C# Windows Form - Serial Port problem / BackgroundWorker

Manuel Santos

7y8kC#

I developed a Windows Form application, using C#, that receives data through the serial port sent by a microcontroller. I'm receiving the data using the serialPort_DataReceived event in which I use ReadLine() to read the serial port. Then I use the Invoke method to call a function that will print the received string into a textBox. The problem is that the app can't keep up with the rate at which it receives the strings, for example, the string that I send from the microcontroller has the time at which it was sent and even though it has already passed 2 or 3 seconds the app is still printing the strings that were sent at the 0.2 second. And when I send a string to the microcontroller to stop sending data, the app onlys stops ptinting the data after a while, this is, it keeps printing the values stored in the receiving buffer.

I believe that is happens given the large amount of data that the app receives and the rate (I'm using a baud rate of 115200), one string for every millisecond. This is, I think that the app is always being interrupted by the DataReceived event and it doesn't has time to print the data and starts falling behind.

One way I though of overcome this problem was with multi-threading but I can't figure it out how. I already tried a few examples using the BackgroundWorker but I didn't manage to make it work at all. I'm still a noob in terms of programming Windows Form apps and even C#.

Can anyone confirm the cause of the problem? And how do I make a thread to print the received data?

10 Replies

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Manuel Santos7y ago
Already did long time ago and it's working perfectly.
Jeff Taylor7y ago
I think the next thing to do is examine the output from the mcu on a terminal emulator and see exactly what is being transmitted.
Manuel Santos7y ago
Everything is as it was. Increased the timeout and I don't get the "operation exceeded time limit" window but I still get the exception.
And when I get start receiving data, the data is printed, in "slow mode" still, but I can't press any other buttons and eventually I get the exception mentioned before.
Jeff Taylor7y ago
I am not getting the timeout exception, this will only happen if there is no newline terminator or the string is taking longer than 20 mS to arrive, I would have thought 20mS was plenty of time so this is a possible indicator of a problem with the mcu transmission. You could extend the timeout period and see if that made a difference and also remove the message in the catch
catch (Exception ex)
          {
             // MessageBox.Show(ex.Message);
          }
Which micro controller are you using?
Manuel Santos7y ago
Once again thanks for the help. I tested your code once in a while I get a pop window saying: "Operation exceeded time limit" it happens multiple times. And I also get an exception that says:

"Managed Debugging Assistant 'DisconnectedContext' : a transition to the COM context 0xaa54e0 for this RuntimeCallableWrapper failed with the following error: the system call failed. (Exception HRESULT: 0x80010100 (RPC_E_SYS_CALL_FAILED)). This is usually due to the fact that the COM context 0xaa54e0 where this RuntimeCallableWrapper was created might have been turned off or might be occupied with another operation. ......"

Besides this it still doesn't print in real time, it keeps falling behind.

About the textBox, I'm actually using a richTextBox aswell.

The string, it's size varies the value term can be any number from 0 to 1024 and the time is in seconds and is always increasing, so assuming that value has it's maximum value 1024 and let's say I exchange data for 999.9999 seconds (around 17 minutes, never did for this long, maximum I did was 30 seconds) (the time term has always 4 decimal places) the string would be: "1024 999.9999\n" that is 14 characters or 14 bytes per ms or 14000 bytes per second.
Jeff Taylor7y ago
In my last question I was asking how much data you were collecting, for example I ran a simple test to collect 5000 samples of a 16 byte string, 80000 bytes in total. I didn't time it but it came in as quick as I would expect and without error. I didn't try and manipulate the string and I don't think it is the solution just yet but it takes us a step closer. In the example I ran I used a richTextbox as opposed to a textBox, I believe it updates quicker.

This is the receive and display that I used, very similar to what you are using.
public delegate void myDelegate(string sData);

        private void myPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            myPort.ReadTimeout = 20;

            while(myPort.BytesToRead>0)
            {
            try
            {
                string str = myPort.ReadLine();
                this.BeginInvoke((new myDelegate(strDebug)), str);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            }
        }

        private void strDebug(string sData)
        {

            richTextBox1.AppendText(sData + '\n');

        }
Manuel Santos7y ago
I also prefer to use ReadLine because it is easier to split each string individually but as I said in the original post it is too slow. I also tried instead of invoking a function I printed the string to the Console inside the DataReceived event and it works better but still fall behind, at the 20th second is showing me data from the 13th second.

Yes I have control over the format of the string, and yes, there is a space character between value and time.

I don't quite understand the last question but, if I understood it right, the microcontroller every 1ms samples an analog signal, determines at what time (seconds) it was sampled and sends a string with the sampled value and the time through it's serial port (the string that the app receives). I used an serial terminal and can confirm that the microcontroller is sending all the string perfectly.
Jeff Taylor7y ago
I would stick with ReadLine especially if your strings are terminated with a newline character, which it appears they are.

Do you have any control over the format of the string, you mention it as being "value time \n" so can I assume there is a space character between value and time?

You code looks like it should work ok, how many samples are you collecting @ 1 per mS
Manuel Santos7y ago
I'm just going to show the serialport related code otherwise it would very long.
//At start
String[] ports = SerialPort.GetPortNames();
comboBox1.Items.AddRange(ports);

//Pressing the connect button
serialPort1.PortName = comboBox1.Text;
serialPort1.BaudRate = 115200;
serialPort1.Open();

//Received data event
private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
      ReceivedData = serialPort1.ReadLine();
       this.Invoke(new EventHandler(interp_string));
}

private void interp_string(object sender, EventArgs e)
{
       textBox.Text += ReceivedData + "\n";
}
Meanwhile, I changed, in the serialPort1_DataReceived event, the ReadLine() to ReadExisting() and now I can print in the textBox as I wanted, in real time. But given that now I don't have just one string but many strings stored in just one string (ReceivedData variable) I can't, or I don't know how to, split the strings to plot the values received. What I mean is, the app receives strings with the following format: "value time \n" where value goes from 0 to 1024 and time is in seconds (and is always increasing) and has 4 decimal places. All of these strings are stored in the ReceivedData variable and I need to separate each value and it's corresponding time and plot it in a chart.
Any suggestion how to split the strings and get each value? I did some attempts with the following code, changing the invoked function "interp_string":
private void interp_string(object sender, EventArgs e)
{
      words = ReceivedData.Split(' ');
      foreach (string word in words)
      {
             textBox.Text += word + "\n";
}
}
And I can see each value and time separeted but it slows me down the printing just like my original problem. And this code doesn't allows me to identify which one is the value and which one are the seconds, to convert them from string to double and then plot them.
By the way, thanks for replying.
Jeff Taylor7y ago
Can we see your code