Tooltron

#include <stdint.h>

#include <avr/io.h>

#include <avr/interrupt.h>

#include "time.h"

/* F_CPU / PRESCALE = OCR * 1000 + ERROR */

#define OCR (F_CPU / PRESCALE / 1000UL)

#define ERROR (F_CPU / PRESCALE - OCR * 1000UL)

static char ready, ms;

static uint16_t error;

ISR(TIMER0_COMPA_vect) {

  error += ERROR;

  if (error >= 1000) {

    error -= 1000;

    OCR0A = OCR+1;

  } else {

    OCR0A = OCR;

  }

  if (++ms == TICK_MS) {

    ready = 1;

    ms = 0;

  }

}

void time_init() {

  OCR0A = OCR;

  TIMSK = _BV(OCIE0A);

  TCCR0A = _BV(WGM01);

  TCCR0B = CLOCK_SEL;

}

void time_wait() {

  while (!ready);

  ready = 0;

}