i86/mtx-16-bit/mtx/samples/SERIAL/timer.c

   1 /* timer parameters. */
   2 #define LATCH_COUNT     0x00    /* cc00xxxx, c = channel, x = any */
   3 #define SQUARE_WAVE     0x36    /* ccaammmb, a = access, m = mode, b = BCD */
   4
   5 /************************ NOTICE THE DIVISOR VALUE ***********************/
   6 #define TIMER_FREQ   1193182L   /* timer frequency for timer in PC and AT */
   7 #define TIMER_COUNT ((unsigned) (TIMER_FREQ/10)) /* initial value for counter*/
   8
   9 #define TIMER0       0x40
  10 #define TIMER_MODE   0x43
  11 #define TIMER_IRQ       0
  12
  13
  14 int enable_irq(irq_nr) unsigned irq_nr;
  15 {
  16   lock();
  17     out_byte(0x21, in_byte(0x21) & ~(1 << irq_nr));
  18
  19 }
  20
  21 /*===========================================================================*
  22  *                              timer_init                                   *
  23  *===========================================================================*/
  24
  25 ushort tick;
  26
  27 int timer_init()
  28 {
  29   /* Initialize channel 0 of the 8253A timer to e.g. 60 Hz. */
  30
  31   printf("timer init\n");
  32   tick = 0;
  33
  34   out_byte(TIMER_MODE, SQUARE_WAVE);    /* set timer to run continuously */
  35   out_byte(TIMER0, TIMER_COUNT);        /* load timer low byte */
  36   out_byte(TIMER0, TIMER_COUNT >> 8);   /* load timer high byte */
  37   enable_irq(TIMER_IRQ);
  38 }
  39
  40 /*===========================================================================*
  41  *                              timer_handler                                *
  42  *===========================================================================*/
  43
  44 int thandler()
  45 {
  46     tick++;
  47     tick %= 60;
  48
  49     if (tick % 60 == 0)
  50        printf("1 second timer interrupt\n");
  51
  52     out_byte(0x20, 0x20);
  53
  54 }
  55
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