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
  24 // counter resolution 1ms
  25 volatile uint16_t timer_count = 0;
  26
  27 void timer_init(void)
  28 {
  29     // Timer0 CTC mode
  30     TCCR0A = 0x02;
  31
  32 #if TIMER_PRESCALER == 1
  33     TCCR0B = 0x01;
  34 #elif TIMER_PRESCALER == 8
  35     TCCR0B = 0x02;
  36 #elif TIMER_PRESCALER == 64
  37     TCCR0B = 0x03;
  38 #elif TIMER_PRESCALER == 256
  39     TCCR0B = 0x04;
  40 #elif TIMER_PRESCALER == 1024
  41     TCCR0B = 0x05;
  42 #else
  43 #   error "Timer prescaler value is NOT vaild."
  44 #endif
  45
  46     OCR0A = TIMER_RAW_TOP;
  47     TIMSK0 = (1<<OCIE0A);
  48 }
  49
  50 inline
  51 void timer_clear(void)
  52 {
  53     uint8_t sreg = SREG;
  54     cli();
  55     timer_count = 0;
  56     SREG = sreg;
  57 }
  58
  59 inline
  60 uint16_t timer_read(void)
  61 {
  62     uint16_t t;
  63
  64     uint8_t sreg = SREG;
  65     cli();
  66     t = timer_count;
  67     SREG = sreg;
  68
  69     return t;
  70 }
  71
  72 inline
  73 uint16_t timer_elapsed(uint16_t last)
  74 {
  75     uint16_t t;
  76
  77     uint8_t sreg = SREG;
  78     cli();
  79     t = timer_count;
  80     SREG = sreg;
  81
  82     return TIMER_DIFF_MS(t, last);
  83 }
  84
  85 // excecuted once per 1ms.(excess for just timer count?)
  86 ISR(TIMER0_COMPA_vect)
  87 {
  88     timer_count++;
  89 }