From fc53fc9647353e3757a8538c01d6fd1e9a0ed3ca Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Tue, 27 Mar 2018 20:33:13 -0700
Subject: [PATCH] GBA Timer: Fix timers sometimes being late (fixes #1012)

---
 CHANGES         | 1 +
 src/gba/timer.c | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/CHANGES b/CHANGES
index 6032c5f54..61b8d113f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -55,6 +55,7 @@ Bugfixes:
  - Python: Fix package directory
  - GB Memory: Fix OAM DMA blocking regions (fixes mgba.io/i/1013)
  - Wii: Fix various setup and teardown drawing issues (fixes mgba.io/i/988)
+ - GBA Timer: Fix timers sometimes being late (fixes mgba.io/i/1012)
 Misc:
  - GBA Timer: Use global cycles for timers
  - GBA: Extend oddly-sized ROMs to full address space (fixes mgba.io/i/722)
diff --git a/src/gba/timer.c b/src/gba/timer.c
index 985ef0744..282263364 100644
--- a/src/gba/timer.c
+++ b/src/gba/timer.c
@@ -51,7 +51,7 @@ static void GBATimerUpdate(struct GBA* gba, int timerId, uint32_t cyclesLate) {
 	int32_t tickMask = (1 << GBATimerFlagsGetPrescaleBits(timer->flags)) - 1;
 	currentTime &= ~tickMask;
 	timer->lastEvent = currentTime;
-	GBATimerUpdateRegister(gba, timerId, 0);
+	GBATimerUpdateRegister(gba, timerId, TIMER_RELOAD_DELAY + cyclesLate);
 
 	if (GBATimerFlagsIsDoIrq(timer->flags)) {
 		timer->flags = GBATimerFlagsFillIrqPending(timer->flags);
@@ -155,7 +155,7 @@ void GBATimerUpdateRegister(struct GBA* gba, int timer, int32_t cyclesLate) {
 	if (!mTimingIsScheduled(&gba->timing, &currentTimer->event)) {
 		tickIncrement = (0x10000 - tickIncrement) << prescaleBits;
 		currentTime -= mTimingCurrentTime(&gba->timing) - cyclesLate;
-		mTimingSchedule(&gba->timing, &currentTimer->event, TIMER_RELOAD_DELAY + tickIncrement + currentTime);
+		mTimingSchedule(&gba->timing, &currentTimer->event, tickIncrement + currentTime);
 	}
 }