Diff: PPM.cpp

Revision:

0:083ed8cea5ff

Child:

1:fb0ab71eb0ea

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PPM.cpp	Tue Aug 26 15:54:34 2014 +0000
@@ -0,0 +1,98 @@
+#include "PPM.h"    
+
+//PPM reader by Joe Roberts, based on work by John Wolter
+//This program takes the PPM Signal (Pulse Position Modulation) from your RC transmitter and outputs the data between the min/max outputs passed into the constructor
+//See 
+PPM::PPM(InterruptIn *ppmPin, float minimumOutput, float maximumOutput, int minimumPulseTime, int maximumPulseTime, int numberOfChannels, int throttleChannel) 
+{    
+    //Assign local variables passed into constructor
+    _ppmPin = ppmPin;
+    _minimumOutput = minimumOutput;
+    _maximumOutput = maximumOutput;
+    _minimumPulseTime = minimumPulseTime;
+    _maximumPulseTime = maximumPulseTime;
+    _numberOfChannels = numberOfChannels;
+    _throttleChannel = throttleChannel;
+        
+    //Set other variables
+    _currentChannel = 0;  
+    _timeElapsed = 0; 
+    _minFrameTime = 6000;
+    _shortTime = 800;
+
+    //Initialise arrays
+    for(int i = 0; i < _numberOfChannels; i++)
+    {
+        _times[i] = 0;
+        _completeTimes[i] = 0;
+    }
+    
+    //Assign interrupt
+    _ppmPin->mode (PullUp);
+    _ppmPin->rise (this, &PPM::SignalRise);
+
+    //Start timer
+    _timer.start();
+}
+   
+//Here is where all the work decoding the PPM signal takes place
+void PPM::SignalRise()
+{
+    //Get the time taken since the last interrupt
+    _timeElapsed = _timer.read_us();
+    
+    //If time is less than _shortTime then the channel timing is too short - ignore
+    if (_timeElapsed < _shortTime) return;
+    
+    //Disable the interrupt
+    _ppmPin->rise(NULL);
+
+    //Reset the timer
+    _timer.reset();
+    
+    //Check for a new frame signal, if before start of new frame then its a glitch - start a new frame
+    if ((_timeElapsed > _minFrameTime) && (_currentChannel != 0)) _currentChannel = 0;
+    
+    //Check for a new frame signal, if it is the start of a new frame then start new frame
+    if ((_timeElapsed > _minFrameTime ) && (_currentChannel == 0))
+    {
+        //Assign interrupt
+        _ppmPin->rise (this, &PPM::SignalRise);
+        return;
+    }
+ 
+    //Save the time to the times array
+    _times[_currentChannel] = _timeElapsed;
+    _currentChannel++;
+    
+    //Check for a complete frame
+    if (_currentChannel == _numberOfChannels)
+    {
+        //Set channel iterator to 0
+        _currentChannel = 0;
+        //Copy times array to complete times array
+        memcpy(_completeTimes, _times, sizeof(_times));
+    }
+
+    //Assign interrupt
+    _ppmPin->rise(this, &PPM::SignalRise);
+    return;
+}
+
+//Place mapped channel data into the passed in array
+void PPM::GetChannelData(float * channelData)
+{
+    //Iterate over the channel times array
+    for(int i = 0; i < _numberOfChannels; i++)
+    {
+        //Check the transmitter is still connected by checking the thottle
+        if((i == _throttleChannel - 1) && (_completeTimes[i] < _minimumPulseTime)) channelData[i] = -1;
+        else
+        {
+            //Map the channel times to value between the channel min and channel max
+            channelData[i] = (_completeTimes[i] - _minimumPulseTime) * (_maximumOutput - _minimumOutput) / (_maximumPulseTime - _minimumPulseTime) + _minimumOutput;
+        }
+    }
+    
+    return; 
+}
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