Ian Hua
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Edit: WITHDRAWN: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
PwmIn.h@7:2a58e3363242, 2014-05-19 (annotated)
- Committer:
- pHysiX
- Date:
- Mon May 19 16:04:34 2014 +0000
- Revision:
- 7:2a58e3363242
- Parent:
- 6:e1df0b4f36e4
Removed mutex. Bad and incorrect of mutex for an ISR
Who changed what in which revision?
| User | Revision | Line number | New contents of line |
|---|---|---|---|
| pHysiX | 3:38bd7aa1d4d2 | 1 | /* mbed PwmIn Library |
| pHysiX | 3:38bd7aa1d4d2 | 2 | * Copyright (c) 2008-2010, sford |
| pHysiX | 3:38bd7aa1d4d2 | 3 | * Subsequently modified by Trung Tin Ian HUA 2014 to add lost signal detection. |
| pHysiX | 3:38bd7aa1d4d2 | 4 | * |
| pHysiX | 3:38bd7aa1d4d2 | 5 | * Permission is hereby granted, free of charge, to any person obtaining a copy |
| pHysiX | 3:38bd7aa1d4d2 | 6 | * of this software and associated documentation files (the "Software"), to deal |
| pHysiX | 3:38bd7aa1d4d2 | 7 | * in the Software without restriction, including without limitation the rights |
| pHysiX | 3:38bd7aa1d4d2 | 8 | * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell |
| pHysiX | 3:38bd7aa1d4d2 | 9 | * copies of the Software, and to permit persons to whom the Software is |
| pHysiX | 3:38bd7aa1d4d2 | 10 | * furnished to do so, subject to the following conditions: |
| pHysiX | 3:38bd7aa1d4d2 | 11 | * |
| pHysiX | 3:38bd7aa1d4d2 | 12 | * The above copyright notice and this permission notice shall be included in |
| pHysiX | 3:38bd7aa1d4d2 | 13 | * all copies or substantial portions of the Software. |
| pHysiX | 3:38bd7aa1d4d2 | 14 | * |
| pHysiX | 3:38bd7aa1d4d2 | 15 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
| pHysiX | 3:38bd7aa1d4d2 | 16 | * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
| pHysiX | 3:38bd7aa1d4d2 | 17 | * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE |
| pHysiX | 3:38bd7aa1d4d2 | 18 | * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
| pHysiX | 3:38bd7aa1d4d2 | 19 | * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
| pHysiX | 3:38bd7aa1d4d2 | 20 | * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN |
| pHysiX | 3:38bd7aa1d4d2 | 21 | * THE SOFTWARE. |
| pHysiX | 3:38bd7aa1d4d2 | 22 | */ |
| pHysiX | 0:1ae106ada18a | 23 | #include "mbed.h" |
| pHysiX | 0:1ae106ada18a | 24 | |
| pHysiX | 3:38bd7aa1d4d2 | 25 | #ifndef MBED_PWMIN_H_ |
| pHysiX | 3:38bd7aa1d4d2 | 26 | #define MBED_PWMIN_H_ |
| pHysiX | 0:1ae106ada18a | 27 | |
| pHysiX | 3:38bd7aa1d4d2 | 28 | /** PwmIn class to read PWM inputs |
| pHysiX | 3:38bd7aa1d4d2 | 29 | * |
| pHysiX | 3:38bd7aa1d4d2 | 30 | * Uses InterruptIn to measure the changes on the input |
| pHysiX | 3:38bd7aa1d4d2 | 31 | * and record the time they occur |
| pHysiX | 3:38bd7aa1d4d2 | 32 | * |
| pHysiX | 3:38bd7aa1d4d2 | 33 | * @note uses InterruptIn, so not available on p19/p20 |
| pHysiX | 3:38bd7aa1d4d2 | 34 | */ |
| pHysiX | 0:1ae106ada18a | 35 | class PwmIn |
| pHysiX | 0:1ae106ada18a | 36 | { |
| pHysiX | 0:1ae106ada18a | 37 | public: |
| pHysiX | 3:38bd7aa1d4d2 | 38 | /** Create a PwmIn |
| pHysiX | 3:38bd7aa1d4d2 | 39 | * |
| pHysiX | 3:38bd7aa1d4d2 | 40 | * @param p The pwm input pin (must support InterruptIn) |
| pHysiX | 3:38bd7aa1d4d2 | 41 | */ |
| pHysiX | 0:1ae106ada18a | 42 | PwmIn(PinName p); |
| pHysiX | 0:1ae106ada18a | 43 | |
| pHysiX | 0:1ae106ada18a | 44 | void rise(); |
| pHysiX | 0:1ae106ada18a | 45 | void fall(); |
| pHysiX | 3:38bd7aa1d4d2 | 46 | |
| pHysiX | 3:38bd7aa1d4d2 | 47 | /** Read the current period |
| pHysiX | 3:38bd7aa1d4d2 | 48 | * |
| pHysiX | 3:38bd7aa1d4d2 | 49 | * @returns the period in seconds |
| pHysiX | 3:38bd7aa1d4d2 | 50 | */ |
| pHysiX | 0:1ae106ada18a | 51 | float period(); |
| pHysiX | 3:38bd7aa1d4d2 | 52 | |
| pHysiX | 3:38bd7aa1d4d2 | 53 | /** Read the current pulsewidth |
| pHysiX | 3:38bd7aa1d4d2 | 54 | * |
| pHysiX | 3:38bd7aa1d4d2 | 55 | * @returns the pulsewidth in seconds |
| pHysiX | 3:38bd7aa1d4d2 | 56 | */ |
| pHysiX | 0:1ae106ada18a | 57 | float pulsewidth(); |
| pHysiX | 3:38bd7aa1d4d2 | 58 | |
| pHysiX | 3:38bd7aa1d4d2 | 59 | /** Read the current dutycycle |
| pHysiX | 3:38bd7aa1d4d2 | 60 | * |
| pHysiX | 3:38bd7aa1d4d2 | 61 | * @returns the dutycycle as a percentage, represented between 0.0-1.0 |
| pHysiX | 3:38bd7aa1d4d2 | 62 | */ |
| pHysiX | 0:1ae106ada18a | 63 | float dutycycle(); |
| pHysiX | 0:1ae106ada18a | 64 | |
| pHysiX | 3:38bd7aa1d4d2 | 65 | /** Timer to detect when a pulse has not changed over time (Ian). |
| pHysiX | 3:38bd7aa1d4d2 | 66 | */ |
| pHysiX | 0:1ae106ada18a | 67 | Timer stallTimer; |
| pHysiX | 0:1ae106ada18a | 68 | protected: |
| pHysiX | 0:1ae106ada18a | 69 | InterruptIn _p; |
| pHysiX | 0:1ae106ada18a | 70 | Timer _t; |
| pHysiX | 4:44dd41c989d0 | 71 | volatile int _pulsewidth, _period; |
| pHysiX | 0:1ae106ada18a | 72 | bool stallInit; |
| pHysiX | 0:1ae106ada18a | 73 | }; |
| pHysiX | 0:1ae106ada18a | 74 | |
| pHysiX | 0:1ae106ada18a | 75 | #endif |