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Mildly adjust layout of inner loop.

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This commit is contained in:
Thomas Harte 2023-11-27 15:16:22 -05:00
parent 032eeb4757
commit 2a0375e9c2
1 changed files with 34 additions and 14 deletions
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48
Components/68901/MFP68901.cpp
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@ -275,21 +275,41 @@ template void MFP68901::set_timer_event_input<3>(bool);
template <int timer>
void MFP68901::decrement_timer(int amount) {
while(amount--) {
--timers_[timer].value;
if(timers_[timer].value < 1) {
switch(timer) {
case 0: begin_interrupts(Interrupt::TimerA); break;
case 1: begin_interrupts(Interrupt::TimerB); break;
case 2: begin_interrupts(Interrupt::TimerC); break;
case 3: begin_interrupts(Interrupt::TimerD); break;
}
while(amount) {
if(timers_[timer].value > amount) {
timers_[timer].value -= amount;
return;
}
// Re: reloading when in event counting mode; I found the data sheet thoroughly unclear on
// this, but it appears empirically to be correct. See e.g. Pompey Pirates menu 27.
if(timers_[timer].mode == TimerMode::Delay || timers_[timer].mode == TimerMode::EventCount) {
timers_[timer].value += timers_[timer].reload_value; // TODO: properly.
}
// Keep this check here to avoid the case where a decrement to zero occurs during one call to
// decrement_timer, triggering an interrupt, then the timer is already 0 at the next instance,
// causing a second interrupt.
//
// ... even though it would be nice to move it down below, after value has overtly been set to 0.
if(!timers_[timer].value) {
--timers_[timer].value;
--amount;
continue;
}
// If here then amount is sufficient to, at least once, decrement the timer
// from 1 to 0. So there's an interrupt.
//
// (and, this switch is why this function is templated on timer ID)
switch(timer) {
case 0: begin_interrupts(Interrupt::TimerA); break;
case 1: begin_interrupts(Interrupt::TimerB); break;
case 2: begin_interrupts(Interrupt::TimerC); break;
case 3: begin_interrupts(Interrupt::TimerD); break;
}
// Re: reloading when in event counting mode; I found the data sheet thoroughly unclear on
// this, but it appears empirically to be correct. See e.g. Pompey Pirates menu 27.
amount -= timers_[timer].value;
if(timers_[timer].mode == TimerMode::Delay || timers_[timer].mode == TimerMode::EventCount) {
timers_[timer].value = timers_[timer].reload_value; // TODO: properly.
} else {
timers_[timer].value = 0;
}
}
}