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This commit is contained in:
Braiden Gent
2024-04-12 16:52:12 -07:00
parent b680c4f390
commit 8effdf132d
11 changed files with 293 additions and 118 deletions
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33
src/timing.cpp
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@@ -2,9 +2,42 @@
//handles most of the behavoir as described here: https://gbdev.io/pandocs/Timer_and_Divider_Registers.html#ff04--div-divider-register
void GameBoy::timingHandler() {
//can't do this as we use cycles for PPU timing but this is what should happen
//addressSpace.memoryLayout.DIV = ((cycles / 4) >> 6) & 0xFF;
if (cycles - lastDivUpdate >= DIVIDER_REGISTER_FREQ) {
const uint8_t increments = (cycles - lastDivUpdate) / DIVIDER_REGISTER_FREQ;
addressSpace.memoryLayout.DIV += increments;
lastDivUpdate += increments * DIVIDER_REGISTER_FREQ;
}
//if enabled
uint64_t TIMAFrequency = 0;
if (addressSpace.memoryLayout.TAC & 0x04) {
switch (addressSpace.memoryLayout.TAC & 0x03) {
case 0:
TIMAFrequency = 1024;
break;
case 1:
TIMAFrequency = 16;
break;
case 2:
TIMAFrequency = 64;
break;
case 3:
TIMAFrequency = 256;
break;
}
//if TIMA overflowed and prevTMA != current TMA, use prevTMA (ie use prevTMA regardless)
const int increments = (cycles - lastTIMAUpdate) / TIMAFrequency;
if (cycles - lastTIMAUpdate >= TIMAFrequency) {
if (static_cast<int>(addressSpace.memoryLayout.TIMA) + increments > 255) {
addressSpace.memoryLayout.TIMA = prevTMA + ((addressSpace.memoryLayout.TIMA + increments) % 256);
setInterrupt(TIMER_INTERRUPT);
}
else
addressSpace.memoryLayout.TIMA += increments;
lastTIMAUpdate += increments * TIMAFrequency;
}
}
}