all repos — mgba @ d2f84e625b824c329b1653ad9cd178e83eb88bfd

mGBA Game Boy Advance Emulator

GB MBC: Fix MBC2 bit selection
Vicki Pfau vi@endrift.com
Tue, 16 Jun 2020 20:49:07 -0700
commit

d2f84e625b824c329b1653ad9cd178e83eb88bfd

parent

38d9a1c003ef0570610cab9cab70e414aa46db14

2 files changed, 11 insertions(+), 4 deletions(-)

jump to
M CHANGES → CHANGES 
@@ -1,6 +1,7 @@
 0.8.3: (Future)
 Emulation fixes:
  - GB MBC: Fix MBC1 RAM enable bit selection
+ - GB MBC: Fix MBC2 bit selection
 
 0.8.2: (2020-06-14)
 Emulation fixes:
M src/gb/mbc.c → src/gb/mbc.c 
@@ -474,9 +474,9 @@ void _GBMBC2(struct GB* gb, uint16_t address, uint8_t value) {
 	struct GBMemory* memory = &gb->memory;
 	int shift = (address & 1) * 4;
 	int bank = value & 0xF;
-	switch (address >> 13) {
+	switch ((address & 0xC100) >> 8) {
 	case 0x0:
-		switch (value) {
+		switch (value & 0x0F) {
 		case 0:
 			memory->sramAccess = false;
 			break;

@@ -485,7 +485,7 @@ memory->sramAccess = true;
 			break;
 		default:
 			// TODO
-			mLOG(GB_MBC, STUB, "MBC1 unknown value %02X", value);
+			mLOG(GB_MBC, STUB, "MBC2 unknown value %02X", value);
 			break;
 		}
 		break;

@@ -495,7 +495,10 @@ ++bank;
 		}
 		GBMBCSwitchBank(gb, bank);
 		break;
-	case 0x5:
+	case 0x80:
+	case 0x81:
+	case 0x82:
+	case 0x83:
 		if (!memory->sramAccess) {
 			return;
 		}

@@ -511,6 +514,9 @@ }
 }
 
 static uint8_t _GBMBC2Read(struct GBMemory* memory, uint16_t address) {
+	if (!memory->sramAccess) {
+		return 0xFF;
+	}
 	address &= 0x1FF;
 	int shift = (address & 1) * 4;
 	return (memory->sramBank[(address >> 1)] >> shift) | 0xF0;