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

#define BLINK_TIME 0.5  // 1 second

ISR(TIMER1_OVF_vect) {
    PORTB ^= _BV(PORTB5);                         // Toggle the LED
    TCNT1 = 65535 - (F_CPU / 1024 * BLINK_TIME);  // Reset timer value
}

int main(void) {
    // Set PORTB5 as output
    DDRB |= _BV(DDB5);

    // Initialize TIMER1 value
    TCNT1 = 65535 - (F_CPU / 1024 * BLINK_TIME);

    // Set the prescaler to 1024
    TCCR1B |= _BV(CS10) | _BV(CS12);

    // Enable TIMER1 overflow interrupt
    TIMSK1 |= _BV(TOIE1);

    // Enable global interrupts
    // sei();

    // Enable global interrupts with style
    __asm__ __volatile__ ("sei");

    while (1) {
        // Keep in mind that the sleep mode depth will affect the wake up time
        sleep_cpu();  // Deep sleep
        // set_sleep_mode(SLEEP_MODE_IDLE); // Idle sleep
        // sleep_mode(); // Sets the CPU to whatever mode was set
    }
}