Stoppino

volatile bool rs = false;
volatile unsigned long ti[4] = {0,0,0,0};

int _7SEG[] = {B00111111, B00000110, B01011011, B01001111,   //0 1 2 3
               B01100110, B01101101, B01111101, B00000111,   //4 5 6 7
               B01111111, B01101111, B00000000};              //8 9 /

void printNum();

void setup(){
  Serial.begin(9600);
  for(byte i = 0; i <= 1; i++)
    pinMode(18+i, INPUT);
  for(byte i = 0; i <= 19; i++)
    pinMode(22+i, OUTPUT);

  pinMode(2, INPUT);
  attachInterrupt(digitalPinToInterrupt(2), timestamp, CHANGE);
  attachInterrupt(digitalPinToInterrupt(18), rsInt, RISING);
}

void loop(){
  if(ti[3]){
    Serial.println(ti[3]);
  }
}

void timestamp(){
  volatile byte i = 0;
  while(ti[i] && i <= 3)
    i++;

  if(i <= 3)
    ti[i] = micros();
}

void rsInt(){
  ti[0] = 0;
  ti[1] = 0;
  ti[2] = 0;
  ti[3] = 0;
}

/*void printNum(unsigned long num){
  for(byte i = 0; i <= 6; i++){
    for(byte j = 0; j <= 7; j++)
      digitalWrite(22+j, bitRead(_7SEG[num%10],j));
    num = num/10;

    digitalWrite(36-i, HIGH);
    delay(1);
    digitalWrite(36-i, LOW);
  }
}*/