QSerialPort cannot open rfcomm socket

[radoslav006]

Hi,
I try to open rfcomm socket (bluetooth -> serial port), but QSerialPort library cannot open it. QSerialPort::open() returns false and QSerialPort::errorString() returns "Unknown Error" (error code 0). But when I open this socket by GtkTerm 0.99.7-rc1 everything works ok.
I use Qt 5.3.1 (GCC 4.6.1, 64 bit) on Ubuntu 14.04 64 bit
There is my piece of code that I use to connect to my socket:
@
serialPort->setPortName(ui->comboBoxPorts->currentText()); //"rfcomm0"
serialPort->setBaudRate(ui->lineEditBaud->text().toInt()); //250000
serialPort->setDataBits(QSerialPort::Data8);
serialPort->setParity(QSerialPort::NoParity);
serialPort->setStopBits(QSerialPort::OneStop);
serialPort->setFlowControl(QSerialPort::NoFlowControl);

if (!serialPort->open(QIODevice::ReadWrite)) {
    qDebug() << "Error: " << serialPort->error(); //returns 0
    ui->labelStatus->setText("Error: " + serialPort->errorString()); //returns "Unknown error"
    return;
}

@
Have you any idea what may be wrong?
Thanks in advance,
Radek

[ambershark]

What does QSerialPortInfo::availablePorts() report? Is rfcomm0 a valid serial port according to it?

[radoslav006]

Thanks for reply.
QSerialPortInfo::availablePorts() detect the "rfcomm0" correctly. QSerialPortInfo::isValid() returns true.

[NetZwerg]

Are you using the same serial port settings in GtkTerm?

Try using different settings, i.e. Baud9600, ...
Is it possible to only open for read-only or write-only?

[radoslav006]

Thanks for help. It's working on standard baud rates (9600, 115200, 230400...). QSerialPort accepts only standard baud rates??

[NetZwerg]

Actually it does accept all.

I did find a huge mistake your up to. You have to first open the port then apply the settings. Otherwise the settings will be applied to "default" on open. Try:

@serialPort->setPortName(...)
if(serialPort->open(QIODevice::ReadWrite))
{
  serialPort->setBaudRate(ui->lineEditBaud->text().toInt()); //250000
  serialPort->setDataBits(QSerialPort::Data8);
  serialPort->setParity(QSerialPort::NoParity);
  serialPort->setStopBits(QSerialPort::OneStop);
  serialPort->setFlowControl(QSerialPort::NoFlowControl);
}@

[radoslav006]

Thanks a lot. I have one another question about sockets. I don't understand why I get opening error "Device or resocues is busy" (error code 2) while QSerialPort::isBusy() returns "false" and QSerialPort::isOpen() returns "false". This occur when I open rfcomm0 port with GtkTerm, close it and then try to open it with my aplication. Is there any way to reset socket?

[NetZwerg]

QSerialPort::isOpen():
Returns true if the device is open; otherwise returns false. A device is open if it can be read from and/or written to.

This means if your application did open the port and is readable/writable isOpen() returns true.

QSerialPortInfo::isBusy():
Not sure about this, if this really returns true if the port is still locked by another application.

QSerialPort::open()
This returns true if the port cannot be opened and false if not. So if you cannot open it, it probably is still locked.