@JonB Yes I noticed the change. I am not sure why they do it the way they are doing it. I am starting a single shot timer and immediately after I am starting the event loop which exits with exit code 1 with the readyRead() signal received or with exit code 0 if the timer runs out. If I have the exit code of 1 I read the port and start the process again till the exit code of 0 is received. Seems simple and works every time.

@J-Hilk Thank you so much, it fixed the problem :)

When working with QSerialPort in Qt, you can perform reading and writing operations without using interrupts explicitly. However, it's essential to manage the communication in a way that doesn't block the main thread, especially in a GUI application where blocking operations can freeze the user interface.

@JonB @mrjj It's coming back to me. I once had the same problem with an IMU sensor that I could not solve under windows. But once under linux with the same code, I receive the data perfectly. Same thing, I just tested under linux for the GPS, I receive the data but not under Windows. To this day I don't know where the problem comes from

@kuzulis Thank you so much for your response. That is a great idea. But you are right, the communication protocol would make a lot more sense if it followed the <length><data><crc> structure. @JonB 's Idea works well with my existing Program structure.

@Christian-Ehrlicher Yup, it worked! Thanks a lot.

The issue was that it had to be byte \x05 and QByteArray.setnum(5) will result in \x35 so I had to use QByteArray::append()

Here the bug report for this issue: https://bugreports.qt.io/browse/QTBUG-78086

@elypheldia said in How I listen serial port with writing client code?: Sorry if used the wrong term. I am new on qt. I wanted to indicate that I read the data I wrote to the tnt0 serial port from terminal with using cat /dev/tnt0. But How can I do this with client code instead of reading from terminal. I just wanna open the tnt1 serial port from code., and I wanna read from there. You are confusing to me. Do you want to use /dev/tnt0 or /dev/tnt1? With the code example you have provided, you are writing hello on serial device /dev/tnt0. Is this working? You have defined a slot MySerialPort::readData() , which is called when data are ready to be read from serial port. I have proposed you some changes to display debug message when slot is called. Is this slot called? I don't know: what kind of device is connected to this serial port? if the serial port configuration is correct according to attached device? the attached device communication protocol: It is a binary or text protocol? Are carriage return or line feed required?

@J-Hilk Thank you all guys for your patient and sorry for my basic mistakes :). I fixed my issue. As you said, I expect the read without writing a data to serial port.

@Tague-Carlyon the event loop of QCoreApplications needs to be running, otherwise this won't work at all.

Ok well here's an interesting discovery I've made, for anyone who finds this thread in the future: There seems to be an issue with the driver for the off-brand Arduino Nanos possibly not signalling to the OS correctly, or the implementation that Qt uses just really doesn't like the way that the driver responds. I am referring specifically to the nano clone which uses the QinHeng HL-340 serial peripheral. Not sure why this caused a problem, but there it is. Once I used an official Uno the code worked no problem. If I were more patient and had better resources I could possibly trace back the issue, but I do not, so sorry everyone lol. As such I'm marking this as resolved.

@SGaist That's precisely the idea! :)

@BurSer if your issue is solved please don't forget to mark your post as such!

@IRBaboon If your PC have no obvious lagging, my issue is an error direction. Here are some ideas you can try: read help doc seriously or test one other poeple's credible demo on your devie, is it possible to call it incorrectly?(for serial device, It is difficult for others to run your demo) try the lastest verion of QT

Here's my solution for this, in case anyone's interested: The header file: #include <windows.h> #include <dbt.h> #include <QObject> #include <QAbstractNativeEventFilter> class DeviceEventFilter: public QObject, public QAbstractNativeEventFilter { Q_OBJECT public: DeviceEventFilter(QObject *parent); bool nativeEventFilter(const QByteArray &eventType, void *message, long *result) Q_DECL_OVERRIDE; Q_SIGNALS: void notify(); }; And the source file: #include "eventfilter.h" DeviceEventFilter::DeviceEventFilter(QObject *parent) { Q_UNUSED(parent) } bool DeviceEventFilter::nativeEventFilter(const QByteArray &eventType, void *message, long *result) { Q_UNUSED(eventType) // unneeded as long as we're only running on Windows Q_UNUSED(result) MSG *msg = (MSG *)(message); if ((msg->message == WM_DEVICECHANGE) && (msg->wParam == DBT_DEVNODES_CHANGED)) { emit notify(); } return false; }

Sounds like you should not be using QSerial and instead design a custom solution outside of Qt. Qt is not for real-time processing and your description of the task seems to imply real-time constraints.

Thank you, the problem was, that I didn't wait for the Bytes to be written.

@hskoglund thanks for the help! I did not try your solution, but I guess it should work because the solution from @KroMignon works and you have the same diagnostic.

@J-Hilk Tks, I will do a test. Btw, I want to know more the root cause of QSerialport did not emit readyRead () signal.