/// <summary>
/// Provides validation that the sentence is a complete and valid NMEA sentence
/// </summary>
/// <param name="sentence">The sentence to be validated.</param>
/// <returns>True if the sentence is a valid NMEA formated sentence.</returns>
/// <remarks>
/// NMEA sentences are of the form $GPRMC,11,22,33,44,55*CC
/// A valid sentence starts with a $.
/// Has comma seperated data values.
/// Has a * indicating the end of the data and position of the checksum.
/// The two checksum characters are correct.
/// </remarks>
public bool ValidateNMEASentence(string sentence)
{
// Does it begin with a dollar sign?
if (!sentence.StartsWith("$", StringComparison.Ordinal))
{
CNXLog.WarnFormat("NMEAClient Validation failed, no $.");
return(false);
}
// make sure there are data fields
if (sentence.IndexOf(",", StringComparison.Ordinal) == -1)
{
CNXLog.WarnFormat("NMEAClient Validation failed, no data fields.");
return(false);
}
// Next, get the index of the asterisk
int asteriskIndex = sentence.IndexOf("*", StringComparison.Ordinal);
// Is an asterisk present?
if (asteriskIndex == -1)
{
CNXLog.WarnFormat("NMEAClient Validation failed, no *.");
return(false);
}
// The checksum is calculated over the command and data portion of the sentence
byte checksum = (byte)sentence[1];
for (int index = 2; index < asteriskIndex; ++index)
{
checksum ^= (byte)sentence[index];
}
// The checksum is the two-character hexadecimal value
string calculatedChecksum = checksum.ToString("X2", NMEACultureInfo);
string sentenceChecksum = sentence.Substring(asteriskIndex + 1, 2);
if (!calculatedChecksum.Equals(sentenceChecksum, StringComparison.Ordinal))
{
++mChecksumErrors;
CNXLog.WarnFormat("NMEAClient checksum errors {0}, sentence ratio {1}/{2}.", mChecksumErrors, mValidSentences, mSentencesRecieved);
return(false);
}
return(true);
}
/// <summary>
/// Event firing method.
/// </summary>
/// <param name="frame">The CAN frame just received.</param>
//protected virtual void OnRaiseFrameReceivedEvent(FrameReceivedEventArgs frameEvent)
//{
// // copy the event handler to avoid mid process subscribe/un-subscribe
// EventHandler<FrameReceivedEventArgs> handler = RaiseFrameReceivedEvent;
// // Check if there are any Subscribers
// if (handler != null)
// // Call the Event
// handler(this, frameEvent);
//}
private void ReceiveFrames()
{
byte[] buffer = new byte[13];
EndPoint ep = mRxEndPoint;
CANFrame frame = new CANFrame();
while (mKeepReceiving)
{
try
{
if (mRxSocket.ReceiveFrom(buffer, ref ep) > 0)
{
CNXLog.Debug(BitConverter.ToString(buffer));
// populate a CAN frame
frame.WireFormatArray = buffer;
CNXLog.Debug(BitConverter.ToString(frame.Data));
CNXLog.Debug(frame.MailboxId.ToString("X"));
OnRaiseFrameReceivedEvent(new FrameReceivedEventArgs(frame));
}
}
catch (SocketException se)
{
// may be OK to continue.
CNXLog.WarnFormat("ReceiveFrames {0}.", se.Message);
}
catch (Exception e)
{
// stuffed.
mKeepReceiving = false;
CNXLog.ErrorFormat("ReceiveFrames {0}.", e.Message);
break;
}
}
mRxSocket.Close();
}