//press any button to invoke led sequence
#include <stdint.h>

#define DDRA   (*(volatile uint8_t*)0x21)
#define PORTA  (*(volatile uint8_t*)0x22)

void delay1sec(void){
    TCNT1  = 0;
    TCCR1A = 0x00;
    TCCR1B = 0x05;          // prescaler 1024
    while (TCNT1 < 15625); // ~1 second
    TCCR1B = 0x00;
}

int main(void){
    DDRA = 0xFF;    // PORT A as output

    while(1){
        for(uint8_t i = 0; i < 8; i++){
            PORTA = (1 << i);   // LED sequence 0 → 7
            delay1sec();
        }
    }
}