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

int main(void) {
    // Set PORTD pins 2 to 5 as output
    DDRD |= (1 << PD2) | (1 << PD3) | (1 << PD4) | (1 << PD5);

    while (1) {
        // Inline assembly to cycle LEDs on and off
        asm volatile (
            "ldi r16, 0x04" "\n"   // Initialize with the bit pattern for PD2
            "ldi r20, 4" "\n"      // Loop 4 times (for 4 LEDs)

            "cycle_leds:" "\n"
            "out %0, r16" "\n"     // Output to PORTD
            // Inline delay
            "ldi r18, 20" "\n"
            "ldi r19, 0" "\n"
            "ldi r21, 0" "\n"
            "delay_loop:" "\n"
            "dec r21" "\n"
            "brne delay_loop" "\n"
            "dec r19" "\n"
            "brne delay_loop" "\n"
            "dec r18" "\n"
            "brne delay_loop" "\n"
            // End of delay
            "lsl r16" "\n"         // Shift left to move to the next LED
            "dec r20" "\n"         // Decrement the loop counter
            "brne cycle_leds" "\n" // If not zero, repeat the loop
            "out %0, r1" "\n"      // Clear PORTD (r1 is assumed to be zero)
            :
            : "I" (_SFR_IO_ADDR(PORTD))
            : "r16", "r18", "r19", "r20", "r21"
        );

        _delay_ms(500); // Delay between each full cycle
    }

    return 0;
}