main.c

#define LEDPORT PORTD
#define LEDBIT PD6
#define LEDDDR DDRD

#include <avr/io.h>

int main (void)
{
    LEDDDR |= (1 << LEDBIT);  // set LED pin as an output
    TCCR1B |= ((1 << CS10) | (1 << CS11));  // configure timer prescaling

    for(;;)
    {
        if (TCNT1 >= 15624)  // when the timer counts one second
        {
            LEDPORT ^= (1 << LEDBIT);  // toggle the LED
            TCNT1 = 0;  // and reset the timer value
        }
    }

    return 0;  // the program executed successfully
}