From 7ea686a7d937de42533ca15989d3a48d6bf6d51d Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sat, 3 Feb 2018 23:12:57 -0800
Subject: [PATCH] GB Timer: Fix TIMA/TMA timing

---
 CHANGES                                               |  1 +
 .../timer/tima_write_reloading/manifest.yml           |  1 -
 .../acceptance/timer/tma_write_reloading/manifest.yml |  1 -
 src/gb/io.c                                           | 11 ++++++++++-
 src/gb/timer.c                                        |  8 ++++----
 5 files changed, 15 insertions(+), 7 deletions(-)
 delete mode 100644 cinema/gb/mooneye-gb/acceptance/timer/tima_write_reloading/manifest.yml
 delete mode 100644 cinema/gb/mooneye-gb/acceptance/timer/tma_write_reloading/manifest.yml

diff --git a/CHANGES b/CHANGES
index ed885288f..24ce59c25 100644
--- a/CHANGES
+++ b/CHANGES
@@ -48,6 +48,7 @@ Bugfixes:
  - Wii: Fix screen tear when unpausing
  - GBA: Fix some GBA ROM misdetection (fixes mgba.io/i/978)
  - GBA Hardware: RTC accuracy improvements
+ - GB Timer: Minor accuracy improvements
 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/cinema/gb/mooneye-gb/acceptance/timer/tima_write_reloading/manifest.yml b/cinema/gb/mooneye-gb/acceptance/timer/tima_write_reloading/manifest.yml
deleted file mode 100644
index a697ada66..000000000
--- a/cinema/gb/mooneye-gb/acceptance/timer/tima_write_reloading/manifest.yml
+++ /dev/null
@@ -1 +0,0 @@
-fail: true
diff --git a/cinema/gb/mooneye-gb/acceptance/timer/tma_write_reloading/manifest.yml b/cinema/gb/mooneye-gb/acceptance/timer/tma_write_reloading/manifest.yml
deleted file mode 100644
index a697ada66..000000000
--- a/cinema/gb/mooneye-gb/acceptance/timer/tma_write_reloading/manifest.yml
+++ /dev/null
@@ -1 +0,0 @@
-fail: true
diff --git a/src/gb/io.c b/src/gb/io.c
index c6e065b95..21a7f696e 100644
--- a/src/gb/io.c
+++ b/src/gb/io.c
@@ -380,8 +380,17 @@ void GBIOWrite(struct GB* gb, unsigned address, uint8_t value) {
 		}
 		break;
 	case REG_TIMA:
+		if (value && mTimingUntil(&gb->timing, &gb->timer.irq) > 1) {
+			mTimingDeschedule(&gb->timing, &gb->timer.irq);
+		}
+		if (mTimingUntil(&gb->timing, &gb->timer.irq) == -1) {
+			return;
+		}
+		break;
 	case REG_TMA:
-		// Handled transparently by the registers
+		if (mTimingUntil(&gb->timing, &gb->timer.irq) == -1) {
+			gb->memory.io[REG_TIMA] = value;
+		}
 		break;
 	case REG_TAC:
 		value = GBTimerUpdateTAC(&gb->timer, value);
diff --git a/src/gb/timer.c b/src/gb/timer.c
index d5fe20089..736ca3cfb 100644
--- a/src/gb/timer.c
+++ b/src/gb/timer.c
@@ -27,7 +27,7 @@ static void _GBTimerDivIncrement(struct GBTimer* timer, uint32_t cyclesLate) {
 		if (timer->timaPeriod > 0 && (timer->internalDiv & (timer->timaPeriod - 1)) == timer->timaPeriod - 1) {
 			++timer->p->memory.io[REG_TIMA];
 			if (!timer->p->memory.io[REG_TIMA]) {
-				mTimingSchedule(&timer->p->timing, &timer->irq, 4 - cyclesLate);
+				mTimingSchedule(&timer->p->timing, &timer->irq, 7 - ((timer->p->cpu->executionState - cyclesLate) & 3));
 			}
 		}
 		++timer->internalDiv;
@@ -69,11 +69,11 @@ void GBTimerReset(struct GBTimer* timer) {
 void GBTimerDivReset(struct GBTimer* timer) {
 	timer->nextDiv -= mTimingUntil(&timer->p->timing, &timer->event);
 	mTimingDeschedule(&timer->p->timing, &timer->event);
-	_GBTimerDivIncrement(timer, (timer->p->cpu->executionState + 1) & 3);
+	_GBTimerDivIncrement(timer, 0);
 	if (((timer->internalDiv << 1) | ((timer->nextDiv >> 3) & 1)) & timer->timaPeriod) {
 		++timer->p->memory.io[REG_TIMA];
 		if (!timer->p->memory.io[REG_TIMA]) {
-			mTimingSchedule(&timer->p->timing, &timer->irq, 4 - ((timer->p->cpu->executionState + 1) & 3));
+			mTimingSchedule(&timer->p->timing, &timer->irq, 7 - (timer->p->cpu->executionState & 3));
 		}
 	}
 	timer->p->memory.io[REG_DIV] = 0;
@@ -101,7 +101,7 @@ uint8_t GBTimerUpdateTAC(struct GBTimer* timer, GBRegisterTAC tac) {
 
 		timer->nextDiv -= mTimingUntil(&timer->p->timing, &timer->event);
 		mTimingDeschedule(&timer->p->timing, &timer->event);
-		_GBTimerDivIncrement(timer, (timer->p->cpu->executionState + 1) & 3);
+		_GBTimerDivIncrement(timer, (timer->p->cpu->executionState + 2) & 3);
 		timer->nextDiv += GB_DMG_DIV_PERIOD;
 		mTimingSchedule(&timer->p->timing, &timer->event, timer->nextDiv);
 	} else {