serialport read not working(no errors)

agmar

Hi,
im wondering if the following has a problem:

private:
    Ui::MainWindow *ui;
    QLabel *label;
    QSerialPort *m_serial = nullptr;
};

Since the QSerialPort is a seperate class in a private window, would that be a problem when trying to display the read values with the following code?

connect(ui->lineEdit, &QLineEdit::textChanged, this, &MainWindow::inputGet);
      connect(m_serial, &QSerialPort::readyRead, this, &MainWindow::readData);
...
serial.setPortName(portName); // replace with the name of the serial port
serial.setBaudRate(QSerialPort::Baud19200);
serial.setDataBits(QSerialPort::Data8);
serial.setParity(QSerialPort::NoParity);
serial.setStopBits(QSerialPort::OneStop);
serial.setFlowControl(QSerialPort::NoFlowControl);
if (serial.open(QIODevice::ReadWrite)) {

const QByteArray data = serial.readAll();
plswork = data;
ui->labTest2->setText(plswork);
QString resultat = "data received";

std::cout << resultat.toStdString() << std::endl;
std::cout << lol.toStdString() << std::endl;

}else {

QString err = "we have a problem here";
std::cout << err.toStdString() << std::endl;

The output is the following:
data received
(blank)

Emre MUTLU

@agmar

serial.setPortName(portName); // replace with the name of the serial port
serial.setBaudRate(QSerialPort::Baud19200);
serial.setDataBits(QSerialPort::Data8);
serial.setParity(QSerialPort::NoParity);
serial.setStopBits(QSerialPort::OneStop);
serial.setFlowControl(QSerialPort::NoFlowControl);
if (serial.open(QIODevice::ReadWrite)) {
qDebug()<<"port Open";
} else {
qDebug()<<"Port OpenError";
}
if(serial.waitForBytesWritten(2000)){//it waits to bytes written
    while(serial.waitForReadyRead(1000)){//it waits to read
               const QByteArray data = serial.readAll();
             }
}

jsulm

@agmar said in serialport read not working(no errors):

if (serial.open(QIODevice::ReadWrite)) {
const QByteArray data = serial.readAll();

Please read documentation.
This simply can't work. Calling readAll does not mean that data was already received.
Proper way to implement is to use signals slots: connect a slot to https://doc.qt.io/qt-6/qiodevice.html#readyRead signal of your QSerialPort instance and call readAll there.
There are also examples showing how to do it: https://doc.qt.io/qt-6/qtserialport-examples.html

SGaist

@agmar Please use proper coding tags around all your code snippets.

That said, you do not show how you initialize nor configure m_serial.

With the code you posted, you are likely not using m_serial at all, or are trying to access the same device twice which should fail.

Qt is an asynchronous framework, you should first learn how it works especially with regards to serial ports.

Please take the time to properly read and understand the links @jsulm provided.

agmar

@Emre-MUTLU from my understanding, this is blocking code isnt it? this is not optimal and usable in a real time application if that's the case.
I did read in the documentation that readAll() would allow asynchronous operation, is there anyway to rewrite that to provide async operation?

JonB

@agmar Yes, follow the links @jsulm gave you!

agmar

@jsulm

@jsulm I have an MCU connected to to the serial port that sends back what i received(tested,works) , and i did read the documentation, but its only useful if you already know how QT works and i know about the terminal and enumerator ,blocking sender and receiver examples, they're not clear to me...

this is the whole function:

void MainWindow::sendMessage()sd
{
QSerialPort serial;
serial.setPortName(portNsame); // replace with the name of the serial port
serial.setBaudRate(QSerialPort::Baud19200);
serial.setDataBits(QSerialPort::Data8);
serial.setParity(QSerialPort::NoParity);
serial.setStopBits(QSerialPort::OneStop);
serial.setFlowControl(QSerialPort::NoFlowControl);
if (serial.open(QIODevice::ReadWrite)) {
QString message = ui->lineEdit->text();
std::cout << message.toStdString() << std::endl;
QByteArray messageData = message.toUtf8();
std::cout << messageData.toStdString() << std::endl;
serial.write(message.toUtf8());
serial.waitForBytesWritten(-1);
serial.close();

}

serial.setPortName(portName); // replace with the name of the serial port
serial.setBaudRate(QSerialPort::Baud19200);
serial.setDataBits(QSerialPort::Data8);
serial.setParity(QSerialPort::NoParity);
serial.setStopBits(QSerialPort::OneStop);
serial.setFlowControl(QSerialPort::NoFlowControl);
if (serial.open(QIODevice::ReadWrite)) {

const QByteArray data = serial.readAll();
lol = data;
ui->labTest2->setText(lol);
QString resultat = "data received";

std::cout << resultat.toStdString() << std::endl;
std::cout << lol.toStdString() << std::endl;

}else {

QString erri = "we have a problem here";
std::cout << erri.toStdString() << std::endl;

}
}

is the
connect(m_serial, &QSerialPort::readyRead, this, &MainWindow::readData);
not valid?

JonB

@agmar
The connect() looks right [edit, No, see end of my post?]. But not the

if (serial.open(QIODevice::ReadWrite)) {

const QByteArray data = serial.readAll();

All readAll()s belong in the MainWindow::readData() slot. And don't forget that can/will be called multiple times, and each time there is a only a guarantee that at least 1 byte is ready to read, not more than that. So you may have to buffer the received data.

As a separate issue. You seem to have one QSerialPort serial; local variable in sendMessage(), and some other serial used outside that. You open and close serial port for each read or write?? You are supposed to have one serial port open across a number of/all read/writes.

Furthermore, that actually seems to make

connect(m_serial, &QSerialPort::readyRead, this, &MainWindow::readData);

wrong, what is m_serial here?? Elsewhere you use serial. I don't know what you are up to. Your application should (presumably) have just one instance of QSerialPort, with its settings performed and opened only once.

agmar

@SGaist How do i use proper coding tags all around my code snippets? i have no idea how to do it...

JonB

@agmar
When you type a post here you have a "toolbar" of icons above where you type, right? The one which looks like </> has a tooltip of Code and puts tags around whatever you have selected, or put lines of just 3 backtick characters ``` before & after your snippet.

agmar

@JonB
I tried making it into serial, but this is what the compiler kept throwing at me, and thanks for the info earlier!

JonB

@agmar
I don't know what to say. This is straightforward C++ stuff. You are not supposed to just change things without understanding.

Your code seems to have at least 3 QSerialPort declarations as far as I can see, one for m_serial and 2 for serial. I don't know why you would want any more than just one. Whatever you need to understand and sort out your code.

agmar

@JonB
I know, but to understand and learn you need to change, and if i need to understand everything to change anything, how will i ever be able to understand in the first place(catch22)?

As for m_serial, that was used in the terminal example and just 'serial' in the other, this code is made from pieces of example code i found, too bad its not commented...

JonB

@agmar
My guess is you would just use the m_serial everywhere, like I said I don't think you will want to have any more that one QSerialPort instance.

Sorry, but if you take bits of code from different places you have to understand how it works to get it right.