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GB: Improved timer implementaion

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Passes all(?) mooneye-gb timer tests
This commit is contained in:
Sour 2020-05-23 15:41:30 -04:00
parent b758e97753
commit fb3bf73ba6
2 changed files with 70 additions and 17 deletions
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82
Core/GbTimer.cpp
View file

@ -9,7 +9,6 @@ GbTimer::GbTimer(GbMemoryManager* memoryManager, GbApu* apu)
_apu = apu;
_memoryManager = memoryManager;
//Passes boot_div-dmgABCmgb
//But that test depends on LCD power on timings, so may be wrong.
_divider = 0x06;
@ -21,12 +20,27 @@ GbTimer::~GbTimer()
void GbTimer::Exec()
{
uint16_t newValue = _divider + 4;
_reloaded = false;
if(_needReload) {
ReloadCounter();
}
SetDivider(_divider + 4);
}
void GbTimer::ReloadCounter()
{
_counter = _modulo;
_memoryManager->RequestIrq(GbIrqSource::Timer);
_needReload = false;
_reloaded = true;
}
void GbTimer::SetDivider(uint16_t newValue)
{
if(_timerEnabled && !(newValue & _timerDivider) && (_divider & _timerDivider)) {
_counter++;
if(_counter == 0) {
_counter = _modulo;
_memoryManager->RequestIrq(GbIrqSource::Timer);
_needReload = true;
}
}
@ -54,30 +68,64 @@ void GbTimer::Write(uint16_t addr, uint8_t value)
//TODO properly detect edges when setting new values to registers or disabling timer, etc.
switch(addr) {
case 0xFF04:
_divider = 0;
SetDivider(0);
break;
case 0xFF05:
//FF05 - TIMA - Timer counter (R/W)
_counter = value;
if(_needReload) {
//Writing to TIMA when a reload is pending will cancel the reload and IRQ request
_needReload = false;
}
if(!_reloaded) {
//Writes to TIMA on the cycle TIMA was reloaded with TMA are ignored
_counter = value;
}
break;
case 0xFF06:
//FF06 - TMA - Timer Modulo (R/W)
_modulo = value;
break;
case 0xFF07:
//FF07 - TAC - Timer Control (R/W)
_control = value;
_timerEnabled = (value & 0x04) != 0;
switch(value & 0x03) {
case 0: _timerDivider = 1 << 9; break;
case 1: _timerDivider = 1 << 3; break;
case 2: _timerDivider = 1 << 5; break;
case 3: _timerDivider = 1 << 7; break;
if(_reloaded) {
//Writing to TMA on the same cycle it was reloaded into TIMA will also update TIMA
_counter = value;
}
break;
case 0xFF07: {
//FF07 - TAC - Timer Control (R/W)
_control = value;
bool enabled = (value & 0x04) != 0;
uint16_t newDivider = 0;
switch(value & 0x03) {
case 0: newDivider = 1 << 9; break;
case 1: newDivider = 1 << 3; break;
case 2: newDivider = 1 << 5; break;
case 3: newDivider = 1 << 7; break;
}
if(_timerEnabled) {
//When changing the value of TAC, the TIMA register can get incremented due to a glitch
bool incrementCounter;
if(enabled) {
incrementCounter = (_divider & _timerDivider) != 0 && (_divider & newDivider) == 0;
} else {
incrementCounter = (_divider & _timerDivider) != 0;
}
if(incrementCounter) {
_counter++;
if(_counter == 0) {
ReloadCounter();
}
}
}
_timerEnabled = enabled;
_timerDivider = newDivider;
break;
}
}
}

5
Core/GbTimer.h
View file

@ -14,12 +14,17 @@ private:
uint16_t _divider = 0;
bool _needReload = false; //Set after TIMA (_counter) overflowed, next cycle will reload TMA into TIMA
bool _reloaded = false; //Set during the cycle on which TIMA is reloaded (affects TMA/TIMA writes)
uint8_t _counter = 0;
uint8_t _modulo = 0;
uint8_t _control = 0;
bool _timerEnabled = false;
uint16_t _timerDivider = 1024;
void SetDivider(uint16_t value);
void ReloadCounter();
public:
GbTimer(GbMemoryManager* memoryManager, GbApu* apu);