[Solved] qtserialport read problem.

rafae11

i can write to the serial port with the code i have below.
i was wondering why am i not getting a response from the serial device.
could somebody let me know what i am doing wrong thanks.

@void MainWindow::ExitSurfaceMode()
{
QSerialPort serial;
QString text("\\.\");
text.append(ui->serialport->currentText());

qDebug() << text;
serial.setPortName(text);

if (serial.open(QIODevice::ReadWrite))
{
    serial.setBaudRate(QSerialPort::Baud9600);
    serial.setDataBits(QSerialPort::Data8);
    serial.setParity(QSerialPort::NoParity);
    serial.setStopBits(QSerialPort::OneStop);
    serial.setFlowControl(QSerialPort::NoFlowControl);

    SerialCommands start;
    std::vector<char> exit_mode = start.ExitCommand();
    QByteArray latin = QByteArray::fromRawData(exit_mode.data(),exit_mode.size());
    qDebug() << "exit command sent";
    qDebug() << latin;

    serial.write(latin);
    Sleep(500);
    QString data = serial.readAll();
    qDebug() << "This is the data -" << data << endl;
    serial.close();
}

}
@

kuzulis

@
...
serial.write(latin);
serial.waitForBytesWritten(500);
serial.waitForReadyRead(500);
QString data = serial.readAll();
...
@

Of course, need to add a check for the returns values.

BTW: See "examples":https://qt.gitorious.org/qt/qtserialport/source/dda7449d18cf8aaa542f869dcaea28634d21ecb0:examples/serialport.

kqt-mr-nv6

use asynchronous receive methods
to receive data efficiently

rafae11

i tried to use the following

@serial.waitForBytesWritten(500);
serial.waitForReadyRead(500);@

i received the data but it is not reliable. sometimes i get the whole message sometimes i only get part of the response.

kuzulis

Nobody guarantees that you will receive at once all package of data (1 byte? 15 bytes? 1000 bytes? 100000 bytes?).

It is necessary to do waiting of expected number of bytes, like:

@
...
for (;;) {
bool ret = serial.waitForReadyRead(500); // wait at least one byte available
if (ret) {

    qint64 bav = serial.bytesAvailable();
    if (bav < expected)
        continue;

    QByteArray recvData = serial.read(expected);

    // do something

} else {
    // error or timeout, no more bytes received

    // do something

}

}
...
@

But in any case is better to use the async approach instead of sync.

rafae11

thanks i am receving data reliably now. :)