#include <avr/io.h>
#include <stdlib.h>
#include <string.h>
#include <util/delay.h>
 
#ifndef _BV
#define _BV(bit)        (1<<(bit))
#endif
#ifndef sbi
#define sbi(reg,bit)    reg |= (_BV(bit))
#endif
 
#ifndef cbi
#define cbi(reg,bit)    reg &= ~(_BV(bit))
#endif

#ifndef tbi
#define tbi(reg,bit)    reg ^= (_BV(bit))
#endif

void blinkLEDsSequentially() {
  for (uint8_t i = 0; i < 8; i++) {
    PORTD |= (1<<i);
    _delay_ms(500);
    PORTD ^= (1<<i);
  }
  for (uint8_t i = 6; i > 0 ; i--) {
    PORTD |= (1<<i);
    _delay_ms(500);
    PORTD ^= (1<<i);
  }
}

int main() {
 
  
  DDRD=0xff;

  _delay_ms(500);

  while(1) {
    blinkLEDsSequentially();
  }
}