timer.c

   1 /*
   2 Copyright 2011 Jun Wako <wakojun@gmail.com>
   3
   4 This program is free software: you can redistribute it and/or modify
   5 it under the terms of the GNU General Public License as published by
   6 the Free Software Foundation, either version 2 of the License, or
   7 (at your option) any later version.
   8
   9 This program is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 GNU General Public License for more details.
  13
  14 You should have received a copy of the GNU General Public License
  15 along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16 */
  17
  18 #include <avr/io.h>
  19 #include <avr/interrupt.h>
  20 #include <stdint.h>
  21 #include "timer.h"
  22
  23 volatile uint16_t timer_count = 0;
  24
  25 // Configure timer 0 to generate a timer overflow interrupt every
  26 // 256*1024 clock cycles, or approx 61 Hz when using 16 MHz clock
  27 // This demonstrates how to use interrupts to implement a simple
  28 // inactivity timeout.
  29 void timer_init(void)
  30 {
  31     TCCR0A = 0x00;
  32     TCCR0B = 0x05;
  33     TIMSK0 = (1<<TOIE0);
  34 }
  35
  36 inline
  37 void timer_clear(void)
  38 {
  39     uint8_t sreg = SREG;
  40     cli();
  41     timer_count = 0;
  42     SREG = sreg;
  43 }
  44
  45 inline
  46 uint16_t timer_read(void)
  47 {
  48     uint16_t t;
  49
  50     uint8_t sreg = SREG;
  51     cli();
  52     t = timer_count;
  53     SREG = sreg;
  54
  55     return t;
  56 }
  57
  58 inline
  59 uint16_t timer_elapsed(uint16_t last)
  60 {
  61     uint16_t t;
  62
  63     uint8_t sreg = SREG;
  64     cli();
  65     t = timer_count;
  66     SREG = sreg;
  67
  68     return TIMER_DIFF(t, last);
  69 }
  70
  71 // This interrupt routine is run approx 61 times per second.
  72 // A very simple inactivity timeout is implemented, where we
  73 // will send a space character and print a message to the
  74 // hid_listen debug message window.
  75 ISR(TIMER0_OVF_vect)
  76 {
  77     timer_count++;
  78 }