M src/gb/io.c → src/gb/io.c

@@ -55,10 +55,8 @@ switch (address) {
 	case REG_DIV:
 		GBTimerDivReset(&gb->timer);
 		return;
-	case REG_TIMA:
-		// ???
-		return;
 	case REG_JOYP:
+	case REG_TIMA:
 	case REG_TMA:
 	case REG_LYC:
 		// Handled transparently by the registers

M src/gb/timer.c → src/gb/timer.c

@@ -71,15 +71,19 @@ case 3:
 			timer->timaPeriod = 256;
 			break;
 		}
-		timer->nextTima = timer->eventDiff + timer->timaPeriod;
-		if (timer->nextTima < timer->nextEvent) {
-			timer->nextEvent = timer->nextTima;
-			if (timer->nextEvent < timer->p->cpu->nextEvent) {
-				timer->p->cpu->nextEvent = timer->nextEvent;
-			}
-		}
+		GBTimerUpdateTIMA(timer);
 	} else {
 		timer->nextTima = INT_MAX;
 	}
 	return tac;
 }
+
+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->nextEvent < timer->p->cpu->nextEvent) {
+			timer->p->cpu->nextEvent = timer->nextEvent;
+		}
+	}
+}

M src/gb/timer.h → src/gb/timer.h

@@ -32,5 +32,6 @@ void GBTimerReset(struct GBTimer*);
 int32_t GBTimerProcessEvents(struct GBTimer*, int32_t cycles);
 void GBTimerDivReset(struct GBTimer*);
 uint8_t GBTimerUpdateTAC(struct GBTimer*, GBRegisterTAC tac);
+void GBTimerUpdateTIMA(struct GBTimer* timer);
 
 #endif