void IBusSlave.Write(ushort address, byte value)
{
if (address == 0x0000)
{
_controller.Value = value;
UpdateNametableBaseAddress();
UpdateBgPatternTableBaseAddress();
}
else if (address == 0x0001)
{
_mask.Value = value;
}
else if (address == 0x0003)
{
_oamAddress = value;
}
else if (address == 0x0004)
{
_oamMemory[_oamAddress++] = value;
}
else if (address == 0x0005)
{
if (_writingCameraPosY)
{
_cameraPosY = value;
}
else
{
_cameraPosX = value;
}
_writingCameraPosY = !_writingCameraPosY;
}
else if (address == 0x0006)
{
if (_writingPPUAddrLow)
{
_ppuAddr |= value;
}
else
{
_ppuAddr = (ushort)(value << 8);
}
_writingPPUAddrLow = !_writingPPUAddrLow;
}
else if (address == 0x0007)
{
_masterClient.Value = value;
_masterClient.Write(_ppuAddr);
_ppuAddr += _controller.I ? (byte)32 : (byte)1;
}
else
{
throw new NotImplementedException();
}
}
void IClockSink.OnTick()
{
if (_enabled)
{
_masterClient.Read(_srcAddr++);
_masterClient.Write(0x2014);
_writeCount++;
if (_writeCount == 0)
{
_enabled = false;
_masterClient.Release();
}
}
}
private void DispatchAddressing()
{
void ReadSource(AddressOperand addressOperand, ref byte result)
{
switch (addressOperand)
{
// In Result
case AddressOperand.None:
break;
case AddressOperand.Memory:
if (_addressState.Destination != AddressOperand.PC)
{
_masterClient.Read(_addressState.MemoryAddress);
result = _masterClient.Value;
}
break;
case AddressOperand.X:
result = Registers.X;
break;
case AddressOperand.Y:
result = Registers.Y;
break;
case AddressOperand.A:
result = Registers.A;
break;
default:
throw new ArgumentException(nameof(_addressState.SourceA));
}
}
// Read Source
ReadSource(_addressState.SourceA, ref _addressState.ResultA);
ReadSource(_addressState.SourceB, ref _addressState.ResultB);
// Do Operation
switch (_addressState.Operation)
{
case AddressOperation.None:
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
break;
case AddressOperation.Inc:
_addressState.ResultA++;
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
break;
case AddressOperation.Dec:
_addressState.ResultA--;
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
break;
case AddressOperation.BitTest:
if (_addressState.AffectFlags)
{
Status.Z = (_addressState.ResultA & _addressState.ResultB) == 0;
Status.N = (_addressState.ResultB & 0x80) != 0;
Status.V = (_addressState.ResultB & 0x40) != 0;
}
break;
case AddressOperation.Compare:
if (_addressState.AffectFlags)
{
Status.C = _addressState.ResultA >= _addressState.ResultB;
UpdateNZ((byte)(_addressState.ResultA - _addressState.ResultB));
}
break;
case AddressOperation.And:
_addressState.ResultA &= _addressState.ResultB;
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
break;
case AddressOperation.Or:
_addressState.ResultA |= _addressState.ResultB;
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
break;
case AddressOperation.Adc:
{
var value = (short)(_addressState.ResultA + _addressState.ResultB + (Status.C ? 1 : 0));
if (_addressState.AffectFlags)
{
UpdateCV(_addressState.ResultA, _addressState.ResultB, value);
}
_addressState.ResultA = (byte)value;
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
}
break;
case AddressOperation.Rol:
{
var c = Status.C;
if (_addressState.AffectFlags)
{
Status.C = (_addressState.ResultA & 0x80) != 0;
}
_addressState.ResultA = (byte)((_addressState.ResultA << 1) | (Status.C ? 1 : 0));
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
}
break;
case AddressOperation.Asl:
{
if (_addressState.AffectFlags)
{
Status.C = (_addressState.ResultA & 0x80) != 0;
}
_addressState.ResultA = (byte)(_addressState.ResultA << 1);
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
}
break;
case AddressOperation.Xor:
_addressState.ResultA ^= _addressState.ResultB;
if (_addressState.AffectFlags)
{
UpdateNZ(_addressState.ResultA);
}
break;
default:
throw new ArgumentException(nameof(_addressState.Operation));
}
// Write Destination
switch (_addressState.Destination)
{
case AddressOperand.None:
break;
case AddressOperand.Memory:
_masterClient.Value = _addressState.ResultA;
_masterClient.Write(_addressState.MemoryAddress);
break;
case AddressOperand.X:
Registers.X = _addressState.ResultA;
break;
case AddressOperand.Y:
Registers.Y = _addressState.ResultA;
break;
case AddressOperand.A:
Registers.A = _addressState.ResultA;
break;
case AddressOperand.S:
Registers.S = _addressState.ResultA;
break;
case AddressOperand.PC:
Registers.PC = _addressState.MemoryAddress;
break;
default:
throw new ArgumentException(nameof(_addressState.Destination));
}
}