Mesen-SX/Core/GbDmaController.cpp

#include "stdafx.h"
#include "GbDmaController.h"
#include "GbMemoryManager.h"
#include "GbPpu.h"
#include "GbCpu.h"

void GbDmaController::Init(GbMemoryManager* memoryManager, GbPpu* ppu, GbCpu* cpu)
{
	_memoryManager = memoryManager;
	_ppu = ppu;
	_cpu = cpu;
	_state = {};
}

GbDmaControllerState GbDmaController::GetState()
{
	return _state;
}

void GbDmaController::Exec()
{
	if (_cpu->IsHalted())
	{
		//OAM DMA is halted while the CPU is in halt mode, and resumes when the CPU resumes
		return;
	}

	if (_state.DmaCounter > 0)
	{
		if (_state.DmaCounter <= 160)
		{
			_memoryManager->WriteDma(0xFE00 + (160 - _state.DmaCounter), _state.DmaReadBuffer);
		}

		_state.DmaCounter--;
		_state.DmaReadBuffer = _memoryManager->ReadDma((_state.OamDmaSource << 8) + (160 - _state.DmaCounter));
	}

	if (_state.DmaStartDelay > 0)
	{
		if (--_state.DmaStartDelay == 0)
		{
			_state.InternalDest = _state.OamDmaSource;
			_state.DmaCounter = 161;
		}
	}
}

bool GbDmaController::IsOamDmaRunning()
{
	return _state.DmaCounter > 0 && _state.DmaCounter < 161;
}

uint8_t GbDmaController::Read()
{
	return _state.OamDmaSource;
}

void GbDmaController::Write(uint8_t value)
{
	_state.DmaStartDelay = 1;
	_state.OamDmaSource = value;
}

uint8_t GbDmaController::ReadCgb(uint16_t addr)
{
	switch (addr)
	{
	case 0xFF55: return _state.CgbDmaLength | (_state.CgbHdmaDone ? 0x80 : 0);
	}

	return 0;
}

void GbDmaController::WriteCgb(uint16_t addr, uint8_t value)
{
	switch (addr)
	{
	case 0xFF51: _state.CgbDmaSource = (_state.CgbDmaSource & 0xFF) | (value << 8);
		break;
	case 0xFF52: _state.CgbDmaSource = (_state.CgbDmaSource & 0xFF00) | (value & 0xF0);
		break;
	case 0xFF53: _state.CgbDmaDest = (_state.CgbDmaDest & 0xFF) | (value << 8);
		break;
	case 0xFF54: _state.CgbDmaDest = (_state.CgbDmaDest & 0xFF00) | (value & 0xF0);
		break;
	case 0xFF55:
		{
			bool hdmaMode = (value & 0x80) != 0;
			_state.CgbDmaLength = value & 0x7F;

			if (!hdmaMode)
			{
				if (_state.CgbHdmaRunning)
				{
					//"If HDMA5 is written during a HDMA copy, the behaviour depends on the written bit 7. 
					//  - New bit 7 is 0: Stop copy. HDMA5 new value is ( 80h OR written_value ).
					//  - New bit 7 is 1: Restart copy. New size is the value of written_value bits 0-6.
					//This means that HDMA can't switch to GDMA with only one write. It must be stopped first."
					_state.CgbHdmaRunning = false;
					_state.CgbHdmaDone = true;
				}
				else
				{
					//4 cycles for setup
					_memoryManager->Exec();
					_memoryManager->Exec();

					do
					{
						ProcessDmaBlock();
					}
					while (_state.CgbDmaLength != 0x7F);
				}
			}
			else
			{
				//"After writing a value to HDMA5 that starts the HDMA copy, the upper bit (that indicates HDMA mode when set to '1') will be cleared"
				_state.CgbHdmaDone = false;
				_state.CgbHdmaRunning = true;

				//"If a HDMA transfer is started when the screen is off, one block is copied. "
				//" When a HDMA transfer is started during HBL it will start right away."
				if (!_ppu->IsLcdEnabled() || _ppu->GetMode() == PpuMode::HBlank)
				{
					ProcessHdma();
				}
			}
			break;
		}
	}
}

void GbDmaController::ProcessHdma()
{
	if (_state.CgbHdmaRunning)
	{
		//4 cycles for setup
		_memoryManager->Exec();
		_memoryManager->Exec();

		ProcessDmaBlock();
	}
}

void GbDmaController::ProcessDmaBlock()
{
	//TODO check invalid dma sources/etc.
	for (int i = 0; i < 16; i++)
	{
		uint16_t dst = 0x8000 | ((_state.CgbDmaDest + i) & 0x1FFF);

		//2 or 4 cycles per byte transfered (2x more cycles in high speed mode - effective speed is the same in both modes
		_memoryManager->Exec();
		uint8_t value = _memoryManager->Read<MemoryOperationType::DmaRead>(_state.CgbDmaSource + i);
		if (_memoryManager->IsHighSpeed())
		{
			_memoryManager->Exec();
		}
		_memoryManager->Write<MemoryOperationType::DmaWrite>(dst, value);
	}

	//Source/Dest/Length are all modified by the DMA process and keep their last value after DMA completes
	_state.CgbDmaSource += 16;
	_state.CgbDmaDest += 16;
	_state.CgbDmaLength = (_state.CgbDmaLength - 1) & 0x7F;

	if (_state.CgbHdmaRunning && _state.CgbDmaLength == 0x7F)
	{
		_state.CgbHdmaRunning = false;
		_state.CgbHdmaDone = true;
	}
}

void GbDmaController::Serialize(Serializer& s)
{
	s.Stream(
		_state.OamDmaSource, _state.DmaStartDelay, _state.InternalDest, _state.DmaCounter, _state.DmaReadBuffer,
		_state.CgbDmaDest, _state.CgbDmaLength, _state.CgbDmaSource, _state.CgbHdmaDone, _state.CgbHdmaRunning
	);
}