From fc2a0955f4031992f694662cbaf2f7185240417f Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sat, 8 Jul 2017 17:04:05 -0700
Subject: [PATCH] GBA Timer: Fix timer regression when prefetch is enabled
 (fixes #781)

---
 src/gba/io.c    | 8 ++++----
 src/gba/timer.c | 4 ----
 2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/src/gba/io.c b/src/gba/io.c
index ae76e09e4..60d1a7c83 100644
--- a/src/gba/io.c
+++ b/src/gba/io.c
@@ -709,16 +709,16 @@ uint16_t GBAIORead(struct GBA* gba, uint32_t address) {
 	switch (address) {
 	// Reading this takes two cycles (1N+1I), so let's remove them preemptively
 	case REG_TM0CNT_LO:
-		GBATimerUpdateRegister(gba, 0, 2);
+		GBATimerUpdateRegister(gba, 0, 4);
 		break;
 	case REG_TM1CNT_LO:
-		GBATimerUpdateRegister(gba, 1, 2);
+		GBATimerUpdateRegister(gba, 1, 4);
 		break;
 	case REG_TM2CNT_LO:
-		GBATimerUpdateRegister(gba, 2, 2);
+		GBATimerUpdateRegister(gba, 2, 4);
 		break;
 	case REG_TM3CNT_LO:
-		GBATimerUpdateRegister(gba, 3, 2);
+		GBATimerUpdateRegister(gba, 3, 4);
 		break;
 
 	case REG_KEYINPUT:
diff --git a/src/gba/timer.c b/src/gba/timer.c
index d4ee0776a..305660aa9 100644
--- a/src/gba/timer.c
+++ b/src/gba/timer.c
@@ -143,10 +143,6 @@ void GBATimerUpdateRegister(struct GBA* gba, int timer, int32_t cyclesLate) {
 		return;
 	}
 
-	if (gba->memory.lastPrefetchedPc > (uint32_t) gba->cpu->gprs[ARM_PC]) {
-		cyclesLate -= ((gba->memory.lastPrefetchedPc - gba->cpu->gprs[ARM_PC]) * gba->cpu->memory.activeSeqCycles16) / WORD_SIZE_THUMB;
-	}
-
 	int prescaleBits = GBATimerFlagsGetPrescaleBits(currentTimer->flags);
 	int32_t currentTime = mTimingCurrentTime(&gba->timing) - cyclesLate;
 	int32_t tickMask = (1 << prescaleBits) - 1;