M include/mgba/core/timing.h → include/mgba/core/timing.h

@@ -38,6 +38,7 @@ bool mTimingIsScheduled(const struct mTiming* timing, const struct mTimingEvent*);
 int32_t mTimingTick(struct mTiming* timing, int32_t cycles);
 int32_t mTimingCurrentTime(const struct mTiming* timing);
 int32_t mTimingNextEvent(struct mTiming* timing);
+int32_t mTimingUntil(const struct mTiming* timing, const struct mTimingEvent*);
 
 CXX_GUARD_END
 

M src/core/timing.c → src/core/timing.c

@@ -91,3 +91,7 @@ return INT_MAX;
 	}
 	return next->when - timing->masterCycles;
 }
+
+int32_t mTimingUntil(const struct mTiming* timing, const struct mTimingEvent* event) {
+	return event->when - timing->masterCycles;
+}

M src/gb/timer.c → src/gb/timer.c

@@ -9,8 +9,6 @@ #include <mgba/internal/gb/gb.h>
 #include <mgba/internal/gb/io.h>
 #include <mgba/internal/gb/serialize.h>
 
-static void _GBTimerUpdateDIV(struct GBTimer* timer, uint32_t cyclesLate);
-
 void _GBTimerIRQ(struct mTiming* timing, void* context, uint32_t cyclesLate) {
 	UNUSED(timing);
 	UNUSED(cyclesLate);
@@ -36,12 +34,8 @@ }
 		++timer->internalDiv;
 		timer->p->memory.io[REG_DIV] = timer->internalDiv >> 4;
 	}
-	_GBTimerUpdateDIV(timer, cyclesLate);
-}
-
-void _GBTimerUpdateDIV(struct GBTimer* timer, uint32_t cyclesLate) {
 	// Batch div increments
-	int divsToGo = 16 - (timer->internalDiv & 15) + (timer->nextDiv / GB_DMG_DIV_PERIOD);
+	int divsToGo = 16 - (timer->internalDiv & 15);
 	int timaToGo = INT_MAX;
 	if (timer->timaPeriod) {
 		timaToGo = timer->timaPeriod - (timer->internalDiv & (timer->timaPeriod - 1));
@@ -49,12 +43,8 @@ }
 	if (timaToGo < divsToGo) {
 		divsToGo = timaToGo;
 	}
-	if (divsToGo > 16) {
-		divsToGo = 16;
-	}
-	timer->nextDiv &= GB_DMG_DIV_PERIOD - 1;
-	timer->nextDiv += GB_DMG_DIV_PERIOD * divsToGo;
-	mTimingSchedule(&timer->p->timing, &timer->event, timer->nextDiv - cyclesLate);
+	timer->nextDiv = GB_DMG_DIV_PERIOD * divsToGo;
+	mTimingSchedule(timing, &timer->event, timer->nextDiv - cyclesLate);
 }
 
 void GBTimerReset(struct GBTimer* timer) {
@@ -96,11 +86,13 @@ case 3:
 			timer->timaPeriod = 256 >> 4;
 			break;
 		}
+
+		timer->nextDiv -= mTimingUntil(&timer->p->timing, &timer->event);
+		mTimingDeschedule(&timer->p->timing, &timer->event);
+		mTimingSchedule(&timer->p->timing, &timer->event, 0);
 	} else {
 		timer->timaPeriod = 0;
 	}
-	mTimingDeschedule(&timer->p->timing, &timer->event);
-	_GBTimerUpdateDIV(timer, 0);
 	return tac;
 }