#include <avr/io.h>

int main(void) {
    // 1. Set PB1 (OC1A) as output
    DDRB |= (1 << PB1);

    // 2. Fast PWM mode (WGM13:0 = 14)
    TCCR1A = (1 << COM1A1) | (1 << WGM11);
    TCCR1B = (1 << WGM12) | (1 << WGM13);

    // 3. Prescaler = 8 (start timer)
    TCCR1B |= (1 << CS11);

    // 4. Set TOP value (frequency)
    ICR1 = 19999;   // ~50 Hz (good for visible LED dimming demo)

    // 5. Initial duty cycle
    OCR1A = 0;

    while (1) {
        // Increase brightness
        for (uint16_t i = 0; i < 2000; i++) {
            OCR1A = i * 10;   // increase duty
            for (volatile uint32_t d = 0; d < 5000; d++); // small delay
        }

        // Decrease brightness
        for (int16_t i = 2000; i > 0; i--) {
            OCR1A = i * 10;
            for (volatile uint32_t d = 0; d < 5000; d++);
        }
    }
}