CLK/Machines/Electron/Electron.cpp

//
//  Electron.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 03/01/2016.
//  Copyright © 2016 Thomas Harte. All rights reserved.
//

#include "Electron.hpp"

using namespace Electron;

#pragma mark - Lifecycle

Machine::Machine() :
	interrupt_control_(0),
	interrupt_status_(Interrupt::PowerOnReset | Interrupt::TransmitDataEmpty | 0x80),
	cycles_since_display_update_(0),
	cycles_since_audio_update_(0),
	use_fast_tape_hack_(false),
	cycles_until_display_interrupt_(0)
{
	memset(key_states_, 0, sizeof(key_states_));
	for(int c = 0; c < 16; c++)
		memset(roms_[c], 0xff, 16384);

	tape_.set_delegate(this);
	set_clock_rate(2000000);
}

#pragma mark - Output

void Machine::setup_output(float aspect_ratio)
{
	video_output_.reset(new VideoOutput(ram_));

	// The maximum output frequency is 62500Hz and all other permitted output frequencies are integral divisions of that;
	// however setting the speaker on or off can happen on any 2Mhz cycle, and probably (?) takes effect immediately. So
	// run the speaker at a 2000000Hz input rate, at least for the time being.
	speaker_.reset(new Speaker);
	speaker_->set_input_rate(2000000 / Speaker::clock_rate_divider);
}

void Machine::close_output()
{
	video_output_.reset();
}

std::shared_ptr<Outputs::CRT::CRT> Machine::get_crt()
{
	return video_output_->get_crt();
}

std::shared_ptr<Outputs::Speaker> Machine::get_speaker()
{
	return speaker_;
}

#pragma mark - The keyboard

void Machine::clear_all_keys()
{
	memset(key_states_, 0, sizeof(key_states_));
}

void Machine::set_key_state(uint16_t key, bool isPressed)
{
	if(key == KeyBreak)
	{
		set_reset_line(isPressed);
	}
	else
	{
		if(isPressed)
			key_states_[key >> 4] |= key&0xf;
		else
			key_states_[key >> 4] &= ~(key&0xf);
	}
}

#pragma mark - Machine configuration

void Machine::configure_as_target(const StaticAnalyser::Target &target)
{
	if(target.tapes.size())
	{
		tape_.set_tape(target.tapes.front());
	}

	if(target.disks.size())
	{
		plus3_.reset(new Plus3);

		if(target.acorn.has_dfs)
		{
			set_rom(ROMSlot0, dfs_, true);
		}
		if(target.acorn.has_adfs)
		{
			set_rom(ROMSlot4, adfs_, true);
			set_rom(ROMSlot5, std::vector<uint8_t>(adfs_.begin() + 16384, adfs_.end()), true);
		}

		plus3_->set_disk(target.disks.front(), 0);
	}

	ROMSlot slot = ROMSlot12;
	for(std::shared_ptr<Storage::Cartridge::Cartridge> cartridge : target.cartridges)
	{
		set_rom(slot, cartridge->get_segments().front().data, false);
		slot = (ROMSlot)(((int)slot + 1)&15);
	}

	if(target.loadingCommand.length())	// TODO: and automatic loading option enabled
	{
		set_typer_for_string(target.loadingCommand.c_str());
	}

	if(target.acorn.should_hold_shift)
	{
		set_key_state(KeyShift, true);
		is_holding_shift_ = true;
	}
}

void Machine::set_rom(ROMSlot slot, std::vector<uint8_t> data, bool is_writeable)
{
	uint8_t *target = nullptr;
	switch(slot)
	{
		case ROMSlotDFS:	dfs_ = data;			return;
		case ROMSlotADFS:	adfs_ = data;			return;

		case ROMSlotOS:		target = os_;			break;
		default:
			target = roms_[slot];
			rom_write_masks_[slot] = is_writeable;
		break;
	}

	memcpy(target, &data[0], std::min((size_t)16384, data.size()));
}

#pragma mark - The bus

unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t address, uint8_t *value)
{
	unsigned int cycles = 1;

	if(address < 0x8000)
	{
		if(isReadOperation(operation))
		{
			*value = ram_[address];
		}
		else
		{
			if(address >= video_access_range_.low_address && address <= video_access_range_.high_address) update_display();
			ram_[address] = *value;
		}

		// for the entire frame, RAM is accessible only on odd cycles; in modes below 4
		// it's also accessible only outside of the pixel regions
		cycles += video_output_->get_cycles_until_next_ram_availability((int)(cycles_since_display_update_ + 1));
	}
	else
	{
		switch(address & 0xff0f)
		{
			case 0xfe00:
				if(isReadOperation(operation))
				{
					*value = interrupt_status_;
					interrupt_status_ &= ~PowerOnReset;
				}
				else
				{
					interrupt_control_ = (*value) & ~1;
					evaluate_interrupts();
				}
			break;
			case 0xfe07:
				if(!isReadOperation(operation))
				{
					// update speaker mode
					bool new_speaker_is_enabled = (*value & 6) == 2;
					if(new_speaker_is_enabled != speaker_is_enabled_)
					{
						update_audio();
						speaker_->set_is_enabled(new_speaker_is_enabled);
						speaker_is_enabled_ = new_speaker_is_enabled;
					}

					tape_.set_is_enabled((*value & 6) != 6);
					tape_.set_is_in_input_mode((*value & 6) == 0);
					tape_.set_is_running(((*value)&0x40) ? true : false);

					// TODO: caps lock LED
				}

			// deliberate fallthrough
			case 0xfe02: case 0xfe03:
			case 0xfe08: case 0xfe09: case 0xfe0a: case 0xfe0b:
			case 0xfe0c: case 0xfe0d: case 0xfe0e: case 0xfe0f:
				if(!isReadOperation(operation))
				{
					update_display();
					video_output_->set_register(address, *value);
					video_access_range_ = video_output_->get_memory_access_range();
					queue_next_display_interrupt();
				}
			break;
			case 0xfe04:
				if(isReadOperation(operation))
				{
					*value = tape_.get_data_register();
					tape_.clear_interrupts(Interrupt::ReceiveDataFull);
				}
				else
				{
					tape_.set_data_register(*value);
					tape_.clear_interrupts(Interrupt::TransmitDataEmpty);
				}
			break;
			case 0xfe05:
				if(!isReadOperation(operation))
				{
					const uint8_t interruptDisable = (*value)&0xf0;
					if( interruptDisable )
					{
						if( interruptDisable&0x10 ) interrupt_status_ &= ~Interrupt::DisplayEnd;
						if( interruptDisable&0x20 ) interrupt_status_ &= ~Interrupt::RealTimeClock;
						if( interruptDisable&0x40 ) interrupt_status_ &= ~Interrupt::HighToneDetect;
						evaluate_interrupts();

						// TODO: NMI
					}

					// latch the paged ROM in case external hardware is being emulated
					active_rom_ = (Electron::ROMSlot)(*value & 0xf);

					// apply the ULA's test
					if(*value & 0x08)
					{
						if(*value & 0x04)
						{
							keyboard_is_active_ = false;
							basic_is_active_ = false;
						}
						else
						{
							keyboard_is_active_ = !(*value & 0x02);
							basic_is_active_ = !keyboard_is_active_;
						}
					}
				}
			break;
			case 0xfe06:
				if(!isReadOperation(operation))
				{
					update_audio();
					speaker_->set_divider(*value);
					tape_.set_counter(*value);
				}
			break;

			case 0xfc04: case 0xfc05: case 0xfc06: case 0xfc07:
				if(plus3_ && (address&0x00f0) == 0x00c0)
				{
					if(is_holding_shift_ && address == 0xfcc4)
					{
						is_holding_shift_ = false;
						set_key_state(KeyShift, false);
					}
					if(isReadOperation(operation))
						*value = plus3_->get_register(address);
					else
						plus3_->set_register(address, *value);
				}
			break;
			case 0xfc00:
				if(plus3_ && (address&0x00f0) == 0x00c0)
				{
					if(!isReadOperation(operation))
					{
						plus3_->set_control_register(*value);
					}
					else
						*value = 1;
				}
			break;

			default:
				if(address >= 0xc000)
				{
					if(isReadOperation(operation))
					{
						if(
							use_fast_tape_hack_ &&
							tape_.has_tape() &&
							(operation == CPU6502::BusOperation::ReadOpcode) &&
							(
								(address == 0xf4e5) || (address == 0xf4e6) ||	// double NOPs at 0xf4e5, 0xf6de, 0xf6fa and 0xfa51
								(address == 0xf6de) || (address == 0xf6df) ||	// act to disable the normal branch into tape-handling
								(address == 0xf6fa) || (address == 0xf6fb) ||	// code, forcing the OS along the serially-accessed ROM
								(address == 0xfa51) || (address == 0xfa52) ||	// pathway.

								(address == 0xf0a8)								// 0xf0a8 is from where a service call would normally be
																				// dispatched; we can check whether it would be call 14
																				// (i.e. read byte) and, if so, whether the OS was about to
																				// issue a read byte call to a ROM despite being the tape
																				// FS being selected. If so then this is a get byte that
																				// we should service synthetically. Put the byte into Y
																				// and set A to zero to report that action was taken, then
																				// allow the PC read to return an RTS.
							)
						)
						{
							uint8_t service_call = (uint8_t)get_value_of_register(CPU6502::Register::X);
							if(address == 0xf0a8)
							{
								if(!ram_[0x247] && service_call == 14)
								{
									tape_.set_delegate(nullptr);

									// TODO: handle tape wrap around.

									int cycles_left_while_plausibly_in_data = 50;
									tape_.clear_interrupts(Interrupt::ReceiveDataFull);
									while(!tape_.get_tape()->is_at_end())
									{
										tape_.run_for_input_pulse();
										cycles_left_while_plausibly_in_data--;
										if(!cycles_left_while_plausibly_in_data) fast_load_is_in_data_ = false;
										if(	(tape_.get_interrupt_status() & Interrupt::ReceiveDataFull) &&
											(fast_load_is_in_data_ || tape_.get_data_register() == 0x2a)
										) break;
									}
									tape_.set_delegate(this);
									tape_.clear_interrupts(Interrupt::ReceiveDataFull);
									interrupt_status_ |= tape_.get_interrupt_status();

									fast_load_is_in_data_ = true;
									set_value_of_register(CPU6502::Register::A, 0);
									set_value_of_register(CPU6502::Register::Y, tape_.get_data_register());
									*value = 0x60; // 0x60 is RTS
								}
								else
									*value = os_[address & 16383];
							}
							else
								*value = 0xea;
						}
						else
						{
							*value = os_[address & 16383];
						}
					}
				}
				else
				{
					if(isReadOperation(operation))
					{
						*value = roms_[active_rom_][address & 16383];
						if(keyboard_is_active_)
						{
							*value &= 0xf0;
							for(int address_line = 0; address_line < 14; address_line++)
							{
								if(!(address&(1 << address_line))) *value |= key_states_[address_line];
							}
						}
						if(basic_is_active_)
						{
							*value &= roms_[ROMSlotBASIC][address & 16383];
						}
					} else if(rom_write_masks_[active_rom_])
					{
						roms_[active_rom_][address & 16383] = *value;
					}
				}
			break;
		}
	}

	cycles_since_display_update_ += cycles;
	cycles_since_audio_update_ += cycles;
	if(cycles_since_audio_update_ > 16384) update_audio();
	tape_.run_for_cycles(cycles);

	cycles_until_display_interrupt_ -= cycles;
	if(cycles_until_display_interrupt_ < 0)
	{
		signal_interrupt(next_display_interrupt_);
		update_display();
		queue_next_display_interrupt();
	}

	if(typer_) typer_->update((int)cycles);
	if(plus3_) plus3_->run_for_cycles(4*cycles);

	return cycles;
}

void Machine::synchronise()
{
	update_display();
	update_audio();
	speaker_->flush();
}

#pragma mark - Deferred scheduling

inline void Machine::update_display()
{
	if(cycles_since_display_update_)
	{
		video_output_->run_for_cycles((int)cycles_since_display_update_);
		cycles_since_display_update_ = 0;
	}
}

inline void Machine::queue_next_display_interrupt()
{
	VideoOutput::Interrupt next_interrupt = video_output_->get_next_interrupt();
	cycles_until_display_interrupt_ = next_interrupt.cycles;
	next_display_interrupt_ = next_interrupt.interrupt;
}

inline void Machine::update_audio()
{
	if(cycles_since_audio_update_)
	{
		unsigned int difference = cycles_since_audio_update_ / Speaker::clock_rate_divider;
		cycles_since_audio_update_ %= Speaker::clock_rate_divider;
		speaker_->run_for_cycles(difference);
	}
}

#pragma mark - Interrupts

inline void Machine::signal_interrupt(Electron::Interrupt interrupt)
{
	interrupt_status_ |= interrupt;
	evaluate_interrupts();
}

inline void Machine::clear_interrupt(Electron::Interrupt interrupt)
{
	interrupt_status_ &= ~interrupt;
	evaluate_interrupts();
}

inline void Machine::evaluate_interrupts()
{
	if(interrupt_status_ & interrupt_control_)
	{
		interrupt_status_ |= 1;
	}
	else
	{
		interrupt_status_ &= ~1;
	}
	set_irq_line(interrupt_status_ & 1);
}

#pragma mark - Tape::Delegate

void Machine::tape_did_change_interrupt_status(Tape *tape)
{
	interrupt_status_ = (interrupt_status_ & ~(Interrupt::TransmitDataEmpty | Interrupt::ReceiveDataFull | Interrupt::HighToneDetect)) | tape_.get_interrupt_status();
	evaluate_interrupts();
}