public static int DEC_r(IZ80CPU cpu, byte[] instruction)
{
var reg = instruction[0].ExtractBits(3, 3);
byte val;
switch (reg)
{
case 0b111: cpu.Registers.A--; val = cpu.Registers.A; break;
case 0b000: cpu.Registers.B--; val = cpu.Registers.B; break;
case 0b001: cpu.Registers.C--; val = cpu.Registers.C; break;
case 0b010: cpu.Registers.D--; val = cpu.Registers.D; break;
case 0b011: cpu.Registers.E--; val = cpu.Registers.E; break;
case 0b100: cpu.Registers.H--; val = cpu.Registers.H; break;
case 0b101: cpu.Registers.L--; val = cpu.Registers.L; break;
default: throw new InvalidOperationException();
}
DecrementByteSetConditionBits(cpu, val);
return(4);
}
public static int LD_IY_nn_mem(IZ80CPU cpu, byte[] instruction)
{
var nn = Utilities.LETo16Bit(instruction[2], instruction[3]);
cpu.Registers.IY = cpu.ReadWord(nn);
return(20);
}
private static byte RotateByteRight(IZ80CPU cpu, byte val)
{
cpu.Registers.HalfCarry = false;
cpu.Registers.Subtract = false;
cpu.Registers.Carry = val.GetBit(0);
return((byte)((val >> 1) | (val.GetBitAsByte(0) << 7)));
}
private static void AddWordsWithCarryAndSetConditionBits(IZ80CPU cpu, bool subtract, ushort b)
{
var a = cpu.Registers.HL;
var c = (ushort)(cpu.Registers.Carry ? 1 : 0);
if (subtract)
{
b = b.TwosComplement();
c = c.TwosComplement();
}
var sum = a + b + c;
var noCarrySum = a ^ b ^ c;
var carryInto = sum ^ noCarrySum;
var halfCarry = carryInto & 0x1000;
var carry = carryInto & 0x10000;
var overflow = carryInto & 0x8000;
var result = (ushort)sum;
cpu.Registers.Sign = result.IsNegative();
cpu.Registers.Zero = result == 0;
cpu.Registers.HalfCarry = halfCarry != 0;
cpu.Registers.ParityOrOverflow = overflow != 0;
cpu.Registers.Subtract = subtract;
cpu.Registers.Carry = carry != 0;
cpu.Registers.HL = result;
}
public static int JP_cc_nn(IZ80CPU cpu, byte[] instruction)
{
var condition = instruction[0].ExtractBits(3, 3);
var shouldJump = false;
switch (condition)
{
case 0b000: shouldJump = !cpu.Registers.Zero; break;
case 0b001: shouldJump = cpu.Registers.Zero; break;
case 0b010: shouldJump = !cpu.Registers.Carry; break;
case 0b011: shouldJump = cpu.Registers.Carry; break;
case 0b100: shouldJump = !cpu.Registers.ParityOrOverflow; break;
case 0b101: shouldJump = cpu.Registers.ParityOrOverflow; break;
case 0b110: shouldJump = !cpu.Registers.Sign; break;
case 0b111: shouldJump = cpu.Registers.Sign; break;
default: throw new InvalidOperationException();
}
if (shouldJump)
{
cpu.Registers.PC = Utilities.LETo16Bit(instruction[1], instruction[2]);
}
return(10);
}
private static void SubBytes(IZ80CPU cpu, byte a, byte b, bool useCarryFlag = false)
{
var carryFlagValue = ((byte)(useCarryFlag ? 1 : 0)).TwosComplement();
b = b.TwosComplement();
AddMultipleBytesAndSetConditionBits(cpu, true, a, b, carryFlagValue);
}
public static int ADD_IY_pp(IZ80CPU cpu, byte[] instruction)
{
cpu.InsertWaitMachineCycle(4);
ushort val = 0;
switch (instruction[1])
{
case 0x09: val = cpu.Registers.BC; break;
case 0x19: val = cpu.Registers.DE; break;
case 0x29: val = cpu.Registers.IY; break;
case 0x39: val = cpu.Registers.SP; break;
default: throw new InvalidOperationException();
}
var upperReg = val.GetUpperByte();
var upperIY = cpu.Registers.IXUpper;
cpu.Registers.IY += val;
cpu.Registers.HalfCarry = upperIY.WillHalfCarry(upperReg);
cpu.Registers.Subtract = false;
cpu.Registers.Carry = upperIY.WillCarry(upperReg);
cpu.InsertWaitMachineCycle(3);
return(15);
}
public static int CPDR(IZ80CPU cpu, byte[] instruction)
{
var data = cpu.ReadMemory(cpu.Registers.HL);
var cmp = cpu.Registers.A - data;
cpu.Registers.HL--;
cpu.Registers.BC--;
cpu.Registers.Sign = cmp < 0;
cpu.Registers.Zero = cmp == 0;
cpu.Registers.HalfCarry = cpu.Registers.A.WillHalfCarry(data);
cpu.Registers.Subtract = true;
cpu.Registers.ParityOrOverflow = cpu.Registers.BC != 0;
cpu.InsertWaitMachineCycle(5);
if (cpu.Registers.Zero || cpu.Registers.BC == 0)
{
return(16);
}
cpu.Registers.PC -= 2;
cpu.InsertWaitMachineCycle(5);
return(21);
}
public static int RET(IZ80CPU cpu, byte[] instruction)
{
cpu.Registers.PC = cpu.Registers.PC.SetLowerByte(cpu.PopByte());
cpu.Registers.PC = cpu.Registers.PC.SetUpperByte(cpu.PopByte());
return(10);
}
public static int DJNZ_e(IZ80CPU cpu, byte[] instruction)
{
// FIXME: The opcode fetch has the tick after it, then the memory read for the operand
cpu.ControlLines.SystemClock.Tick();
cpu.Registers.B--;
if (cpu.Registers.B == 0)
{
return(8);
}
var offset = (int)instruction[1];
offset += 2;
if (offset < 0)
{
cpu.Registers.PC -= (ushort)Math.Abs(offset);
}
else
{
cpu.Registers.PC += (ushort)offset;
}
cpu.InsertWaitMachineCycle(5);
return(13);
}
public static int CALL_nn(IZ80CPU cpu, byte[] instruction)
{
cpu.PushWord(cpu.Registers.PC, 1);
cpu.Registers.PC = Utilities.LETo16Bit(instruction[1], instruction[2]);
return(17);
}
public static int POP_IY(IZ80CPU cpu, byte[] instruction)
{
cpu.Registers.IYLower = cpu.PopByte();
cpu.Registers.IYUpper = cpu.PopByte();
return(14);
}
private static byte RotateByteLeft(IZ80CPU cpu, byte val)
{
cpu.Registers.HalfCarry = false;
cpu.Registers.Subtract = false;
cpu.Registers.Carry = cpu.Registers.A.GetBit(7);
return((byte)((cpu.Registers.A << 1) | (cpu.Registers.A.GetBitAsByte(7) >> 7)));
}
public static int LD_IY_plus_d_mem_n(IZ80CPU cpu, byte[] instruction)
{
cpu.ControlLines.SystemClock.TickMultiple(2);
cpu.WriteMemory(cpu.Registers.IX.CalculateIndex(instruction[2]), instruction[3]);
return(19);
}
public static int DEC_IX(IZ80CPU cpu, byte[] instruction)
{
cpu.ControlLines.SystemClock.TickMultiple(2);
cpu.Registers.IX--;
return(10);
}
public static int LD_nn_mem_A(IZ80CPU cpu, byte[] instruction)
{
var addr = Utilities.LETo16Bit(instruction[1], instruction[2]);
cpu.WriteMemory(addr, cpu.Registers.A);
return(13);
}
public static int LD_A_nn_mem(IZ80CPU cpu, byte[] instruction)
{
var addr = Utilities.LETo16Bit(instruction[1], instruction[2]);
cpu.Registers.A = cpu.ReadMemory(addr);
return(13);
}
public static int EI(IZ80CPU cpu, byte[] instruction)
{
cpu.Registers.IFF1 = true;
cpu.Registers.IFF2 = true;
return(4);
}
public static int LD_SP_IY(IZ80CPU cpu, byte[] instruction)
{
cpu.ControlLines.SystemClock.TickMultiple(2);
cpu.Registers.SP = cpu.Registers.IY;
return(10);
}
public static int LD_r_n(IZ80CPU cpu, byte[] instruction)
{
var dst = instruction[0].ExtractBits(3, 3);
WriteByteToCpuRegister(cpu, dst, instruction[1]);
return(7);
}
public static int RST_p(IZ80CPU cpu, byte[] instruction)
{
cpu.ControlLines.SystemClock.Tick();
cpu.PushWord(cpu.Registers.PC);
cpu.Registers.PC = (ushort)(instruction[0].ExtractBits(3, 3) * 8);
return(11);
}
public static int LD_HL_nn_mem(IZ80CPU cpu, byte[] instruction)
{
var nn = Utilities.LETo16Bit(instruction[1], instruction[2]);
cpu.Registers.HL = cpu.ReadWord(nn);
return(16);
}
public static int LD_IY_nn(IZ80CPU cpu, byte[] instruction)
{
var nn = Utilities.LETo16Bit(instruction[2], instruction[3]);
cpu.Registers.IY = nn;
return(14);
}
public static int LD_R_A(IZ80CPU cpu, byte[] instruction)
{
cpu.ControlLines.SystemClock.Tick();
cpu.Registers.R = cpu.Registers.A;
return(9);
}
public static int RETI(IZ80CPU cpu, byte[] instruction)
{
cpu.Registers.PC = cpu.Registers.PC.SetLowerByte(cpu.PopByte());
cpu.Registers.PC = cpu.Registers.PC.SetUpperByte(cpu.PopByte());
cpu.InterruptsBeingServiced.Pop();
return(14);
}
public static int LD_nn_mem_IY(IZ80CPU cpu, byte[] instruction)
{
var addr = Utilities.LETo16Bit(instruction[2], instruction[3]);
cpu.WriteWord(addr, cpu.Registers.IY);
return(20);
}
public static int ADC_A_n(IZ80CPU cpu, byte[] instruction)
{
var data = instruction[1];
AddBytes(cpu, cpu.Registers.A, data, true);
return(7);
}
public static int ADC_A_HL_mem(IZ80CPU cpu, byte[] instruction)
{
var data = cpu.ReadMemory(cpu.Registers.HL);
AddBytes(cpu, cpu.Registers.A, data, true);
return(7);
}
public static int LD_nn_mem_HL(IZ80CPU cpu, byte[] instruction)
{
var addr = Utilities.LETo16Bit(instruction[1], instruction[2]);
cpu.WriteWord(addr, cpu.Registers.HL);
return(16);
}
public static int SCF(IZ80CPU cpu, byte[] instruction)
{
cpu.Registers.HalfCarry = false;
cpu.Registers.Subtract = false;
cpu.Registers.Carry = true;
return(4);
}