Ian Hua / PwmInRC

Code to read a PPM/PWM pulse, interrupt driven. Most useful for RC receivers. Code is non-blocking, and a poll of the stall timer can detect if a signal has been lost (signal changes will reset the timer). Code originally written by Simon Ford, modified by me to add in a lost-signal guard.

Dependents:   triforce-control usbjoystick_prg

Code is simple to use.

Will add a quick tutorial on use, and how to use the lost-signal/stall detection in due course.

Pulsewidth and period variables are:

  • Declared volatile to make sure the value read is not compiler optimised, since the values are modified through an ISR; and

Edit: WITHDRAWN:

  • Protected by mutex to make sure that values read are true (such as when an ISR is occurring, but a thread tries to read the value during the ISR). Reason:
  • Mutexes are not meant to be called in an ISR (asynchronous). They are costly and may block a thread

PwmIn.cpp

Committer:
pHysiX
Date:
2014-05-19
Revision:
7:2a58e3363242
Parent:
6:e1df0b4f36e4

File content as of revision 7:2a58e3363242:

/* mbed PwmIn Library
 * Copyright (c) 2008-2010, sford
 * Subsequently modified by Trung Tin Ian HUA 2014 to add lost signal detection.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include "PwmIn.h"

PwmIn::PwmIn(PinName p) : _p(p)
{
    _p.rise(this, &PwmIn::rise);
    _p.fall(this, &PwmIn::fall);

    _period = 0;
    _pulsewidth = 0;
    stallInit = false;

    _t.start();
}

void PwmIn::rise()
{
    _period = _t.read_us();
    stallTimer.reset();
    _t.reset();
}

void PwmIn::fall()
{
    _pulsewidth = _t.read_us();
    if (!stallInit)
        stallTimer.start();
}

float PwmIn::period()
{
    return _period;
}

float PwmIn::pulsewidth()
{
    return _pulsewidth;
}

float PwmIn::dutycycle()
{
    return _pulsewidth / _period;
}