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

#define DELAY 75
#define LEN sizeof(PORTB) * CHAR_BIT - 1
#define LED_DDR DDRB
#define LED_PORT PORTB

int main(void) {
    uint8_t i;

    LED_DDR = 0xff;

    for (;;) {
        for (i = 0; i < LEN; i++) {
            _delay_ms(DELAY);
            LED_PORT = (1 << i);
            // LED_PORT = ~(1 << i);
            // LED_PORT |= (1 << i);
        }
        for (i = LEN; i > 0; i--) {
            _delay_ms(DELAY);
            LED_PORT = (1 << i);
            // LED_PORT = ~(1 << i);
            // LED_PORT |= (1 << i);
        }
    }

    return 0;
}