// Using interrupts - detect FALLING

volatile bool buttonPressed2, buttonPressed3; // "volatile" inside interrupt service routeine (ISR)

int buttonPin2 = 2; // INT0
int buttonPin3 = 3; // INT1
int ledPin4 = 4; // GRN LED
int ledPin5 = 5; // RED LED

unsigned long startTime, stopTime;
bool firstRead2 = 1, firstRead3 = 1;

void setup() {
  Serial.begin(115200); // start serial monitor

  pinMode(buttonPin2, INPUT_PULLUP);
  pinMode(buttonPin3, INPUT_PULLUP);
  pinMode(ledPin4, OUTPUT);
  pinMode(ledPin5, OUTPUT);

  attachInterrupt(digitalPinToInterrupt(buttonPin2), buttonISR2, FALLING); // PIN#, ISR, TRIGGER
  attachInterrupt(digitalPinToInterrupt(buttonPin3), buttonISR3, FALLING);
}

void loop() {
  checkButton2();
  checkButton3();
}

int buttonISR2() {
  noInterrupts(); // disable interrupts in ISR
  buttonPressed2 = true; // set flag
  interrupts(); // enable interrupts
}

int buttonISR3() {
  noInterrupts();
  buttonPressed3 = true;
  interrupts();
}

void checkButton2() {
  if (buttonPressed2 && firstRead2) {
    startTime = micros();
    firstRead2 = 0;
    digitalWrite(ledPin4, HIGH);
  }
}

void checkButton3() {
  if (buttonPressed3 && firstRead3) {
    stopTime = micros();
    firstRead3 = 0;
    digitalWrite(ledPin5, HIGH);
    Serial.print("Start: ");
    Serial.println(startTime);
    Serial.print(" Stop: ");
    Serial.println(stopTime);
    Serial.print("Split: ");
    Serial.println(stopTime - startTime);
    delay(500);
    Serial.println("Press RESET button.");
  }
}