arduino_uno_blink.c

#include <avr/io.h>
#define F_CPU 16000000UL
#include <util/delay.h>
 
int main(void) {
 
  DDRB |= _BV(5);
 
  while (1) {
    PORTB |= _BV(5);
    _delay_ms(1000);
    PORTB &= ~(_BV(5));
    _delay_ms(1000);
  }
  return 0;
}