CODEWITHSUNDEEP
c++qtarduino
FutureJJ
FutureJJ

Reputation: 2678

QSerialPort continuous reading accumulative delay

I am trying to do communication from QT Application to Arduino. The flow is like this: QT Application sends a '1' and Arduino is expected to respond with some data(the data String length is huge, around 300). QT Application is sending '1' at the rate of around 5Hz(every 200ms).

The problem I am facing is, there is an accumulative delay between the Arduino to QT communication. That is, the data I receive from Arduino is not recent data but the frequency of data coming of Arduino is 5Hz only(which is as expected), just the data coming is not recent. This delay keeps on increasing with time. I believe there is some problem with buffer or something.

What I tried:

QSerialPort serialPort; is my device port

  1. serialPort.clear()
  2. serialPort.flush()
  3. Increasing and decreasing Baud Rate from both ends.
  4. Reduce character length from Arduino, here delay reduces significantly but the accumulated delay is observed after a long time.

to clear serial communication buffer, but the issue still persists.

Here is my code snippet:

connect(timer_getdat, SIGNAL(timeout()), this, SLOT(Rec()));
        timer_getdat->start(200);

where Rec() is the function where I do communication part.

In Rec():

serialPort.write("1", 2);
//            serialPort.waitForBytesWritten(100);

long long bytes_available = serialPort.bytesAvailable();

if (bytes_available >= 1)
{
            serialPort.readLine(temp, 500);
            serialPort.flush(); // no change
            serialPort.clear(); // no change by .clear() also
}

I have been stuck on this issue for a quite long time. The above code snippet is what I think is necessary but if anyone needs more clarification, I may reveal more of the code.

Upvotes: 1

Views: 487

Answers (1)

slamarseillebg
slamarseillebg

Reputation: 306

I also encountered with the same issue, and yes QSerialPort.clear() and QSerialPort.flush() doesn't help. Try doing readAll()

So change the part in your Rec() function to something like this:

serialPort.write("1", 2);
long long bytes_available = serialPort.bytesAvailable();

if (bytes_available >= 1)
{
            serialPort.readLine(temp, 500);
            serialPort.readAll(); // This reads all the data in buffer at once and clears the queue.
}

Even on QT forums, I didn't find the answer to this, was playing with all functions available with QSerialPort class and readAll() seems to work.

About readAll(), Qt documentation says:

Reads all remaining data from the device, and returns it as a byte array.

My explanation for the resolution is that readAll captures all of the data from the communication buffer and empties it.

This should be the job of clear() function but apparently readAll() seems to work.

Upvotes: 1

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