firmware/timer.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3 #include "timer.h"
   4
   5 #define BIT(n) (1<<(n))
   6
   7 static TimerCallback *timer_callback;
   8
   9 void timer_init(uint16_t freq_p, uint8_t freq_q)
  10 {
  11         uint32_t period = F_CPU*freq_q/freq_p;
  12         uint8_t cs;
  13
  14         if(period<0x10000)
  15         {
  16                 cs = BIT(CS10);
  17         }
  18         else if(period<0x80000)
  19         {
  20                 cs = BIT(CS11);
  21                 period /= 8;
  22         }
  23         else if(period<0x400000)
  24         {
  25                 cs = BIT(CS11) | BIT(CS10);
  26                 period /= 64;
  27         }
  28         else if(period<0x1000000)
  29         {
  30                 cs = BIT(CS12);
  31                 period /= 256;
  32         }
  33         else
  34         {
  35                 cs = BIT(CS12) | BIT(CS10);
  36                 period /= 1024;
  37                 if(period>0xFFFF)
  38                         period = 0xFFFF;
  39         }
  40         TCCR1A = 0;
  41         TCCR1B = BIT(WGM12) | cs;
  42         OCR1AH = period>>8;
  43         OCR1AL = period;
  44 }
  45
  46 void timer_set_callback(TimerCallback *cb)
  47 {
  48         timer_callback = cb;
  49         TIMSK1 |= BIT(OCIE1A);
  50 }
  51
  52 ISR(TIMER1_COMPA_vect)
  53 {
  54         timer_callback();
  55 }