From 5ff3e339fe3ce5613b1e3e7439395cba7f52733d Mon Sep 17 00:00:00 2001
From: Jeffrey Pfau <jeffrey@endrift.com>
Date: Sat, 8 Oct 2016 09:57:01 -0700
Subject: [PATCH] GB Timer: Improve DIV reset behavior

---
 CHANGES        |  1 +
 src/gb/timer.c | 13 ++++++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/CHANGES b/CHANGES
index 39ad5517c..bfc303bd7 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3,6 +3,7 @@ Features:
  - GBA: Support printing debug strings from inside a game
 Bugfixes:
  - LR35902: Fix core never exiting with certain event patterns
+ - GB Timer: Improve DIV reset behavior
 Misc:
  - SDL: Remove scancode key input
  - GBA Video: Clean up unused timers
diff --git a/src/gb/timer.c b/src/gb/timer.c
index 4b4502961..a1acdb574 100644
--- a/src/gb/timer.c
+++ b/src/gb/timer.c
@@ -30,9 +30,6 @@ int32_t GBTimerProcessEvents(struct GBTimer* timer, int32_t cycles) {
 			timer->nextEvent += timer->nextDiv;
 		}
 		while (timer->nextDiv <= 0) {
-			if ((timer->internalDiv & 15) == 15) {
-				++timer->p->memory.io[REG_DIV];
-			}
 			timer->nextDiv += GB_DMG_DIV_PERIOD;
 
 			// Make sure to trigger when the correct bit is a falling edge
@@ -44,6 +41,7 @@ int32_t GBTimerProcessEvents(struct GBTimer* timer, int32_t cycles) {
 				}
 			}
 			++timer->internalDiv;
+			timer->p->memory.io[REG_DIV] = timer->internalDiv >> 4;
 		}
 		if (timer->nextEvent <= 0) {
 			// Batch div increments
@@ -64,6 +62,15 @@ int32_t GBTimerProcessEvents(struct GBTimer* timer, int32_t cycles) {
 
 void GBTimerDivReset(struct GBTimer* timer) {
 	timer->p->memory.io[REG_DIV] = 0;
+	timer->internalDiv = 0;
+	timer->nextDiv = timer->p->cpu->cycles + GB_DMG_DIV_PERIOD;
+	if (timer->nextDiv < timer->nextEvent) {
+		timer->nextEvent = timer->nextDiv;
+	}
+	if (timer->nextDiv < timer->p->cpu->nextEvent) {
+		timer->p->cpu->nextEvent = timer->nextDiv;
+	}
+	timer->nextDiv += timer->eventDiff;
 }
 
 uint8_t GBTimerUpdateTAC(struct GBTimer* timer, GBRegisterTAC tac) {