git rekt — mgba.git: ab9b398317aef256f2aa2f0a2da524149c1a1c76

GBA Timer: Use global cycles for timers

Vicki Pfau vi@endrift.com

Mon, 03 Jul 2017 23:53:01 -0700

commit

ab9b398317aef256f2aa2f0a2da524149c1a1c76

parent

4cd249e632f7337adf061e3e1a25442506938a84

5 files changed, 81 insertions(+), 42 deletions(-)

jump to

CHANGES

include/mgba/internal/gba/gba.h

include/mgba/internal/gba/timer.h

src/gba/io.c

src/gba/timer.c

M CHANGES → CHANGES

@@ -1,3 +1,7 @@
+0.7.0: (Future)
+Misc:
+ - GBA Timer: Use global cycles for timers
+
 0.6.0: (Future)
 Features:
  - GBA: Support printing debug strings from inside a game

M include/mgba/internal/gba/gba.h → include/mgba/internal/gba/gba.h

@@ -79,6 +79,7 @@
 	uint32_t bus;
 	int performingDMA;
 
+	struct mTimingEvent timerMaster;
 	struct GBATimer timers[4];
 
 	int springIRQ;

M include/mgba/internal/gba/timer.h → include/mgba/internal/gba/timer.h

@@ -21,15 +21,14 @@
 struct GBA;
 struct GBATimer {
 	uint16_t reload;
-	uint16_t oldReload;
-	uint32_t lastEvent;
+	int32_t lastEvent;
 	struct mTimingEvent event;
 	int32_t overflowInterval;
 	GBATimerFlags flags;
 };
 
 void GBATimerInit(struct GBA* gba);
-void GBATimerUpdateRegister(struct GBA* gba, int timer);
+void GBATimerUpdateRegister(struct GBA* gba, int timer, int32_t cyclesLate);
 void GBATimerWriteTMCNT_LO(struct GBA* gba, int timer, uint16_t value);
 void GBATimerWriteTMCNT_HI(struct GBA* gba, int timer, uint16_t value);

M src/gba/io.c → src/gba/io.c

@@ -707,17 +707,18 @@ gba->haltPending = false;
 	}
 
 	switch (address) {
+	// Reading this takes two cycles (1N+1I), so let's remove them preemptively
 	case REG_TM0CNT_LO:
-		GBATimerUpdateRegister(gba, 0);
+		GBATimerUpdateRegister(gba, 0, 2);
 		break;
 	case REG_TM1CNT_LO:
-		GBATimerUpdateRegister(gba, 1);
+		GBATimerUpdateRegister(gba, 1, 2);
 		break;
 	case REG_TM2CNT_LO:
-		GBATimerUpdateRegister(gba, 2);
+		GBATimerUpdateRegister(gba, 2, 2);
 		break;
 	case REG_TM3CNT_LO:
-		GBATimerUpdateRegister(gba, 3);
+		GBATimerUpdateRegister(gba, 3, 2);
 		break;
 
 	case REG_KEYINPUT:
@@ -925,7 +926,6 @@
 	for (i = 0; i < 4; ++i) {
 		STORE_16(gba->memory.io[(REG_DMA0CNT_LO + i * 12) >> 1], (REG_DMA0CNT_LO + i * 12), state->io);
 		STORE_16(gba->timers[i].reload, 0, &state->timers[i].reload);
-		STORE_16(gba->timers[i].oldReload, 0, &state->timers[i].oldReload);
 		STORE_32(gba->timers[i].lastEvent - mTimingCurrentTime(&gba->timing), 0, &state->timers[i].lastEvent);
 		STORE_32(gba->timers[i].event.when - mTimingCurrentTime(&gba->timing), 0, &state->timers[i].nextEvent);
 		STORE_32(gba->timers[i].overflowInterval, 0, &state->timers[i].overflowInterval);
@@ -952,9 +952,12 @@ }
 	}
 
 	uint32_t when;
+	LOAD_32(when, 0, &state->masterCycles);
+	when += state->cpu.cycles;
+	when = 0x400 - (when & 0x3FF);
+	mTimingSchedule(&gba->timing, &gba->timerMaster, when);
 	for (i = 0; i < 4; ++i) {
 		LOAD_16(gba->timers[i].reload, 0, &state->timers[i].reload);
-		LOAD_16(gba->timers[i].oldReload, 0, &state->timers[i].oldReload);
 		LOAD_32(gba->timers[i].overflowInterval, 0, &state->timers[i].overflowInterval);
 		LOAD_32(gba->timers[i].flags, 0, &state->timers[i].flags);
 		if (i > 0 && GBATimerFlagsIsCountUp(gba->timers[i].flags)) {

M src/gba/timer.c → src/gba/timer.c

@@ -8,11 +8,12 @@
 #include <mgba/internal/gba/gba.h>
 #include <mgba/internal/gba/io.h>
 
-static void GBATimerUpdate(struct mTiming* timing, struct GBA* gba, int timerId, uint32_t cyclesLate) {
+#define TIMER_MASTER 1024
+
+static void GBATimerUpdate(struct GBA* gba, int timerId, uint32_t cyclesLate) {
 	struct GBATimer* timer = &gba->timers[timerId];
 	gba->memory.io[(REG_TM0CNT_LO >> 1) + (timerId << 1)] = timer->reload;
-	timer->oldReload = timer->reload;
-	timer->lastEvent = timing->masterCycles - cyclesLate;
+	GBATimerUpdateRegister(gba, timerId, cyclesLate);
 
 	if (GBATimerFlagsIsDoIrq(timer->flags)) {
 		GBARaiseIRQ(gba, IRQ_TIMER0 + timerId);
@@ -33,74 +34,106 @@ struct GBATimer* nextTimer = &gba->timers[timerId + 1];
 		if (GBATimerFlagsIsCountUp(nextTimer->flags)) { // TODO: Does this increment while disabled?
 			++gba->memory.io[(REG_TM1CNT_LO >> 1) + (timerId << 1)];
 			if (!gba->memory.io[(REG_TM1CNT_LO >> 1) + (timerId << 1)] && GBATimerFlagsIsEnable(nextTimer->flags)) {
-				mTimingSchedule(timing, &nextTimer->event, -cyclesLate);
+				GBATimerUpdate(gba, timerId + 1, cyclesLate);
 			}
 		}
 	}
+}
 
-	if (!GBATimerFlagsIsCountUp(timer->flags)) {
-		uint32_t nextEvent = timer->overflowInterval - cyclesLate;
-		mTimingSchedule(timing, &timer->event, nextEvent);
-	}
+static void GBATimerMasterUpdate(struct mTiming* timing, void* context, uint32_t cyclesLate) {
+	struct GBA* gba = context;
+	mTimingSchedule(timing, &gba->timerMaster, TIMER_MASTER - cyclesLate);
+	GBATimerUpdateRegister(gba, 0, cyclesLate);
+	GBATimerUpdateRegister(gba, 1, cyclesLate);
+	GBATimerUpdateRegister(gba, 2, cyclesLate);
+	GBATimerUpdateRegister(gba, 3, cyclesLate);
 }
 
 static void GBATimerUpdate0(struct mTiming* timing, void* context, uint32_t cyclesLate) {
-	GBATimerUpdate(timing, context, 0, cyclesLate);
+	UNUSED(timing);
+	GBATimerUpdate(context, 0, cyclesLate);
 }
 
 static void GBATimerUpdate1(struct mTiming* timing, void* context, uint32_t cyclesLate) {
-	GBATimerUpdate(timing, context, 1, cyclesLate);
+	UNUSED(timing);
+	GBATimerUpdate(context, 1, cyclesLate);
 }
 
 static void GBATimerUpdate2(struct mTiming* timing, void* context, uint32_t cyclesLate) {
-	GBATimerUpdate(timing, context, 2, cyclesLate);
+	UNUSED(timing);
+	GBATimerUpdate(context, 2, cyclesLate);
 }
 
 static void GBATimerUpdate3(struct mTiming* timing, void* context, uint32_t cyclesLate) {
-	GBATimerUpdate(timing, context, 3, cyclesLate);
+	UNUSED(timing);
+	GBATimerUpdate(context, 3, cyclesLate);
 }
 
 void GBATimerInit(struct GBA* gba) {
+	gba->timerMaster.name = "GBA Timer Master";
+	gba->timerMaster.callback = GBATimerMasterUpdate;
+	gba->timerMaster.context = gba;
+	gba->timerMaster.priority = 0x20;
+	mTimingSchedule(&gba->timing, &gba->timerMaster, TIMER_MASTER);
 	memset(gba->timers, 0, sizeof(gba->timers));
 	gba->timers[0].event.name = "GBA Timer 0";
 	gba->timers[0].event.callback = GBATimerUpdate0;
 	gba->timers[0].event.context = gba;
-	gba->timers[0].event.priority = 0x20;
+	gba->timers[0].event.priority = 0x21;
 	gba->timers[1].event.name = "GBA Timer 1";
 	gba->timers[1].event.callback = GBATimerUpdate1;
 	gba->timers[1].event.context = gba;
-	gba->timers[1].event.priority = 0x21;
+	gba->timers[1].event.priority = 0x22;
 	gba->timers[2].event.name = "GBA Timer 2";
 	gba->timers[2].event.callback = GBATimerUpdate2;
 	gba->timers[2].event.context = gba;
-	gba->timers[2].event.priority = 0x22;
+	gba->timers[2].event.priority = 0x23;
 	gba->timers[3].event.name = "GBA Timer 3";
 	gba->timers[3].event.callback = GBATimerUpdate3;
 	gba->timers[3].event.context = gba;
-	gba->timers[3].event.priority = 0x23;
+	gba->timers[3].event.priority = 0x24;
 }
 
-void GBATimerUpdateRegister(struct GBA* gba, int timer) {
+void GBATimerUpdateRegister(struct GBA* gba, int timer, int32_t cyclesLate) {
 	struct GBATimer* currentTimer = &gba->timers[timer];
-	if (GBATimerFlagsIsEnable(currentTimer->flags) && !GBATimerFlagsIsCountUp(currentTimer->flags)) {
-		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;
+	if (!GBATimerFlagsIsEnable(currentTimer->flags) || GBATimerFlagsIsCountUp(currentTimer->flags)) {
+		return;
+	}
+
+	if (gba->memory.lastPrefetchedPc > (uint32_t) gba->cpu->gprs[ARM_PC]) {
+		cyclesLate -= ((gba->memory.lastPrefetchedPc - gba->cpu->gprs[ARM_PC]) * gba->cpu->memory.activeSeqCycles16) / WORD_SIZE_THUMB;
+	}
+
+	int prescaleBits = GBATimerFlagsGetPrescaleBits(currentTimer->flags);
+	int32_t currentTime = mTimingCurrentTime(&gba->timing) - cyclesLate;
+	int32_t tickMask = (1 << prescaleBits) - 1;
+	currentTime &= ~tickMask;
+	int32_t tickIncrement = currentTime - currentTimer->lastEvent;
+	currentTimer->lastEvent = currentTime;
+	tickIncrement >>= prescaleBits;
+	tickIncrement += gba->memory.io[(REG_TM0CNT_LO + (timer << 2)) >> 1];
+	gba->memory.io[(REG_TM0CNT_LO + (timer << 2)) >> 1] = tickIncrement;
+	tickIncrement -= 0x10000;
+	mTimingDeschedule(&gba->timing, &currentTimer->event);
+	if (tickIncrement >= 0) {
+		mTimingSchedule(&gba->timing, &currentTimer->event, 7 - (tickIncrement << prescaleBits));
+	} else {
+		int32_t nextIncrement = mTimingUntil(&gba->timing, &gba->timerMaster);
+		tickIncrement = -tickIncrement;
+		tickIncrement <<= prescaleBits;
+		if (nextIncrement - tickIncrement > 0) {
+			mTimingSchedule(&gba->timing, &currentTimer->event, 7 + tickIncrement);
 		}
-		// 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 + prefetchSkew) >> GBATimerFlagsGetPrescaleBits(currentTimer->flags));
 	}
 }
 
 void GBATimerWriteTMCNT_LO(struct GBA* gba, int timer, uint16_t reload) {
 	gba->timers[timer].reload = reload;
-	gba->timers[timer].overflowInterval = (0x10000 - gba->timers[timer].reload) << GBATimerFlagsGetPrescaleBits(gba->timers[timer].flags);
 }
 
 void GBATimerWriteTMCNT_HI(struct GBA* gba, int timer, uint16_t control) {
 	struct GBATimer* currentTimer = &gba->timers[timer];
-	GBATimerUpdateRegister(gba, timer);
+	GBATimerUpdateRegister(gba, timer, 0);
 
 	unsigned oldPrescale = GBATimerFlagsGetPrescaleBits(currentTimer->flags);
 	unsigned prescaleBits;
@@ -121,21 +154,20 @@ }
 	currentTimer->flags = GBATimerFlagsSetPrescaleBits(currentTimer->flags, prescaleBits);
 	currentTimer->flags = GBATimerFlagsTestFillCountUp(currentTimer->flags, timer > 0 && (control & 0x0004));
 	currentTimer->flags = GBATimerFlagsTestFillDoIrq(currentTimer->flags, control & 0x0040);
-	currentTimer->overflowInterval = (0x10000 - currentTimer->reload) << GBATimerFlagsGetPrescaleBits(currentTimer->flags);
 	bool wasEnabled = GBATimerFlagsIsEnable(currentTimer->flags);
 	currentTimer->flags = GBATimerFlagsTestFillEnable(currentTimer->flags, control & 0x0080);
 	if (!wasEnabled && GBATimerFlagsIsEnable(currentTimer->flags)) {
 		mTimingDeschedule(&gba->timing, &currentTimer->event);
-		if (!GBATimerFlagsIsCountUp(currentTimer->flags)) {
-			mTimingSchedule(&gba->timing, &currentTimer->event, currentTimer->overflowInterval + 7 - 6 * prescaleBits);
-		}
 		gba->memory.io[(REG_TM0CNT_LO + (timer << 2)) >> 1] = currentTimer->reload;
-		currentTimer->oldReload = currentTimer->reload;
-		currentTimer->lastEvent = gba->timing.masterCycles + gba->cpu->cycles;
+		int32_t tickMask = (1 << prescaleBits) - 1;
+		currentTimer->lastEvent = (mTimingCurrentTime(&gba->timing)) & ~tickMask;
+		GBATimerUpdateRegister(gba, timer, 0);
 	} else if (wasEnabled && !GBATimerFlagsIsEnable(currentTimer->flags)) {
 		mTimingDeschedule(&gba->timing, &currentTimer->event);
 	} else if (GBATimerFlagsIsEnable(currentTimer->flags) && GBATimerFlagsGetPrescaleBits(currentTimer->flags) != oldPrescale && !GBATimerFlagsIsCountUp(currentTimer->flags)) {
 		mTimingDeschedule(&gba->timing, &currentTimer->event);
-		mTimingSchedule(&gba->timing, &currentTimer->event, currentTimer->overflowInterval - currentTimer->lastEvent);
+		int32_t tickMask = (1 << prescaleBits) - 1;
+		currentTimer->lastEvent = (mTimingCurrentTime(&gba->timing)) & ~tickMask;
+		GBATimerUpdateRegister(gba, timer, 0);
 	}
 }

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