rgbyteclock-code/timer.c

/*
 * "THE BEER-WARE LICENSE" (Revision 42):
 * Martin Wenger <martin.wenger@arcormail.de> and Stefan Rupp <struppi@struppi.name>
 * wrote this file. As long as you retain this notice you can do whatever you want
 * with this stuff. If we meet some day, and you think this stuff is worth it,
 * you can buy me/us a beer in return.
 * (c) 2005-2010 Martin Wenger, Stefan Rupp
 * (c) 2013,2014 Stefan Rupp
 */
 
#include <avr/io.h>
#include "timer.h"
#include <stdlib.h>
#include <avr/interrupt.h>


/* timer_time gets increased on every interrupt
 * those interrupts happen every 1ms
 */
static volatile uint32_t _timer_time;

ISR(TIMER0_COMPA_vect) {
  ++_timer_time;
  return;
}

/**
 * Initialize the timer
 * This function has to be called first, before calling timer_wait and/or timer_get,
 * else timer_get will always return 0, and timer_wait will wait forever!
 */

void timer_init(void)
{

  uint8_t sreg = SREG;
  // Stop all interrupts
  cli();

  // Reset timer to zero
  _timer_time = 0;
  
  // - Time accuracy: 1 millisecond (corresponding frequency: 1kHz)
  // ==> F_CPU = 20Mhz
  // ==> 20Mhz / 256 = 78.125 kHz
  // ==> let timer count to 77 to get (almost) 1kHz frequency
  // therefore:
  // - Set Timer/Counter0 prescaler to 256 ==> (1<<CS02)
  // - Set OCR0 to 77
  // - CTC ( i.e. clear counter, when COUNTER == OCR0A) ==> (1<<WGM01)
  // unfortunately, due to the 20MHz and the coarse prescaler dividers
  // provided, we can't get any closer to the desired frequency of
  // 1kHz :(
  OCR0A = 77;
  TCCR0A = (1<<WGM01);
  TCCR0B = (1<<CS02);

  // Interrupts setzen
  TIMSK0 |= (1<<OCIE0A);
  SREG = sreg;
}


/**
 * Get the current time
 * \return the current time (in ms)
 */
inline uint32_t timer_get(void)
{
  uint32_t t;
  uint8_t sreg;

  sreg = SREG;
  cli();
  t = _timer_time;
  SREG = sreg;
  return t;
}

/**
 * Wait for (at least) the specified amount of time
 * \param delay The time to wait (in ms)
 */

void timer_wait(uint32_t delay)
{
  uint32_t end = timer_get() + delay +1;
  while ( end > timer_get() );
  return;
}

/**
 * Decode a integer timestamp (in microseconds)
 * into hours, minutes, seconds, microseconds
 * \param time the time in microseconds
 * \param hours will be filled in to contain the hours after return
 * \param minutes will be filled in to contain the minutes after return
 * \param seconds will be filled in to contain the seconds after return
 * \param ms be filled in to contain the microseconds after return
 */
void timer_decode(uint32_t time, uint8_t *hours, uint8_t *minutes, uint8_t *seconds, uint16_t *ms)
{
  if (ms != NULL) {
    *ms = time % 1000;
  }
  time /= 1000;
  if (seconds != NULL) {
    *seconds = time % 60;
  }
  time /= 60;
  if (minutes != NULL) {
    *minutes = time % 60;
  }
  time /= 60;
  if (hours != NULL) {
    *hours = time;
  }
  return;
}

/**
 * Encode a time given as hours, minutes, seconds and microsecods into a integer storing micorseconds
 * \param time the variable to store the time into
 * \param hour the hours to store
 * \param hour the minutes to store
 * \param hour the seconds to store
 * \param hour the microseconds to store
 */
void timer_encode(uint32_t *time, uint8_t hours, uint8_t minutes, uint8_t seconds, uint16_t ms)
{

  *time = hours;
  *time *= 60;

  *time += minutes;
  *time *= 60;

  *time += seconds;
  *time *= 1000U;

  *time += ms;

  return;
}

/*
void timer_validate(uint8_t *hours, uint8_t *minutes, uint8_t *seconds, uint16_t *ms)
{ 

  while (*ms >= 1000) {
    *ms -= 1000;
    (*seconds)++;
  }

  while (*seconds >= 60) {
    *ms -= 60;
    (*minutes)++;
  }

  while (*minutes >= 60) {
    *minutes -= 60;
    (*hours)++;
  }

  return;
}
*/