/// <summary>
/// Writes one byte of the microcode word currently pointed to by
/// TPC[6].
/// </summary>
/// <param name="b"></param>
/// <param name="value"></param>
private void WriteIOPMicrocodeWord(int b, byte value)
{
//
// In true Xerox fashion, the 48 bits of the microcode word provided by the IOP
// are not in order from MSB to LSB or anything simple like that. Though most of them are.
// From SysDefs.asm:
//
// "; Write (all CSi are complemented values):
// CSa equ CSBase + 0; CS Byte a: rA[0:3],,rB[0:3]
// CSb equ CSBase + 1; CS Byte b: aS[0:2],,aF[0:2],,aD[0:1]
// CSc equ CSBase + 2; CS Byte c: EP,,CIN,,EnSU,,mem,,fS[0:3]
// CSd equ CSBase + 3; CS Byte d: fY[0:3], INIA[0:3]
// CSe equ CSBase + 4; CS Byte e: fX[0:3], INIA[4:7]
// CSf equ CSBase + 5; CS Byte f: fZ[0:3], INIA[8:11]"
//
// "value" is expected to already be complemented on call to WriteIOPMicrocodeWord.
//
// TPC register 6 is always used for IOP microcode writes.
ulong word = _microcode[_tpc[6]];
switch (b)
{
case 0:
word = (word & 0x00ffffffffff) | ((ulong)value << 40);
break;
case 1:
word = (word & 0xff00ffffffff) | ((ulong)value << 32);
break;
case 2:
word = (word & 0xffff00ffffff) | ((ulong)value << 24);
break;
case 3:
{
// FY[0:3], INIA[0:3]
ulong fy = ((ulong)value & 0xf0) >> 4;
ulong inia = ((ulong)value & 0xf);
word = (word & 0xfffffff0f0ff) | (fy << 16) | (inia << 8);
}
break;
case 4:
{
// FX[0:3], INIA[4:7]
ulong fx = ((ulong)value & 0xf0) >> 4;
ulong inia = ((ulong)value & 0xf);
word = (word & 0xffffff0fff0f) | (fx << 20) | (inia << 4);
}
break;
case 5:
{
// FZ[0:3], INIA[8:11]
ulong fz = ((ulong)value & 0xf0) >> 4;
ulong inia = ((ulong)value & 0xf);
word = (word & 0xffffffff0ff0) | (fz << 12) | inia;
}
break;
default:
throw new InvalidOperationException("Invalid byte number for microcode word.");
}
_microcode[_tpc[6]] = word;
_microcodeCache[_tpc[6]] = new Microinstruction(word);
}
/// <summary>
/// Executes the ALU operation specified by the given microinstruction.
/// </summary>
/// <param name="i">The microinstruction</param>
/// <param name="d">The ALU D input</param>
/// <param name="carryIn">The ALU Carry in</param>
/// <param name="loadMAR">Whether this operation is taking place during an MAR<- operation,
/// in which case the top half of the ALU needs to be treated specially.</param>
public ushort Execute(Microinstruction i, ushort d, bool carryIn, bool loadMAR)
{
//
// Save R[a] for the A-bypass case.
// (If the ALU op ends up modifying R[a] in A-Bypass mode (because a == b)
// it will happen much later than A-bypass and we want
// Y to get the original value of R[a], not the later value.)
//
// Select source data
int r, s;
switch (i.aS)
{
case AluSourcePair.AQ:
r = _r[i.rA];
s = _q;
break;
case AluSourcePair.AB:
r = _r[i.rA];
s = _r[i.rB];
break;
case AluSourcePair.ZQ:
r = 0;
s = _q;
break;
case AluSourcePair.ZB:
r = 0;
s = _r[i.rB];
break;
case AluSourcePair.ZA:
r = 0;
s = _r[i.rA];
break;
case AluSourcePair.DA:
r = d;
s = _r[i.rA];
break;
case AluSourcePair.DQ:
r = d;
s = _q;
break;
case AluSourcePair.D0:
r = d;
s = 0;
break;
default:
throw new InvalidOperationException(
String.Format("Unhandled source pair {0}", i.aS));
}
//
// Do ALU op
//
int f;
int cIn = (carryIn ? 1 : 0);
switch (i.aF)
{
case AluFunction.RplusS:
{
f = r + s + cIn;
CarryOut = (f > 0xffff);
NibCarry = (r & 0xf) + (s & 0xf) + cIn > 0xf;
PgCarry = (r & 0xff) + (s & 0xff) + cIn > 0xff;
int cn = (r & 0xfff) + (s & 0xfff) + cIn > 0xfff ? 1 : 0;
Overflow = _overflowTable[r >> 12, s >> 12, cn];
}
break;
case AluFunction.SminusR:
{
f = s + (~r & 0xffff) + cIn;
CarryOut = (f > 0xffff);
NibCarry = ((~r & 0xf) + (s & 0xf) + cIn > 0xf);
PgCarry = ((~r & 0xff) + (s & 0xff) + cIn > 0xff);
int cn = (~r & 0xfff) + (s & 0xfff) + cIn > 0xfff ? 1 : 0;
Overflow = _overflowTable[(~r & 0xffff) >> 12, s >> 12, cn];
}
break;
case AluFunction.RminusS:
{
f = r + (~s & 0xffff) + cIn;
CarryOut = (f > 0xffff);
NibCarry = ((r & 0xf) + (~s & 0xf) + cIn > 0xf);
PgCarry = ((r & 0xff) + (~s & 0xff) + cIn > 0xff);
int cn = (r & 0xfff) + (~s & 0xfff) + cIn > 0xfff ? 1 : 0;
Overflow = _overflowTable[r >> 12, (~s & 0xffff) >> 12, cn];
}
break;
case AluFunction.RorS:
f = r | s;
// A few microinstructions do an MAR<- with RorS and expect PgCarry to be set appropriately.
NibCarry = _carryTableOr[r & 0xf, s & 0xf, cIn];
PgCarry = _carryTableOr[(r >> 4) & 0xf, (s >> 4) & 0xf, NibCarry ? 1 : 0];
CarryOut = false;
Overflow = false;
break;
case AluFunction.RandS:
f = r & s;
NibCarry = false;
PgCarry = false;
CarryOut = false;
Overflow = false;
break;
case AluFunction.notRandS:
f = (~r) & s;
NibCarry = false;
PgCarry = false;
CarryOut = false;
Overflow = false;
break;
case AluFunction.RxorS:
f = r ^ s;
NibCarry = false;
PgCarry = false;
CarryOut = false;
Overflow = false;
break;
case AluFunction.notRxorS:
f = (~r) ^ s;
NibCarry = false;
PgCarry = false;
CarryOut = false;
Overflow = false;
break;
default:
throw new InvalidOperationException(
String.Format("Unhandled function {0}", i.aF));
}
// Clip F to 16 bits
f = f & 0xffff;
if (loadMAR)
{
//
// If the ALU is being run during a MAR<- operation, the top 8 bits of the ALU are
// computed using an operator specified by aF | 3, with the source set to 0,B.
// The CarryOut and Overflow flags are clear (since they are not affected by the
// OR/notXOR operation), and the carry from the least-significant byte of the ALU does not
// carry over to the most-significant byte.
//
// See page 25 of the microcode ref for details.
//
// We implement this here by overwriting the upper byte of F with the upper bits of rB
// (or its complement). Interlisp microcode expects Overflow and Carry to be set appropriately.
//
switch ((AluFunction)((int)i.aF | 0x3))
{
case AluFunction.RorS:
{
f = (f & 0xff) | (_r[i.rB] & 0xff00);
bool midCarry = _carryTableOr[(r >> 8) & 0xf, (s >> 8) & 0xf, PgCarry ? 1 : 0];
Overflow = CarryOut = _carryTableOr[(r >> 12) & 0xf, (s >> 12) & 0xf, midCarry ? 1 : 0];
}
break;
case AluFunction.notRxorS:
{
f = (f & 0xff) | ((~_r[i.rB]) & 0xff00);
bool midCarry = _carryTableNotXor[(r >> 8) & 0xf, (s >> 8) & 0xf, PgCarry ? 1 : 0];
CarryOut = _carryTableNotXor[(r >> 12) & 0xf, (s >> 12) & 0xf, midCarry ? 1 : 0];
Overflow = _overflowNotXor[(r >> 12) & 0xf, (s >> 12) & 0xf, midCarry ? 1 : 0];
}
break;
}
}
Zero = (f == 0);
Neg = ((f & 0x8000) != 0);
//
// Write outputs, do shifts and cycles as appropriate before writing back.
// (Shifts and cycles do not affect the Y output, only the register being written back to.)
//
switch (i.AluDestination)
{
case 0:
_q = (ushort)f;
Y = (ushort)f;
break;
case 1:
Y = (ushort)f;
break;
case 2:
Y = _r[i.rA];
_r[i.rB] = (ushort)f;
break;
case 3:
_r[i.rB] = (ushort)f;
Y = (ushort)f;
break;
case 4:
Y = (ushort)f;
if (i.Cycle)
{
// double-word right shift
// MSB of Q gets inverted LSB of F.
_q = (ushort)((_q >> 1) | ((~f & 0x1) << 15));
// MSB of F gets Carry in.
f = (ushort)((f >> 1) | (carryIn ? 0x8000 : 0x0));
}
else
{
// double-word arithmetic right shift.
// MSB of Q gets inverted LSB of F.
_q = (ushort)((_q >> 1) | ((~f & 0x1) << 15));
// MSB of F gets Carry out.
f = (ushort)((f >> 1) | (CarryOut ? 0x8000 : 0x0));
}
_r[i.rB] = (ushort)f;
break;
case 5:
Y = (ushort)f;
if (i.Cycle)
{
// F: single-word right rotate:
f = (ushort)((f >> 1) | ((f & 0x1) << 15));
}
else
{
// F: single-word right shift w/carryIn to MSB:
f = (ushort)((f >> 1) | (carryIn ? 0x8000 : 0x0));
}
_r[i.rB] = (ushort)f;
break;
case 6:
Y = (ushort)f;
// double-word left shift (apparently identical for cycle and shift)
// LSB of F gets MSB of Q, not inverted.
f = (ushort)((f << 1) | ((_q & 0x8000) >> 15));
// LSB of Q gets Cin, inverted
_q = (ushort)((_q << 1) | (1 - cIn));
_r[i.rB] = (ushort)f;
break;
case 7:
Y = (ushort)f;
if (i.Cycle)
{
// F: single-word left rotate:
f = (ushort)((f << 1) | ((f & 0x8000) >> 15));
}
else
{
// F: single-word left shift w/carryIn to LSB:
f = (ushort)((f << 1) | cIn);
}
_r[i.rB] = (ushort)f;
break;
default:
throw new InvalidOperationException(
String.Format("Unhandled destination {0}", i.aF));
}
return(Y);
}