From fac10eae96d38c4a4f78b4d06eb23022263fff75 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Wed, 21 Mar 2018 09:11:24 -0700
Subject: [PATCH] GB Memory: Fix OAM DMA blocking regions (fixes #1013)

---
 CHANGES                          |  1 +
 include/mgba/internal/gb/video.h |  1 -
 src/gb/memory.c                  | 58 +++++++++++++++++---------------
 3 files changed, 32 insertions(+), 28 deletions(-)

diff --git a/CHANGES b/CHANGES
index 6313f9097..547e9dcd3 100644
--- a/CHANGES
+++ b/CHANGES
@@ -53,6 +53,7 @@ Bugfixes:
  - GBA: Fix SharkPort saves for EEPROM games
  - Qt: Fix opening in fullscreen (fixes mgba.io/i/993)
  - Python: Fix package directory
+ - GB Memory: Fix OAM DMA blocking regions (fixes mgba.io/i/1013)
 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/include/mgba/internal/gb/video.h b/include/mgba/internal/gb/video.h
index 90cfd7bbb..7fd731be6 100644
--- a/include/mgba/internal/gb/video.h
+++ b/include/mgba/internal/gb/video.h
@@ -26,7 +26,6 @@ enum {
 
 	GB_VIDEO_HORIZONTAL_LENGTH = 456,
 
-	GB_VIDEO_MODE_1_LENGTH = 65664,
 	GB_VIDEO_TOTAL_LENGTH = 70224,
 
 	GB_BASE_MAP = 0x1800,
diff --git a/src/gb/memory.c b/src/gb/memory.c
index 1dae0b988..089558011 100644
--- a/src/gb/memory.c
+++ b/src/gb/memory.c
@@ -16,31 +16,33 @@
 
 mLOG_DEFINE_CATEGORY(GB_MEM, "GB Memory", "gb.memory");
 
-struct OAMBlock {
-	uint16_t low;
-	uint16_t high;
+enum GBBus {
+	GB_BUS_CPU,
+	GB_BUS_MAIN,
+	GB_BUS_VRAM,
+	GB_BUS_RAM
 };
 
-static const struct OAMBlock _oamBlockDMG[] = {
-	{ 0xA000, 0xFE00 },
-	{ 0xA000, 0xFE00 },
-	{ 0xA000, 0xFE00 },
-	{ 0xA000, 0xFE00 },
-	{ 0x8000, 0xA000 },
-	{ 0xA000, 0xFE00 },
-	{ 0xA000, 0xFE00 },
-	{ 0xA000, 0xFE00 },
+static const enum GBBus _oamBlockDMG[] = {
+	GB_BUS_MAIN, // 0x0000
+	GB_BUS_MAIN, // 0x2000
+	GB_BUS_MAIN, // 0x4000
+	GB_BUS_MAIN, // 0x6000
+	GB_BUS_VRAM, // 0x8000
+	GB_BUS_MAIN, // 0xA000
+	GB_BUS_MAIN, // 0xC000
+	GB_BUS_CPU, // 0xE000
 };
 
-static const struct OAMBlock _oamBlockCGB[] = {
-	{ 0xA000, 0xC000 },
-	{ 0xA000, 0xC000 },
-	{ 0xA000, 0xC000 },
-	{ 0xA000, 0xC000 },
-	{ 0x8000, 0xA000 },
-	{ 0xA000, 0xC000 },
-	{ 0xC000, 0xFE00 },
-	{ 0xA000, 0xC000 },
+static const enum GBBus _oamBlockCGB[] = {
+	GB_BUS_MAIN, // 0x0000
+	GB_BUS_MAIN, // 0x2000
+	GB_BUS_MAIN, // 0x4000
+	GB_BUS_MAIN, // 0x6000
+	GB_BUS_VRAM, // 0x8000
+	GB_BUS_MAIN, // 0xA000
+	GB_BUS_RAM, // 0xC000
+	GB_BUS_CPU // 0xE000
 };
 
 static void _pristineCow(struct GB* gba);
@@ -192,9 +194,10 @@ uint8_t GBLoad8(struct LR35902Core* cpu, uint16_t address) {
 	struct GB* gb = (struct GB*) cpu->master;
 	struct GBMemory* memory = &gb->memory;
 	if (gb->memory.dmaRemaining) {
-		const struct OAMBlock* block = gb->model < GB_MODEL_CGB ? _oamBlockDMG : _oamBlockCGB;
-		block = &block[memory->dmaSource >> 13];
-		if (address >= block->low && address < block->high) {
+		const enum GBBus* block = gb->model < GB_MODEL_CGB ? _oamBlockDMG : _oamBlockCGB;
+		enum GBBus dmaBus = block[memory->dmaSource >> 13];
+		enum GBBus accessBus = block[address >> 13];
+		if (dmaBus != GB_BUS_CPU && dmaBus == accessBus) {
 			return 0xFF;
 		}
 		if (address >= GB_BASE_OAM && address < GB_BASE_UNUSABLE) {
@@ -264,9 +267,10 @@ void GBStore8(struct LR35902Core* cpu, uint16_t address, int8_t value) {
 	struct GB* gb = (struct GB*) cpu->master;
 	struct GBMemory* memory = &gb->memory;
 	if (gb->memory.dmaRemaining) {
-		const struct OAMBlock* block = gb->model < GB_MODEL_CGB ? _oamBlockDMG : _oamBlockCGB;
-		block = &block[memory->dmaSource >> 13];
-		if (address >= block->low && address < block->high) {
+		const enum GBBus* block = gb->model < GB_MODEL_CGB ? _oamBlockDMG : _oamBlockCGB;
+		enum GBBus dmaBus = block[memory->dmaSource >> 13];
+		enum GBBus accessBus = block[address >> 13];
+		if (dmaBus != GB_BUS_CPU && dmaBus == accessBus) {
 			return;
 		}
 		if (address >= GB_BASE_OAM && address < GB_BASE_UNUSABLE) {