/* Program 5-4: Timestamp the press of SW using micros() */

const int SW = 7;              /* SW */

void setup()
{
    pinMode(SW, INPUT);  /* configure input pin for switch */
    Serial.begin(9600);         /* initialize Serial and set Baud rate */
}

void loop() {
    static unsigned int lastTime = 0;   /* last timestamp */
    unsigned int thisTime;              /* current timestamp */
    unsigned int elapsedTime;           /* time elapsed since last switch press */
    static int before = HIGH;           /* stored switch input state */
    int now = digitalRead(SW);          /* current switch input state */
    
    if (before == HIGH && now == LOW) { /* switch pressed */
        thisTime = micros();            /* take the timestamp */
        elapsedTime = thisTime - lastTime;  /* calculate time elapsed */
        Serial.print(thisTime);         /* display current timestamp */
        Serial.print(", ");
        Serial.println(elapsedTime);    /*    and time elapsed */
        lastTime = thisTime;            /* update last timestamp */
    }            
    
    before = now;                       /* update stored switch state */
}