Frequency Counter

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

volatile unsigned int one_second_ready;
volatile unsigned int overflow_ticks;

/*--------------------------INTERUPTS----------------------------*/

// TIMER 0 OVERFLOW INTERRUPT
ISR (TIMER0_OVF_vect) {
    overflow_ticks++;
}


// TIMER 1 COMPARE VALUE INTERRUPT
ISR (TIMER1_COMPA_vect) {

    // T0 DISABLE
    TCCR0 &= ~(1 << CS02) & ~(1 << CS01) & ~(1 << CS00);
    TIMSK &= ~(1 << TOIE0);

    // T1 DISABLE
    TCCR1B &= ~(1 << WGM12) & ~(1 << CS12) & ~(1 << CS10);
    TIMSK &= ~(1 << OCIE1A);

    one_second_ready = 1;   // Send Signal To sensorMeasurement() Function
}

/*---------------------------------------------------------------*/


int sensorMeasurement() {
    one_second_ready = 0;
    overflow_ticks = 0;

//  T0 INITIALIZE
    TCCR0 |= (1 << CS02) | (1 << CS01) | (1 << CS00);   // External Clock T0 Rising Edge
    TIMSK |= (1 << TOIE0);  // Enable T0 Interrupt

//   T1 INITIALIZE
    TCCR1B |= (1 << WGM12) | (1 << CS12) | (1 << CS10);     // CTC MODE
    OCR1A = F_CPU / 1024;       // 1 Second Delay
    TIMSK |= (1 << OCIE1A);     // Enable T1 Interrupt

    sei();  // Enable Interrupts

    while (one_second_ready == 0);  // Wait until T1 is 1 second

    cli();  // Disable Interrupts

    return overflow_ticks * 256;    // Signal Frequency
}


int main() {

    DDRB |= (1 << PB0);

    int measure = sensorMeasurement();

    for (int i = 0 ; i < measure / 1000 ; i++) {
        PORTB ^= (1 << PB0);
        _delay_ms(300);
    }

    while(1) {

    }

    return 0;
}