#define	F_CPU   8000000UL

#include <avr/io.h>
#include <util/delay.h>
#include <stdbool.h>

int main(void) {
    // FastPWM: 1.25kHz
    TCCR0A = (1 << WGM01) | (1 << WGM00) | (1 << COM0B1);
    TCCR0B = (1 << CS01) | (1 << WGM02); // prescaler = 8;
    OCR0A = 100;
    OCR0B = 10;
    DDRD |= (1 << PD5);

    bool reverse = 0;

    while (1) {
        _delay_ms(1);

        if (OCR0B > 100)
            reverse = !reverse;

        if (reverse)
            OCR0B++;
        else
            if (OCR0B > 0)
                OCR0B--;
            else
                reverse = !reverse;
    }
}