public static byte DEY(I6502 cpu)
{
cpu.Y--;
UpdateNegative(cpu, cpu.Y);
UpdateZero(cpu, cpu.Y);
return(0);
}
public static byte LDA(I6502 cpu)
{
UpdateNegative(cpu, cpu.Fetched);
UpdateZero(cpu, cpu.Fetched);
cpu.A = cpu.Fetched;
return(1);
}
public static byte ROR(I6502 cpu)
{
UInt16 shifted = cpu.Fetched;
// Add carry to bit 8 if set
if (cpu.GetFlag(Flags.C))
{
shifted |= 0x100;
}
// Update carry flag if bit 0 is 1.
cpu.SetFlag(Flags.C, (shifted & 0x01) == 0x01);
// Shift
shifted = (byte)(shifted >> 1);
UpdateZero(cpu, (byte)shifted);
UpdateNegative(cpu, shifted);
if (cpu.ImpliedAddress)
{
cpu.A = (byte)(shifted & 0x00FF);
}
else
{
cpu.Bus.Write(cpu.Address, (byte)shifted);
}
return(0);
}
public static byte CPY(I6502 cpu)
{
cpu.SetFlag(Flags.C, cpu.Y >= cpu.Fetched);
cpu.SetFlag(Flags.Z, cpu.Y == cpu.Fetched);
cpu.SetFlag(Flags.N, ((cpu.Y - cpu.Fetched) & 0x80) == 0x80);
return(0);
}
public static byte CMP(I6502 cpu)
{
cpu.SetFlag(Flags.C, cpu.A >= cpu.Fetched);
cpu.SetFlag(Flags.Z, cpu.A == cpu.Fetched);
cpu.SetFlag(Flags.N, ((cpu.A - cpu.Fetched) & 0x80) == 0x80);
return(1);
}
public static byte ORA(I6502 cpu)
{
cpu.A |= cpu.Fetched;
UpdateNegative(cpu, cpu.A);
UpdateZero(cpu, cpu.A);
return(1);
}
public static byte TAY(I6502 cpu)
{
cpu.Y = cpu.A;
UpdateNegative(cpu, cpu.Y);
UpdateZero(cpu, cpu.Y);
return(0);
}
public static byte INX(I6502 cpu)
{
cpu.X++;
UpdateNegative(cpu, cpu.X);
UpdateZero(cpu, cpu.X);
return(0);
}
public static byte DEC(I6502 cpu)
{
byte decrementedValue = (byte)(cpu.Fetched - 1);
cpu.Bus.Write(cpu.Address, decrementedValue);
UpdateNegative(cpu, decrementedValue);
UpdateZero(cpu, decrementedValue);
return(0);
}
public static byte TSX(I6502 cpu)
{
cpu.X = cpu.StackPointer;
UpdateNegative(cpu, cpu.X);
UpdateZero(cpu, cpu.X);
return(0);
}
public static byte TYA(I6502 cpu)
{
cpu.A = cpu.Y;
UpdateNegative(cpu, cpu.A);
UpdateZero(cpu, cpu.A);
return(0);
}
public static byte PLA(I6502 cpu)
{
cpu.StackPointer++;
cpu.A = cpu.Bus.Read(cpu.GetFullStackAddress());
UpdateZero(cpu, cpu.A);
UpdateNegative(cpu, cpu.A);
return(0);
}
public static byte BIT(I6502 cpu)
{
byte test = (byte)(cpu.A & cpu.Fetched);
UpdateZero(cpu, test);
UpdateNegative(cpu, cpu.Fetched);
cpu.SetFlag(Flags.V, (cpu.Fetched & 0x40) == 0x40);
return(0);
}
public static byte JSR(I6502 cpu)
{
cpu.Bus.Write(cpu.GetFullStackAddress(), (byte)((cpu.ProgramCounter - 1 >> 8) & 0x00FF));
cpu.StackPointer--;
cpu.Bus.Write(cpu.GetFullStackAddress(), (byte)(cpu.ProgramCounter - 1 & 0x00FF));
cpu.StackPointer--;
cpu.ProgramCounter = cpu.Address;
return(0);
}
static void PrintMe(I6502 mos6502)
{
Console.WriteLine("ProgramCounter = " + mos6502.ProgramCounter);
Console.WriteLine("StackPointer = " + mos6502.StackPointer);
Console.WriteLine("Accumulator = " + mos6502.Accumulator);
Console.WriteLine("IndexX = " + mos6502.IndexX);
Console.WriteLine("IndexY = " + mos6502.IndexY);
Console.WriteLine("Status = " + Convert.ToString(mos6502.Status, 2));
Console.WriteLine("Clock = " + mos6502.Clock);
Console.WriteLine();
}
public static byte RTS(I6502 cpu)
{
cpu.StackPointer++;
UInt16 lo = cpu.Bus.Read(cpu.GetFullStackAddress());
cpu.StackPointer++;
UInt16 hi = cpu.Bus.Read(cpu.GetFullStackAddress());
cpu.ProgramCounter = (UInt16)(((hi << 8) | lo) + 1);
return(0);
}
public static byte ADC(I6502 cpu)
{
UInt16 sum = (UInt16)(cpu.A + cpu.Fetched + (cpu.GetFlag(Flags.C) ? 1 : 0));
UpdateCarry(cpu, sum);
UpdateZero(cpu, sum);
UpdateNegative(cpu, sum);
cpu.SetFlag(Flags.V, ((cpu.A ^ (byte)sum) & ~(cpu.A ^ cpu.Fetched) & 0x0080) == 0x0080);
cpu.A = (byte)(sum & 0x00FF);
return(1);
}
/**
* Mirror of OLC add Overflow truth table for subtraction
* A M ~A ~M R | V | A^M | A^R | ~M^R | M^R |
* --------------------------------------------
* 0 0 1 1 0 | 0 | 0 | 0 | 1 | 0
* 0 0 1 1 1 | 0 | 0 | 1 | 0 | 1
* 0 1 1 0 0 | 0 | 1 | 0 | 0 | 1
* 0 1 1 0 1 | 1 | 1 | 1 | 1 | 0
* 1 0 0 1 0 | 0 | 1 | 1 | 1 | 0
* 1 0 0 1 1 | 1 | 1 | 0 | 0 | 1
* 1 1 0 0 0 | 0 | 0 | 1 | 0 | 1
* 1 1 0 0 1 | 0 | 0 | 0 | 1 | 0
*/
public static byte SBC(I6502 cpu)
{
UInt16 inverse = (byte)~cpu.Fetched;
UInt16 difference = (UInt16)(cpu.A + inverse + (cpu.GetFlag(Flags.C) ? 1 : 0));
cpu.SetFlag(Flags.C, difference > 255);
cpu.SetFlag(Flags.Z, (difference & 0x00FF) == 0);
cpu.SetFlag(Flags.N, (difference & 0x0080) == 0x0080);
cpu.SetFlag(Flags.V, ((cpu.A ^ difference) & (cpu.A ^ cpu.Fetched) & 0x0080) == 0x0080);
cpu.A = (byte)(difference & 0x00FF);
return(1);
}
public EmulationShell(INesRomReader romReader, INesVideoOut videoOut)
{
m_cpu = new Nmos6502(m_sync);
m_ppu = new NesPpu(m_sync)
{
Cpu = m_cpu, VideoOut = videoOut
};
InitializeSpriteMemory(romReader);
InitializeCpuMemory(romReader);
InitializePpuMemory(romReader);
m_cpu.BeginRun();
m_ppu.BeginRun();
}
public static byte RTI(I6502 cpu)
{
cpu.StackPointer++;
cpu.Status = cpu.Bus.Read(cpu.GetFullStackAddress());
cpu.StackPointer++;
UInt16 lo = cpu.Bus.Read(cpu.GetFullStackAddress());
cpu.StackPointer++;
UInt16 hi = cpu.Bus.Read(cpu.GetFullStackAddress());
cpu.ProgramCounter = (UInt16)((hi << 8) | lo);
cpu.SetFlag(Flags.I, false);
return(0);
}
public static byte LSR(I6502 cpu)
{
byte shifted = (byte)(cpu.Fetched >> 1);
cpu.SetFlag(Flags.C, (cpu.Fetched & 0x01) == 0x01);
cpu.SetFlag(Flags.N, false);
UpdateZero(cpu, shifted);
if (cpu.ImpliedAddress)
{
cpu.A = shifted;
}
else
{
cpu.Bus.Write(cpu.Address, shifted);
}
return(0);
}
public static byte ASL(I6502 cpu)
{
UInt16 shiftedValue = (UInt16)(cpu.Fetched << 1);
UpdateCarry(cpu, shiftedValue);
UpdateZero(cpu, shiftedValue);
UpdateNegative(cpu, shiftedValue);
if (cpu.ImpliedAddress)
{
cpu.A = (byte)(shiftedValue & 0x00FF);
}
else
{
cpu.Bus.Write(cpu.Address, (byte)shiftedValue);
}
return(0);
}
public static byte BCS(I6502 cpu)
{
byte extraCycles = 0;
if (cpu.GetFlag(Flags.C))
{
extraCycles++;
cpu.Address = (UInt16)(cpu.ProgramCounter + cpu.BranchRelativeAddress);
if ((cpu.Address & 0xFF00) != (cpu.ProgramCounter & 0xFF00))
{
extraCycles++;
}
cpu.ProgramCounter = cpu.Address;
}
return(extraCycles);
}
public static byte ROL(I6502 cpu)
{
UInt16 shifted = (UInt16)(cpu.Fetched << 1);
if (cpu.GetFlag(Flags.C))
{
shifted++;
}
UpdateCarry(cpu, shifted);
UpdateZero(cpu, (byte)shifted);
UpdateNegative(cpu, shifted);
if (cpu.ImpliedAddress)
{
cpu.A = (byte)(shifted & 0x00FF);
}
else
{
cpu.Bus.Write(cpu.Address, (byte)shifted);
}
return(0);
}
public static byte PLP(I6502 cpu)
{
cpu.StackPointer++;
cpu.Status = cpu.Bus.Read(cpu.GetFullStackAddress());
return(0);
}
public static byte XXX(I6502 cpu)
{
throw new NotImplementedException("Invalid Op code");
}
public static byte PHP(I6502 cpu)
{
cpu.Bus.Write(cpu.GetFullStackAddress(), (byte)(cpu.Status | (byte)Flags.B | (byte)Flags.U));
cpu.StackPointer--;
return(0);
}
public static byte TXS(I6502 cpu)
{
cpu.StackPointer = cpu.X;
return(0);
}
public static byte SEI(I6502 cpu)
{
cpu.SetFlag(Flags.I, true);
return(0);
}
public static byte STY(I6502 cpu)
{
cpu.Bus.Write(cpu.Address, cpu.Y);
return(0);
}