public static ushort GetAbsolute(MOS6502 CPU)
{
var nextShort = CPU.ReadNextShort();
CPU.IncrementPC(2);
return(nextShort);
}
public static ushort GetZeroPage(MOS6502 CPU)
{
var pc = CPU.ReadNextByte();
CPU.IncrementPC();
return(pc);
}
public static ushort GetAbsoluteX(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextShort();
var nextShort = (ushort)(intermediateAddress + CPU.Registers.X);
CPU.IncrementPC(2);
return(nextShort);
}
public static ushort GetImmediate(MOS6502 CPU)
{
var pc = CPU.Registers.PC.Read();
operandValue = CPU.ReadNextByte(isCycle: false);
CPU.IncrementPC();
return(pc);
}
public static ushort GetZeroPageY(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextByte();
var address = (ushort)(intermediateAddress + CPU.Registers.Y);
address &= 0xFF;
CPU.CycleFinished();
CPU.IncrementPC();
return(address);
}
public static ushort GetIndirectX(MOS6502 CPU)
{
var incompleteXAddress = CPU.ReadNextByte();
CPU.IncrementPC();
var intermediateAddress = (byte)(incompleteXAddress + CPU.Registers.X);
return(intermediateAddress == 0xFF
? (ushort)(CPU.ReadByteAt(0xFF) | CPU.ReadByteAt(0x00) << 8)
: CPU.ReadShortAt(intermediateAddress));
}
public static ushort GetIndirectYWrite(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextByte();
CPU.IncrementPC();
var baseAddress = intermediateAddress == 0xFF
? (ushort)(CPU.ReadByteAt(0xFF) | CPU.ReadByteAt(0x00) << 8)
: CPU.ReadShortAt((ushort)intermediateAddress);
CPU.CycleFinished();
return((ushort)(baseAddress + CPU.Registers.Y));
}
public static string GetAddressAsString(MOS6502 CPU, OpcodeContainer container)
{
if (container.Name == "RTS")
{
return("");
}
switch (container.AddressingMode)
{
case AddressingModes.Implied:
return("");
case AddressingModes.Accumulator:
return("A");
case AddressingModes.Indirect:
return($"(${intermediateAddress:X4}) @ ${address:X4}");
case AddressingModes.IndirectYWrite:
case AddressingModes.IndirectY:
return($"(${intermediateAddress:X2}),Y @ ${address:X4}");
case AddressingModes.IndirectX:
return($"(${intermediateAddress:X2},X) @ ${address:X4}");
case AddressingModes.ZeroPage:
return($"${address:X2}");
case AddressingModes.ZeroPageX:
return($"${intermediateAddress:X2},X @ ${address:X2}");
case AddressingModes.ZeroPageY:
return($"${intermediateAddress:X2},Y @ ${address:X2}");
case AddressingModes.AbsoluteY:
return($"${intermediateAddress:X4},Y @ ${address:X4}");
case AddressingModes.AbsoluteX:
case AddressingModes.AbsoluteXWrite:
return($"${intermediateAddress:X4},X @ ${address:X4}");
case AddressingModes.Absolute:
return($"${address:X4}");
case AddressingModes.Immediate:
return($"#${operandValue:X2}");
default:
return($"0x{address:X4}");
}
}
public Opcodes(MOS6502 cpu)
{
this.CPU = cpu;
var bindingFlags = BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance;
foreach (var methodInfo in typeof(Opcodes).GetMethods(bindingFlags).Where(m => m.CustomAttributes.Any(ca => ca.AttributeType == typeof(MOS6502OpcodeAttribute))))
{
foreach (var attrib in methodInfo.GetCustomAttributes <MOS6502OpcodeAttribute>())
{
this.OpCodeMap.Add(attrib.Code, new OpcodeContainer(attrib, this, methodInfo));
}
}
}
public static ushort GetIndirect(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextShort();
// 6502 bug in indirect JMP...
if ((intermediateAddress & 0x00FF) == 0xFF)
{
byte lowByte = CPU.ReadByteAt(intermediateAddress);
byte highByte = CPU.ReadByteAt((ushort)(intermediateAddress - 0x00FF));
return((ushort)(highByte << 8 | lowByte));
}
return(CPU.ReadShortAt(intermediateAddress));
}
public static ushort GetIndirectY(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextByte();
CPU.IncrementPC();
var baseAddress = intermediateAddress == 0xFF
? (ushort)(CPU.ReadByteAt(0xFF) | CPU.ReadByteAt(0x00) << 8)
: CPU.ReadShortAt((ushort)intermediateAddress);
var finalAddress = (ushort)(baseAddress + CPU.Registers.Y);
if (AddressingMode.NotSamePage(baseAddress, CPU.Registers.Y))
{
CPU.CycleFinished();
}
return(finalAddress);
}
public static ushort GetAddressedOperand(MOS6502 CPU, OpcodeContainer container)
{
operandValue = 0;
intermediateAddress = 0;
address = 0;
switch (container.AddressingMode)
{
case AddressingModes.Implied:
address = 0x0000;
CPU.CycleFinished();
break;
case AddressingModes.Accumulator:
address = 0x0000;
CPU.CycleFinished();
break;
case AddressingModes.Immediate:
address = AddressingMode.GetImmediate(CPU);
break;
case AddressingModes.Absolute:
address = AddressingMode.GetAbsolute(CPU);
break;
case AddressingModes.AbsoluteX:
address = AddressingMode.GetAbsoluteX(CPU);
break;
case AddressingModes.AbsoluteXWrite:
address = AddressingMode.GetAbsoluteXWrite(CPU);
break;
case AddressingModes.AbsoluteY:
address = AddressingMode.GetAbsoluteY(CPU);
break;
case AddressingModes.Indirect:
address = AddressingMode.GetIndirect(CPU);
break;
case AddressingModes.IndirectX:
address = AddressingMode.GetIndirectX(CPU);
break;
case AddressingModes.IndirectY:
address = AddressingMode.GetIndirectY(CPU);
break;
case AddressingModes.IndirectYWrite:
address = AddressingMode.GetIndirectYWrite(CPU);
break;
case AddressingModes.ZeroPage:
address = AddressingMode.GetZeroPage(CPU);
break;
case AddressingModes.ZeroPageX:
address = AddressingMode.GetZeroPageX(CPU);
break;
case AddressingModes.ZeroPageY:
address = AddressingMode.GetZeroPageY(CPU);
break;
case AddressingModes.Relative:
address = AddressingMode.GetRelative(CPU);
break;
default:
throw new InvalidOperationException();
}
if (MOS6502.IsDebug)
{
CPU.LastAccessedAddress = AddressingMode.GetAddressAsString(CPU, container);
}
return(address);
}
private static ushort GetRelative(MOS6502 CPU) => 0x0000;