M CHANGES → CHANGES

@@ -25,6 +25,7 @@ - DS: Fix exposed CPU frequencies and audio timing
  - DS Audio: Fix audio sampling slightly too quickly
  - Feature: Fix resizing GIF buffer (fixes mgba.io/i/695)
  - DS GX: Retain translucent polygon ID when drawing opaque fragments (fixes mgba.io/i/661)
+ - DS Timers: Fix ARM9 timers running too fast
 Misc:
  - DS: Set boot complete bit in RAM on boot (fixes mgba.io/i/576, mgba.io/i/580, mgba.io/i/586)
  - DS Memory: Ensure DS9 I/O is 8-byte aligned

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

@@ -25,6 +25,7 @@ uint32_t lastEvent;
 	struct mTimingEvent event;
 	int32_t overflowInterval;
 	GBATimerFlags flags;
+	int forcedPrescale;
 };
 
 struct ARMCore;

M src/ds/timer.c → src/ds/timer.c

@@ -71,18 +71,22 @@ ds->ds9.timers[0].event.name = "DS9 Timer 0";
 	ds->ds9.timers[0].event.callback = DSTimerUpdate0;
 	ds->ds9.timers[0].event.context = &ds->ds9;
 	ds->ds9.timers[0].event.priority = 0x20;
+	ds->ds9.timers[0].forcedPrescale = 1;
 	ds->ds9.timers[1].event.name = "DS9 Timer 1";
 	ds->ds9.timers[1].event.callback = DSTimerUpdate1;
 	ds->ds9.timers[1].event.context = &ds->ds9;
 	ds->ds9.timers[1].event.priority = 0x21;
+	ds->ds9.timers[1].forcedPrescale = 1;
 	ds->ds9.timers[2].event.name = "DS9 Timer 2";
 	ds->ds9.timers[2].event.callback = DSTimerUpdate2;
 	ds->ds9.timers[2].event.context = &ds->ds9;
 	ds->ds9.timers[2].event.priority = 0x22;
+	ds->ds9.timers[2].forcedPrescale = 1;
 	ds->ds9.timers[3].event.name = "DS9 Timer 3";
 	ds->ds9.timers[3].event.callback = DSTimerUpdate3;
 	ds->ds9.timers[3].event.context = &ds->ds9;
 	ds->ds9.timers[3].event.priority = 0x23;
+	ds->ds9.timers[3].forcedPrescale = 1;
 }
 
 void DSTimerWriteTMCNT_HI(struct GBATimer* timer, struct mTiming* timing, struct ARMCore* cpu, uint16_t* io, uint16_t value) {

M src/gba/timer.c → src/gba/timer.c

@@ -128,16 +128,16 @@ void GBATimerWriteTMCNT_HI(struct GBATimer* timer, struct mTiming* timing, struct ARMCore* cpu, uint16_t* io, uint16_t control) {
 	unsigned oldPrescale = GBATimerFlagsGetPrescaleBits(timer->flags);
 	switch (control & 0x0003) {
 	case 0x0000:
-		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, 0);
+		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, timer->forcedPrescale);
 		break;
 	case 0x0001:
-		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, 6);
+		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, 6 + timer->forcedPrescale);
 		break;
 	case 0x0002:
-		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, 8);
+		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, 8 + timer->forcedPrescale);
 		break;
 	case 0x0003:
-		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, 10);
+		timer->flags = GBATimerFlagsSetPrescaleBits(timer->flags, 10 + timer->forcedPrescale);
 		break;
 	}
 	timer->flags = GBATimerFlagsTestFillCountUp(timer->flags, timer > 0 && (control & 0x0004));