git.sur5r.net Git - cc65/blob - samples/atari2600hello.c

   1 /*****************************************************************************/
   2 /*                                                                           */
   3 /* Atari VCS 2600 sample C program                                           */
   4 /*                                                                           */
   5 /* Florent Flament (contact@florentflament.com), 2017                        */
   6 /*                                                                           */
   7 /*****************************************************************************/
   8
   9 #include <atari2600.h>
  10
  11 // PAL Timings
  12 // Roughly computed based on Stella Programmer's guide (Steve Wright)
  13 // scanlines count per section.
  14 #define VBLANK_TIM64 51 // 45 lines * 76 cycles/line / 64 cycles/tick
  15 #define KERNAL_T1024 17 // 228 lines * 76 cycles/line / 1024 cycles/tick
  16 #define OVERSCAN_TIM64 42 // 36 lines * 76 cycles/line / 64 cycles/tick
  17
  18 // Testing memory zones
  19 const unsigned char rodata_v[] = "Hello!";
  20 unsigned char data_v = 0x77;
  21 unsigned char bss_v;
  22
  23 void main(void) {
  24     unsigned char color = 0x79; // Stack variable
  25     bss_v = 0x88; // Testing BSS variable
  26
  27     for/*ever*/(;;) {
  28         // Vertical Sync signal
  29         TIA.vsync = 0x02;
  30         TIA.wsync = 0x00;
  31         TIA.wsync = 0x00;
  32         TIA.wsync = 0x00;
  33         TIA.vsync = 0x00;
  34
  35         // Vertical Blank timer setting
  36         RIOT.tim64t = VBLANK_TIM64;
  37
  38         // Doing frame computation during blank
  39         TIA.colubk = color++; // Update color
  40
  41         // Wait for end of Vertical Blank
  42         while (RIOT.timint == 0) {}
  43         TIA.wsync = 0x00;
  44         TIA.vblank = 0x00; // Turn on beam
  45
  46         // Display frame
  47         RIOT.t1024t = KERNAL_T1024;
  48         while (RIOT.timint == 0) {}
  49         TIA.wsync = 0x00;
  50         TIA.vblank = 0x02; // Turn off beam
  51
  52         // Overscan
  53         RIOT.tim64t = OVERSCAN_TIM64;
  54         while (RIOT.timint == 0) {}
  55     }
  56 }