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Moves contention delays up to the time of MREQ going active.

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Thomas Harte 2021-03-21 23:04:20 -04:00
parent f37f89a7d3
commit 7965772745
1 changed files with 19 additions and 20 deletions
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39
Machines/Sinclair/ZXSpectrum/ZXSpectrum.cpp
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@ -141,36 +141,35 @@ template<Model model> class ConcreteMachine:
// MARK: - BusHandler
forceinline HalfCycles perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {
// Ignore all but terminal cycles.
// TODO: I doubt this is correct for timing.
if(!cycle.is_terminal()) {
advance(cycle.length);
return HalfCycles(0);
}
using PartialMachineCycle = CPU::Z80::PartialMachineCycle;
HalfCycles delay(0);
uint16_t address = cycle.address ? *cycle.address : 0x0000;
using PartialMachineCycle = CPU::Z80::PartialMachineCycle;
const uint16_t address = cycle.address ? *cycle.address : 0x0000;
switch(cycle.operation) {
default: break;
case PartialMachineCycle::ReadOpcodeStart:
case PartialMachineCycle::ReadStart:
case PartialMachineCycle::WriteStart:
// Apply contention if necessary.
// For now this causes a video sync up every time any contended area is written to.
// TODO: flush only upon a video-area write.
//
// Assumption here: the trigger for the ULA inserting a delay is the falling edge
// of MREQ, which is always half a cycle into a read or write.
//
// TODO: somehow provide that information in the PartialMachineCycle?
if(is_contended_[address >> 14]) {
delay = video_->access_delay(HalfCycles(1));
}
break;
case PartialMachineCycle::ReadOpcode:
case PartialMachineCycle::Read:
// Apply contention if necessary.
if(is_contended_[address >> 14]) {
delay = video_.last_valid()->access_delay(video_.time_since_flush());
}
*cycle.value = read_pointers_[address >> 14][address];
break;
case PartialMachineCycle::Write:
// Apply contention if necessary.
// For now this causes a video sync up every time any contended area is written to.
// TODO: flush only upon a video-area write.
if(is_contended_[address >> 14]) {
delay = video_->access_delay(HalfCycles(0));
}
write_pointers_[address >> 14][address] = *cycle.value;
break;