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LR35902: Optimize core loop to always run one M-cycle at a time

This commit is contained in:
Jeffrey Pfau 2016-05-28 01:44:05 -07:00
parent d242638e28
commit 334963511b
1 changed files with 23 additions and 9 deletions
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32
src/lr35902/lr35902.c
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@ -104,8 +104,7 @@ static void _LR35902InstructionIRQ(struct LR35902Core* cpu) {
static void _LR35902Step(struct LR35902Core* cpu) {
++cpu->cycles;
enum LR35902ExecutionState state = cpu->executionState;
++cpu->executionState;
cpu->executionState &= 3;
cpu->executionState = LR35902_CORE_IDLE_0;
switch (state) {
case LR35902_CORE_FETCH:
if (cpu->irqPending) {
@ -119,9 +118,6 @@ static void _LR35902Step(struct LR35902Core* cpu) {
cpu->instruction = _lr35902InstructionTable[cpu->bus];
++cpu->pc;
break;
case LR35902_CORE_EXECUTE:
cpu->instruction(cpu);
break;
case LR35902_CORE_MEMORY_LOAD:
cpu->bus = cpu->memory.load8(cpu, cpu->index);
break;
@ -142,6 +138,17 @@ static void _LR35902Step(struct LR35902Core* cpu) {
void LR35902Tick(struct LR35902Core* cpu) {
_LR35902Step(cpu);
if (cpu->cycles + 2 >= cpu->nextEvent) {
int32_t diff = cpu->nextEvent - cpu->cycles;
cpu->cycles = cpu->nextEvent;
cpu->irqh.processEvents(cpu);
cpu->cycles += 2 - diff;
} else {
cpu->cycles += 2;
}
cpu->executionState = LR35902_CORE_FETCH;
cpu->instruction(cpu);
++cpu->cycles;
if (cpu->cycles >= cpu->nextEvent) {
cpu->irqh.processEvents(cpu);
}
@ -150,12 +157,19 @@ void LR35902Tick(struct LR35902Core* cpu) {
void LR35902Run(struct LR35902Core* cpu) {
while (true) {
_LR35902Step(cpu);
if (cpu->cycles + 2 >= cpu->nextEvent) {
int32_t diff = cpu->nextEvent - cpu->cycles;
cpu->cycles = cpu->nextEvent;
cpu->irqh.processEvents(cpu);
cpu->cycles += 2 - diff;
} else {
cpu->cycles += 2;
}
cpu->executionState = LR35902_CORE_FETCH;
cpu->instruction(cpu);
++cpu->cycles;
if (cpu->cycles >= cpu->nextEvent) {
break;
} else if (cpu->executionState < LR35902_CORE_EXECUTE) {
// Silly hack: keep us from calling step if we know the next step is a no-op
++cpu->cycles;
++cpu->executionState;
}
}
cpu->irqh.processEvents(cpu);