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Edit: WITHDRAWN: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.h
- Committer:
- pHysiX
- Date:
- 2014-05-08
- Revision:
- 3:38bd7aa1d4d2
- Parent:
- 2:1f00548c2aa6
- Child:
- 4:44dd41c989d0
File content as of revision 3:38bd7aa1d4d2:
/* 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 "mbed.h" #ifndef MBED_PWMIN_H_ #define MBED_PWMIN_H_ /** PwmIn class to read PWM inputs * * Uses InterruptIn to measure the changes on the input * and record the time they occur * * @note uses InterruptIn, so not available on p19/p20 */ class PwmIn { public: /** Create a PwmIn * * @param p The pwm input pin (must support InterruptIn) */ PwmIn(PinName p); void rise(); void fall(); /** Read the current period * * @returns the period in seconds */ float period(); /** Read the current pulsewidth * * @returns the pulsewidth in seconds */ float pulsewidth(); /** Read the current dutycycle * * @returns the dutycycle as a percentage, represented between 0.0-1.0 */ float dutycycle(); /** Timer to detect when a pulse has not changed over time (Ian). */ Timer stallTimer; protected: InterruptIn _p; Timer _t; int _pulsewidth, _period; bool stallInit; }; #endif