#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>

#define LEDOFF PORTB &= ~(1 << 1)
#define LEDON PORTB |= (1 << 1)

volatile uint16_t ms;

ISR ( TIMER0_COMPA_vect )
{
  // event to be executed every 1ms here
  if ( ms != 0 )
    ms--;
}

void delay_ms ( uint16_t nms )
{
  ms = nms;
  while ( ms );
}

void Tim0_Init()
{
  // Tt0 = 1/(Fcpu/k) = 1/(8000000/64) = 0,000008s = 0.008ms
  // n = t/Tto - 1 = 1/0,008 - 1 = 124

  // Set the Timer Mode to CTC
  TCCR0A |= ( 1 << WGM01 );

  // Set the value that you want to count to
  OCR0A = 124;

  // Set the ISR COMPA vect
  TIMSK0 |= ( 1 << OCIE0A );

  // set prescaler to 64 and start the timer
  TCCR0B |= ( 1 << CS01 ) | ( 1 << CS00 );
}

int main()
{
  CLKPR = 0x80;
  CLKPR = 0x00;

  // Analog Comparator: Off
  ACSR = 0x80;
  ADCSRB = 0x00;

  DDRB |= ( uint8_t ) ( 1 << 1 );
  Tim0_Init();
  sei(); // enable interrupts
  while ( 1 )
    {
      LEDON;
      delay_ms ( 1000 );
      LEDOFF;
      delay_ms ( 1000 );
    }
}