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QSerialPort: problem with waitForReadyRead()

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  • K Offline
    K Offline
    kuzulis
    Qt Champions 2020
    wrote on last edited by
    #3

    What is OS, and what is Qt version?

    O 1 Reply Last reply
    0
    • JonBJ JonB

      @oBOXPOH said in QSerialPort: problem with waitForReadyRead():

                      output = deviceControl_SerialPort->readAll(); // <-- READ
                      while (deviceControl_SerialPort->waitForReadyRead(10)) // <-- READ AGAIN
                          output += deviceControl_SerialPort->readAll();
      

      readAll() only reads whatever is available at the instant it is called. This can be anywhere from 1 byte to the total number you expect. Your while (waitForReadyRead(10)) may return false, and so exit the loop, when there is no data right now but there will be later on, meaning that you will miss the data this time round and pick it up only next time.

      I don't know much about serial ports, but at least try upping that 10 to a bigger number and see if it makes any difference?

      Make sure the other end is flushing whatever it writes immediately.

      You're not really "supposed to" use waitForReadyRead(10). You're "supposed to" use the readyRead() slot with signals. You could try that and see if it makes a difference.

      O Offline
      O Offline
      oBOXPOH
      wrote on last edited by
      #4

      @JonB said in QSerialPort: problem with waitForReadyRead():

      @oBOXPOH said in QSerialPort: problem with waitForReadyRead():

                      output = deviceControl_SerialPort->readAll(); // <-- READ
                      while (deviceControl_SerialPort->waitForReadyRead(10)) // <-- READ AGAIN
                          output += deviceControl_SerialPort->readAll();
      

      readAll() only reads whatever is available at the instant it is called. This can be anywhere from 1 byte to the total number you expect. Your while (waitForReadyRead(10)) may return false, and so exit the loop, when there is no data right now but there will be later on, meaning that you will miss the data this time round and pick it up.

      I don't know much about serial ports, but at least try upping that 10 to a bigger number and see if it makes any difference?

      Make sure the other end is flushing whatever it writes immediately.

      You're not really "supposed to" use waitForReadyRead(10). You're "supposed to" use the readyRead() slot with signals. You could try that and see if it makes a difference.

      In order to get data with readAll() I need to go through waitForReadyRead(), but sometimes I wait even 10 seconds - and no data anyway. When waitForReadyRead() returns true, then readAll() works fine.

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      • J.HilkJ Offline
        J.HilkJ Offline
        J.Hilk
        Moderators
        wrote on last edited by
        #5

        while loops and sleeps... why don't you simply use the asynchronous signals that QSerialPort provides ?

        Also connect the error signal to an output see if something is triggered there


        Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


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        • K kuzulis

          What is OS, and what is Qt version?

          O Offline
          O Offline
          oBOXPOH
          wrote on last edited by
          #6

          @kuzulis said in QSerialPort: problem with waitForReadyRead():

          What is OS, and what is Qt version?

          OS: Windows 10
          Qt Version: 5.13.1
          Building: MinGW 32-bit

          JonBJ J.HilkJ 2 Replies Last reply
          0
          • O oBOXPOH

            @kuzulis said in QSerialPort: problem with waitForReadyRead():

            What is OS, and what is Qt version?

            OS: Windows 10
            Qt Version: 5.13.1
            Building: MinGW 32-bit

            JonBJ Online
            JonBJ Online
            JonB
            wrote on last edited by
            #7

            @oBOXPOH
            Like I & @J-Hilk have said, suggest you at least try it with readyRead signal instead of waits and see if that makes the difference?

            O 1 Reply Last reply
            1
            • O oBOXPOH

              @kuzulis said in QSerialPort: problem with waitForReadyRead():

              What is OS, and what is Qt version?

              OS: Windows 10
              Qt Version: 5.13.1
              Building: MinGW 32-bit

              J.HilkJ Offline
              J.HilkJ Offline
              J.Hilk
              Moderators
              wrote on last edited by
              #8

              @oBOXPOH
              I would suggest to use a different Qt version QSerialPort has some serious issues in 5.13.1

              see this bugreport
              https://bugreports.qt.io/browse/QTBUG-78086


              Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


              Q: What's that?
              A: It's blue light.
              Q: What does it do?
              A: It turns blue.

              O D 2 Replies Last reply
              4
              • J.HilkJ J.Hilk

                @oBOXPOH
                I would suggest to use a different Qt version QSerialPort has some serious issues in 5.13.1

                see this bugreport
                https://bugreports.qt.io/browse/QTBUG-78086

                O Offline
                O Offline
                oBOXPOH
                wrote on last edited by oBOXPOH
                #9

                @J-Hilk said in QSerialPort: problem with waitForReadyRead():

                @oBOXPOH
                I would suggest to use a different Qt version QSerialPort has some serious issues in 5.13.1

                see this bugreport
                https://bugreports.qt.io/browse/QTBUG-78086

                Tried Qt 5.9.8.

                In this case waitForReadyRead() always returns false with accepted write command.

                1 Reply Last reply
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                • JonBJ JonB

                  @oBOXPOH
                  Like I & @J-Hilk have said, suggest you at least try it with readyRead signal instead of waits and see if that makes the difference?

                  O Offline
                  O Offline
                  oBOXPOH
                  wrote on last edited by oBOXPOH
                  #10

                  @JonB said in QSerialPort: problem with waitForReadyRead():

                  @oBOXPOH
                  Like I & @J-Hilk have said, suggest you at least try it with readyRead signal instead of waits and see if that makes the difference?

                  I tried next (all is inside the class):

                  connect(deviceControl_SerialPort, &QSerialPort::readyRead, this, &Class::readData_slot);
                  
                  void Class::readData_slot()
                  {
                      qDebug() << "Ready Read" << endl;
                      deviceControl_readData.append(deviceControl_SerialPort->readAll());
                  }
                  

                  In this case I can't reach readData_slot() method.

                  Then I tried next:

                  connect(deviceControl_SerialPort, &QSerialPort::errorOccurred, this, &Class::serialPortError_slot);
                  
                  void Class::serialPortError_slot(QSerialPort::SerialPortError error)
                  {
                      qDebug() << error << endl;
                  }
                  
                  

                  and got some error (see log below):

                  WRITTEN  1 
                  
                  READING... 
                  
                  QSerialPort::TimeoutError 
                  
                  WRITTEN  2 
                  
                  READING... 
                  
                  QSerialPort::TimeoutError 
                  
                  WRITTEN  3 
                  
                  QSerialPort::TimeoutError 
                  
                  I AM NOT READY! 
                  
                  Ready Read 
                  
                  Ready Read 
                  

                  and, by the way, message for readyRead signal. Strangely, that I got it only after 2 real readings...

                  aha_1980A 1 Reply Last reply
                  0
                  • O oBOXPOH

                    @JonB said in QSerialPort: problem with waitForReadyRead():

                    @oBOXPOH
                    Like I & @J-Hilk have said, suggest you at least try it with readyRead signal instead of waits and see if that makes the difference?

                    I tried next (all is inside the class):

                    connect(deviceControl_SerialPort, &QSerialPort::readyRead, this, &Class::readData_slot);
                    
                    void Class::readData_slot()
                    {
                        qDebug() << "Ready Read" << endl;
                        deviceControl_readData.append(deviceControl_SerialPort->readAll());
                    }
                    

                    In this case I can't reach readData_slot() method.

                    Then I tried next:

                    connect(deviceControl_SerialPort, &QSerialPort::errorOccurred, this, &Class::serialPortError_slot);
                    
                    void Class::serialPortError_slot(QSerialPort::SerialPortError error)
                    {
                        qDebug() << error << endl;
                    }
                    
                    

                    and got some error (see log below):

                    WRITTEN  1 
                    
                    READING... 
                    
                    QSerialPort::TimeoutError 
                    
                    WRITTEN  2 
                    
                    READING... 
                    
                    QSerialPort::TimeoutError 
                    
                    WRITTEN  3 
                    
                    QSerialPort::TimeoutError 
                    
                    I AM NOT READY! 
                    
                    Ready Read 
                    
                    Ready Read 
                    

                    and, by the way, message for readyRead signal. Strangely, that I got it only after 2 real readings...

                    aha_1980A Offline
                    aha_1980A Offline
                    aha_1980
                    Lifetime Qt Champion
                    wrote on last edited by
                    #11

                    Hi @oBOXPOH,

                    Qt is an event-driven framework. By using endless loops, wait routines you create problems if you don't know what you are exactly doing.

                    You should use QSerialPort with signals and slots. An example is shown here: https://doc.qt.io/qt-5/qtserialport-terminal-example.html

                    Regards

                    Qt has to stay free or it will die.

                    O 1 Reply Last reply
                    5
                    • aha_1980A aha_1980

                      Hi @oBOXPOH,

                      Qt is an event-driven framework. By using endless loops, wait routines you create problems if you don't know what you are exactly doing.

                      You should use QSerialPort with signals and slots. An example is shown here: https://doc.qt.io/qt-5/qtserialport-terminal-example.html

                      Regards

                      O Offline
                      O Offline
                      oBOXPOH
                      wrote on last edited by
                      #12

                      @aha_1980 said in QSerialPort: problem with waitForReadyRead():

                      Hi @oBOXPOH,

                      Qt is an event-driven framework. By using endless loops, wait routines you create problems if you don't know what you are exactly doing.

                      You should use QSerialPort with signals and slots. An example is shown here: https://doc.qt.io/qt-5/qtserialport-terminal-example.html

                      Regards

                      Terminal Example also works badly -> https://forum.qt.io/topic/108848/terminal-example-for-qserialport-doesn-t-work-correctly

                      O 1 Reply Last reply
                      0
                      • O oBOXPOH

                        @aha_1980 said in QSerialPort: problem with waitForReadyRead():

                        Hi @oBOXPOH,

                        Qt is an event-driven framework. By using endless loops, wait routines you create problems if you don't know what you are exactly doing.

                        You should use QSerialPort with signals and slots. An example is shown here: https://doc.qt.io/qt-5/qtserialport-terminal-example.html

                        Regards

                        Terminal Example also works badly -> https://forum.qt.io/topic/108848/terminal-example-for-qserialport-doesn-t-work-correctly

                        O Offline
                        O Offline
                        oBOXPOH
                        wrote on last edited by
                        #13

                        @oBOXPOH said in QSerialPort: problem with waitForReadyRead():

                        @aha_1980 said in QSerialPort: problem with waitForReadyRead():

                        Hi @oBOXPOH,

                        Qt is an event-driven framework. By using endless loops, wait routines you create problems if you don't know what you are exactly doing.

                        You should use QSerialPort with signals and slots. An example is shown here: https://doc.qt.io/qt-5/qtserialport-terminal-example.html

                        Regards

                        Terminal Example also works badly -> https://forum.qt.io/topic/108848/terminal-example-for-qserialport-doesn-t-work-correctly

                        Solution is to install 5.13.2 or more version of Qt.

                        1 Reply Last reply
                        2
                        • D Offline
                          D Offline
                          DiaaQTdev
                          wrote on last edited by
                          #14

                          @oBOXPOH Hello i am having the same exact problem with QT, i don't receive any output by triggering the readyread signal or by using the return value of waitForReadyRead(), is it really issue related to QT version??
                          => I do have 5.12 version of QT, i want to make sure that that is the problem before deciding to do an upgrade..

                          Thank you in advance for your reply!

                          1 Reply Last reply
                          0
                          • J.HilkJ J.Hilk

                            @oBOXPOH
                            I would suggest to use a different Qt version QSerialPort has some serious issues in 5.13.1

                            see this bugreport
                            https://bugreports.qt.io/browse/QTBUG-78086

                            D Offline
                            D Offline
                            DiaaQTdev
                            wrote on last edited by
                            #15

                            @J-Hilk Hello, is it really a QT bug for versions under 5.13?

                            J.HilkJ 1 Reply Last reply
                            0
                            • D DiaaQTdev

                              @J-Hilk Hello, is it really a QT bug for versions under 5.13?

                              J.HilkJ Offline
                              J.HilkJ Offline
                              J.Hilk
                              Moderators
                              wrote on last edited by
                              #16

                              @DiaaQTdev

                              iirc 5.12 should work fine, only 5.13 had the issues


                              Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                              Q: What's that?
                              A: It's blue light.
                              Q: What does it do?
                              A: It turns blue.

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                              1
                              • D Offline
                                D Offline
                                DiaaQTdev
                                wrote on last edited by
                                #17

                                @J-Hilk Thank you for your reply, i had upgraded my QT and i still had the same issue, when i send one byte i don't receive any feedback from my device(readyRead is not triggered), it has to be more than one byte in order to receive something. do you please have any idea why is this happening?

                                J.HilkJ 1 Reply Last reply
                                0
                                • D DiaaQTdev

                                  @J-Hilk Thank you for your reply, i had upgraded my QT and i still had the same issue, when i send one byte i don't receive any feedback from my device(readyRead is not triggered), it has to be more than one byte in order to receive something. do you please have any idea why is this happening?

                                  J.HilkJ Offline
                                  J.HilkJ Offline
                                  J.Hilk
                                  Moderators
                                  wrote on last edited by
                                  #18

                                  @DiaaQTdev
                                  Can you show your code?


                                  Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                                  Q: What's that?
                                  A: It's blue light.
                                  Q: What does it do?
                                  A: It turns blue.

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