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Respond with 0xff during an interrupt acknowledge.

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This commit is contained in:
Thomas Harte 2021-04-18 11:56:00 -04:00
parent 9fd53c9c91
commit 80d4846a27
1 changed files with 21 additions and 11 deletions
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32
Machines/Sinclair/ZXSpectrum/ZXSpectrum.cpp
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@ -224,6 +224,17 @@ template<Model model> class ConcreteMachine:
}
} else {
switch(cycle.operation) {
case CPU::Z80::PartialMachineCycle::Input:
case CPU::Z80::PartialMachineCycle::Output:
case CPU::Z80::PartialMachineCycle::Read:
case CPU::Z80::PartialMachineCycle::Write:
case CPU::Z80::PartialMachineCycle::ReadOpcode:
case CPU::Z80::PartialMachineCycle::Interrupt:
// For these, carry on into the actual handler, below.
break;
// For anything else that isn't listed below, just advance
// time and conclude here.
default:
advance(cycle.length);
return HalfCycles(0);
@ -250,7 +261,7 @@ template<Model model> class ConcreteMachine:
advance(cycle.length + delay);
return delay;
}
} break;
case PartialMachineCycle::ReadOpcodeStart:
case PartialMachineCycle::ReadStart:
@ -263,7 +274,7 @@ template<Model model> class ConcreteMachine:
advance(cycle.length + delay);
return delay;
}
}
} break;
case PartialMachineCycle::Internal: {
// Whatever's on the address bus will remain there, without IOREQ or
@ -284,15 +295,7 @@ template<Model model> class ConcreteMachine:
advance(cycle.length + delay);
return delay;
}
}
case CPU::Z80::PartialMachineCycle::Input:
case CPU::Z80::PartialMachineCycle::Output:
case CPU::Z80::PartialMachineCycle::Read:
case CPU::Z80::PartialMachineCycle::Write:
case CPU::Z80::PartialMachineCycle::ReadOpcode:
// For these, carry on into the actual handler, below.
break;
} break;
}
}
@ -496,6 +499,13 @@ template<Model model> class ConcreteMachine:
}
}
} break;
case PartialMachineCycle::Interrupt:
// At least one piece of Spectrum software, Escape from M.O.N.J.A.S. explicitly
// assumes that a 0xff value will be on the bus during an interrupt acknowledgment.
// I wasn't otherwise aware that this value is reliable.
*cycle.value = 0xff;
break;
}
return HalfCycles(0);