all repos — mgba @ cf8868d5cb5cfd8244713328f96d8fdd814f1f83

mGBA Game Boy Advance Emulator

GB: Fix timer resetting
Jeffrey Pfau jeffrey@endrift.com
Mon, 30 May 2016 12:52:03 -0700
commit

cf8868d5cb5cfd8244713328f96d8fdd814f1f83

parent

f40b9ec82edbb852f2ac0677fda01b5728a3bfba

1 files changed, 12 insertions(+), 6 deletions(-)

jump to
M src/gb/timer.c → src/gb/timer.c 
@@ -30,13 +30,19 @@
 		if (timer->nextTima != INT_MAX) {
 			timer->nextTima -= timer->eventDiff;
 			if (timer->nextTima <= 0) {
-				++timer->p->memory.io[REG_TIMA];
 				if (!timer->p->memory.io[REG_TIMA]) {
 					timer->p->memory.io[REG_TIMA] = timer->p->memory.io[REG_TMA];
 					timer->p->memory.io[REG_IF] |= (1 << GB_IRQ_TIMER);
 					GBUpdateIRQs(timer->p);
+					timer->nextTima = timer->timaPeriod - 4;
+				} else {
+					++timer->p->memory.io[REG_TIMA];
+					if (!timer->p->memory.io[REG_TIMA]) {
+						timer->nextTima = 4;
+					} else {
+						timer->nextTima = timer->timaPeriod;
+					}
 				}
-				timer->nextTima = timer->timaPeriod;
 			}
 			if (timer->nextTima < timer->nextEvent) {
 				timer->nextEvent = timer->nextTima;

@@ -51,8 +57,8 @@
 void GBTimerDivReset(struct GBTimer* timer) {
 	timer->p->memory.io[REG_DIV] = 0;
 	timer->nextDiv = timer->eventDiff + timer->p->cpu->cycles + GB_DMG_DIV_PERIOD;
-	if (timer->eventDiff + GB_DMG_DIV_PERIOD < timer->nextEvent) {
-		timer->nextEvent = timer->eventDiff + GB_DMG_DIV_PERIOD;
+	if (timer->nextDiv - timer->eventDiff < timer->nextEvent) {
+		timer->nextEvent = timer->nextDiv - timer->eventDiff;
 		if (timer->nextEvent < timer->p->cpu->nextEvent) {
 			timer->p->cpu->nextEvent = timer->nextEvent;
 		}

@@ -84,8 +90,8 @@ }
 
 void GBTimerUpdateTIMA(struct GBTimer* timer) {
 	timer->nextTima = timer->eventDiff + timer->p->cpu->cycles + timer->timaPeriod;
-	if (timer->eventDiff + timer->timaPeriod < timer->nextEvent) {
-		timer->nextEvent = timer->eventDiff + timer->timaPeriod;
+	if (timer->nextTima - timer->eventDiff < timer->nextEvent) {
+		timer->nextEvent = timer->nextTima - timer->eventDiff;
 		if (timer->nextEvent < timer->p->cpu->nextEvent) {
 			timer->p->cpu->nextEvent = timer->nextEvent;
 		}