segment;
			segments_.did_update(Segments::Source::CS);
			registers_.ip() = address;
		}

		void halt() {
			halted_ = true;
		}
		void wait() {
			printf("WAIT ????\n");
		}

		void repeat_last() {
			should_repeat_ = true;
		}

		// Other actions.
		void begin_instruction() {
			should_repeat_ = false;
		}
		bool should_repeat() const {
			return should_repeat_;
		}

		void unhalt() {
			halted_ = false;
		}
		bool halted() const {
			return halted_;
		}

	private:
		Registers &registers_;
		Segments &segments_;
		bool should_repeat_ = false;
		bool halted_ = false;
};

class ConcreteMachine:
	public Machine,
	public MachineTypes::TimedMachine,
	public MachineTypes::AudioProducer,
	public MachineTypes::MappedKeyboardMachine,
	public MachineTypes::MediaTarget,
	public MachineTypes::ScanProducer,
	public Activity::Source
{
	public:
		ConcreteMachine(
			[[maybe_unused]] const Analyser::Static::Target &target,
			const ROMMachine::ROMFetcher &rom_fetcher
		) :
			keyboard_(pic_),
			fdc_(pic_, dma_),
			pit_observer_(pic_, speaker_),
			ppi_handler_(speaker_, keyboard_),
			pit_(pit_observer_),
			ppi_(ppi_handler_),
			context(pit_, dma_, ppi_, pic_, mda_, fdc_)
		{
			// Set up DMA source/target.
			dma_.set_memory(&context.memory);

			// Use clock rate as a MIPS count; keeping it as a multiple or divisor of the PIT frequency is easy.
			static constexpr int pit_frequency = 1'193'182;
			set_clock_rate(double(pit_frequency));
			speaker_.speaker.set_input_rate(double(pit_frequency));

			// Fetch the BIOS. [8088 only, for now]
			const auto bios = ROM::Name::PCCompatibleGLaBIOS;
			const auto font = ROM::Name::PCCompatibleMDAFont;

			ROM::Request request = ROM::Request(bios) && ROM::Request(font);
			auto roms = rom_fetcher(request);
			if(!request.validate(roms)) {
				throw ROMMachine::Error::MissingROMs;
			}

			const auto &bios_contents = roms.find(bios)->second;
			context.memory.install(0x10'0000 - bios_contents.size(), bios_contents.data(), bios_contents.size());

			// Give the MDA something to read from.
			const auto &font_contents = roms.find(font)->second;
			mda_.set_source(context.memory.at(0xb'0000), font_contents);

			// ... and insert media.
			insert_media(target.media);
		}

		~ConcreteMachine() {
			speaker_.queue.flush();
		}

		// MARK: - TimedMachine.
		void run_for(const Cycles duration) override {
			const auto pit_ticks = duration.as_integral();
			cpu_divisor_ += pit_ticks;
			int ticks = cpu_divisor_ / 3;
			cpu_divisor_ %= 3;

			while(ticks--) {
				//
				// First draft: all hardware runs in lockstep, as a multiple or divisor of the PIT frequency.
				//

				//
				// Advance the PIT and audio.
				//
				pit_.run_for(1);
				++speaker_.cycles_since_update;
				pit_.run_for(1);
				++speaker_.cycles_since_update;
				pit_.run_for(1);
				++speaker_.cycles_since_update;

				//
				// Advance CRTC at a more approximate rate.
				//
				mda_.run_for(Cycles(3));

				//
				// Perform one CPU instruction every three PIT cycles.
				// i.e. CPU instruction rate is 1/3 * ~1.19Mhz ~= 0.4 MIPS.
				//

				keyboard_.run_for(Cycles(1));

				// Query for interrupts and apply if pending.
				if(pic_.pending() && context.flags.flag<InstructionSet::x86::Flag::Interrupt>()) {
					// Regress the IP if a REP is in-progress so as to resume it later.
					if(context.flow_controller.should_repeat()) {
						context.registers.ip() = decoded_ip_;
						context.flow_controller.begin_instruction();
					}

					// Signal interrupt.
					context.flow_controller.unhalt();
					InstructionSet::x86::interrupt(
						pic_.acknowledge(),
						context
					);
				}

				// Do nothing if halted.
				if(context.flow_controller.halted()) {
					continue;
				}

				// Get the next thing to execute.
				if(!context.flow_controller.should_repeat()) {
					// Decode from the current IP.
					decoded_ip_ = context.registers.ip();
					const auto remainder = context.memory.next_code();
					decoded = decoder.decode(remainder.first, remainder.second);

					// If that didn't yield a whole instruction then the end of memory must have been hit;
					// continue from the beginning.
					if(decoded.first <= 0) {
						const auto all = context.memory.all();
						decoded = decoder.decode(all.first, all.second);
					}

					context.registers.ip() += decoded.first;
				} else {
					context.flow_controller.begin_instruction();
				}

/*				if(decoded_ip_ >= 0x7c00 && decoded_ip_ < 0x7c00 + 1024) {
					const auto next = to_string(decoded, InstructionSet::x86::Model::i8086);
//					if(next != previous) {
						std::cout << std::hex << decoded_ip_ << " " << next;

						if(decoded.second.operation() == InstructionSet::x86::Operation::INT) {
							std::cout << " dl:" << std::hex << +context.registers.dl() << "; ";
							std::cout << "ah:" << std::hex << +context.registers.ah() << "; ";
							std::cout << "ch:" << std::hex << +context.registers.ch() << "; ";
							std::cout << "cl:" << std::hex << +context.registers.cl() << "; ";
							std::cout << "dh:" << std::hex << +context.registers.dh() << "; ";
							std::cout << "es:" << std::hex << +context.registers.es() << "; ";
							std::cout << "bx:" << std::hex << +context.registers.bx();
						}

						std::cout << std::endl;
//						previous = next;
//					}
				}*/

				// Execute it.
				InstructionSet::x86::perform(
					decoded.second,
					context
				);
			}
		}

		// MARK: - ScanProducer.
		void set_scan_target(Outputs::Display::ScanTarget *scan_target) override {
			mda_.set_scan_target(scan_target);
		}
		Outputs::Display::ScanStatus get_scaled_scan_status() const override {
			return mda_.get_scaled_scan_status();
		}

		// MARK: - AudioProducer.
		Outputs::Speaker::Speaker *get_speaker() override {
			return &speaker_.speaker;
		}

		void flush_output(int outputs) final {
			if(outputs & Output::Audio) {
				speaker_.update();
				speaker_.queue.perform();
			}
		}

		// MARK: - MediaTarget
		bool insert_media(const Analyser::Static::Media &media) override {
			int c = 0;
			for(auto &disk : media.disks) {
				fdc_.set_disk(disk, c);
				c++;
				if(c == 4) break;
			}
			return true;
		}

		// MARK: - MappedKeyboardMachine.
		MappedKeyboardMachine::KeyboardMapper *get_keyboard_mapper() override {
			return &keyboard_mapper_;
		}

		void set_key_state(uint16_t key, bool is_pressed) override {
			keyboard_.post(uint8_t(key | (is_pressed ? 0x00 : 0x80)));
		}

		// MARK: - Activity::Source.
		void set_activity_observer(Activity::Observer *observer) final {
			fdc_.set_activity_observer(observer);
		}

	private:
		PIC pic_;
		DMA dma_;
		PCSpeaker speaker_;
		MDA mda_;

		KeyboardController keyboard_;
		FloppyController fdc_;
		PITObserver pit_observer_;
		i8255PortHandler ppi_handler_;

		PIT pit_;
		PPI ppi_;

		PCCompatible::KeyboardMapper keyboard_mapper_;

		struct Context {
			Context(PIT &pit, DMA &dma, PPI &ppi, PIC &pic, MDA &mda, FloppyController &fdc) :
				segments(registers),
				memory(registers, segments),
				flow_controller(registers, segments),
				io(pit, dma, ppi, pic, mda, fdc)
			{
				reset();
			}

			void reset() {
				registers.reset();
				segments.reset();
			}

			InstructionSet::x86::Flags flags;
			Registers registers;
			Segments segments;
			Memory memory;
			FlowController flow_controller;
			IO io;
			static constexpr auto model = InstructionSet::x86::Model::i8086;
		} context;

		// TODO: eliminate use of Decoder8086 and Decoder8086 in gneral in favour of the templated version, as soon
		// as whatever error is preventing GCC from picking up Decoder's explicit instantiations becomes apparent.
		InstructionSet::x86::Decoder8086 decoder;
//		InstructionSet::x86::Decoder<InstructionSet::x86::Model::i8086> decoder;

		uint16_t decoded_ip_ = 0;
		std::pair<int, InstructionSet::x86::Instruction<false>> decoded;

		int cpu_divisor_ = 0;
};


}

using namespace PCCompatible;

// See header; constructs and returns an instance of the Amstrad CPC.
Machine *Machine::PCCompatible(const Analyser::Static::Target *target, const ROMMachine::ROMFetcher &rom_fetcher) {
	return new PCCompatible::ConcreteMachine(*target, rom_fetcher);
}

Machine::~Machine() {}