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Edit: WITHDRAWN: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

Diff: PwmIn.h

Revision:
3:38bd7aa1d4d2
Parent:
2:1f00548c2aa6
Child:
4:44dd41c989d0
--- a/PwmIn.h	Thu May 08 09:42:36 2014 +0000
+++ b/PwmIn.h	Thu May 08 09:52:48 2014 +0000
@@ -1,25 +1,70 @@
-/* PWM In by Simon Ford */
-/* Includes a stall guard */
-
+/* 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 _PWMIN_H_
-#define _PWMIN_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;