/// <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();
}