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GBA Memory: Simplify prefetch logic (possibly more accurate, but more failing tests)

This commit is contained in:
Vicki Pfau 2017-06-12 21:06:06 -07:00
parent e2dc5575b9
commit fec4c06447
2 changed files with 16 additions and 17 deletions
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25
src/gba/memory.c
View File

@ -1505,33 +1505,32 @@ int32_t GBAMemoryStall(struct ARMCore* cpu, int32_t wait) {
previousLoads = dist;
}
int32_t s = cpu->memory.activeSeqCycles16 + 1;
int32_t n2s = cpu->memory.activeNonseqCycles16 - cpu->memory.activeSeqCycles16 + 1;
int32_t s = cpu->memory.activeSeqCycles16;
int32_t n2s = cpu->memory.activeNonseqCycles16 - cpu->memory.activeSeqCycles16;
// Figure out how many sequential loads we can jam in
int32_t stall = s;
int32_t loads = 1;
if (stall > wait && !previousLoads) {
// We might need to stall a bit extra if we haven't finished the first S cycle
wait = stall;
} else {
while (stall < wait) {
if (stall < wait) {
int32_t maxLoads = 8 - previousLoads;
while (stall < wait && loads < maxLoads) {
stall += s;
++loads;
}
if (loads + previousLoads > 8) {
loads = 8 - previousLoads;
}
}
if (stall > wait) {
// The wait cannot take less time than the prefetch stalls
wait = stall;
}
// This instruction used to have an N, convert it to an S.
wait -= n2s;
// TODO: Invalidate prefetch on branch
memory->lastPrefetchedPc = cpu->gprs[ARM_PC] + WORD_SIZE_THUMB * loads;
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;
cpu->cycles -= stall;
return wait;
}

8
src/gba/timer.c
View File

@ -83,13 +83,13 @@ void GBATimerInit(struct GBA* gba) {
void GBATimerUpdateRegister(struct GBA* gba, int timer) {
struct GBATimer* currentTimer = &gba->timers[timer];
if (GBATimerFlagsIsEnable(currentTimer->flags) && !GBATimerFlagsIsCountUp(currentTimer->flags)) {
int32_t prefetchSkew = 0;
if (gba->memory.lastPrefetchedPc >= (uint32_t) gba->cpu->gprs[ARM_PC]) {
prefetchSkew = (gba->memory.lastPrefetchedPc - gba->cpu->gprs[ARM_PC]) * (gba->cpu->memory.activeSeqCycles16 + 1) / WORD_SIZE_THUMB;
int32_t prefetchSkew = -2;
if (gba->memory.lastPrefetchedPc > (uint32_t) gba->cpu->gprs[ARM_PC]) {
prefetchSkew += ((gba->memory.lastPrefetchedPc - gba->cpu->gprs[ARM_PC]) * gba->cpu->memory.activeSeqCycles16) / WORD_SIZE_THUMB;
}
// Reading this takes two cycles (1N+1I), so let's remove them preemptively
int32_t diff = gba->cpu->cycles - (currentTimer->lastEvent - gba->timing.masterCycles);
gba->memory.io[(REG_TM0CNT_LO + (timer << 2)) >> 1] = currentTimer->oldReload + ((diff - 2 + prefetchSkew) >> GBATimerFlagsGetPrescaleBits(currentTimer->flags));
gba->memory.io[(REG_TM0CNT_LO + (timer << 2)) >> 1] = currentTimer->oldReload + ((diff + prefetchSkew) >> GBATimerFlagsGetPrescaleBits(currentTimer->flags));
}
}