M include/mgba/internal/gb/mbc.h → include/mgba/internal/gb/mbc.h

@@ -19,6 +19,7 @@ struct GBMemory;
 void GBMBCInit(struct GB* gb);
 void GBMBCSwitchBank(struct GB* gb, int bank);
 void GBMBCSwitchBank0(struct GB* gb, int bank);
+void GBMBCSwitchHalfBank(struct GB* gb, int half, int bank);
 void GBMBCSwitchSramBank(struct GB* gb, int bank);
 
 enum GBCam {

M include/mgba/internal/gb/memory.h → include/mgba/internal/gb/memory.h

@@ -22,6 +22,8 @@
 enum {
 	GB_BASE_CART_BANK0 = 0x0000,
 	GB_BASE_CART_BANK1 = 0x4000,
+	GB_BASE_CART_HALFBANK1 = 0x4000,
+	GB_BASE_CART_HALFBANK2 = 0x6000,
 	GB_BASE_VRAM = 0x8000,
 	GB_BASE_EXTERNAL_RAM = 0xA000,
 	GB_BASE_WORKING_RAM_BANK0 = 0xC000,
@@ -46,6 +48,7 @@ };
 
 enum {
 	GB_SIZE_CART_BANK0 = 0x4000,
+	GB_SIZE_CART_HALFBANK = 0x2000,
 	GB_SIZE_CART_MAX = 0x800000,
 	GB_SIZE_VRAM = 0x4000,
 	GB_SIZE_VRAM_BANK0 = 0x2000,
@@ -104,6 +107,11 @@ int mode;
 	int multicartStride;
 };
 
+struct GBMBC6State {
+	int currentBank1;
+	uint8_t* romBank1;
+};
+
 struct GBMBC7State {
 	enum GBMBC7MachineState state;
 	uint16_t sr;
@@ -127,6 +135,7 @@ };
 
 union GBMBCState {
 	struct GBMBC1State mbc1;
+	struct GBMBC6State mbc6;
 	struct GBMBC7State mbc7;
 	struct GBPocketCamState pocketCam;
 	struct GBTAMA5State tama5;

M src/gb/mbc.c → src/gb/mbc.c

@@ -68,6 +68,28 @@ gb->cpu->memory.setActiveRegion(gb->cpu, gb->cpu->pc);
 	}
 }
 
+void GBMBCSwitchHalfBank(struct GB* gb, int half, int bank) {
+	size_t bankStart = bank * GB_SIZE_CART_HALFBANK;
+	if (bankStart + GB_SIZE_CART_HALFBANK > gb->memory.romSize) {
+		mLOG(GB_MBC, GAME_ERROR, "Attempting to switch to an invalid ROM bank: %0X", bank);
+		bankStart &= (gb->memory.romSize - 1);
+		bank = bankStart / GB_SIZE_CART_HALFBANK;
+		if (!bank) {
+			++bank;
+		}
+	}
+	if (!half) {
+		gb->memory.romBank = &gb->memory.rom[bankStart];
+		gb->memory.currentBank = bank;
+	} else {
+		gb->memory.mbcState.mbc6.romBank1 = &gb->memory.rom[bankStart];
+		gb->memory.mbcState.mbc6.currentBank1 = bank;
+	}
+	if (gb->cpu->pc < GB_BASE_VRAM) {
+		gb->cpu->memory.setActiveRegion(gb->cpu, gb->cpu->pc);
+	}
+}
+
 static bool _isMulticart(const uint8_t* mem) {
 	bool success = true;
 	struct VFile* vf;
@@ -496,11 +518,34 @@ }
 }
 
 void _GBMBC6(struct GB* gb, uint16_t address, uint8_t value) {
-	// TODO
-	mLOG(GB_MBC, STUB, "MBC6 unimplemented");
-	UNUSED(gb);
-	UNUSED(address);
-	UNUSED(value);
+	struct GBMemory* memory = &gb->memory;
+	int bank = value & 0x7F;
+	switch (address >> 10) {
+	case 0:
+		switch (value) {
+		case 0:
+			memory->sramAccess = false;
+			break;
+		case 0xA:
+			memory->sramAccess = true;
+			GBMBCSwitchSramBank(gb, memory->sramCurrentBank);
+			break;
+		default:
+			// TODO
+			mLOG(GB_MBC, STUB, "MBC6 unknown value %02X", value);
+			break;
+		}
+		break;
+	case 0x9:
+		GBMBCSwitchHalfBank(gb, 0, bank);
+		break;
+	case 0xD:
+		GBMBCSwitchHalfBank(gb, 1, bank);
+		break;
+	default:
+		mLOG(GB_MBC, STUB, "MBC6 unknown address: %04X:%02X", address, value);
+		break;
+	}
 }
 
 void _GBMBC7(struct GB* gb, uint16_t address, uint8_t value) {

M src/gb/memory.c → src/gb/memory.c

@@ -207,10 +207,14 @@ case GB_REGION_CART_BANK0 + 1:
 	case GB_REGION_CART_BANK0 + 2:
 	case GB_REGION_CART_BANK0 + 3:
 		return memory->romBase[address & (GB_SIZE_CART_BANK0 - 1)];
-	case GB_REGION_CART_BANK1:
-	case GB_REGION_CART_BANK1 + 1:
 	case GB_REGION_CART_BANK1 + 2:
 	case GB_REGION_CART_BANK1 + 3:
+		if (memory->mbcType == GB_MBC6) {
+			return memory->mbcState.mbc6.romBank1[address & (GB_SIZE_CART_HALFBANK - 1)];
+		}
+		// Fall through
+	case GB_REGION_CART_BANK1:
+	case GB_REGION_CART_BANK1 + 1:
 		return memory->romBank[address & (GB_SIZE_CART_BANK0 - 1)];
 	case GB_REGION_VRAM:
 	case GB_REGION_VRAM + 1: