public override void write(ushort address, byte val)
{
if (address < 0x6000)
{
// A couple of games have tried to write here. It's undefined behavior as far as I know.
return;
}
// First handle RAM. Everything else uses the shift register
if (address < 0x8000)
{
int offset = address - 0x6000;
PRG_RAM[offset] = val;
return;
}
// Writing with bit 7 set, this write just resets the shift register
if ((val & 0x80) != 0)
{
shift_register = 0x00;
ControlRegister |= 0x0C;
shift_register_write_counter = 0;
updateOffsets();
return;
}
// We're shifting in a bit to the shift register..
shift_register >>= 1;
shift_register |= (byte)((val & 1) << 4);
shift_register_write_counter++;
// Should we do an actual write?
if (shift_register_write_counter == 5)
{
if (address < 0xA000)
{
ControlRegister = shift_register;
NametableMirroringMode oldMode = cartridge.NametableMirroring;
switch (ControlRegister & 3)
{
case 0: cartridge.NametableMirroring = NametableMirroringMode.OneScreenLowBank; break;
case 1: cartridge.NametableMirroring = NametableMirroringMode.OneScreenHighBank; break;
case 2: cartridge.NametableMirroring = NametableMirroringMode.Vertical; break;
case 3: cartridge.NametableMirroring = NametableMirroringMode.Horizontal; break;
}
if (oldMode != cartridge.NametableMirroring)
{
Console.WriteLine("Switched to {0}", cartridge.NametableMirroring.ToString());
}
}
else if (address < 0xC000)
{
CHR0Select = shift_register;
}
else if (address < 0xE000)
{
CHR1Select = shift_register;
}
else
{
Console.WriteLine("Switched to PRG {0}", shift_register & 0x0F);
PRGSelect = shift_register;
}
// Update offsets
updateOffsets();
shift_register = 0x00;
shift_register_write_counter = 0;
}
}
/// <summary>
/// Load a rom file using the iNES file format, the de facto NES rom file format.
/// http://wiki.nesdev.com/w/index.php/INES
/// </summary>
/// <param name="romPath"></param>
private void loadRomData(string romPath)
{
byte[] fullRomData = File.ReadAllBytes(romPath);
byte[] header = new ArraySegment <byte>(fullRomData, 0, 16).ToArray();
// First confirm this is actually an iNES rom...
uint fileSignature = BitConverter.ToUInt32(header, 0);
if (fileSignature != INES_FILE_SIGNATURE)
{
log.error("Did not find expected iNES Rom File Signature");
throw new InvalidDataException();
}
PRGROM_16KBankCount = header[4];
PRGRAM_8KBankCount = header[8];
CHRROM_8KBankCount = header[5];
// iNES has a number of flags all rolled up into 4 flag bytes.
int flag6 = header[6];
int flag7 = header[7];
int flag9 = header[9];
int flag10 = header[10];
NametableMirroring = (flag6 & 1) == 1 ? NametableMirroringMode.Vertical : NametableMirroringMode.Horizontal;
bool usesTrainer = (flag6 & 4) != 0;
if (usesTrainer)
{
log.error("ROM uses a trainer. This is unsupported.");
throw new NotImplementedException();
}
isNTSC = (flag10 & 1) == 0;
if (!isNTSC)
{
log.error("ROM is PAL. This is unsupported...");
throw new NotImplementedException();
}
if ((flag6 & 2) == 1)
{
BatteryBackedRAM = true;
}
MapperNumber = flag6 >> 4 | (flag7 & 0xf0);
// Now that we know all the 'metadata' about the file, load the actual data.
int prgStart = 16 + (usesTrainer ? 512 : 0);
int prgBytes = 0x4000 * PRGROM_16KBankCount;
PRGRomData = new ArraySegment <byte>(fullRomData, prgStart, prgBytes).ToArray();
int chrStart = prgStart + prgBytes;
int chrBytes = 0x2000 * CHRROM_8KBankCount;
CHRRomData = new ArraySegment <byte>(fullRomData, chrStart, chrBytes).ToArray();
log.info("ROM Details --");
log.info(" * Mapper #{0}", MapperNumber);
log.info(" * Nametable mirroring mode is {0}.", NametableMirroring.ToString());
log.info(" * {0} Output", isNTSC ? "NTSC" : "PAL");
if (BatteryBackedRAM)
{
log.info(" * Battery-backed RAM ('Game Saves' supported)");
}
log.info(" * ROM Bank Data");
log.info(" - {0}x 16 KB PRG ROM", PRGROM_16KBankCount);
log.info(" - {0}x 8 KB PRG RAM", PRGRAM_8KBankCount);
log.info(" - {0}x 8 KB CHR ROM", CHRROM_8KBankCount);
log.info("Finished loading '{0}'.", romPath);
}
