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Edit: WITHDRAWN: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

/* PWM In by Simon Ford */

#include "mbed.h"

#ifndef _PWMIN_H_
#define _PWMIN_H_

class PwmIn
{
public:
    PwmIn(PinName p);

    void rise();
    void fall();
    
    float period();
    float pulsewidth();
    float dutycycle();

    Timer stallTimer;
    
protected:
    InterruptIn _p;
    Timer _t;
    int _pulsewidth, _period;
    bool stallInit;
};

#endif