public override void Reset()
{
this.romBank = 1;
this.ramBank = 0;
this.enableExternalRam = false;
Array.Clear(this.externalRam, 0, this.externalRam.Length);
this.bankingMode = BankingMode.ROM;
}
public void WriteByte(byte data, int address)
{
if (address < MemorySchema.ROM_END)
{
//TODO determine how to get rid of magic numbers
if (address < 0x2000)
{
switch (_header.BankingMode)
{
case CartridgeSchema.MBCMode.MBC1:
case CartridgeSchema.MBCMode.MBC2:
case CartridgeSchema.MBCMode.MBC3:
case CartridgeSchema.MBCMode.MBC5:
if (_header.BankingMode == CartridgeSchema.MBCMode.MBC2 && Helpers.TestBit((ushort)address, 4))
{
return;
}
_externalRAM.Enabled = Helpers.GetBits(data, 4) == 0x0A;
break;
}
}
else if (address < 0x4000)
{
int newBank;
switch (_header.BankingMode)
{
case CartridgeSchema.MBCMode.NoMBC:
break;
case CartridgeSchema.MBCMode.MBC1:
//Override the lower 5 bits of the ROM Bank
newBank = _romBank;
Helpers.ResetLowBits(ref newBank, 5);
newBank |= Helpers.GetBits(data, 5);
SetROMBank(newBank);
break;
case CartridgeSchema.MBCMode.MBC2:
SetROMBank(Helpers.GetBits(data, 4));
break;
case CartridgeSchema.MBCMode.MBC3:
SetROMBank(Helpers.GetBits(data, 7));
break;
case CartridgeSchema.MBCMode.MBC5:
if (address < 0x3000)
{
//Override the lower 5 bits of the ROM Bank
newBank = _romBank;
Helpers.ResetLowBits(ref newBank, 8);
newBank |= Helpers.GetBits(data, 8);
SetROMBank(newBank);
}
else
{
newBank = _romBank;
Helpers.SetBit(ref newBank, 9, Helpers.TestBit(data, 1));
SetROMBank(newBank);
}
break;
default:
throw new ArgumentOutOfRangeException();
}
}
else if (address < 0x6000)
{
switch (_header.BankingMode)
{
case CartridgeSchema.MBCMode.MBC1:
if (_bankMode == BankingMode.ROMBank)
{
//Override the bits 5-6 of the romBank
int newBank = _romBank;
Helpers.ResetHighBits(ref newBank, 3);
newBank |= (byte)(data << 5);
SetROMBank(newBank);
}
else
{
_ramBank = _header.RAMBanks == 0 ? 0 : Helpers.GetBits(data, 2) % _header.RAMBanks;
}
break;
case CartridgeSchema.MBCMode.MBC3:
//TODO RTC register select
_ramBank = Helpers.GetBits(data, 2) % _header.RAMBanks;
break;
case CartridgeSchema.MBCMode.MBC5:
_ramBank = Helpers.GetBits(data, 4) % _header.RAMBanks;
break;
}
}
else if (address < 0x8000)
{
if (_header.BankingMode == CartridgeSchema.MBCMode.MBC1)
{
_bankMode = (BankingMode)Helpers.GetBits(data, 1);
}
}
}
else if (address >= MemorySchema.EXTERNAL_RAM_START && address < MemorySchema.EXTERNAL_RAM_END && _externalRAM.Enabled)
{
address = (address - MemorySchema.EXTERNAL_RAM_START) + ((_bankMode == BankingMode.RAMBank ? _ramBank : 0) * CartridgeSchema.RAM_BANK_SIZE);
if (address < _externalRAM.Length)
{
_externalRAM.WriteByte(data, address);
}
}
}
public override void Write(ushort addr, byte value)
{
// RAM Enable
if (addr >= 0x0000 && addr <= 0x1FFF)
{
if ((value & 0xF) == 0x0A)
{
this.enableExternalRam = true;
}
else
{
this.enableExternalRam = false;
}
return;
}
// ROM Bank Number Lower 5 Bits
if (addr >= 0x2000 && addr <= 0x3FFF)
{
this.romBank &= 0b11100000; // Erase 5 bits
this.romBank |= (byte)(value & 0b00011111); // Whole 5 bits
if (this.romBank == 0)
{
this.romBank = 1;
}
return;
}
// RAM Bank Number / Upper Bits of ROM Bank Number
if (addr >= 0x4000 && addr <= 0x5FFF)
{
value &= 0b11;
if (this.bankingMode == BankingMode.RAM)
{
Console.WriteLine("Set RAM Bank to: " + value);
this.ramBank = value;
}
else
{
this.romBank &= 0b00011111; // Erase high bits
this.romBank |= (byte)(value << 5);
}
return;
}
// RAM Bank 00-03
if (addr >= 0xA000 && addr <= 0xBFFF && this.enableExternalRam)
{
this.externalRam[this.calcBankAddrRam(addr, this.ramBank)] = value;
return;
}
if (addr >= 0x6000 && addr <= 0x7FFF)
{
if ((value & 1) != 0)
{
this.bankingMode = BankingMode.RAM;
}
else
{
this.bankingMode = BankingMode.ROM;
}
return;
}
}