#include <LiquidCrystal.h>

//lcd and timer objects declaration
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

uint8_t inputCapturePin = 13;

volatile uint16_t startingEdge = 0;
volatile uint16_t endingEdge = 0;
volatile uint16_t currentOverflowCounter = 0;
volatile uint16_t startOverflowCounter = 0;
volatile uint32_t timer3Clocks = 0;


void setup() {
  noInterrupts();
  Serial.begin(9600);

  lcd.setCursor(1,0);
  lcd.print("IMPULSE LENGTH");
  lcd.setCursor(3,1);
  lcd.print("MEASURMENT");

  pinMode(13, INPUT);
  pinMode(3, OUTPUT);
  digitalWrite(3, HIGH);

  //T3 registers configuration
  TCCR3A = 0;

  TCCR3B |= (1 << CS30); // prescaler = 0
  TCCR3B &= ~(1 << CS31);
  TCCR3B &= ~(1 << CS32);

  TCCR3B &= ~(1 << ICES3); //input capture on falling edge


  TCNT3 = 0; // initialize counter

  TIMSK3 |= (1 << ICIE3)|(1 << TOIE3); //enable input capture interrupt, enable timer ovf interrupt
  interrupts();
}


//loop method
void loop() {
  int result = timer3Clocks / 16;

}

ISR (TIMER3_OVF_vect) {
  currentOverflowCounter++;
}

ISR (TIMER3_CAPT_vect) {
  if(((TCCR3B & (1 << ICES3)) >> ICES3) == 0) //checking state of ICES3bit (ICES3 == 1 input capture on rising edge)
  {                                           //(ICES3 == 0 input capture on falling edge)
    startingEdge = ICR3;
    startOverflowCounter = currentOverflowCounter;
  } else {
    endingEdge = ICR3;
    timer3Clocks = (uint16_t)endingEdge + ((uint16_t)currentOverflowCounter * 65536) - ((uint16_t)startingEdge + (startOverflowCounter * 65536));
    currentOverflowCounter = 0;
  }
  TCCR3B ^= (1 << ICES3);
}