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

#define LED_PIN PB4 // Pin 12 on Arduino Uno corresponds to PB5 on ATmega328P

void setupTimer1() {
    // Set Timer1 in CTC (Clear Timer on Compare Match) mode
    TCCR1A = 0; // Normal port operation, CTC mode
    TCCR1B = (1 << WGM12); // CTC mode with OCR1A as top

    // Set compare match value for 1 Hz blink
    // Formula: OCR1A = (F_CPU / (Prescaler * DesiredFrequency)) - 1
    // For 16 MHz, prescaler = 256, DesiredFrequency = 1 Hz:
    // OCR1A = (16,000,000 / (256 * 1)) - 1 = 62449
    OCR1A = 62499;

    // Set prescaler to 256
    TCCR1B |= (1 << CS12);

    // Enable Timer1 Compare Match A interrupt
    TIMSK1 = (1 << OCIE1A);
}

int main(void) {
    // Configure LED_PIN as output
    DDRB |= (1 << LED_PIN);

    // Initialize Timer1
    setupTimer1();

    // Enable global interrupts
    sei();

    // Main loop does nothing; the ISR handles the LED toggling
    while (1) {
        // Idle loop
    }
}

// Timer1 Compare Match A interrupt service routine
ISR(TIMER1_COMPA_vect) {
    // Toggle LED_PIN
    PORTB ^= (1 << LED_PIN);
}

// Assignment:
// 1. Change the delay to 300ms
// 2. Control a Green LED  using SW in while(1)
// 3. Control Green LED with Switch connected at INT0 interrupt