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Edit: WITHDRAWN: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

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PwmIn.h	Wed Apr 30 06:37:19 2014 +0000
@@ -0,0 +1,29 @@
+/* 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