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NES: Tweaked DMA behavior for PAL/Famicom

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Sour 2023-01-05 17:41:39 +09:00
parent e6b4d23f70
commit a157edb670
1 changed files with 14 additions and 2 deletions
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16
Core/NES/NesCpu.cpp
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@ -336,16 +336,28 @@ void NesCpu::ProcessPendingDma(uint16_t readAddress)
return;
}
//On PAL, the dummy/idle reads done by the DMA don't appear to be done on the
//address that the CPU was about to read. This prevents the 2+x reads on registers issues.
//The exact specifics of where the CPU reads instead aren't known yet - so just disable read side-effects entirely on PAL
bool allowReadSideEffects = _console->GetRegion() != ConsoleRegion::Pal;
//"If this cycle is a read, hijack the read, discard the value, and prevent all other actions that occur on this cycle (PC not incremented, etc)"
StartCpuCycle(true);
_memoryManager->Read(readAddress, MemoryOperationType::DummyRead);
if(allowReadSideEffects) {
_memoryManager->Read(readAddress, MemoryOperationType::DummyRead);
}
EndCpuCycle(true);
_needHalt = false;
uint16_t spriteDmaCounter = 0;
uint8_t spriteReadAddr = 0;
uint8_t readValue = 0;
bool skipDummyReads = (readAddress == 0x4016 || readAddress == 0x4017);
//On Famicom, each dummy/idle read to 4016/4017 is intepreted as a read of the joypad registers
//On NES (or AV Famicom), only the first dummy/idle read causes side effects (e.g only a single bit is lost)
NesConsoleType type = _console->GetNesConfig().ConsoleType;
bool isNesBehavior = type != NesConsoleType::Hvc001;
bool skipDummyReads = !allowReadSideEffects || (isNesBehavior && (readAddress == 0x4016 || readAddress == 0x4017));
auto processCycle = [this] {
//Sprite DMA cycles count as halt/dummy cycles for the DMC DMA when both run at the same time