extrange behavior of serial port using Qt

Question

I am performing an app with QT for communicate my PC with an 8 bits microcontroller through rs-232. I am using the QtSerialPort library and the communication is working fine, but each time I write something from the PC to the micro and I receive the response, I have to close and open the serial port or I can't continue communicating.. My configuration is: 10500 bps, 8 bits, 1 stop, no parity, no flow control.

The code used for the configuration and the lecture/writting of the port is the next:

bool DriverS::configure(int port, int baudRate)
{
    if(port!=22)
        return false;

     serialPort->setPortName("COM22");

 if (serialPort->open(QIODevice::ReadWrite)==true){

        if (!serialPort->setBaudRate(baudRate)) {
            return false ;
        }

        if (!serialPort->setDataBits(QSerialPort::Data8)) {
            return false ;
        }

        if (!serialPort->setParity(QSerialPort::NoParity)) {
            return false;
        }

        if (!serialPort->setStopBits(QSerialPort::OneStop)) {
            return false;
        }

        if (!serialPort->setFlowControl(QSerialPort::NoFlowControl)){
            return false;
            }
    };

    return true;
}



bool DriverS::read(QByteArray & rxData, int * size)
{

    Sleep(200); 
    *size = 0;
    if (serialPort->waitForReadyRead(TIMEOUT_SERIAL)) {
        rxData = serialPort->readAll();
        *size = rxData.size() ;

    if (!this->checkCRC(rxData))
        {
            qDebug()<< "Rx Checksum Error";
            return false;
        }

    return true;
    }
    qDebug()<< "Rx Timeout";
    return false;
}

bool DriverS::write(QByteArray txData)
{

    unsigned int chk = 0;
    int ret ;

    for(int i = 0;i<txData.size();i++)
    {
        chk+=txData.at(i);
    }

    txData.append(chk);
    ret = serialPort->write(txData);
    return (txData.size()==ret);

}

Answer 1

I just found myself with exactly the same situation. I was getting stuck in the read routine. Try opening the port in unbuffered mode.

port->open(QIODevice::ReadWrite | QIODevice::Unbuffered)

It was just on one computer I found this, I've never had to do it before, but it might get you out of a hole.

Answer 2

I fixed my two problems (despite I am not sure about the methods).

For problem num 1 (open and close the port each time I wanted to communicate) I just added a waitFoBytesWritten() in my write method.

For my problem num 2, (I only was able to work with port22), I have modified the configuration and now I first detect wich ports are available with availablePorts() instead to force the port I want to use. Now I can connect my device to any free port and it works..