#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdint.h>

volatile uint32_t ms = 0;

void timer1_init(void) {
    TCCR1A = 0;
    TCCR1B = 0;
    TCNT1  = 0;

    TCCR1B |= (1 << WGM12);
    OCR1A = 249;
    TIMSK1 |= (1 << OCIE1A);
    TCCR1B |= (1 << CS11) | (1 << CS10);
    sei();
}

ISR(TIMER1_COMPA_vect) {
    ms++;
}

void delay_ms(uint32_t delay){
    uint32_t start = ms;
    while ((ms - start) < delay) {
    }
}

int main(void) {
    DDRC |= (1<<PC0);
    timer1_init();

    while(1) {
        PORTC |= (1<<PC0);
        delay_ms(500);
        PORTC &= ~(1<<PC0);
        delay_ms(500);
    }
}