blink.c

#ifndef F_CPU
#define F_CPU 16000000UL // cpu frequency
#endif

#include <avr/io.h>
#include <util/delay.h>

#ifndef DELAY_MS
#define DELAY_MS 2000
#endif

int main(void)
{
  DDRB |= (1<<DDB5); // set led (pin 13 / PB5) on PORTB to output
  while(1)
  {
    PORTB |= (1<<PORTB5);    // set pin 13 / PB5 on
    _delay_ms(DELAY_MS);     // delay ms amount
    PORTB &= ~(1<<PORTB5);   // set pin 13 / PB5 off
    _delay_ms(DELAY_MS);     // delay ms amount
  }
}