timer.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3 #include <stdint.h>
   4 #include "timer.h"
   5
   6 volatile uint16_t timer_count = 0;
   7
   8 // Configure timer 0 to generate a timer overflow interrupt every
   9 // 256*1024 clock cycles, or approx 61 Hz when using 16 MHz clock
  10 // This demonstrates how to use interrupts to implement a simple
  11 // inactivity timeout.
  12 void timer_init(void)
  13 {
  14     TCCR0A = 0x00;
  15     TCCR0B = 0x05;
  16     TIMSK0 = (1<<TOIE0);
  17 }
  18
  19 inline
  20 void timer_clear(void)
  21 {
  22     uint8_t sreg = SREG;
  23     cli();
  24     timer_count = 0;
  25     SREG = sreg;
  26 }
  27
  28 inline
  29 uint16_t timer_read(void)
  30 {
  31     uint16_t t;
  32
  33     uint8_t sreg = SREG;
  34     cli();
  35     t = timer_count;
  36     SREG = sreg;
  37
  38     return t;
  39 }
  40
  41 inline
  42 uint16_t timer_elapsed(uint16_t last)
  43 {
  44     uint16_t t;
  45
  46     uint8_t sreg = SREG;
  47     cli();
  48     t = timer_count;
  49     SREG = sreg;
  50
  51     return TIMER_DIFF(t, last);
  52 }
  53
  54 // This interrupt routine is run approx 61 times per second.
  55 // A very simple inactivity timeout is implemented, where we
  56 // will send a space character and print a message to the
  57 // hid_listen debug message window.
  58 ISR(TIMER0_OVF_vect)
  59 {
  60     timer_count++;
  61 }