pulsein function, source code?


I need a function to measure the time between a Start- and Stop-pulse applied to different pins.

I guess the best would be to write the functions based on the code of the pulseIn function. However I couldn't find the source code. Does any one of you know where to get it? Or is there a good tutorial how to write time measuring functions?

regards Peter

It's in wiring_pulse.c, in IDE 1.0.

  wiring_pulse.c - pulseIn() function
  Part of Arduino - http://www.arduino.cc/

  Copyright (c) 2005-2006 David A. Mellis

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General
  Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA

  $Id: wiring.c 248 2007-02-03 15:36:30Z mellis $

#include "wiring_private.h"
#include "pins_arduino.h"

/* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
 * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
 * to 3 minutes in length, but must be called at least a few dozen microseconds
 * before the start of the pulse. */
unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
    // cache the port and bit of the pin in order to speed up the
    // pulse width measuring loop and achieve finer resolution.  calling
    // digitalRead() instead yields much coarser resolution.
    uint8_t bit = digitalPinToBitMask(pin);
    uint8_t port = digitalPinToPort(pin);
    uint8_t stateMask = (state ? bit : 0);
    unsigned long width = 0; // keep initialization out of time critical area

    // convert the timeout from microseconds to a number of times through
    // the initial loop; it takes 16 clock cycles per iteration.
    unsigned long numloops = 0;
    unsigned long maxloops = microsecondsToClockCycles(timeout) / 16;

    // wait for any previous pulse to end
    while ((*portInputRegister(port) & bit) == stateMask)
        if (numloops++ == maxloops)
            return 0;

    // wait for the pulse to start
    while ((*portInputRegister(port) & bit) != stateMask)
        if (numloops++ == maxloops)
            return 0;

    // wait for the pulse to stop
    while ((*portInputRegister(port) & bit) == stateMask) {
        if (numloops++ == maxloops)
            return 0;

    // convert the reading to microseconds. The loop has been determined
    // to be 20 clock cycles long and have about 16 clocks between the edge
    // and the start of the loop. There will be some error introduced by
    // the interrupt handlers.
    return clockCyclesToMicroseconds(width * 21 + 16); 

He dxw00d, that's exactly what I had been looking for and how fast you answered. Thank you very much. Peter

I was looking for this too. Thanks dxw00d!

No problem. Find and grep makes it pretty easy to track stuff down.

All of the Arduino functions are included with the IDE.

In OSX in it is /Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/cores/arduino/

Other operating systems are in their appropriate locations.

on Ubuntu it is generally in /usr/share/arduino/hardware/arduino/cores/arduino/