GBA DMA: Linger last DMA on bus (fixes mgba.io/i/301, fixes mgba.io/i/1320)

CHANGES

@@ -2,6 +2,7 @@
 Emulation fixes:
  - ARM: Fix ALU reading PC after shifting
  - ARM: Fix STR storing PC after address calculation
+ - GBA DMA: Linger last DMA on bus (fixes mgba.io/i/301 and mgba.io/i/1320)
  - GBA Memory: Misaligned SRAM writes are ignored
  - GBA Serialize: Fix serializing DMA transfer register
 Other fixes:

include/mgba/internal/gba/gba.h

@@ -109,6 +109,7 @@ struct GBA {
 	bool haltPending;
 	bool cpuBlocked;
 	bool earlyExit;
+	uint32_t dmaPC;
 	int idleDetectionStep;
 	int idleDetectionFailures;
 	int32_t cachedRegisters[16];

include/mgba/internal/gba/serialize.h

@@ -300,8 +300,9 @@ struct GBASerializedState {
 	} hw;
 
 	uint32_t dmaTransferRegister;
+	uint32_t dmaBlockPC;
 
-	uint32_t reservedHardware[5];
+	uint32_t reservedHardware[4];
 
 	struct {
 		uint8_t type;

src/gba/dma.c

@@ -219,6 +219,7 @@ void GBADMAUpdate(struct GBA* gba) {
 	}
 
 	if (memory->activeDMA >= 0) {
+		gba->dmaPC = gba->cpu->gprs[ARM_PC];
 		mTimingDeschedule(&gba->timing, &memory->dmaEvent);
 		mTimingSchedule(&gba->timing, &memory->dmaEvent, memory->dma[memory->activeDMA].when - currentTime);
 	} else {

src/gba/gba.c

@@ -203,6 +203,7 @@ void GBAReset(struct ARMCore* cpu) {
 
 	gba->cpuBlocked = false;
 	gba->earlyExit = false;
+	gba->dmaPC = 0;
 	if (gba->yankedRomSize) {
 		gba->memory.romSize = gba->yankedRomSize;
 		gba->memory.romMask = toPow2(gba->memory.romSize) - 1;

src/gba/io.c

@@ -951,6 +951,7 @@ void GBAIOSerialize(struct GBA* gba, struct GBASerializedState* state) {
 	}
 
 	STORE_32(gba->memory.dmaTransferRegister, 0, &state->dmaTransferRegister);
+	STORE_32(gba->dmaPC, 0, &state->dmaBlockPC);
 
 	GBAHardwareSerialize(&gba->memory.hw, state);
 }
@@ -995,6 +996,7 @@ void GBAIODeserialize(struct GBA* gba, const struct GBASerializedState* state) {
 	GBAAudioWriteSOUNDCNT_X(&gba->audio, gba->memory.io[REG_SOUNDCNT_X >> 1]);
 
 	LOAD_32(gba->memory.dmaTransferRegister, 0, &state->dmaTransferRegister);
+	LOAD_32(gba->dmaPC, 0, &state->dmaBlockPC);
 
 	GBADMAUpdate(gba);
 	GBAHardwareDeserialize(&gba->memory.hw, state);

src/gba/memory.c

@@ -337,7 +337,7 @@ static void GBASetActiveRegion(struct ARMCore* cpu, uint32_t address) {
 }
 
 #define LOAD_BAD \
-	if (gba->performingDMA) { \
+	if (gba->performingDMA || cpu->gprs[ARM_PC] - gba->dmaPC == (gba->cpu->executionMode == MODE_THUMB ? WORD_SIZE_THUMB : WORD_SIZE_ARM)) { \
 		value = gba->bus; \
 	} else { \
 		value = cpu->prefetch[1]; \