preliminary support for 16 bit pwm. The 16 bit counter ist still used for

[moodlight.git] / timers.c

/* $Id: timers.c,v 1.2 2010/07/25 20:40:44 simimeie Exp $
 * Functions for timing.
 * This mainly allows you to get a timestamp value
 */

#include <avr/io.h>
#include <avr/interrupt.h>
#include "timers.h"

/* Internal ticks */
static volatile uint16_t ticks = 0;

void ledpwm_TIMER1OVF_hook(void);

/* Executes every 65536 cpu cycles when the timer overflows */
ISR(TIMER1_OVF_vect)
{
  ticks++;
  ledpwm_TIMER1OVF_hook();
}

uint16_t getticks(void)
{
  uint16_t res;
  cli();
  res = ticks;
  sei();
  return res;
}

uint16_t getticks_noirq(void)
{
  return ticks;
}

struct timestamp gettimestamp(void)
{
  uint16_t cou1, cou2, tick1;
  struct timestamp res;
  /* Low byte must be read first for 16bit registers */
  cou1 = TCNT1L;
  cou1 |= (uint16_t)(TCNT1H) << 8;
  tick1 = getticks(); /* enables interrupts! */
  cou2 = TCNT1L;
  cou2 |= (uint16_t)(TCNT1H) << 8;
  if (cou1 > cou2) { /* An overflow occured in between */
    /* get new ticks value - we could already have it, but we do not know
     * for sure. If we get another one now, we do - because there is no
     * way we're going to need another 65k cpu cycles. */
    res.ticks = getticks();
  } else { /* no overflow. */
    res.ticks = tick1;
  }
  res.partticks = cou2;
  return res;
}

struct timestamp gettimestamp_noirq(void)
{
  uint16_t cou1, cou2; uint8_t ovf;
  struct timestamp res;
  /* Low byte must be read first for 16bit registers */
  cou1 = TCNT1L;
  cou1 |= (uint16_t)(TCNT1H) << 8;
  /* Check if there is an overflow pending */
  ovf = TIFR1 & _BV(TOV1);
  if (ovf) {
    /* Overflow pending, reread the counter to be sure */
    cou2 = TCNT1L;
    cou2 |= (uint16_t)(TCNT1H) << 8;
    res.ticks = ticks + 1;
    res.partticks = cou2;
  } else {
    res.ticks = ticks;
    res.partticks = cou1;
  }
  return res;
}

void timers_init(void)
{
  /* Enable counter1, no prescaling (1 increment per clock cycle!) */
  TCCR1B |= _BV(CS10);
  /* Enable interrupt when timer overflows (at 65536) */
  TIMSK1 |= _BV(TOIE1);
}