protected override void ExecuteSpecialFunction2(MicroInstruction instruction)
{
EmulatorF2 ef2 = (EmulatorF2)instruction.F2;
switch (ef2)
{
case EmulatorF2.LoadIR:
// Load IR from the bus
_cpu._ir = _busData;
// "IR<- also merges bus bits 0, 5, 6 and 7 into NEXT[6-9] which does a first level
// instruction dispatch."
_nextModifier |= (ushort)(((_busData & 0x8000) >> 12) | ((_busData & 0x0700) >> 8));
// "IR<- clears SKIP"
_skip = 0;
break;
case EmulatorF2.IDISP:
// "The IDISP function (F2=15B) does a 16 way dispatch under control of a PROM and a
// multiplexer. The values are tabulated below:
// Conditions ORed onto NEXT Comment
//
// if IR[0] = 1 3-IR[8-9] complement of SH field of IR
// elseif IR[1-2] = 0 IR[3-4] JMP, JSR, ISZ, DSZ ; dispatch selects register
// elseif IR[1-2] = 1 4 LDA
// elseif IR[1-2] = 2 5 STA
// elseif IR[4-7] = 0 1
// elseif IR[4-7] = 1 0
// elseif IR[4-7] = 6 16B CONVERT
// elseif IR[4-7] = 16B 6
// else IR[4-7]
// NB: as always, Xerox labels bits in the opposite order from modern convention;
// (bit 0 is the msb...)
//
// NOTE: The above table is accurate and functions correctly; using the PROM is faster.
//
if ((_cpu._ir & 0x8000) != 0)
{
_nextModifier |= (ushort)(3 - ((_cpu._ir & 0xc0) >> 6));
}
else
{
_nextModifier |= ControlROM.ACSourceROM[((_cpu._ir & 0x7f00) >> 8) + 0x80];
}
break;
case EmulatorF2.ACSOURCE:
// Late:
// "...a dispatch is performed:
// Conditions ORed onto NEXT Comment
//
// if IR[0] = 1 3-IR[8-9] complement of SH field of IR
// if IR[1-2] != 3 IR[5] the Indirect bit of R
// if IR[3-7] = 0 2 CYCLE
// if IR[3-7] = 1 5 RAMTRAP
// if IR[3-7] = 2 3 NOPAR -- parameterless opcode group
// if IR[3-7] = 3 6 RAMTRAP
// if IR[3-7] = 4 7 RAMTRAP
// if IR[3-7] = 11B 4 JSRII
// if IR[3-7] = 12B 4 JSRIS
// if IR[3-7] = 16B 1 CONVERT
// if IR[3-7] = 37B 17B ROMTRAP -- used by Swat, the debugger
// else 16B ROMTRAP
//
// NOTE: The above table is accurate and functions correctly; using the PROM is faster.
//
if ((_cpu._ir & 0x8000) != 0)
{
// 3-IR[8-9] (shift field of arithmetic instruction)
_nextModifier |= (ushort)(3 - ((_cpu._ir & 0xc0) >> 6));
}
else
{
// Use the PROM.
_nextModifier |= ControlROM.ACSourceROM[((_cpu._ir & 0x7f00) >> 8)];
}
break;
case EmulatorF2.ACDEST:
// Handled in early handler, nothing to do here.
break;
case EmulatorF2.BUSODD:
// "...merges BUS[15] into NEXT[9]."
_nextModifier |= (ushort)(_busData & 0x1);
break;
case EmulatorF2.MAGIC:
Shifter.SetModifier(ShifterModifier.Magic);
break;
case EmulatorF2.LoadDNS:
// DNS<- does the following:
// - modifies the normal shift operations to perform Nova-style shifts (done here)
// - addresses R from 3-IR[3-4] (destination AC) (see Early LoadDNS handler)
// - stores into R unless IR[12] is set (done here)
// [NOTE: This overrides a LoadR BS field if present -- that is, if IR[12] is set and
// BS=LoadR, no load into R will take place. Note also that the standard
// microcode apparently always specifies a LoadR BS for LoadDNS microinstructions. Need to
// look at the schematics more closely to see if this is required or just a convention
// of the PARC microassembler.]
// - calculates Nova-style CARRY bit (done here)
// - sets the SKIP and CARRY flip-flops appropriately (see Late LoadDNS handler)
int carry = 0;
// Also indicates modifying CARRY
_loadR = (_cpu._ir & 0x0008) == 0;
// At this point the ALU has already done its operation but the shifter has not yet run.
// We need to set the CARRY bit that will be passed through the shifter appropriately.
// Select carry input value based on carry control
switch ((_cpu._ir & 0x30) >> 4)
{
case 0x0:
// Nothing; CARRY unaffected.
carry = _carry;
break;
case 0x1:
carry = 0; // Z
break;
case 0x2:
carry = 1; // O
break;
case 0x3:
carry = (~_carry) & 0x1; // C
break;
}
// Now modify the result based on the current ALU result
switch ((_cpu._ir & 0x700) >> 8)
{
case 0x0:
case 0x2:
case 0x7:
// COM, MOV, AND - Carry unaffected
break;
case 0x1:
case 0x3:
case 0x4:
case 0x5:
case 0x6:
// NEG, INC, ADC, SUB, ADD - invert the carry bit
if (_cpu._aluC0 != 0)
{
carry = (~carry) & 0x1;
}
break;
}
// Tell the Shifter to do a Nova-style shift with the
// given carry bit.
Shifter.SetModifier(ShifterModifier.DNS);
Shifter.DNSCarry = carry;
break;
default:
throw new InvalidOperationException(String.Format("Unhandled emulator F2 {0}.", ef2));
}
}
/// <summary>
/// ExecuteInstruction causes the Task to execute the next instruction (the one
/// _mpc is pointing to). The base implementation covers non-task specific logic,
/// subclasses (specific task implementations) may provide their own implementations.
/// </summary>
/// <returns>An InstructionCompletion indicating whether this instruction calls for a task switch or not.</returns>
protected virtual InstructionCompletion ExecuteInstruction(MicroInstruction instruction)
{
InstructionCompletion completion = InstructionCompletion.Normal;
bool swMode = false;
ushort aluData;
ushort nextModifier;
bool softReset = _softReset;
_loadR = false;
_loadS = false;
_rSelect = 0;
_busData = 0;
_softReset = false;
Shifter.Reset();
//
// Wait for memory state machine if a memory operation is requested by this instruction and
// the memory isn't ready yet.
//
if (instruction.MemoryAccess)
{
if (!_cpu._system.MemoryBus.Ready(instruction.MemoryOperation))
{
// Suspend operation for this cycle.
return(InstructionCompletion.MemoryWait);
}
}
// If we have a modified next field from the last instruction, make sure it gets applied to this one.
nextModifier = _nextModifier;
_nextModifier = 0;
_rSelect = instruction.RSELECT;
// Give tasks the chance to modify parameters early on (like RSELECT)
ExecuteSpecialFunction2Early(instruction);
// Select BUS data.
if (!instruction.ConstantAccess)
{
// Normal BUS data (not constant ROM access).
switch (instruction.BS)
{
case BusSource.ReadR:
_busData = _cpu._r[_rSelect];
break;
case BusSource.LoadR:
_busData = 0; // "Loading R forces the BUS to 0 so that an ALU function of 0 and T may be executed simultaneously"
_loadR = true;
break;
case BusSource.None:
_busData = 0xffff; // "Enables no source to the BUS, leaving it all ones"
break;
case BusSource.TaskSpecific1:
case BusSource.TaskSpecific2:
_busData = GetBusSource(instruction); // task specific -- call into specific implementation
break;
case BusSource.ReadMD:
_busData = _cpu._system.MemoryBus.ReadMD();
break;
case BusSource.ReadMouse:
// "BUS[12-15]<-MOUSE; BUS[0-13]<- -1"
// (Note -- BUS[0-13] appears to be a typo, and should likely be BUS[0-11]).
_busData = (ushort)(_cpu._system.MouseAndKeyset.PollMouseBits() | 0xfff0);
break;
case BusSource.ReadDisp:
// "The high-order bits of IR cannot be read directly, but the displacement field of IR (8 low order bits),
// may be read with the <-DISP bus source. If the X field of the instruction is zero (i.e. it specifies page 0
// addressing) then the DISP field of the instruction is put on BUS[8-15] and BUS[0-7] is zeroed. If the X
// field of the instruction is nonzero (i.e. it specifies PC-relative or base-register addressing) then the DISP
// field is sign-extended and put on the bus."
// NB: the "X" field of the NOVA instruction is IR[6-7]
_busData = (ushort)(_cpu._ir & 0xff);
if ((_cpu._ir & 0x300) != 0)
{
// sign extend if necessary
if ((_cpu._ir & 0x80) != 0)
{
_busData |= (0xff00);
}
}
break;
default:
throw new InvalidOperationException(String.Format("Unhandled bus source {0}.", instruction.BS));
}
}
else
{
// See also comments below.
_busData = instruction.ConstantValue;
}
// Constant ROM access:
// "The constant memory is gated to the bus by F1=7, F2=7, or BS>4. The constant memory is addressed by the
// (8 bit) concatenation of RSELECT and BS. The intent in enabling constants with BS>4 is to provide a masking
// facility, particularly for the <-MOUSE and <-DISP bus sources. This works because the processor bus ANDs if
// more than one source is gated to it. Up to 32 such mask contans can be provided for each of the four bus sources
// > 4."
// This is precached by the MicroInstruction object.
if (instruction.BS4)
{
_busData &= instruction.ConstantValue;
}
//
// Let F2s that need to modify bus data before the ALU runs do their thing.
// (This is used by the Trident KDTA special functions)
//
ExecuteSpecialFunction2PostBusSource(instruction);
//
// If there was a RDRAM operation last cycle, we AND in the uCode RAM data here.
//
if (_rdRam)
{
_busData &= UCodeMemory.ReadRAM();
_rdRam = false;
}
//
// Let F1s that need to modify bus data before the ALU runs do their thing
// (this is used by the emulator RSNF and Ethernet EILFCT)
//
ExecuteSpecialFunction1Early(instruction);
// Do ALU operation.
// Small optimization: if we're just taking bus data across the ALU, we
// won't go through the ALU.Execute call; this is a decent performance gain for a bit
// more ugly code...
if (instruction.ALUF != AluFunction.Bus)
{
aluData = ALU.Execute(instruction.ALUF, _busData, _cpu._t, _skip);
}
else
{
aluData = _busData;
ALU.Carry = 0;
}
//
// If there was a WRTRAM operation last cycle, we write the uCode RAM here
// using the results of this instruction's ALU operation and the M register
// from the last instruction.
//
if (_wrtRam)
{
UCodeMemory.WriteRAM(aluData, _cpu._m);
_wrtRam = false;
}
//
// If there was an SWMODE operation last cycle, we set the flag to ensure it
// takes effect at the end of this cycle.
//
if (_swMode)
{
_swMode = false;
swMode = true;
}
//
// Do Special Functions
//
switch (instruction.F1)
{
case SpecialFunction1.None:
// Do nothing. Well, that was easy.
break;
case SpecialFunction1.LoadMAR:
// Do MAR or XMAR reference based on whether F2 is MD<- (for Alto IIs), indicating an extended memory reference.
_cpu._system.MemoryBus.LoadMAR(
aluData,
_taskType,
_systemType == SystemType.AltoI ? false : instruction.F2 == SpecialFunction2.StoreMD);
break;
case SpecialFunction1.Task:
//
// If the first uOp executed after a task switch contains a TASK F1, it does not take effect.
// This is observed on the real hardware, and does not appear to be documented.
// It also doesn't appear to affect the execution of the standard Alto uCode in any significant
// way, but is included here for correctness.
//
if (!_firstInstructionAfterSwitch)
{
// Yield to other more important tasks
completion = InstructionCompletion.TaskSwitch;
}
break;
case SpecialFunction1.Block:
// Technically this is to be invoked by the hardware device associated with a task.
// That logic would be circuituous and unless there's a good reason not to that is discovered
// later, I'm just going to directly block the current task here.
_cpu.BlockTask(this._taskType);
break;
case SpecialFunction1.LLSH1:
Shifter.SetOperation(ShifterOp.ShiftLeft);
break;
case SpecialFunction1.LRSH1:
Shifter.SetOperation(ShifterOp.ShiftRight);
break;
case SpecialFunction1.LLCY8:
Shifter.SetOperation(ShifterOp.RotateLeft);
break;
case SpecialFunction1.Constant:
// Ignored here; handled by Constant ROM access logic above.
break;
default:
// Let the specific task implementation take a crack at this.
ExecuteSpecialFunction1(instruction);
break;
}
switch (instruction.F2)
{
case SpecialFunction2.None:
// Nothing!
break;
case SpecialFunction2.BusEq0:
if (_busData == 0)
{
_nextModifier |= 1;
}
break;
case SpecialFunction2.ShLt0:
// Handled below, after the Shifter runs
break;
case SpecialFunction2.ShEq0:
// Same as above.
break;
case SpecialFunction2.Bus:
// Select bits 6-15 (bits 0-9 in modern parlance) of the bus
_nextModifier |= (ushort)(_busData & 0x3ff);
break;
case SpecialFunction2.ALUCY:
// ALUC0 is the carry produced by the ALU during the most recent microinstruction
// that loaded L. It is *not* the carry produced during the execution of the microinstruction
// that contains the ALUCY function.
_nextModifier |= _cpu._aluC0;
break;
case SpecialFunction2.StoreMD:
// Special case for XMAR on non-Alto I machines: if F1 is a LoadMAR we do nothing here;
// the handler for LoadMAR will load the correct bank.
if (_systemType == SystemType.AltoI)
{
_cpu._system.MemoryBus.LoadMD(_busData);
}
else if (instruction.F1 != SpecialFunction1.LoadMAR)
{
_cpu._system.MemoryBus.LoadMD(_busData);
}
break;
case SpecialFunction2.Constant:
// Ignored here; handled by Constant ROM access logic above.
break;
default:
// Let the specific task implementation take a crack at this.
ExecuteSpecialFunction2(instruction);
break;
}
//
// Do the shifter operation if we're doing an operation that requires the shifter output (loading R, doing a LoadDNS,
// modifying NEXT based on the shifter output.)
//
if (_loadR || instruction.NeedShifterOutput)
{
// A crude optimization: if there's no shifter operation,
// we bypass the call to DoOperation and stuff L in Shifter.Output ourselves.
if (Shifter.Op == ShifterOp.None)
{
Shifter.Output = _cpu._l;
}
else
{
Shifter.DoOperation(_cpu._l, _cpu._t);
}
}
//
// Handle NEXT modifiers that rely on the Shifter output.
//
switch (instruction.F2)
{
case SpecialFunction2.ShLt0:
//
// Note:
// "the value of SHIFTER OUTPUT is determined by the value of L as the microinstruction
// *begins* execution and the shifter function specified during the *current* microinstruction.
//
// Since we haven't modifed L yet, and we've calculated the shifter output above, we're good to go here.
//
if ((short)Shifter.Output < 0)
{
_nextModifier |= 1;
}
break;
case SpecialFunction2.ShEq0:
// See note above.
if (Shifter.Output == 0)
{
_nextModifier |= 1;
}
break;
}
//
// Write back to registers:
//
// Do writeback to selected R register from shifter output.
//
if (_loadR)
{
_cpu._r[_rSelect] = Shifter.Output;
}
// Do writeback to selected S register from M
if (_loadS)
{
_cpu._s[_rb][instruction.RSELECT] = _cpu._m;
}
// Load T
if (instruction.LoadT)
{
// Does this operation change the source for T?
_cpu._t = instruction.LoadTFromALU ? aluData : _busData;
//
// Control RAM: "...the control RAM address is specified by the control RAM
// address register... which is loaded from the ALU output whenver T is loaded
// from its source."
//
UCodeMemory.LoadControlRAMAddress(aluData);
}
// Load L (and M) from ALU outputs.
if (instruction.LoadL)
{
_cpu._l = aluData;
// Only RAM-related tasks can modify M.
if (_ramTask)
{
_cpu._m = aluData;
}
// Save ALUC0 for use in the next ALUCY special function.
_cpu._aluC0 = (ushort)ALU.Carry;
}
//
// Execute special functions that happen late in the cycle
//
ExecuteSpecialFunction2Late(instruction);
//
// Switch banks if the last instruction had an SWMODE F1;
// this depends on the value of the NEXT field in this instruction.
// (And apparently the modifier applied to NEXT in this instruction -- MADTEST expects this.)
//
if (swMode)
{
//Log.Write(LogType.Verbose, LogComponent.Microcode, "SWMODE: uPC {0}, next uPC {1} (NEXT is {2})", Conversion.ToOctal(_mpc), Conversion.ToOctal(instruction.NEXT | nextModifier), Conversion.ToOctal(instruction.NEXT));
UCodeMemory.SwitchMode((ushort)(instruction.NEXT | nextModifier), _taskType);
}
//
// Do task-specific BLOCK behavior if the last instruction had a BLOCK F1.
//
if (instruction.F1 == SpecialFunction1.Block)
{
ExecuteBlock();
}
//
// Select next address, using the address modifier from the last instruction.
// (Unless a soft reset occurred during this instruction)
//
if (!softReset)
{
_mpc = (ushort)(instruction.NEXT | nextModifier);
}
else
{
_cpu.SoftReset();
}
_firstInstructionAfterSwitch = false;
return(completion);
}
