private void ComputeFlagsForIOBlockInstruction(IOBlockInstructionType instructionType)
{
// The out instructions behave differently than the in instructions, which doesn’t make the CPU very symmetrical.
// First of all, all instructions affect the following flags:
F = 0;
// SF, ZF, YF, XF flags Affected by decreasing register B, as in DEC B.
// For OUT instructions, B has already been decremented when we compute flags
byte decB = B;
// For IN instructions, B has not yet been decremented when we compute flags, so we consider B-1
if (instructionType == IOBlockInstructionType.IND || instructionType == IOBlockInstructionType.INI)
{
decB = (byte)(B - 1);
}
// Flags bit 7 - SF flag - Set if the 2-complement value is negative. It's simply a copy of the most signifcant bit of the result.
F |= (byte)(decB & B10000000);
// Flags bit 6 - ZF flag Set if the result is zero.
if (decB == 0) F |= B01000000;
// Flags bit 5 - YF flag - A copy of bit 5 of the result.
// Flags bit 3 - XF flag - A copy of bit 3 of the result.
F |= (byte)(decB & B00101000);
// NF flag A copy of bit 7 of the value read from or written to an I/O port.
NF = (InternalDataBus & B10000000) != 0;
int k = 0;
// And now the for OUTI/OTIR/OUTD/OTDR instructions.
if (instructionType == IOBlockInstructionType.OUT)
{
// Take state of the L after the increment or decrement of HL; add the value written to the I/O port to; call that k for now.
// HF and CF Both set if ((HL) + L > 255)
// PF The parity of ((((HL) + L) & 7) xor B)
k = InternalDataBus + L;
}
else
{
// INI/INIR/IND/INDR use the C register in stead of the L register.
// There is a catch though, because not the value of C is used, but C + 1 if it’s INI/INIR or C - 1 if it’s IND/INDR.
// So, first of all INI/INIR:
if (instructionType == IOBlockInstructionType.INI)
{
// HF and CF Both set if ((HL) + ((C + 1) & 255) > 255)
// PF The parity of (((HL) + ((C + 1) & 255)) & 7) xor B)
k = InternalDataBus + ((C + 1) & 255);
}
// And last IND/INDR:
else if (instructionType == IOBlockInstructionType.IND)
{
// HF and CF Both set if ((HL) + ((C - 1) & 255) > 255)
// PF The parity of (((HL) + ((C - 1) & 255)) & 7) xor B)
k = InternalDataBus + ((C - 1) & 255);
}
}
// If k > 255, then the CF and HF flags are set.
// HF and CF Both set if ((HL) + L > 255)
CF = k > 255;
HF = k > 255;
// The PF flags is set like the parity of k bitwise and’ed with 7, bitwise xor’ed with B.
// PF The parity of ((((HL) + L) & 7) xor B)
PF = numberOfBitsInByteParityTable[(byte)((k & 7) ^ decB)];
if (TraceMicroInstructions)
{
TraceMicroInstruction(new MicroInstruction(Z80MicroInstructionTypes.FlagsOperationComputeFlagsForIOBlockInstruction));
}
}
private void ComputeFlagsForIOBlockInstruction(IOBlockInstructionType instructionType)
{
// The out instructions behave differently than the in instructions, which doesn’t make the CPU very symmetrical.
// First of all, all instructions affect the following flags:
F = 0;
// SF, ZF, YF, XF flags Affected by decreasing register B, as in DEC B.
// For OUT instructions, B has already been decremented when we compute flags
byte decB = B;
// For IN instructions, B has not yet been decremented when we compute flags, so we consider B-1
if (instructionType == IOBlockInstructionType.IND || instructionType == IOBlockInstructionType.INI)
{
decB = (byte)(B - 1);
}
// Flags bit 7 - SF flag - Set if the 2-complement value is negative. It's simply a copy of the most signifcant bit of the result.
F |= (byte)(decB & B10000000);
// Flags bit 6 - ZF flag Set if the result is zero.
if (decB == 0)
{
F |= B01000000;
}
// Flags bit 5 - YF flag - A copy of bit 5 of the result.
// Flags bit 3 - XF flag - A copy of bit 3 of the result.
F |= (byte)(decB & B00101000);
// NF flag A copy of bit 7 of the value read from or written to an I/O port.
NF = (InternalDataBus & B10000000) != 0;
int k = 0;
// And now the for OUTI/OTIR/OUTD/OTDR instructions.
if (instructionType == IOBlockInstructionType.OUT)
{
// Take state of the L after the increment or decrement of HL; add the value written to the I/O port to; call that k for now.
// HF and CF Both set if ((HL) + L > 255)
// PF The parity of ((((HL) + L) & 7) xor B)
k = InternalDataBus + L;
}
else
{
// INI/INIR/IND/INDR use the C register in stead of the L register.
// There is a catch though, because not the value of C is used, but C + 1 if it’s INI/INIR or C - 1 if it’s IND/INDR.
// So, first of all INI/INIR:
if (instructionType == IOBlockInstructionType.INI)
{
// HF and CF Both set if ((HL) + ((C + 1) & 255) > 255)
// PF The parity of (((HL) + ((C + 1) & 255)) & 7) xor B)
k = InternalDataBus + ((C + 1) & 255);
}
// And last IND/INDR:
else if (instructionType == IOBlockInstructionType.IND)
{
// HF and CF Both set if ((HL) + ((C - 1) & 255) > 255)
// PF The parity of (((HL) + ((C - 1) & 255)) & 7) xor B)
k = InternalDataBus + ((C - 1) & 255);
}
}
// If k > 255, then the CF and HF flags are set.
// HF and CF Both set if ((HL) + L > 255)
CF = k > 255;
HF = k > 255;
// The PF flags is set like the parity of k bitwise and’ed with 7, bitwise xor’ed with B.
// PF The parity of ((((HL) + L) & 7) xor B)
PF = numberOfBitsInByteParityTable[(byte)((k & 7) ^ decB)];
if (TraceMicroInstructions)
{
TraceMicroInstruction(new MicroInstruction(Z80MicroInstructionTypes.FlagsOperationComputeFlagsForIOBlockInstruction));
}
}