(QtSerialPort) Linux Serial port buffer is not empty when opening port

[mostefa]

Hello,

I Working on Bluetooth Communication using Qt Serial port (with QT 4),

But when i am opening a port, i directly have bytesAvailabe,and after deep test and research i conluded that the problem is from buffer of linux , actually the buffer is not empty , even when i made just a

cat /dev/NumberOfMyPort 

My question is what is the best way to correctly clear buffer when opening my serial port ?

I am doing this in my program

Constructor()
{
    cmdSerial = new QSerialPort();
    cmdSerial->setPortName("ttyUSB0");
    cmdSerial->setBaudRate(QSerialPort::Baud115200);
    cmdSerial->setParity(QSerialPort::NoParity);
    cmdSerial->setDataBits(QSerialPort::Data8);
    cmdSerial->setStopBits(QSerialPort::OneStop);
    cmdSerial->setFlowControl(QSerialPort::HardwareControl);
    cmdSerial->open(QIODevice::ReadWrite);
    cmdSerial->flush();
}

~Destructor()
{
    if (cmdSerial->isOpen())
    {
        cmdSerial->flush();
        cmdSerial->close();

        delete cmdSerial;
    }
}

But this does not seem to be the right way to do...

[kuzulis]

Try QSerialPort::clear().

[mostefa]

@kuzulis

Thank you to your fast reply,

Well, like you suggest, i tried to clear my serial port and i've made it like that:

cmdSerial->open(QSerialPort::ReadWrite);
cmdSerial->clear(QSerialPort::AllDirections);

and although, i made the same thing just before closing my port on my destructor

    if (cmdSerial->isOpen())
    {
       cmdSerial->clear(cmdSerial->AllDirections);
        cmdSerial->close();
        delete cmdSerial;
    }

But when i close , and open my program again i am still having the same problem ,

It seems like the port is never closed ,even when i made myport->close()

Any other suggestion?

Regards !

[michelson]

http://doc.qt.io/qt-5/qserialport.html#flush
mayby because of this one in constructor? Why you flush something there? From the code i can see you didnt write before so the purpose of this line is not clear to me. Get rid of it and give it a try.

[mostefa]

@michelson

Thank you for your fast reply,

But i already tried to replace port->flush with port->clear() , as mentioned in my second reply, and that does not change anything.

Thanks anyway,

Regards !

[Rondog]

What if you were to simply call 'readAll()' after opening the port. If there is data sitting in the read buffer this should clear it. I assume the write buffer is empty at this point.

I have noticed the QSerialPort (from Qt5) uses buffers. The one I used for Qt4 (QExtSerialPort ?) didn't buffer the data. When I was porting from Qt4 to Qt5 and switched to QSerialPort I had some problems related to this. If it is the write buffer you can call 'waitForBytesWritten(-1)' to block until the write buffer is emptied before closing the port (or some variation of this that doesn't have the potential of freezing the application if data cannot be written).

[mostefa]

Hi to all,

The buffer was never empty, cause the readAll() function was not working outside of the SLOTS that are not connected to the readyRead SIGNAL.

I bypassed the problem using the waitForReadyRead function.

here is my solution:

Constructor()
{
    cmdSerial = new QSerialPort();
    cmdSerial->setPortName("ttyUSB0");
    cmdSerial->setBaudRate(QSerialPort::Baud115200);
    cmdSerial->setParity(QSerialPort::NoParity);
    cmdSerial->setDataBits(QSerialPort::Data8);
    cmdSerial->setStopBits(QSerialPort::OneStop);
    cmdSerial->setFlowControl(QSerialPort::HardwareControl);
    cmdSerial->open(QIODevice::ReadWrite);

    connect(this,SIGNAL(isDataPortOpenedChanged(bool)),this,SLOT(checkDataGarbage(bool)));
}

...

void Constructor::checkDataGarbage(bool portOpened)
{
    if(portOpened)
    {
        while(cmdSerial->waitForReadyRead(100));
        {
            dataSerial->clear(QSerialPort::AllDirections);
        }

        connect(cmdSerial,SIGNAL(readyRead()),this,SLOT(onDataReadyRead()));
    }
}

My buffer is then cleared at the start of the port immediately.

Problem solved !

[kickoune103]

i have i think, the same problem in QT5.6 beta.

i have software who received data.
at the beginning data is not correctly.

i tried clear after opening() , more data is not correctly.....
not solved problem.

i will try this solution.
problem in linux or MAC.

[kickoune103]

after my open i have write your loop,
but not pass inside the loop.

https://bugreports.qt.io/browse/QTBUG-50415
https://forum.qt.io/topic/62753/stranges-characters-first-ready-read-qserialport-linux-or-mac