DigitalPinCapture.cpp

00001 ///////////////////////////////////////////////////////////////////////////////
00002 // Signal Capture Library
00003 // Author: Chris Taylor (taylorza)
00004 #include "mbed.h"
00005 #include "DigitalPinCapture.h"
00006 
00007 DigitalPinCapture::DigitalPinCapture(PinName pin, PinMode mode) :
00008     _signalPin(pin, mode),
00009     _readTimeout(10000000)
00010 {
00011     
00012 }
00013 
00014 void DigitalPinCapture::setReadTimeout(uint32_t us)
00015 {
00016     _readTimeout = us;
00017 }
00018 
00019 int DigitalPinCapture::read(bool triggerState, uint32_t *pReadings, int count)
00020 {
00021     return readInternal(&triggerState, pReadings, count, true);
00022 }
00023 
00024 int DigitalPinCapture::read(bool *pInitialState, uint32_t *pReadings, int count)
00025 {
00026     return readInternal(pInitialState, pReadings, count, false);
00027 }
00028 
00029 int DigitalPinCapture::readInternal(bool *pPinState, uint32_t *pReadings, int count, bool waitForTrigger)
00030 {
00031     Timer timer;
00032     
00033     int lastPinState;
00034     int lastTransitionTime;
00035     
00036     timer.start();    
00037     if (waitForTrigger)
00038     {
00039         while (_signalPin == *pPinState)
00040         {
00041             if (timer.read_us() >= _readTimeout) return 0;
00042         }
00043         
00044         while (_signalPin != *pPinState)
00045         {
00046             if (timer.read_us() >= _readTimeout) return 0;
00047         }
00048         lastTransitionTime = timer.read_us();        
00049     }
00050     else
00051     {
00052         *pPinState = _signalPin ? true : false;
00053         lastTransitionTime = timer.read_us();
00054     }
00055     
00056     lastPinState = *pPinState;
00057     
00058     int bufferIndex = 0;
00059     while (bufferIndex < count && timer.read_us() < _readTimeout)
00060     {
00061         if (_signalPin != lastPinState)
00062         {
00063             uint32_t transitionTime = timer.read_us();
00064             pReadings[bufferIndex++] = transitionTime - lastTransitionTime;
00065             lastPinState = !lastPinState;
00066             lastTransitionTime = transitionTime;            
00067         }   
00068     }
00069     
00070     timer.stop();        
00071         
00072     return bufferIndex;
00073 }
00074