From 66842997dc50540c59f9f079aa903ab996fa3172 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Fri, 21 Aug 2020 04:42:50 -0700
Subject: [PATCH] GBA DMA: Fix ordering and timing of overlapping DMAs

---
 CHANGES       |  1 +
 src/gba/dma.c | 12 +++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index 8b414a59d..7b2bce2bf 100644
--- a/CHANGES
+++ b/CHANGES
@@ -28,6 +28,7 @@ Emulation fixes:
  - GBA BIOS: Fix reloading video registers after reset (fixes mgba.io/i/1808)
  - GBA BIOS: Make HLE BIOS calls interruptable (fixes mgba.io/i/1711 and mgba.io/i/1823)
  - GBA DMA: Linger last DMA on bus (fixes mgba.io/i/301 and mgba.io/i/1320)
+ - GBA DMA: Fix ordering and timing of overlapping DMAs
  - GBA Hardware: Fix GB Player detection on big endian platforms
  - GBA Memory: Improve gamepak prefetch timing
  - GBA Memory: Stall on VRAM access in mode 2 (fixes mgba.io/i/190)
diff --git a/src/gba/dma.c b/src/gba/dma.c
index 3343033ec..d30f0291a 100644
--- a/src/gba/dma.c
+++ b/src/gba/dma.c
@@ -219,7 +219,7 @@ void GBADMAUpdate(struct GBA* gba) {
 		struct GBADMA* dma = &memory->dma[i];
 		if (GBADMARegisterIsEnable(dma->reg) && dma->nextCount) {
 			int32_t time = dma->when - currentTime;
-			if (memory->activeDMA == -1 || (dma->count == dma->nextCount && time < leastTime)) {
+			if (memory->activeDMA == -1 || time < leastTime) {
 				leastTime = time;
 				memory->activeDMA = i;
 			}
@@ -303,6 +303,16 @@ void GBADMAService(struct GBA* gba, int number, struct GBADMA* info) {
 	info->nextCount = wordsRemaining;
 	info->nextSource = source;
 	info->nextDest = dest;
+
+	int i;
+	for (i = 0; i < 4; ++i) {
+		struct GBADMA* dma = &memory->dma[i];
+		int32_t time = dma->when - info->when;
+		if (time < 0 && GBADMARegisterIsEnable(dma->reg) && dma->nextCount) {
+			dma->when = info->when;
+		}
+	}
+
 	if (!wordsRemaining) {
 		info->nextCount |= 0x80000000;
 		if (sourceRegion < REGION_CART0 || destRegion < REGION_CART0) {