CLK/Machines/Amiga/Chipset.cpp

//
//  Chipset.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 22/07/2021.
//  Copyright © 2021 Thomas Harte. All rights reserved.
//

#include "Chipset.hpp"

//#define NDEBUG
#define LOG_PREFIX "[Amiga chipset] "
#include "../../Outputs/Log.hpp"

#include <algorithm>
#include <cassert>

using namespace Amiga;

namespace {

template <typename EnumT, EnumT... T> struct Mask {
	static constexpr uint16_t value = 0;
};

template <typename EnumT, EnumT F, EnumT... T> struct Mask<EnumT, F, T...> {
	static constexpr uint16_t value = uint16_t(F) | Mask<EnumT, T...>::value;
};

template <InterruptFlag... Flags> struct InterruptMask: Mask<InterruptFlag, Flags...> {};
template <DMAFlag... Flags> struct DMAMask: Mask<DMAFlag, Flags...> {};

}

Chipset::Chipset(MemoryMap &map, int input_clock_rate) :
	blitter_(*this, reinterpret_cast<uint16_t *>(map.chip_ram.data()), map.chip_ram.size() >> 1),
	bitplanes_(*this, reinterpret_cast<uint16_t *>(map.chip_ram.data()), map.chip_ram.size() >> 1),
	copper_(*this, reinterpret_cast<uint16_t *>(map.chip_ram.data()), map.chip_ram.size() >> 1),
	disk_controller_(Cycles(input_clock_rate)),
	disk_(*this, reinterpret_cast<uint16_t *>(map.chip_ram.data()), map.chip_ram.size() >> 1),
	crt_(908, 4, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red4Green4Blue4),
	cia_a_handler_(map, disk_controller_),
	cia_b_handler_(disk_controller_),
	cia_a(cia_a_handler_),
	cia_b(cia_b_handler_) {
}

Chipset::Changes Chipset::run_for(HalfCycles length) {
	return run<false>(length);
}

Chipset::Changes Chipset::run_until_cpu_slot() {
	return run<true>();
}

void Chipset::set_cia_interrupts(bool cia_a_interrupt, bool cia_b_interrupt) {
	// TODO: are these really latched, or are they active live?
	interrupt_requests_ &= ~InterruptMask<InterruptFlag::IOPortsAndTimers, InterruptFlag::External>::value;
	interrupt_requests_ |=
		(cia_a_interrupt ? InterruptMask<InterruptFlag::IOPortsAndTimers>::value : 0) |
		(cia_b_interrupt ? InterruptMask<InterruptFlag::External>::value : 0);
	update_interrupts();
}

void Chipset::posit_interrupt(InterruptFlag flag) {
	interrupt_requests_ |= uint16_t(flag);
	update_interrupts();
}

template <int cycle> void Chipset::output() {
	// Notes to self on guesses below:
	//
	// Hardware stop is at 0x18;
	// 12/64 * 227 = 42.5625
	//
	// "However, horizontal blanking actually limits the displayable
	// video to 368 low resolution pixel"
	//
	// => 184 windows out of 227 are visible, which concurs.
	//

	// A complete from-thin-air guess:
	//
	//	7 cycles blank;
	//	17 cycles sync;
	//	3 cycles blank;
	//	9 cycles colour burst;
	//	7 cycles blank.
	constexpr int blank1	= 7;
	constexpr int sync		= 17 + blank1;
	constexpr int blank2 	= 3 + sync;
	constexpr int burst 	= 9 + blank2;
	constexpr int blank3 	= 7 + burst;
	static_assert(blank3 == 43);

#define LINK(location, action, length)	\
	if(cycle == (location))	{			\
		crt_.action((length) * 4);		\
	}

	if(y_ < vertical_blank_height_) {
		// Put three lines of sync at the centre of the vertical blank period.
		// Offset by half a line if interlaced and on an odd frame.

		const int midline = vertical_blank_height_ >> 1;
		if(frame_height_ & 1) {
			if(y_ < midline - 1 || y_ > midline + 2) {
				LINK(blank1, output_blank, blank1);
				LINK(sync, output_sync, sync - blank1);
				LINK(line_length_ - 1, output_blank, line_length_ - 1 - sync);
			} else if(y_ == midline - 1) {
				LINK(113, output_blank, 113);
				LINK(line_length_ - 1, output_sync, line_length_ - 1 - 113);
			} else if(y_ == midline + 2) {
				LINK(113, output_sync, 113);
				LINK(line_length_ - 1, output_blank, line_length_ - 1 - 113);
			} else {
				LINK(blank1, output_sync, blank1);
				LINK(sync, output_blank, sync - blank1);
				LINK(line_length_ - 1, output_sync, line_length_ - 1 - sync);
			}
		} else {
			if(y_ < midline - 1 || y_ > midline + 1) {
				LINK(blank1, output_blank, blank1);
				LINK(sync, output_sync, sync - blank1);
				LINK(line_length_ - 1, output_blank, line_length_ - 1 - sync);
			} else {
				LINK(blank1, output_sync, blank1);
				LINK(sync, output_blank, sync - blank1);
				LINK(line_length_ - 1, output_sync, line_length_ - 1 - sync);
			}
		}
	} else {
		// Output the correct sequence of blanks, syncs and burst atomically.
		LINK(blank1, output_blank, blank1);
		LINK(sync, output_sync, sync - blank1);
		LINK(blank2, output_blank, blank2 - sync);
		LINK(burst, output_default_colour_burst, burst - blank2);	// TODO: only if colour enabled.
		LINK(blank3, output_blank, blank3 - burst);

		// TODO: these shouldn't be functions of the fetch window,
		// but of the display window.
		display_horizontal_ |= (cycle << 1) == fetch_window_[0];
		display_horizontal_ &= (cycle << 1) != fetch_window_[1];

		if constexpr (cycle > blank3) {
			const bool is_pixel_display = display_horizontal_ && fetch_vertical_;

			if(
				(is_pixel_display == is_border_) ||
				(is_border_ && border_colour_ != palette_[0])) {
				flush_output();

				is_border_ = !is_pixel_display;
				border_colour_ = palette_[0];
			}

			if(is_pixel_display) {
				if(!pixels_) {
					uint16_t *const new_pixels = reinterpret_cast<uint16_t *>(crt_.begin_data(4 * size_t(line_length_ - cycle)));
					if(new_pixels) {
						flush_output();
					}
					pixels_ = new_pixels;
				}

				if(pixels_) {
					// TODO: this is obviously nonsense. Probably do a table-based
					// planar-to-chunky up front into 8-bit pockets, and just shift that.

					pixels_[0] = palette_[
						((current_bitplanes_[0]&0x8000) >> 15) |
						((current_bitplanes_[1]&0x8000) >> 14) |
						((current_bitplanes_[2]&0x8000) >> 13) |
						((current_bitplanes_[3]&0x8000) >> 12) |
						((current_bitplanes_[4]&0x8000) >> 11)
					];
					current_bitplanes_ <<= is_high_res_;

					pixels_[1] = palette_[
						((current_bitplanes_[0]&0x8000) >> 15) |
						((current_bitplanes_[1]&0x8000) >> 14) |
						((current_bitplanes_[2]&0x8000) >> 13) |
						((current_bitplanes_[3]&0x8000) >> 12) |
						((current_bitplanes_[4]&0x8000) >> 11)
					];
					current_bitplanes_ <<= 1;

					pixels_[2] = palette_[
						((current_bitplanes_[0]&0x8000) >> 15) |
						((current_bitplanes_[1]&0x8000) >> 14) |
						((current_bitplanes_[2]&0x8000) >> 13) |
						((current_bitplanes_[3]&0x8000) >> 12) |
						((current_bitplanes_[4]&0x8000) >> 11)
					];
					current_bitplanes_ <<= is_high_res_;

					pixels_[3] = palette_[
						((current_bitplanes_[0]&0x8000) >> 15) |
						((current_bitplanes_[1]&0x8000) >> 14) |
						((current_bitplanes_[2]&0x8000) >> 13) |
						((current_bitplanes_[3]&0x8000) >> 12) |
						((current_bitplanes_[4]&0x8000) >> 11)
					];
					current_bitplanes_ <<= 1;

					pixels_ += 4;
				}
			}
			++zone_duration_;

			// Output the rest of the line. TODO: optimise border area.
			if(cycle == line_length_ - 1) {
				flush_output();
			}
		}
	}

#undef LINK
}

void Chipset::flush_output() {
	if(!zone_duration_) return;

	if(is_border_) {
		uint16_t *const pixels = reinterpret_cast<uint16_t *>(crt_.begin_data(1));
		if(pixels) {
			*pixels = border_colour_;
		}
		crt_.output_data(zone_duration_ * 4, 1);
	} else {
		crt_.output_data(zone_duration_ * 4);
	}
	zone_duration_ = 0;
	pixels_ = nullptr;
}

/// @returns @c true if this was a CPU slot; @c false otherwise.
template <int cycle, bool stop_if_cpu> bool Chipset::perform_cycle() {
	constexpr auto BlitterFlag	= DMAMask<DMAFlag::Blitter, DMAFlag::AllBelow>::value;
	constexpr auto BitplaneFlag	= DMAMask<DMAFlag::Bitplane, DMAFlag::AllBelow>::value;
	constexpr auto CopperFlag	= DMAMask<DMAFlag::Copper, DMAFlag::AllBelow>::value;
	constexpr auto DiskFlag		= DMAMask<DMAFlag::Disk, DMAFlag::AllBelow>::value;

	// Update state as to whether bitplane fetching should happen now.
	//
	// TODO: figure out how the hard stops factor into this.
	//
	// TODO: eliminate hard-coded 320 below. There's clearly something
	// (well, probably many things) I don't yet understand about the
	// fetch window.
	fetch_horizontal_ |= (cycle << 1) == fetch_window_[0];
	fetch_horizontal_ &= (cycle << 1) != (fetch_window_[0] + 320);
//	fetch_horizontal_ &= (cycle << 1) != fetch_window_[1];
	//fetch_window_[1];

	// Top priority: bitplane collection.
	if((dma_control_ & BitplaneFlag) == BitplaneFlag) {
		// TODO: offer a cycle for bitplane collection.
		// Probably need to indicate odd or even?
		if(fetch_horizontal_ && fetch_vertical_ && bitplanes_.advance(cycle - (fetch_window_[0] >> 1))) {	// TODO: cycle should be relative to start of collection.
			did_fetch_ = true;
			return false;
		}
	}

	if constexpr (cycle & 1) {
		// Odd slot use/priority:
		//
		//	1. Bitplane fetches [dealt with above].
		//	2. Refresh, disk, audio, or sprites. Depending on region.
		//
		// Blitter and CPU priority is dealt with below.
		if constexpr (cycle >= 4 && cycle <= 6) {
			if((dma_control_ & DiskFlag) == DiskFlag) {
				if(disk_.advance()) {
					return false;
				}
			}
		}
	} else {
		// Bitplanes being dealt with, specific odd-cycle responsibility
		// is just possibly to pass to the Copper.
		//
		// The Blitter and CPU are dealt with outside of the odd/even test.
		if((dma_control_ & CopperFlag) == CopperFlag) {
			if(copper_.advance(uint16_t(((y_ & 0xff) << 8) | (cycle & 0xfe)))) {
				return false;
			}
		} else {
			copper_.stop();
		}
	}

	// Down here: give first refusal to the Blitter, otherwise
	// pass on to the CPU.
	return (dma_control_ & BlitterFlag) != BlitterFlag || !blitter_.advance();
}

/// Performs all slots starting with @c first_slot and ending just before @c last_slot.
/// If @c stop_on_cpu is true, stops upon discovery of a CPU slot.
///
/// @returns the number of slots completed if @c stop_on_cpu was true and a CPU slot was found.
///			@c -1 otherwise.
template <bool stop_on_cpu> int Chipset::advance_slots(int first_slot, int last_slot) {
	if(first_slot == last_slot) {
		return -1;
	}

#define C(x) \
	case x: \
		if constexpr(stop_on_cpu) {\
			if(perform_cycle<x, stop_on_cpu>()) {\
				return x - first_slot;\
			}\
		} else {\
			perform_cycle<x, stop_on_cpu>(); \
		} \
		output<x>();	\
		if((x + 1) == last_slot) break;	\
		[[fallthrough]]

#define C10(x)	C(x); C(x+1); C(x+2); C(x+3); C(x+4); C(x+5); C(x+6); C(x+7); C(x+8); C(x+9);
	switch(first_slot) {
		C10(0);		C10(10);	C10(20);	C10(30);	C10(40);
		C10(50);	C10(60);	C10(70);	C10(80);	C10(90);
		C10(100);	C10(110);	C10(120);	C10(130);	C10(140);
		C10(150);	C10(160);	C10(170);	C10(180);	C10(190);
		C10(200);	C10(210);
		C(220);		C(221);		C(222);		C(223);		C(224);
		C(225);		C(226);		C(227);		C(228);
//		break;

		default: assert(false);
	}
#undef C

	return -1;
}

template <bool stop_on_cpu> Chipset::Changes Chipset::run(HalfCycles length) {
	Changes changes;

	// This code uses 'pixels' as a measure, which is equivalent to one pixel clock time,
	// or half a cycle.
	auto pixels_remaining = length.as<int>();
	int hsyncs = 0, vsyncs = 0;

	// Update raster position, spooling out graphics.
	while(pixels_remaining) {
		// Determine number of pixels left on this line.
		const int line_pixels = std::min(pixels_remaining, (line_length_ * 4) - line_cycle_);

		const int start_slot = line_cycle_ >> 2;
		const int end_slot = (line_cycle_ + line_pixels) >> 2;
		const int actual_slots = advance_slots<stop_on_cpu>(start_slot, end_slot);

		if(stop_on_cpu && actual_slots >= 0) {
			// Run until the end of the named slot.
			if(actual_slots) {
				const int actual_line_pixels =
					(4 - (line_cycle_ & 3)) + ((actual_slots - 1) << 2);
				line_cycle_ += actual_line_pixels;
				changes.duration += HalfCycles(actual_line_pixels);
			}

			// Just ensure an exit.
			pixels_remaining = 0;
		} else {
			line_cycle_ += line_pixels;
			changes.duration += HalfCycles(line_pixels);
			pixels_remaining -= line_pixels;
		}

		// Advance intraline counter and pcoossibly ripple upwards into
		// lines and fields.
		if(line_cycle_ == (line_length_ * 4)) {
			++hsyncs;

			line_cycle_ = 0;
			++y_;

			fetch_vertical_ |= y_ == display_window_start_[1];
			fetch_vertical_ &= y_ != display_window_stop_[1];

			if(did_fetch_) {
				// TODO: find out when modulos are actually applied, since
				// they're dynamically programmable.
				bitplanes_.do_end_of_line();
				did_fetch_ = false;
			}

			if(y_ == frame_height_) {
				++vsyncs;
				interrupt_requests_ |= InterruptMask<InterruptFlag::VerticalBlank>::value;
				update_interrupts();

				y_ = 0;

				// TODO: the manual is vague on when this happens. Try to find out.
				copper_.reload<0>();
			}
		}
		assert(line_cycle_ < line_length_ * 4);
	}

	// The CIAs are on the E clock.
	cia_divider_ += changes.duration;
	const HalfCycles e_clocks = cia_divider_.divide(HalfCycles(20));
	if(e_clocks > HalfCycles(0)) {
		cia_a.run_for(e_clocks);
		cia_b.run_for(e_clocks);
	}

	cia_a.advance_tod(vsyncs);
	cia_b.advance_tod(hsyncs);
	set_cia_interrupts(cia_a.get_interrupt_line(), cia_b.get_interrupt_line());

	changes.interrupt_level = interrupt_level_;
	return changes;
}

void Chipset::post_bitplanes(const BitplaneData &data) {
	// TODO: should probably store for potential delay?
	current_bitplanes_ = data;

//	current_bitplanes_[0] = 0xaaaa;
//	current_bitplanes_[1] = 0x3333;
//	current_bitplanes_[2] = 0x4444;
//	current_bitplanes_[3] = 0x1111;

	// Convert to future pixels.
//	const int odd_offset = line_cycle_ + odd_delay_;
//	const int even_offset = line_cycle_ + odd_delay_;
//	for(int x = 0; x < 16; x++) {
//		const uint16_t mask = uint16_t(1 << x);
//		even_playfield_[x + even_offset] = uint8_t(
//			((data[0] & mask) | ((data[2] & mask) << 1) | ((data[4] & mask) << 2)) >> x
//		);
//		odd_playfield_[x + odd_offset] = uint8_t(
//			((data[1] & mask) | ((data[3] & mask) << 1) | ((data[5] & mask) << 2)) >> x
//		);
//	}
}

void Chipset::update_interrupts() {
	interrupt_level_ = 0;

	const uint16_t enabled_requests = interrupt_enable_ & interrupt_requests_ & 0x3fff;
	if(enabled_requests && (interrupt_enable_ & 0x4000)) {
		if(enabled_requests & InterruptMask<InterruptFlag::External>::value) {
			interrupt_level_ = 6;
		} else if(enabled_requests & InterruptMask<InterruptFlag::SerialPortReceive, InterruptFlag::DiskSyncMatch>::value) {
			interrupt_level_ = 5;
		} else if(enabled_requests & InterruptMask<InterruptFlag::AudioChannel0, InterruptFlag::AudioChannel1, InterruptFlag::AudioChannel2, InterruptFlag::AudioChannel3>::value) {
			interrupt_level_ = 4;
		} else if(enabled_requests & InterruptMask<InterruptFlag::Copper, InterruptFlag::VerticalBlank, InterruptFlag::Blitter>::value) {
			interrupt_level_ = 3;
		} else if(enabled_requests & InterruptMask<InterruptFlag::IOPortsAndTimers>::value) {
			interrupt_level_ = 2;
		} else if(enabled_requests & InterruptMask<InterruptFlag::SerialPortTransmit, InterruptFlag::DiskBlock, InterruptFlag::Software>::value) {
			interrupt_level_ = 1;
		}
	}
}

void Chipset::perform(const CPU::MC68000::Microcycle &cycle) {
	using Microcycle = CPU::MC68000::Microcycle;

#define RW(address)		address | ((cycle.operation & Microcycle::Read) << 12)
#define Read(address)	address | (Microcycle::Read << 12)
#define Write(address)	address

#define ApplySetClear(target)	{			\
	const uint16_t value = cycle.value16();	\
	if(value & 0x8000) {					\
		target |= (value & 0x7fff);			\
	} else {								\
		target &= ~(value & 0x7fff);		\
	}										\
}

	const uint32_t register_address = *cycle.address & 0x1fe;
	switch(RW(register_address)) {
		default:
			LOG("Unimplemented chipset " << (cycle.operation & Microcycle::Read ? "read" : "write") <<  " " << PADHEX(6) << *cycle.address);
			assert(false);
		break;

		// Raster position.
		case Read(0x004): {
			const uint16_t position = uint16_t(y_ >> 8);
			LOG("Read vertical position high " << PADHEX(4) << position);
			cycle.set_value16(position);
		} break;
		case Read(0x006): {
//			const uint16_t position = uint16_t(((line_cycle_ << 6) & 0xff00) | (y_ & 0x00ff));
			const uint16_t position = 0xd1ef;	// TODO: !!!
			LOG("Read position low " << PADHEX(4) << position);
			cycle.set_value16(position);
		} break;

		case Write(0x02a):
			LOG("TODO: write vertical position high " << PADHEX(4) << cycle.value16());
		break;
		case Write(0x02c):
			LOG("TODO: write vertical position low " << PADHEX(4) << cycle.value16());
		break;

		// Joystick/mouse input.
		case Read(0x00a):
		case Read(0x00c):
			LOG("TODO: Joystick/mouse position " << PADHEX(4) << *cycle.address);
			cycle.set_value16(0x8080);
		break;

		case Write(0x034):
			LOG("TODO: pot port start");
		break;
		case Read(0x016):
			LOG("TODO: pot port read");
			cycle.set_value16(0xff00);
		break;

		// Disk DMA.
		case Write(0x020):	disk_.set_pointer<0, 16>(cycle.value16());	break;
		case Write(0x022):	disk_.set_pointer<0, 0>(cycle.value16());	break;
		case Write(0x024):	disk_.set_length(cycle.value16());			break;

		case Write(0x026):
			LOG("TODO: disk DMA; " << PADHEX(4) << cycle.value16() << " to " << *cycle.address);
		break;

		// Refresh.
		case Write(0x028):
			LOG("TODO (maybe): refresh; " << PADHEX(4) << cycle.value16() << " to " << *cycle.address);
		break;

		// Serial port.
		case Read(0x018):
			LOG("TODO: serial data and status");
			cycle.set_value16(0x3000);	// i.e. transmit buffer empty.
		break;
		case Write(0x030):
			LOG("TODO: serial data: " << PADHEX(4) << cycle.value16());
		break;
		case Write(0x032):
			LOG("TODO: serial control: " << PADHEX(4) << cycle.value16());
			serial_.set_control(cycle.value16());
		break;

		// DMA management.
		case Read(0x002):
			LOG("DMA control and status read");
			cycle.set_value16(dma_control_ | blitter_.get_status());
		break;
		case Write(0x096):
			ApplySetClear(dma_control_);
			LOG("DMA control modified by " << PADHEX(4) << cycle.value16() << "; is now " << std::bitset<16>{dma_control_});
		break;

		// Interrupts.
		case Write(0x09a):
			ApplySetClear(interrupt_enable_);
			update_interrupts();
			LOG("Interrupt enable mask modified by " << PADHEX(4) << cycle.value16() << "; is now " << std::bitset<16>{interrupt_enable_});
		break;
		case Read(0x01c):
			cycle.set_value16(interrupt_enable_);
			LOG("Interrupt enable mask read: " << PADHEX(4) << interrupt_enable_);
		break;

		case Write(0x09c):
			ApplySetClear(interrupt_requests_);
			update_interrupts();
			LOG("Interrupt request modified by " << PADHEX(4) << cycle.value16() << "; is now " << std::bitset<16>{interrupt_requests_});
		break;
		case Read(0x01e):
			cycle.set_value16(interrupt_requests_);
			LOG("Interrupt requests read: " << PADHEX(4) << interrupt_requests_);
		break;

		// Display management.
		case Write(0x08e): {
			const uint16_t value = cycle.value16();
			display_window_start_[0] = value & 0xff;
			display_window_start_[1] = value >> 8;
			LOG("Display window start set to " << std::dec << display_window_start_[0] << ", " << display_window_start_[1]);
		} break;
		case Write(0x090): {
			const uint16_t value = cycle.value16();
			display_window_stop_[0] = 0x100 | (value & 0xff);
			display_window_stop_[1] = value >> 8;
			display_window_stop_[1] |= ((value >> 7) & 0x100) ^ 0x100;
			LOG("Display window stop set to " << std::dec << display_window_stop_[0] << ", " << display_window_stop_[1]);
		} break;
		case Write(0x092):
			fetch_window_[0] = uint16_t((cycle.value16() & 0xfc) << 1);
			LOG("Fetch window start set to " << std::dec << fetch_window_[0]);
		break;
		case Write(0x094):
			fetch_window_[1] = uint16_t((cycle.value16() & 0xfc) << 1);
			LOG("Fetch window stop set to " << std::dec << fetch_window_[1]);
		break;

		// Bitplanes.
		case Write(0x0e0):	bitplanes_.set_pointer<0, 16>(cycle.value16());	break;
		case Write(0x0e2):	bitplanes_.set_pointer<0, 0>(cycle.value16());	break;
		case Write(0x0e4):	bitplanes_.set_pointer<1, 16>(cycle.value16());	break;
		case Write(0x0e6):	bitplanes_.set_pointer<1, 0>(cycle.value16());	break;
		case Write(0x0e8):	bitplanes_.set_pointer<2, 16>(cycle.value16());	break;
		case Write(0x0ea):	bitplanes_.set_pointer<2, 0>(cycle.value16());	break;
		case Write(0x0ec):	bitplanes_.set_pointer<3, 16>(cycle.value16());	break;
		case Write(0x0ee):	bitplanes_.set_pointer<3, 0>(cycle.value16());	break;
		case Write(0x0f0):	bitplanes_.set_pointer<4, 16>(cycle.value16());	break;
		case Write(0x0f2):	bitplanes_.set_pointer<4, 0>(cycle.value16());	break;
		case Write(0x0f4):	bitplanes_.set_pointer<5, 16>(cycle.value16());	break;
		case Write(0x0f6):	bitplanes_.set_pointer<5, 0>(cycle.value16());	break;

		case Write(0x102): {
			const uint8_t delay = cycle.value8_low();
			odd_delay_ = delay & 0x0f;
			even_delay_ = delay >> 4;
		} break;

		case Write(0x100):
			bitplanes_.set_control(cycle.value16());
			is_high_res_ = cycle.value16() & 0x8000;
		break;

		case Write(0x104):
		case Write(0x106):
			LOG("TODO: Bitplane control; " << PADHEX(4) << cycle.value16() << " to " << *cycle.address);
		break;

		case Write(0x108):
		case Write(0x10a):
			LOG("TODO: Bitplane modulo; " << PADHEX(4) << cycle.value16() << " to " << *cycle.address);
		break;

		case Write(0x110):
		case Write(0x112):
		case Write(0x114):
		case Write(0x116):
		case Write(0x118):
		case Write(0x11a):
			LOG("TODO: Bitplane data; " << PADHEX(4) << cycle.value16() << " to " << *cycle.address);
		break;

		case Read(0x110):	case Read(0x112):	case Read(0x114):	case Read(0x116):
		case Read(0x118):	case Read(0x11a):
			cycle.set_value16(0xffff);
			LOG("Invalid read at " << PADHEX(6) << *cycle.address);
		break;

		// Blitter.
		case Write(0x040):	blitter_.set_control(0, cycle.value16());		break;
		case Write(0x042):	blitter_.set_control(1, cycle.value16());		break;
		case Write(0x044):	blitter_.set_first_word_mask(cycle.value16());	break;
		case Write(0x046):	blitter_.set_last_word_mask(cycle.value16());	break;

		case Write(0x048):	blitter_.set_pointer<2, 16>(cycle.value16());	break;
		case Write(0x04a):	blitter_.set_pointer<2, 0>(cycle.value16());	break;
		case Write(0x04c):	blitter_.set_pointer<1, 16>(cycle.value16());	break;
		case Write(0x04e):	blitter_.set_pointer<1, 0>(cycle.value16());	break;
		case Write(0x050):	blitter_.set_pointer<0, 16>(cycle.value16());	break;
		case Write(0x052):	blitter_.set_pointer<0, 0>(cycle.value16());	break;
		case Write(0x054):	blitter_.set_pointer<3, 16>(cycle.value16());	break;
		case Write(0x056):	blitter_.set_pointer<3, 0>(cycle.value16());	break;

		case Write(0x058):	blitter_.set_size(cycle.value16());				break;
		case Write(0x05a):	blitter_.set_minterms(cycle.value16());			break;
		case Write(0x05c):	blitter_.set_vertical_size(cycle.value16());	break;
		case Write(0x05e):	blitter_.set_horizontal_size(cycle.value16());	break;

		case Write(0x060):	blitter_.set_modulo(2, cycle.value16());		break;
		case Write(0x062):	blitter_.set_modulo(1, cycle.value16());		break;
		case Write(0x064):	blitter_.set_modulo(0, cycle.value16());		break;
		case Write(0x066):	blitter_.set_modulo(3, cycle.value16());		break;

		case Write(0x070):	blitter_.set_data(2, cycle.value16());			break;
		case Write(0x072):	blitter_.set_data(1, cycle.value16());			break;
		case Write(0x074):	blitter_.set_data(0, cycle.value16());			break;

		// Paula.
		case Write(0x09e):
		case Write(0x0a0):	case Write(0x0a2):	case Write(0x0a4):	case Write(0x0a6):
		case Write(0x0a8):	case Write(0x0aa):
		case Write(0x0b0):	case Write(0x0b2):	case Write(0x0b4):	case Write(0x0b6):
		case Write(0x0b8):	case Write(0x0ba):
		case Write(0x0c0):	case Write(0x0c2):	case Write(0x0c4):	case Write(0x0c6):
		case Write(0x0c8):	case Write(0x0ca):
		case Write(0x0d0):	case Write(0x0d2):	case Write(0x0d4):	case Write(0x0d6):
		case Write(0x0d8):	case Write(0x0da):
			LOG("TODO: Paula write " << PADHEX(2) << (*cycle.address & 0xff) << " " << PADHEX(4) << cycle.value16());
		break;

		// Copper.
		case Write(0x02e):
			LOG("Coprocessor control " << PADHEX(4) << cycle.value16());
			copper_.set_control(cycle.value16());
		break;
		case Write(0x080):
			LOG("Coprocessor first location register high " << PADHEX(4) << cycle.value16());
			copper_.set_pointer<0, 16>(cycle.value16());
		break;
		case Write(0x082):
			LOG("Coprocessor first location register low " << PADHEX(4) << cycle.value16());
			copper_.set_pointer<0, 0>(cycle.value16());
		break;
		case Write(0x084):
			LOG("Coprocessor second location register high " << PADHEX(4) << cycle.value16());
			copper_.set_pointer<1, 16>(cycle.value16());
		break;
		case Write(0x086):
			LOG("Coprocessor second location register low " << PADHEX(4) << cycle.value16());
			copper_.set_pointer<1, 0>(cycle.value16());
		break;
		case Write(0x088):	case Read(0x088):
			LOG("Coprocessor restart at first location");
			copper_.reload<0>();
		break;
		case Write(0x08a):	case Read(0x08a):
			LOG("Coprocessor restart at second location");
			copper_.reload<1>();
		break;
		case Write(0x08c):
			LOG("TODO: coprocessor instruction fetch identity " << PADHEX(4) << cycle.value16());
		break;

		// Sprites.
#define Sprite(index, pointer, position)	\
		case Write(pointer + 0):	sprites_[index].set_pointer(16, cycle.value16());		break;	\
		case Write(pointer + 2):	sprites_[index].set_pointer(0, cycle.value16());		break;	\
		case Write(position + 0):	sprites_[index].set_start_position(cycle.value16());	break;	\
		case Write(position + 2):	sprites_[index].set_stop_and_control(cycle.value16());	break;	\
		case Write(position + 4):	sprites_[index].set_image_data(0, cycle.value16());		break;	\
		case Write(position + 6):	sprites_[index].set_image_data(1, cycle.value16());		break;

		Sprite(0, 0x120, 0x140);
		Sprite(1, 0x124, 0x148);
		Sprite(2, 0x128, 0x150);
		Sprite(3, 0x12c, 0x158);
		Sprite(4, 0x130, 0x160);
		Sprite(5, 0x134, 0x168);
		Sprite(6, 0x138, 0x170);
		Sprite(7, 0x13c, 0x178);

#undef Sprite

		// Colour palette.
		case Write(0x180):	case Write(0x182):	case Write(0x184):	case Write(0x186):
		case Write(0x188):	case Write(0x18a):	case Write(0x18c):	case Write(0x18e):
		case Write(0x190):	case Write(0x192):	case Write(0x194):	case Write(0x196):
		case Write(0x198):	case Write(0x19a):	case Write(0x19c):	case Write(0x19e):
		case Write(0x1a0):	case Write(0x1a2):	case Write(0x1a4):	case Write(0x1a6):
		case Write(0x1a8):	case Write(0x1aa):	case Write(0x1ac):	case Write(0x1ae):
		case Write(0x1b0):	case Write(0x1b2):	case Write(0x1b4):	case Write(0x1b6):
		case Write(0x1b8):	case Write(0x1ba):	case Write(0x1bc):	case Write(0x1be): {
			LOG("Colour palette; " << PADHEX(4) << cycle.value16() << " to " << *cycle.address);

			// Store once in regular, linear order.
			const auto entry_address = (register_address - 0x180) >> 1;
			uint8_t *const entry = reinterpret_cast<uint8_t *>(&palette_[entry_address]);
			entry[0] = cycle.value8_high();
			entry[1] = cycle.value8_low();

			// Also store in bit-swizzled order. In this array,
			// instead of being indexed as [b4 b3 b2 b1 b0], index
			// as [b3 b1 b4 b2 b0]. This is related to the dual/single-playfield
			// decision being made relatively late in the planar -> chunky
			// conversion performed by this implementation.
			const auto swizzled_address =
				(entry_address&0x01) |
				((entry_address&0x02) << 2) |
				((entry_address&0x04) >> 1) |
				((entry_address&0x08) << 1) |
				((entry_address&0x10) >> 2);
			uint8_t *const swizzled_entry = reinterpret_cast<uint8_t *>(&swizzled_palette_[swizzled_address]);
			swizzled_entry[0] = cycle.value8_high();
			swizzled_entry[1] = cycle.value8_low();
		} break;
	}

#undef ApplySetClear

#undef Write
#undef Read
#undef RW
}

// MARK: - Bitplanes.

bool Chipset::Bitplanes::advance(int cycle) {
#define BIND_CYCLE(offset, plane)								\
	case offset:												\
		if(plane_count_ > plane) {								\
			next[plane] = ram_[pointer_[plane] & ram_mask_];	\
			++pointer_[plane];									\
			if constexpr (!plane) {								\
				chipset_.post_bitplanes(next);					\
			}													\
			return true;										\
		}														\
	return false;

	if(is_high_res_) {
		// TODO: I'm unclear whether this is correct, or merely
		// an artefact of the way the Hardware Reference Manual
		// depicts per-line DMA responsibilities.
		if(cycle < 4) {
			return false;
		}

		switch(cycle&7) {
			default: return false;
			BIND_CYCLE(0, 3);
			BIND_CYCLE(1, 1);
			BIND_CYCLE(2, 2);
			BIND_CYCLE(3, 0);
			BIND_CYCLE(4, 3);
			BIND_CYCLE(5, 1);
			BIND_CYCLE(6, 2);
			BIND_CYCLE(7, 0);
		}
	} else {
		switch(cycle&7) {
			default: return false;
			BIND_CYCLE(1, 3);
			BIND_CYCLE(2, 5);
			BIND_CYCLE(3, 1);
			BIND_CYCLE(5, 2);
			BIND_CYCLE(6, 4);
			BIND_CYCLE(7, 0);
		}
	}

	return false;

#undef BIND_CYCLE
}

void Chipset::Bitplanes::do_end_of_line() {
	// TODO: apply modulos.
}

void Chipset::Bitplanes::set_control(uint16_t control) {
	is_high_res_ = control & 0x8000;
	plane_count_ = (control >> 12) & 7;

	// TODO: who really has responsibility for clearing the other
	// bit plane fields?
	std::fill(next.begin() + plane_count_, next.end(), 0);
	if(plane_count_ == 7) {
		plane_count_ = 4;
	}
}


// MARK: - Sprites.

void Chipset::Sprite::set_pointer(int shift, uint16_t value) {
	LOG("Sprite pointer with shift " << std::dec << shift << " to " << PADHEX(4) << value);
}

void Chipset::Sprite::set_start_position(uint16_t value) {
	LOG("Sprite start position " << PADHEX(4) << value);
}

void Chipset::Sprite::set_stop_and_control(uint16_t value) {
	LOG("Sprite stop and control " << PADHEX(4) << value);
}

void Chipset::Sprite::set_image_data(int slot, uint16_t value) {
	LOG("Sprite image data " << slot << " to " << PADHEX(4) << value);
}

// MARK: - Disk.

bool Chipset::DiskDMA::advance() {
	if(!dma_enable_) return false;

	if(!write_) {
		// TODO: run an actual PLL, collect actual disk data.
		if(length_) {
			ram_[pointer_[0] & ram_mask_] = 0xffff;
			++pointer_[0];
			--length_;

			if(!length_) {
				chipset_.posit_interrupt(InterruptFlag::DiskBlock);
			}

			return true;
		}
	}

	return false;
}

// MARK: - CRT connection.

void Chipset::set_scan_target(Outputs::Display::ScanTarget *scan_target) {
	crt_.set_scan_target(scan_target);
}

Outputs::Display::ScanStatus Chipset::get_scaled_scan_status() const {
	return crt_.get_scaled_scan_status();
}

void Chipset::set_display_type(Outputs::Display::DisplayType type) {
	crt_.set_display_type(type);
}

Outputs::Display::DisplayType Chipset::get_display_type() const {
	return crt_.get_display_type();
}

// MARK: - CIA A.

Chipset::CIAAHandler::CIAAHandler(MemoryMap &map, DiskController &controller) : map_(map), controller_(controller) {}

void Chipset::CIAAHandler::set_port_output(MOS::MOS6526::Port port, uint8_t value) {
	if(port) {
		// Parallel port output.
		LOG("TODO: parallel output " << PADHEX(2) << +value);
	} else {
		//	b7:	/FIR1
		//	b6:	/FIR0
		//	b5:	/RDY
		//	b4:	/TRK0
		//	b3:	/WPRO
		//	b2:	/CHNG
		//	b1:	/LED		[output]
		//	b0:	OVL			[output]

		LOG("LED & memory map: " << PADHEX(2) << +value);
		if(observer_) {
			observer_->set_led_status(led_name, !(value & 2));
		}
		map_.set_overlay(value & 1);
	}
}

uint8_t Chipset::CIAAHandler::get_port_input(MOS::MOS6526::Port port) {
	if(port) {
		LOG("TODO: parallel input?");
	} else {
		LOG("TODO: CIA A, port A input — FIR, RDY, TRK0, etc");

		// Announce that TRK0 is upon us.
		return 0xef;
	}
	return 0xff;
}

void Chipset::CIAAHandler::set_activity_observer(Activity::Observer *observer) {
	observer_ = observer;
	if(observer) {
		observer->register_led(led_name, Activity::Observer::LEDPresentation::Persistent);
	}
}

// MARK: - CIA B.

Chipset::CIABHandler::CIABHandler(DiskController &controller) : controller_(controller) {}

void Chipset::CIABHandler::set_port_output(MOS::MOS6526::Port port, uint8_t value) {
	if(port) {
		// Serial port control.
		//
		// b7: /DTR
		// b6: /RTS
		// b5: /CD
		// b4: /CTS
		// b3: /DSR
		// b2: SEL
		// b1: POUT
		// b0: BUSY
		LOG("TODO: DTR/RTS/etc: " << PADHEX(2) << +value);
	} else {
		// Disk motor control, drive and head selection,
		// and stepper control:
		//
		// b7: /MTR
		// b6: /SEL3
		// b5: /SEL2
		// b4: /SEL1
		// b3: /SEL0
		// b2: /SIDE
		// b1: DIR
		// b0: /STEP
		LOG("TODO: Stepping, etc; " << PADHEX(2) << +value);

		controller_.set_drive((value >> 3) & 0xf);

		// "[The MTR] signal is nonstandard on the Amiga system.
		// Each drive will latch the motor signal at the time its
		// select signal turns on." — The Hardware Reference Manual.

		previous_select_ = value;
	}
}

uint8_t Chipset::CIABHandler::get_port_input(MOS::MOS6526::Port port) {
	LOG("Unexpected input for CIA B ");
	if(port) {
		return 0xff;
	} else {
		return previous_select_;
	}
}

// MARK: - Disk Controller.

Chipset::DiskController::DiskController(Cycles clock_rate) :
	Storage::Disk::Controller(clock_rate) {

	// Add four drives.
	for(int c = 0; c < 4; c++) {
		emplace_drive(clock_rate.as<int>(), 300, 2, Storage::Disk::Drive::ReadyType::ShugartRDY);
	}
}

void Chipset::DiskController::process_input_bit(int value) {
	// TODO:
	(void)value;
}

void Chipset::DiskController::process_index_hole() {
	// TODO: does the Amiga care?
}