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PPU: Fix for Kick Master (race condition between 2006 writes and Y scrolling increment at cycle 256)

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This commit is contained in:
Souryo 2016-05-31 17:12:43 -04:00
parent aceff6b443
commit 0bd7cfe6ed
2 changed files with 12 additions and 1 deletions
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10
Core/PPU.cpp
View File

@ -38,6 +38,7 @@ void PPU::Reset()
{
_prevRenderingEnabled = false;
_renderingEnabled = false;
_skipScrollingIncrement = true;
_ignoreVramRead = 0;
_openBus = 0;
@ -252,6 +253,10 @@ void PPU::WriteRAM(uint16_t addr, uint8_t value)
//Trigger memory read when setting the vram address - needed by MMC3 IRQ counter
//"4) Should be clocked when A12 changes to 1 via $2006 write"
_memoryManager->ReadVRAM(_state.VideoRamAddr);
if(_cycle == 255) {
_skipScrollingIncrement = true;
}
} else {
_state.TmpVideoRamAddr = (_state.TmpVideoRamAddr & ~0xFF00) | ((value & 0x3F) << 8);
}
@ -622,13 +627,14 @@ void PPU::ProcessPreVBlankScanline()
//Update video ram address according to scrolling logic
if((_cycle > 0 && _cycle < 256 && (_cycle & 0x07) == 0) || _cycle == 328 || _cycle == 336) {
IncHorizontalScrolling();
} else if(_cycle == 256) {
} else if(_cycle == 256 && !_skipScrollingIncrement) {
IncVerticalScrolling();
} else if(_cycle == 257) {
//copy horizontal scrolling value from t
_state.VideoRamAddr = (_state.VideoRamAddr & ~0x041F) | (_state.TmpVideoRamAddr & 0x041F);
}
}
_skipScrollingIncrement = false;
if(_cycle >= 257 && _cycle <= 320) {
if(IsRenderingEnabled()) {
@ -964,6 +970,8 @@ void PPU::StreamState(bool saving)
Stream<uint32_t>(_ignoreVramRead);
Stream<bool>(_skipScrollingIncrement);
if(!saving) {
SetNesModel(_nesModel);
}

3
Core/PPU.h
View File

@ -148,6 +148,9 @@ class PPU : public IMemoryHandler, public Snapshotable
bool _renderingEnabled;
bool _prevRenderingEnabled;
//Used to resolve a race condition when the 2nd write to $2006 occurs at cycle 255 (i.e approx. the same time as the PPU tries to increase Y scrolling)
bool _skipScrollingIncrement;
void UpdateStatusFlag();