From 67fedf8618e7e0f884f3c6ce749c537758cf1962 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sat, 23 Mar 2019 22:46:58 -0700
Subject: [PATCH] GB Timer: Fix timing adjustments when writing to TAC (fixes
 #1340)

---
 CHANGES        | 1 +
 src/gb/timer.c | 7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/CHANGES b/CHANGES
index aaa95489f..9edcc44f9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,7 @@ Emulation fixes:
  - GBA DMA: Fix DMA0-2 lengths (fixes mgba.io/i/1344)
  - GB Video: Fix window y changing mid-window (fixes mgba.io/i/1345)
  - GB Video: Fix more window edge cases (fixes mgba.io/i/1346)
+ - GB Timer: Fix timing adjustments when writing to TAC (fixes mgba.io/i/1340)
 Other fixes:
  - Qt: More app metadata fixes
  - Qt: Fix load recent from archive (fixes mgba.io/i/1325)
diff --git a/src/gb/timer.c b/src/gb/timer.c
index e990b3534..bddb4ad53 100644
--- a/src/gb/timer.c
+++ b/src/gb/timer.c
@@ -92,6 +92,10 @@ void GBTimerDivReset(struct GBTimer* timer) {
 
 uint8_t GBTimerUpdateTAC(struct GBTimer* timer, GBRegisterTAC tac) {
 	if (GBRegisterTACIsRun(tac)) {
+		timer->nextDiv -= mTimingUntil(&timer->p->timing, &timer->event);
+		mTimingDeschedule(&timer->p->timing, &timer->event);
+		_GBTimerDivIncrement(timer, (timer->p->cpu->executionState + 2) & 3);
+
 		switch (GBRegisterTACGetClock(tac)) {
 		case 0:
 			timer->timaPeriod = 1024 >> 4;
@@ -107,9 +111,6 @@ uint8_t GBTimerUpdateTAC(struct GBTimer* timer, GBRegisterTAC tac) {
 			break;
 		}
 
-		timer->nextDiv -= mTimingUntil(&timer->p->timing, &timer->event);
-		mTimingDeschedule(&timer->p->timing, &timer->event);
-		_GBTimerDivIncrement(timer, (timer->p->cpu->executionState + 2) & 3);
 		timer->nextDiv += GB_DMG_DIV_PERIOD;
 		mTimingSchedule(&timer->p->timing, &timer->event, timer->nextDiv);
 	} else {