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GBA Memory: Improve gamepak prefetch timing

This commit is contained in:
Vicki Pfau 2020-01-16 19:21:18 -08:00
parent 0e49b2d391
commit 8a6cf8dc9c
2 changed files with 7 additions and 5 deletions
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1
CHANGES
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@ -92,6 +92,7 @@ Emulation fixes:
- ARM: Fix stepping when events are pending
- GBA DMA: Fix case where DMAs could get misaligned (fixes mgba.io/i/1092)
- GBA Memory: Fix open bus from IWRAM (fixes mgba.io/i/1575)
- GBA Memory: Improve gamepak prefetch timing
- GBA Timers: Improve timer startup emulation
- GBA Video: Fix OpenGL renderer 512x512 backgrounds (fixes mgba.io/i/1572)
- GBA Video: Fix BLDY for semitransparent sprite on non-target-2 backgrounds

11
src/gba/memory.c
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@ -1622,17 +1622,19 @@ int32_t GBAMemoryStall(struct ARMCore* cpu, int32_t wait) {
maxLoads -= previousLoads;
}
int32_t s = cpu->memory.activeSeqCycles16 + 1;
int32_t s = cpu->memory.activeSeqCycles16;
int32_t n2s = cpu->memory.activeNonseqCycles16 - cpu->memory.activeSeqCycles16 + 1;
// Figure out how many sequential loads we can jam in
int32_t stall = s;
int32_t stall = s + 1;
int32_t loads = 1;
while (stall < wait && loads < maxLoads) {
stall += s;
++loads;
}
memory->lastPrefetchedPc = cpu->gprs[ARM_PC] + WORD_SIZE_THUMB * (loads + previousLoads - 1);
if (stall > wait) {
// The wait cannot take less time than the prefetch stalls
wait = stall;
@ -1641,10 +1643,9 @@ int32_t GBAMemoryStall(struct ARMCore* cpu, int32_t wait) {
// This instruction used to have an N, convert it to an S.
wait -= n2s;
memory->lastPrefetchedPc = cpu->gprs[ARM_PC] + WORD_SIZE_THUMB * (loads + previousLoads - 1);
// The next |loads|S waitstates disappear entirely, so long as they're all in a row
cpu->cycles -= (s - 1) * loads;
wait -= stall - 1;
return wait;
}