From b8b7ec0b12cdfa3aab1da32e06e8868e76ed9dbb Mon Sep 17 00:00:00 2001
From: Jeffrey Pfau <jeffrey@endrift.com>
Date: Sun, 25 Oct 2015 14:18:07 -0700
Subject: [PATCH] GBA Memory: Fix DMAs from BIOS while not in BIOS

DMAs appear to have special protections against reading from the BIOS, causing
BIOS reads to be entirely zero. This behavior needs confirmation on hardware,
but seems to make sense.
---
 CHANGES          |  1 +
 src/gba/memory.c | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/CHANGES b/CHANGES
index 0fae58d42..0c1b86dcb 100644
--- a/CHANGES
+++ b/CHANGES
@@ -6,6 +6,7 @@ Features:
 Bugfixes:
  - Util: Fix PowerPC PNG read/write pixel order
  - Qt: Use safer isLoaded check in GameController
+ - GBA Memory: Fix DMAs from BIOS while not in BIOS
 Misc:
  - Qt: Window size command line options are now supported
  - Qt: Increase usability of key mapper
diff --git a/src/gba/memory.c b/src/gba/memory.c
index a0dbaec2f..393ac3b79 100644
--- a/src/gba/memory.c
+++ b/src/gba/memory.c
@@ -330,7 +330,12 @@ static void GBASetActiveRegion(struct ARMCore* cpu, uint32_t address) {
 			LOAD_32(value, address, memory->bios); \
 		} else { \
 			GBALog(gba, GBA_LOG_GAME_ERROR, "Bad BIOS Load32: 0x%08X", address); \
-			value = memory->biosPrefetch; \
+			if (memory->activeDMA) { \
+				/* TODO: Test on hardware */ \
+				value = 0; \
+			} else { \
+				value = memory->biosPrefetch; \
+			} \
 		} \
 	} else { \
 		GBALog(gba, GBA_LOG_GAME_ERROR, "Bad memory Load32: 0x%08X", address); \
@@ -446,7 +451,11 @@ uint32_t GBALoad16(struct ARMCore* cpu, uint32_t address, int* cycleCounter) {
 				LOAD_16(value, address, memory->bios);
 			} else {
 				GBALog(gba, GBA_LOG_GAME_ERROR, "Bad BIOS Load16: 0x%08X", address);
-				value = (memory->biosPrefetch >> ((address & 2) * 8)) & 0xFFFF;
+				if (memory->activeDMA) {
+					value = 0;
+				} else {
+					value = (memory->biosPrefetch >> ((address & 2) * 8)) & 0xFFFF;
+				}
 			}
 		} else {
 			GBALog(gba, GBA_LOG_GAME_ERROR, "Bad memory Load16: 0x%08X", address);