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PPU: Scrolling increments use a "IsRendering" flag delayed by 1 ppu cycle. This fixes Battletoads freezes, but may be incorrect.

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Souryo 2016-02-14 13:57:47 -05:00
parent b4b195d01b
commit cf450bcdb7
2 changed files with 10 additions and 1 deletions
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10
Core/PPU.cpp
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@ -35,6 +35,7 @@ PPU::~PPU()
void PPU::Reset()
{
_sprite0HitCycle = -1;
_prevRenderingEnabled = false;
_renderingEnabled = false;
_ignoreVramRead = 0;
@ -605,7 +606,12 @@ void PPU::DrawPixel()
void PPU::ProcessPreVBlankScanline()
{
//For pre-render scanline & all visible scanlines
if(IsRenderingEnabled()) {
if(_prevRenderingEnabled) {
//Use _prevRenderingEnabled to drive vert/horiz scrolling increments.
//This delays the flag by an extra cycle. So if rendering is disabled at cycle 254,
//the vertical scrolling increment will not be performed.
//This appears to fix freezes in Battletoads (Level 2), but may be incorrect.
//Update video ram address according to scrolling logic
if((_cycle > 0 && _cycle < 256 && (_cycle & 0x07) == 0) || _cycle == 328 || _cycle == 336) {
IncHorizontalScrolling();
@ -848,6 +854,7 @@ void PPU::Exec()
}
//Rendering enabled flag is apparently set with a 1 cycle delay (i.e setting it at cycle 5 will render cycle 6 like cycle 5 and then take the new settings for cycle 7)
_prevRenderingEnabled = _renderingEnabled;
_renderingEnabled = _flags.BackgroundEnabled || _flags.SpritesEnabled;
}
@ -947,6 +954,7 @@ void PPU::StreamState(bool saving)
Stream<uint16_t>(_spriteDmaAddr);
Stream<uint16_t>(_spriteDmaCounter);
Stream<bool>(_prevRenderingEnabled);
Stream<bool>(_renderingEnabled);
Stream<uint8_t>(_openBus);
StreamArray<int32_t>(_openBusDecayStamp, 8);

1
Core/PPU.h
View file

@ -148,6 +148,7 @@ class PPU : public IMemoryHandler, public Snapshotable
bool _oamCopyDone;
bool _renderingEnabled;
bool _prevRenderingEnabled;
void UpdateStatusFlag();