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Had a quick bash at timer overflow.

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This commit is contained in:
Thomas Harte 2015-07-30 16:09:32 -04:00
parent 58908b60ac
commit 14adcd2096
2 changed files with 15 additions and 7 deletions
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21
Machines/Atari2600.cpp
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@ -20,6 +20,7 @@ Machine::Machine()
_lastOutputStateDuration = 0; _lastOutputStateDuration = 0;
_lastOutputState = OutputState::Sync; _lastOutputState = OutputState::Sync;
_crt = new Outputs::CRT(228, 256, 1, 4); _crt = new Outputs::CRT(228, 256, 1, 4);
_piaTimerStatus = 0xff;
reset(); reset();
} }
@ -272,15 +273,15 @@ int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t add
if ((address&0x1280) == 0x280) { if ((address&0x1280) == 0x280) {
if(isReadOperation(operation)) { if(isReadOperation(operation)) {
switch(address & 0xf) { switch(address & 0xf) {
// case 0x00: case 0x04: returnValue &= _piaTimerValue >> _piaTimerShift; break;
case 0x04: returnValue &= _piaTimerValue >> _piaTimerShift; break; case 0x05: returnValue &= _piaTimerStatus; _piaTimerStatus &= ~0x40; break;
} }
} else { } else {
switch(address & 0x0f) { switch(address & 0x0f) {
case 0x04: _piaTimerShift = 0; _piaTimerValue = *value << 0; break; case 0x04: _piaTimerShift = 0; _piaTimerValue = *value << 0; _piaTimerStatus &= ~0xc0; break;
case 0x05: _piaTimerShift = 3; _piaTimerValue = *value << 3; break; case 0x05: _piaTimerShift = 3; _piaTimerValue = *value << 3; _piaTimerStatus &= ~0xc0; break;
case 0x06: _piaTimerShift = 6; _piaTimerValue = *value << 6; break; case 0x06: _piaTimerShift = 6; _piaTimerValue = *value << 6; _piaTimerStatus &= ~0xc0; break;
case 0x07: _piaTimerShift = 10; _piaTimerValue = *value << 10; break; case 0x07: _piaTimerShift = 10; _piaTimerValue = *value << 10; _piaTimerStatus &= ~0xc0; break;
} }
} }
// printf("Uncaught PIA %04x\n", address); // printf("Uncaught PIA %04x\n", address);
@ -290,7 +291,13 @@ int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t add
*value = returnValue; *value = returnValue;
} }
_piaTimerValue -= cycle_count; if(_piaTimerValue < cycle_count) {
_piaTimerValue = 0x100 - cycle_count + _piaTimerValue;
_piaTimerShift = 0;
_piaTimerStatus |= 0xc0;
}
else
_piaTimerValue -= cycle_count;
return cycle_count; return cycle_count;
} }

1
Machines/Atari2600.hpp
View File

@ -37,6 +37,7 @@ class Machine: public CPU6502::Processor<Machine> {
// the timer // the timer
unsigned int _piaTimerValue; unsigned int _piaTimerValue;
unsigned int _piaTimerShift; unsigned int _piaTimerShift;
uint8_t _piaTimerStatus;
// graphics registers // graphics registers
uint8_t _playfield[3], _playfieldControl; uint8_t _playfield[3], _playfieldControl;