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Switched to a down counter and a reset test that remains unconditional but doesn't depend on % (which seems to turn into a big imul-powered deal). Probably pointless mulling around the edges at this point.

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This commit is contained in:
Thomas Harte 2015-07-26 15:45:19 -04:00
parent 6252f6030f
commit 8efd449834
2 changed files with 14 additions and 9 deletions
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20
Machines/Atari2600.cpp
View File

@ -16,7 +16,7 @@ static const char atari2600DataType[] = "Atari2600";
Machine::Machine()
{
_timestamp = 0;
_horizontalTimer = 0;
_horizontalTimer = 227;
_lastOutputStateDuration = 0;
_lastOutputState = OutputState::Sync;
_crt = new Outputs::CRT(228, 256, 1, 4);
@ -56,21 +56,25 @@ void Machine::output_pixels(int count)
// it'll be about 43 cycles from start of hsync to start of visible frame, so...
// guesses, until I can find information: 26 cycles blank, 16 sync, 40 blank, 160 pixels
if(_horizontalTimer < 13) output_state(OutputState::Blank, nullptr);
else if (_horizontalTimer < 39) output_state(OutputState::Sync, nullptr);
else if (_horizontalTimer < 68) output_state(OutputState::Blank, nullptr);
if(_horizontalTimer > 214) output_state(OutputState::Blank, nullptr);
else if (_horizontalTimer > 188) output_state(OutputState::Sync, nullptr);
else if (_horizontalTimer >= 160) output_state(OutputState::Blank, nullptr);
else {
if(_vBlankEnabled) {
output_state(OutputState::Blank, nullptr);
} else {
uint8_t outputPixel[3];
get_output_pixel(outputPixel, _horizontalTimer - 68);
get_output_pixel(outputPixel, 159 - _horizontalTimer);
output_state(OutputState::Pixel, outputPixel);
}
}
}
_horizontalTimer = (_horizontalTimer + 1)%228;
// assumption here: signed shifts right; otherwise it's just
// an attempt to avoid both the % operator and a conditional
_horizontalTimer--;
const int32_t sign_extension = _horizontalTimer >> 31;
_horizontalTimer = (_horizontalTimer&~sign_extension) | (sign_extension&227);
}
}
@ -137,11 +141,11 @@ void Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t ad
case 1: _vBlankEnabled = !!(*value & 0x02); break;
case 2: {
const int cyclesToRunFor = 228 - _horizontalTimer;
const int cyclesToRunFor = _horizontalTimer;
_piaTimerValue -= cyclesToRunFor;
output_pixels(cyclesToRunFor);
} break;
case 3: _horizontalTimer = 0; break;
case 3: _horizontalTimer = 227; break;
case 0x0a: _playFieldControl = *value; break;
case 0x0d: _playField[0] = *value; break;

3
Machines/Atari2600.hpp
View File

@ -11,6 +11,7 @@
#include "../Processors/6502/CPU6502.hpp"
#include "../Outputs/CRT.hpp"
#include <stdint.h>
namespace Atari2600 {
@ -40,7 +41,7 @@ class Machine: public CPU6502::Processor<Machine> {
uint8_t _playField[3], _playFieldControl;
// graphics output
int _horizontalTimer;
int32_t _horizontalTimer;
bool _vSyncEnabled, _vBlankEnabled;
enum OutputState {