(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