From 546688f9fb9ea87589d786cdf7a909a34be0c904 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sat, 12 Aug 2017 14:12:49 -0700
Subject: [PATCH] GB Memory: Fix HDMA count starting in mode 0 (fixes #855)

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

diff --git a/CHANGES b/CHANGES
index bd68c106f..370e58f98 100644
--- a/CHANGES
+++ b/CHANGES
@@ -31,6 +31,7 @@ Bugfixes:
  - Qt: Fix sprite export pausing game indefinitely (fixes mgba.io/i/841)
  - ARM: Fix MSR when T bit is set
  - GB Video: Fix potential hang when ending mode 0
+ - GB Memory: Fix HDMA count starting in mode 0 (fixes mgba.io/i/855)
 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/src/gb/memory.c b/src/gb/memory.c
index 5e0574b2f..362c4b244 100644
--- a/src/gb/memory.c
+++ b/src/gb/memory.c
@@ -469,10 +469,13 @@ void GBMemoryWriteHDMA5(struct GB* gb, uint8_t value) {
 	bool wasHdma = gb->memory.isHdma;
 	gb->memory.isHdma = value & 0x80;
 	if ((!wasHdma && !gb->memory.isHdma) || gb->video.mode == 0) {
-		gb->memory.hdmaRemaining = ((value & 0x7F) + 1) * 0x10;
+		if (gb->memory.isHdma) {
+			gb->memory.hdmaRemaining = 0x10;
+		} else {
+			gb->memory.hdmaRemaining = ((value & 0x7F) + 1) * 0x10;
+		}
 		gb->cpuBlocked = true;
 		mTimingSchedule(&gb->timing, &gb->memory.hdmaEvent, 0);
-		gb->cpu->nextEvent = gb->cpu->cycles;
 	}
 }
 
diff --git a/src/gb/video.c b/src/gb/video.c
index 5ed2ab641..5810be63e 100644
--- a/src/gb/video.c
+++ b/src/gb/video.c
@@ -304,6 +304,7 @@ void _endMode3(struct mTiming* timing, void* context, uint32_t cyclesLate) {
 	GBVideoProcessDots(video);
 	if (video->ly < GB_VIDEO_VERTICAL_PIXELS && video->p->memory.isHdma && video->p->memory.io[REG_HDMA5] != 0xFF) {
 		video->p->memory.hdmaRemaining = 0x10;
+		video->p->cpuBlocked = true;
 		mTimingDeschedule(timing, &video->p->memory.hdmaEvent);
 		mTimingSchedule(timing, &video->p->memory.hdmaEvent, 0);
 	}