@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.

Hi and welcome to devnet, This is a known issue: QTBUG-78086. It's fixed and will be part of Qt 5.12.6 and 5.13.2.

Few place I read, it is generated due to some issue with kernel. So I just update the Ubuntu LTS, and Now it is working with same code.

yup looks like it is that bug, thanks guys

@kent-dorfman Flow control is not implemented on this receiver. GPSD is also not a concern as this receiver does not speak NMEA it conforms to ICD-GPS-153c.

@fcarney You were right. I changed the line where I initialize the serialport to a position before the connect and that works. Thanks!

@Kent-Dorfman Out of curiosity, and not wanting to start a flame war, I'm slightly surprised that you ship I/O access out-of-process. It may well be convenient for debugging/testing, but for production? Then again I know nothing about hardware, so you may so that serial port top speed is slow it doesn't matter, I don't know....

@Dooham You're OK, you are not the first (or the last) here to ask/state this! :)

@smnsmn said in Connecting several readyRead() signals to one slot (QSerialPort): Qt::QueuedConnection The slot is invoked when control returns to the event loop of the receiver's thread. The slot is executed in the receiver's thread. This is for queued connections which are not used by default for signals/slots in same thread. You really need to differentiate between connections in same thread and such between different threads. "Can signal thread == receiver thread?" - sure, it is like this most of the time. Only if you use more than one thread you can have signals and slots in different threads. For signals and slots in same thread queued connection is NOT used, unless you tell Qt to do so (last parameter in connect() call).

@Christian-Ehrlicher Thanks, that was exactly my problem.

@aha_1980 I'm expecting to read and write data with a serial port, but, for some reason, the data sent by my pc is also read by my pc, so the problems is that the data sent is somehow triggering the readyRead signals. @J-Hilk I noticed that ,effectively, the echo wasn't turned off on the pi. For whatever reason, it completely broke my programs when I'm turning it of, so I'm going to install qt and try again on the pi before calling it a win.

@kuzulis I installed com0com and have written a sender, but the behaviour is completely different and I can't reproduce the problem. The sent datablocks are received in the same size (up to 4096bytes) and the same time independent of the blocksize and speed I use to send the data. I don't think this approach helps... PS: The errorOccurred is handled and I doen't get an error. I commented it out for using QT5.7

@dheerendra At this point, we are fairly certain that the problem is in the main thread code. I have uploaded the main thread code in the previous comment. Please suggest any necessary changes that could solve the issue. thank you.

@sykac said in Turning off power to a running QSerialPort: One problem starts probably in the hardware. The COM port of the device disconnects from the PC (I don't why, it could be some driver/firmware issue) Reading you topic title, could it be that the USB connection between PC and FTDI is interrupted? And that's what I said, this may lead to endless loops in the device driver. This kind of problems can hardly be solved in the user space.

I agree you need to use a state machine for that case. http://doc.qt.io/qt-5/qstatemachine.html probably helps putting down the skeleton already

Please try while (true) { if (SerialPort.waitForReadyRead(100)) { while (SerialPort.canReadLine()) qDebug() << SerialPort.readLine(); } } Now you can work on the already ready buffer obtained from "SerialPort.readLine();"

@cesar93 so if your problem is solved, please mark this topic as SOLVED too. Thanks

Solved. The missing libQt5SerialPort.so.5 error on the target device was because that library effectively was not present. On the host side I added that library in the package list of the image and rebuild the image itself.

@kuzulis Thank you. It works perfectly now :-) TLDR: My mistake was to not instantiate and open the QSerialPort in the thread i was reading from.

@aha_1980 Thank you so much for your ideas. Both problems solved. After reconfiguring aptitude stuff to use "stable" instead of hard-coded "jessie" and half-a-day-long upgrades and cleaning the mess I really got not only higher version of Qt, but as well QParallelPort working as planned. Definitely worth the effort (even if I did not expect the upgrade to take so much time.) My mistake. I missed this single character overload to append(). Thank you for pointing me there. Now I got completely rid of that development/release conditionals. Case closed, thanks to all who assisted.

Hi, You can get the native handle with QSerialPort::handle and then modify its properties. Hope it helps

How did you install Qt ?

@tangxinzhou I'm afraid I do not have a solid solutions. I'm running a workaround now. Let me post it for you: void connectDevice(bool connect) { if(connect){ switch (mDevice->state()) { case QModbusDevice::ClosingState: case QModbusDevice::ConnectedState: case QModbusDevice::ConnectingState: mDevice->deleteLater(); mDevice = new QModbusRtuSerialMaster(this); setupSignalSlots(); QTimer::singleShot(100,this, [=]{setConnectParamter(m_port,m_paramter);}); break; case QModbusDevice::UnconnectedState: default: if(!mDevice->connectDevice()){ emit signalModbusError(mDevice->errorString()); mDevice->disconnectDevice(); } break; } }else{ stopPoll(); mDevice->disconnectDevice(); QTimer::singleShot(200,this,[=]{checkDisconnected();}); } } void checkDisconnected() { if(mDevice->state() != QModbusDevice::UnconnectedState){ mDevice->deleteLater(); mDevice = new QModbusRtuSerialMaster(this); setupSignalSlots(); } }

@AngrySkarpeta Well it might be overkill but it´sounds like its not really connected but without actual errors then its not possible to guess at all. Could be a driver issue or trust issue. You should use other tools to try to test if they are really paired.

@QtExchange said in Segmentation fault or overflow when streaming from a QSerialPort: The trick is one QByteArray receives the data (on signal slot basis) QByteArray can receive nothing, it's an array of bytes - a container, nothing more, nothing less. where the other container (which is just a copy of the receiver-QByteArray) is parsing the received Data, as the symbols come in a random order. ??! How can you parse something that doesn't have any order? And where is this other container? I could think of having an extra signal-slot that exchanges the data between both containers whenever it is demanded, but it sounds like I have to double check if I'm actually dealing with the most current data. I don't follow. Why would be this even needed ...? There's an extra mutex for the device access, and another one for the shared message container. Qt imposes thread affinity on QObject instances, you don't need a mutex for device access, and you shouldn't share the message container. and because I'm dealing with QElapsedTimer, that needs the thread. In what universe QElapsedTimer needs a thread ...?! It's like saying that an integer needs a thread ... I don't get it.

It is not a qserialport issue, it is a kernel/driver issue. A driver of your serial port has bugs, you should try to update driver or to use another HW device.

@cdcc0606 Typical, can you upgrade to 5.3?

Hi, What about reading the whole buffer and then search for the first occurrence of '\r' ? That way you avoid to loop on the input

@Basti46 Good work! :)

Just to confirm that QSerialPort can be used on rooted Android. (Some info) Notes: #ifdef Q_OS_ANDROID /* This will open the Superuser app, * prompting for root permisions */ QProcess proc(&a); proc.start("su -c \"chmod 666 /dev/ttyUSB0\""); #endif Don't forget to disable SELinux on Android 4.2 and above :)

I figured out, it was nescessary to set DTR: port.setDataTerminalReady(true); Thanks & br, Clemens

So does the QT appends '\0' terminator after every append? ( For QByteArray - No.

Getting back to document conclusions of my research on best practice of using RaspiComm RS-485 under Qt for anybody, who finds this thread useful (I expect many of it is valid for RS-232 on same board as well, did not test myself): Do not try to implement communication with MAX3140 UART chip yourself (maybe except of asm based implementation, what is however most probably unnecessary exertion). I succeeded to implement it based on kernel /dev/spidev0.0 only to find out that even this partially system driver supported solution is too slow for even 19 200 Bd speed (loosing about 5 characters on one received). I myself feared about RaspiComm RS-485 driver /dev/ttyRPC0 based on some forums complaints and not clear versioning, however found out, that the forum thread was heavy outdated. These official installation instructions worked like a charm and the resulting driver worked out-of-box for my latest Raspbian Wheezy (4.1.7+ #817). So I strongly recommend to take this approach. QSerialPort class has constructor with signature QSerialPort(const QString &, QObject *), where QString may contain even device which is not included in the QList that QSerialPortInfo::availablePorts() returns. This works with no surprise. If one does not set anything than (eventually) baud speed, one gets standard 8 bit, 1 stop bit, no parity without any character translations, good old plain raw binary. So QSerialPort may be used with /dev/ttyRPC0 directly and easily. QSerialPort rpc0("/dev/ttyRPC0"); rpc0.write("Binary request\0even\xffcontaining weird\x03characters", length_of_binary); if(rpc0.waitForReadyRead(100)) // Enough long time in miliseconds QByteArray data = rpc0.readAll(); // You may have to wait/read repetitively in loop // and merge data on higher link speeds Hardware of RaspiComm uses RTS pin to select in/out direction of data. CTS is kept active permanently by wiring, so using default use RTS/CTS mode works properly with no inappropriate blocking. That's all you should need, so enjoy your communication.