#include <avr/io.h> // defines pins and ports
#include <util/delay.h>

#define BLINK_DELAY 500 // number of milliseconds to wait between LED toggles.

int main(void) {
  DDRB |= (1 << PB5); // Data Direction Register B: writing a 1 to the Pin B5
                      // bit enables output

  // Event loop (runs forever)
  while (1) {
    PORTB = 0b00100000; // turn on 5th LED bit/pin in PORT B (Pin13 in Arduino)
    _delay_ms(BLINK_DELAY);

    PORTB = 0b00000000; // turn off all bits/pins on PB
    _delay_ms(BLINK_DELAY);
  }

  return (0); // main() requires a return value, but this will never happen, as
              // the polling loop is infinite.
}