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Edit: WITHDRAWN: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

--- a/PwmIn.h	Fri May 16 23:19:34 2014 +0000
+++ b/PwmIn.h	Sun May 18 09:05:32 2014 +0000
@@ -41,9 +41,6 @@
      */
     PwmIn(PinName p);
 
-    void rise();
-    void fall();
-
     /** Read the current period
      *
      * @returns the period in seconds
@@ -70,6 +67,9 @@
     Timer _t;
     volatile int _pulsewidth, _period;
     bool stallInit;
+
+    void rise();
+    void fall();
 };
 
 #endif