public InvalidInstructionHandler(Instruction instruction)
{
Instruction = (InvalidInstruction)instruction;
}
public void Tick()
{
// If the trap flag is set, trigger interrupt 1
if (CondReg.TrapFlag)
{
var interrupt = new INT(0, 1, this, Bus);
interrupt.Execute();
}
// If interrupts are enabled and there is an interrupt waiting,
// trigger the next interrupt. Only one interrupt is processed per
// tick if multiple are waiting.
if (CondReg.InterruptEnable) // && i8259 has an interrupt waiting
{
// Interrupt( i8259 next interrupt ) ;
}
// Reset the prefix and base pointer flags.
Bus.SegmentOverride = SegmentOverrideState.NoOverride;
Bus.UsingBasePointer = false;
RepeatMode = RepeatModeEnum.NoRepeat;
// Process prefix instructions
bool more = false;
do
{
// Retrieve the next instruction and count stats
InstructionCount++;
CurrentOpCode = Bus.NextImmediate();
Stats.AddOpCode(CurrentOpCode);
more = true;
switch (CurrentOpCode)
{
case 0x26:
{
Bus.SegmentOverride = SegmentOverrideState.UseES;
break;
}
case 0x2e:
{
Bus.SegmentOverride = SegmentOverrideState.UseCS;
break;
}
case 0x36:
{
Bus.SegmentOverride = SegmentOverrideState.UseSS;
break;
}
case 0x3e:
{
Bus.SegmentOverride = SegmentOverrideState.UseDS;
break;
}
case 0xf2:
{
RepeatMode = RepeatModeEnum.REPNZ;
break;
}
case 0xf3:
{
RepeatMode = RepeatModeEnum.REP;
break;
}
default:
{
more = false;
break;
}
}
} while (more);
// Process the next instruction.
if (!instructions.TryGetValue(CurrentOpCode, out var instruction))
{
instruction = new InvalidInstruction(CurrentOpCode, this, Bus);
}
instruction.Execute();
// NOTE: a current minor flaw here is if there is a repeat instruction because the entire loop
// will get executed immediately without allowing for any interrupts. Watch for timing issues
// with PIT if there is a long loop.
// Tick the PIT
// i8253.Tick()
}
