/// <summary>
/// Copies values from another instance.
/// </summary>
/// <param name="source">Source from which to copy values.</param>
public void Copy(PpmCycle source)
{
LowTime = source.LowTime;
LowLength = source.LowLength;
HighTime = source.HighTime;
HighLength = source.HighLength;
}
/// <summary>
/// Runs the decoder thread.
/// </summary>
/// <param name="inputBuffer">Buffer from which new PPM values are read.</param>
/// <param name="inputTrigger">Trigger which is fired by the caller when new data arrives.</param>
/// <param name="outputBuffer">Buffer into which decoded PPM frames are written.</param>
/// <param name="outputTrigger">Trigger which is fired by this decoder when new data has been decoded.</param>
/// <param name="stop">Signals when the decoder should stop.</param>
public void DecodePulse(ConcurrentQueue <PpmPulse> inputBuffer, AutoResetEvent inputTrigger,
ConcurrentQueue <PpmFrame> outputBuffer, AutoResetEvent outputTrigger, CancellationToken stop)
{
// Validate
if (inputBuffer == null)
{
throw new ArgumentNullException(nameof(inputBuffer));
}
if (inputTrigger == null)
{
throw new ArgumentNullException(nameof(inputTrigger));
}
if (outputBuffer == null)
{
throw new ArgumentNullException(nameof(outputBuffer));
}
if (outputTrigger == null)
{
throw new ArgumentNullException(nameof(outputTrigger));
}
// Decode until stopped...
while (!stop.IsCancellationRequested)
{
// Wait for value in queue...
if (!inputBuffer.TryDequeue(out PpmPulse value))
{
inputTrigger.WaitOne(SyncLengthMinimum * 2);
continue;
}
// Decode values into cycles...
var time = value.Time;
if (value.Level)
{
// Low -> high (mid-cycle)
_cycle.HighTime = time;
_cycle.LowLength = time - _cycle.LowTime;
}
else
{
// High -> low (end of cycle)
_cycle.HighLength = time - _cycle.HighTime;
// Prepare next value
var cycle = _cycle;
_cycle = new PpmCycle(time);
// Decode cycles into frames...
var frame = DecodeCycle(cycle);
if (frame != null)
{
// Output frame when decoding complete
outputBuffer.Enqueue(frame);
outputTrigger.Set();
}
}
}
}
/// <summary>
/// Decodes the incoming PPM signal (each complete cycle) using the CPPM protocol.
/// </summary>
/// <param name="cycle">PPM cycle to decode.</param>
/// <returns>
/// <see cref="PpmFrame"/> when complete else null whilst decoding or skipping invalid cycles.
/// </returns>
private PpmFrame DecodeCycle(PpmCycle cycle)
{
// Validate
if (!cycle.IsValid() || cycle.LowLength >= LowLimit)
{
// Discard frame
_channel = null;
return(null);
}
// Detect start frame
if (cycle.HighLength >= SyncLengthMinimum)
{
// Start decoding from channel 0 at next pulse
_channel = 0;
_frame = new PpmFrame(cycle.LowTime, new int[ChannelCount]);
return(null);
}
// Do nothing when not decoding
if (!_channel.HasValue)
{
return(null);
}
var decodeIndex = _channel.Value;
// Store channel value whilst decoding
if (decodeIndex < ChannelCount)
{
// Store channel value
_frame.Channels[decodeIndex] = (int)cycle.Length;
// Wait for next channel...
_channel = decodeIndex + 1;
// Complete frame when all channels decoded...
if (decodeIndex == ChannelCount - 1)
{
var frame = _frame;
_frame = null;
return(frame);
}
}
// Continue...
return(null);
}
/// <summary>
/// Creates an instance.
/// </summary>
public CppmDecoder()
{
_frame = new PpmFrame();
_cycle = new PpmCycle();
}
