QSerialPort

[Tomaz]

Hi
I am running qthread. In this thread I run infinitive loop. In loop I am reading USB0tty port. On usb port I have arduino nano with sensors writing values to usb port.
After work is done in loop I emit signal to another object. If I use clear function with QSerialPort object everything work fine in almost real time but I get error.

QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread.

If I do not use clear method the error goes away but the message/signal from qthread (signal/slot) comes slow (values do not change) from qtgread object to another object in my qt app.
I am not expert in USB port anf QSerialPort but I think it has to do with buffer clearance.

Any Ideas?
Thomas

..h file

#ifndef READTTYUSB0_H
#define READTTYUSB0_H

#include <QObject>
#include "QtSerialPort/QSerialPort"

class readttyUSB0 : public QObject
{
Q_OBJECT

public:
    readttyUSB0();
    ~readttyUSB0();

public slots:
    void doWork();

signals:
    void usb0Data(QString);

private:
    QSerialPort* sPort = new QSerialPort;

    QByteArray data;
    QString str;
};

#endif // READTTYUSB0_H

.cpp file

#include "readttyusb0.h"
#include "QThread"

readttyUSB0::readttyUSB0()
{
    sPort->setPortName("/dev/ttyUSB0");
    sPort->setBaudRate(9600,QSerialPort::AllDirections);
    sPort->setDataBits(QSerialPort::Data8);
    sPort->setFlowControl(QSerialPort::NoFlowControl);
    sPort->setParity(QSerialPort::NoParity);
    sPort->setStopBits(QSerialPort::OneStop);

        if(sPort->open(QIODevice::ReadWrite))
        {
        sPort->setDataTerminalReady(QSerialPort::NoSignal);
        }
}

readttyUSB0::~readttyUSB0()
{
delete sPort;
}

void readttyUSB0::doWork()
{
    while(1)
    {
        if (QThread::currentThread()->isInterruptionRequested())
        {
        return;
        }

        if(sPort->isOpen())
        {
            sPort->waitForReadyRead();
            data=sPort->readLine();
            str=QString::fromStdString(data.toStdString());

            emit usb0Data(str);
            sPort->clear();
        }
    }
}

[Pl45m4]

@Tomaz

What do you expect from emitting a signal in a while(1) loop?!
It will never get processed

Edit:
Ah havent seen your comment. You only emit once when the loop has ended.

Have a look at the synchronous and asynchronous QSerialPort examples here:

• https://doc.qt.io/qt-6/qtserialport-blockingreceiver-example.html
• https://doc.qt.io/qt-6/qtserialport-terminal-example.html

[SGaist]

Hi,

Is it expected that you read only one line ?
You should rather get everything from the serial port, accumulate in a buffer and then process the data once you have a full frame (or more).

[Tomaz]

@SGaist Hi SGaist. Everytime is good to read your replies. Yes. I control what is being red and it is one line from arduino loop (simple sensor data). Thomas

[SGaist]

Can you share also the thread related code ?

[Tomaz]

@Pl45m4 Hi.
I am sorry but the code is correct on syntax, semantic and semiotic/pragmatic level. The creation of and object has to happen inside the working loop I concluded; (in run loop). I think it has to do with usb port access on low level (QSerialPort c/c++ Qt code). I think. The error is gone now.

I got it from one of SGaist comments/replies.

Perhaps SGaist could give us more enlightenment why it has to be inside run loop (or custom loop like I have)? Perhaps because it is made on heap?

regards, Thomas

[Tomaz]

@Tomaz No it is not the heap problem. Perhaps of the scope object is living in?

[kuzulis]

@Tomaz

Right now everything is wrong in your code.

[Christian Ehrlicher]

Where is readttyUSB0 instantiated / is it moved to a thread somewhere? If yes then you forgot to move sPort (btw: very strange name for a member var) as it has no parent.

[Tomaz]

@Christian-Ehrlicher Hi. Sorry for my late reply. Well it is in mainwindow constructor. This is in constructor.

rttyUSB0->moveToThread(threadttyUSB0);
connect(threadttyUSB0,SIGNAL(started()),rttyUSB0,SLOT(doWork()));
connect(rttyUSB0,SIGNAL(usb0Data(QString)),this,SLOT(readSerialCom(QString)));
threadttyUSB0->start();```

Declared in .h file in private part.

What I do in readSerialCom(QString) is not important.

I let this loop to run for a week with no problem. No compile error. Should be ok.

Thomas

[Tomaz]

@SGaist Hi. SGaist. One question. What is the best way (board?) to boot Linux into Qt graphic App (I need access to /dev- USB) in max 2 to 3 seconds? But to be on open source non commercial side. I tried raspberry Pi and eglfs but it needs 10 seconds. regards Thomas

[Ronel_qtmaster]

@Tomaz if you are using yocto, you can disable certain services at start or change the boot order by prioritising your app

[SGaist]

@Tomaz hi,

It depends on what your device has to do, which services are required, etc.

Based on that you can optimize some things to reduce boot time.