Serial port breaks messages

Sam

Hi,
I read the serial port with various length and format messages in bytes.
Some messages that are of csv numerical data of interest enclosed within "FDDD" and "FEEE".
Short messages are fine, but when a long message arrives, more often than not the message is broken down into two streams, which makes it very difficult to parse.
I have the correct baud rate (115200 on both sides), increased the buffer size to significantly bigger than the message (8192), and all seems OK, except that the stream is not contiguous.
How can I make it contiguous ?
(Alternatively, I could try to combine the message parts, but this would be quite complex to make it 100% safe!).
Here is the code snippet:

public void comPort_DataReceived(object sender, SerialDataReceivedEventArgs e)

{

byte[] dataRecord = new byte[4];

if (!comPort.IsOpen) comPort.Open();

string inData = ""; //The incoming string from port.

holdPortOpen = true; //Disable port closure.

//retrieve number of bytes in the buffer

int bytes = comPort.BytesToRead;

//create a byte array to hold the awaiting data

byte[] comBuffer = new byte[bytes];

//read the data and store it

comPort.Read(comBuffer, 0, bytes);

//Convert the bytes stream to ascii

inData += Encoding.ASCII.GetString(comBuffer, 0, bytes);

if (inData.Contains("FDDD") && inData.Contains("FEEE"))

mainForm.displayData(inData);

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes12y ago
Accepted answer
Well, the SerialPort class does have a Handshake property which you've probably looked at already:

http://msdn.microsoft.com/en-us/library/system.io.ports.serialport.handshake(v=vs.110).aspx

Failing that and assuming that no data is being skipped, I think you will have to assemble the bits of data and try and make sense of them.

Sometimes regular expressions can help with a task such as this and, if you're not familiar with these, I may be able to help with that.
0
Sam12y ago
Thanks Vulpes for your ever continued support. Yes, I am aware of the handshake, but still it does not guaranty 100% data, and will slow down the flow significantly for long messages. As you suggested, I already found a way to combine the pieces into one message (I have message start and end codes and length info that makes it possible). Have a nice weekend samtal
0
Sam12y ago
Thanks, but unfortunately following endless tries and tests, I came to the conclusion that without proper hardware handshake there is no way to guaranty safe reading of the serial stream. One critical property is missing, namely the time within which bytesToRead is relevant. Unless someone can show me a better way, I will have to assemble my data of several pieces of read data. Thanks anyway. (If you wish to have more details of what I have tried, let me please know) samtal
0
Vulpes12y ago
Well, first of all, I wouldn't assume that the Read method will read the number of bytes given by the BytesToRead property as this can be unreliable at times.

Instead, I'd use the number of bytes actually read when converting to a string:

//read the data and store it
int bytesRead = comPort.Read(comBuffer, 0, bytes);
//Convert the bytes stream to ascii
inData += Encoding.ASCII.GetString(comBuffer, 0, bytesRead);

If it's still no better, I'd experiment with the SerialPort.ReceivedBytesThreshold property which by default is set to 1.

This controls the number of bytes there needs to be in the input buffer before the DataReceived event is called. If data is being received quickly, it might be better to set this to a higher value to avoid the possibility that some events may be skipped or called out of order.

0