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

//#define SAMPLE_RATE_DIVISOR 4

// F_CPU - 8000000UL

int main(void)
{

    TCCR0A |= (1 << COM0A1) | (1 << WGM01) | (1 << WGM00); // pwm, oc0a channel, clear on compare/non-inverted
    TCCR0B |= (1 << CS00); // timer0 no prescaling
    TIMSK0 |= (1 << TOIE0); // timer0 ovf int
    OCR0A = 0;
    DDRD |= (1 << PD6);
    sei();
    while(1)
    {

    }

    return 0;
}

ISR(TIMER0_OVF_vect)
{
    static uint64_t t = 0;
    OCR0A = (t*9&t>>4|t*5&t>>7|t*3&t/1024)-1;
    t++;
}