#define F_CPU 16000000UL
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <string.h>
#include <stdlib.h>
#include <avr/sfr_defs.h>

#define TRIGGER_PIN PB7 //PA0
uint16_t Measurement;
uint16_t Distance;

uint16_t Measure(void);
uint16_t Calculation(uint16_t);

int main ()
{
    DDRB |= (1 << TRIGGER_PIN); //Make trigger pin as output

    TIMSK4 = (1 << TOIE4);  //Enable Timer1 overflow interrupts
    TCCR4B |= (1 << CS42); //prescaler = 256
    TCCR4B &= ~(1 << CS41);
    TCCR4B &= ~(1 << CS40);

    sei();          /* Enable global interrupt */

    while(1)
    {
        Measure();
    }
}

uint16_t Measure(void)
{
    //Giving 10us trigger pulse on trig pin to HC-SR04, then disabling it without making an interrupt

    if ((TCNT4 == 31250) && (~(PINB & (1 << PB7))))
    {
        PORTB |= (1 << TRIGGER_PIN); //1 on trig pin of HC-SR04
        TCNT4 = 0; //Reseting Timer4 to 0, going back to start
    }

    //  _delay_ms(1000);

    if ((TCNT4 == 31250) && (PINB & (1 << PB7)))
    {
        PORTB &= (~(1 << TRIGGER_PIN)); //0 on trig pin of HC-SR04
        TCNT4 = 0; //Reseting Timer4 to 0, going back to start
    }

    //  _delay_ms(1000);

    return Measurement;
}

uint16_t Calculation(uint16_t Measurement)
{
    Distance = Measurement/932.8;
    return Distance;
}

/*We use Timer 4 */