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/*****************************************************************************/
/* */
/* Atari VCS 2600 sample C program */
/* */
/* Florent Flament (contact@florentflament.com), 2017 */
/* */
/*****************************************************************************/
#include <atari2600.h>
// PAL Timings
// Roughly computed based on Stella Programmer's guide (Steve Wright)
// scanlines count per section.
#define VBLANK_TIM64 51 // 45 lines * 76 cycles/line / 64 cycles/tick
#define KERNAL_T1024 17 // 228 lines * 76 cycles/line / 1024 cycles/tick
#define OVERSCAN_TIM64 42 // 36 lines * 76 cycles/line / 64 cycles/tick
// Testing memory zones
const unsigned char rodata_v[] = "Hello!";
unsigned char data_v = 0x77;
unsigned char bss_v;
void main(void) {
unsigned char color = 0x79; // Stack variable
bss_v = 0x88; // Testing BSS variable
for/*ever*/(;;) {
// Vertical Sync signal
TIA.vsync = 0x02;
TIA.wsync = 0x00;
TIA.wsync = 0x00;
TIA.wsync = 0x00;
TIA.vsync = 0x00;
// Vertical Blank timer setting
RIOT.tim64t = VBLANK_TIM64;
// Doing frame computation during blank
TIA.colubk = color++; // Update color
// Wait for end of Vertical Blank
while (RIOT.timint == 0) {}
TIA.wsync = 0x00;
TIA.vblank = 0x00; // Turn on beam
// Display frame
RIOT.t1024t = KERNAL_T1024;
while (RIOT.timint == 0) {}
TIA.wsync = 0x00;
TIA.vblank = 0x02; // Turn off beam
// Overscan
RIOT.tim64t = OVERSCAN_TIM64;
while (RIOT.timint == 0) {}
}
}
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