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Edit: WITHDRAWN: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.cpp	Mon May 19 15:43:02 2014 +0000
+++ b/PwmIn.cpp	Mon May 19 16:04:34 2014 +0000
@@ -36,18 +36,14 @@
 
 void PwmIn::rise()
 {
-    mutex_var_update.lock();
     _period = _t.read_us();
     stallTimer.reset();
-    mutex_var_update.unlock();
     _t.reset();
 }
 
 void PwmIn::fall()
 {
-    mutex_var_update.lock();
     _pulsewidth = _t.read_us();
-    mutex_var_update.unlock();
     if (!stallInit)
         stallTimer.start();
 }