From f9ff88302f3de521a0f71ffbe8d15d9bfd9d0c8c Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sun, 3 Mar 2019 12:46:46 -0800
Subject: [PATCH] GB Video: Delay LYC STAT check (fixes #1331)

---
 CHANGES        | 1 +
 src/gb/video.c | 9 ++++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index 4e9653d92..e79ec1691 100644
--- a/CHANGES
+++ b/CHANGES
@@ -9,6 +9,7 @@ Bugfixes:
  - GBA BIOS: Fix multiboot entry point (fixes Magic Floor)
  - Qt: More app metadata fixes
  - Qt: Fix load recent from archive (fixes mgba.io/i/1325)
+ - GB Video: Delay LYC STAT check (fixes mgba.io/i/1331)
 Misc:
  - GBA Savedata: EEPROM performance fixes
  - GBA Savedata: Automatically map 1Mbit Flash files as 1Mbit Flash
diff --git a/src/gb/video.c b/src/gb/video.c
index d63460088..8aa978292 100644
--- a/src/gb/video.c
+++ b/src/gb/video.c
@@ -224,7 +224,6 @@ void _endMode0(struct mTiming* timing, void* context, uint32_t cyclesLate) {
 	++video->ly;
 	video->p->memory.io[REG_LY] = video->ly;
 	GBRegisterSTAT oldStat = video->stat;
-	video->stat = GBRegisterSTATSetLYC(video->stat, lyc == video->ly);
 	if (video->ly < GB_VIDEO_VERTICAL_PIXELS) {
 		next = GB_VIDEO_MODE_2_LENGTH;
 		video->mode = 2;
@@ -246,6 +245,14 @@ void _endMode0(struct mTiming* timing, void* context, uint32_t cyclesLate) {
 	if (!_statIRQAsserted(video, oldStat) && _statIRQAsserted(video, video->stat)) {
 		video->p->memory.io[REG_IF] |= (1 << GB_IRQ_LCDSTAT);
 	}
+
+	// LYC stat is delayed 1 T-cycle
+	oldStat = video->stat;
+	video->stat = GBRegisterSTATSetLYC(video->stat, lyc == video->ly);
+	if (!_statIRQAsserted(video, oldStat) && _statIRQAsserted(video, video->stat)) {
+		video->p->memory.io[REG_IF] |= (1 << GB_IRQ_LCDSTAT);
+	}
+
 	GBUpdateIRQs(video->p);
 	video->p->memory.io[REG_STAT] = video->stat;
 	mTimingSchedule(timing, &video->modeEvent, (next << video->p->doubleSpeed) - cyclesLate);