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Modbus RTU: readyRead() not called

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  • aha_1980A aha_1980

    @Mark81

    The documentation also states: https://doc.qt.io/qt-5/qmodbusreply.html#errorOccurred

    The finished() signal will probably follow.

    So it might nevertheless be a good idea to connect to errorOccurred.

    M Offline
    M Offline
    Mark81
    wrote on last edited by Mark81
    #8

    @aha_1980 yes, as reported in the previous reply I added such a connection but it doesn't print anything, so it seems no errors are thrown. Still I can't receive replies in my slot.

    By the way, to me both sentences are in contradiction but perhaps is my poor English that suggests that:

    This signal is emitted when the reply has finished processing. The reply may still have returned with an error.

    The finished() signal will probably follow.

    aha_1980A 1 Reply Last reply
    0
    • M Mark81

      @aha_1980 yes, as reported in the previous reply I added such a connection but it doesn't print anything, so it seems no errors are thrown. Still I can't receive replies in my slot.

      By the way, to me both sentences are in contradiction but perhaps is my poor English that suggests that:

      This signal is emitted when the reply has finished processing. The reply may still have returned with an error.

      The finished() signal will probably follow.

      aha_1980A Offline
      aha_1980A Offline
      aha_1980
      Lifetime Qt Champion
      wrote on last edited by
      #9

      @Mark81 I fully agree that "may still have" and "will probably follow" are very poor documentation statements - and can most likely be improved.

      But for now,that just means you should check every error source you can, if you encounter problems.

      Qt has to stay free or it will die.

      1 Reply Last reply
      0
      • M Mark81

        I'm trying to "port" the example of Modbus master to my application.
        Here some relevant code:

        QModbusClient *_modbus;

bool ModbusMaster::open(QString port)
{
    _modbus = new QModbusRtuSerialMaster(this);

    _modbus->setConnectionParameter(QModbusDevice::SerialPortNameParameter, port);
    _modbus->setConnectionParameter(QModbusDevice::SerialParityParameter, QSerialPort::NoParity);
    _modbus->setConnectionParameter(QModbusDevice::SerialBaudRateParameter, QSerialPort::Baud57600);
    _modbus->setConnectionParameter(QModbusDevice::SerialDataBitsParameter, QSerialPort::Data8);
    _modbus->setConnectionParameter(QModbusDevice::SerialStopBitsParameter, QSerialPort::OneStop);

    _modbus->setTimeout(2000);
    _modbus->setNumberOfRetries(3);

    return _modbus->connectDevice();
}

bool ModbusMaster::read(QModbusDataUnit::RegisterType type, int startAddress, quint16 count)
{
    if (!_modbus) return false;
    if (_modbus->state() != QModbusDevice::ConnectedState) return false;

    qDebug() << "Read" << startAddress;

    QModbusDataUnit req(type, startAddress, count);    
    if (auto *reply = _modbus->sendReadRequest(req, 1))
    {
        qDebug() << reply->isFinished();
        if (!reply->isFinished()) connect(reply, &QModbusReply::finished, this, &ModbusMaster::readyRead);
        else readReady();
        return true;
    }
    return false;
}

void ModbusMaster::readyRead ()
{
    qDebug() << "readyRead executed!";
    auto reply = qobject_cast<QModbusReply *>(sender());
    if (!reply) return;
    reply->deleteLater();

    if (reply->error() == QModbusDevice::NoError)
    {
        const QModbusDataUnit unit = reply->result();
        // do something
    }
    else if (reply->error() == QModbusDevice::ProtocolError)  qDebug() << reply->errorString();
    else qDebug() << reply->errorString();

    // call next reading
    emit readFinished();
}

        but it seems even if received data readyRead() is not called, example:

        Debug: read 495
Debug: false 
Debug: (RTU client) Sent Serial PDU: 0x0301ef0001
Debug: (RTU client) Sent Serial ADU: 0x010301ef0001b403 
Debug: (RTU client) Response buffer: "0103020000b844" 
Debug: (RTU client) Received ADU: "0103020000b844" 
Debug: (RTU client) Send successful: 0x0301ef0001

        after few seconds I got a timeout from my timer. As far as I understand the response is actually received, but the readyRead() slot is not called.

        Is there something obvious I'm missing?

        J.HilkJ Online
        J.HilkJ Online
        J.Hilk
        Moderators
        wrote on last edited by
        #10

        @Mark81

        the QModbusRtuSerialMaster has also errors that can be emitted. And those differ from the reply, check those also.

        connect(_modbus, & QModbusRtuSerialMaster::errorOccurred, this, [](QModbusDevice::Error error)->void{ qDebug() << error;});

        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.

        M 1 Reply Last reply
        2
        • J.HilkJ J.Hilk

          @Mark81

          the QModbusRtuSerialMaster has also errors that can be emitted. And those differ from the reply, check those also.

          connect(_modbus, & QModbusRtuSerialMaster::errorOccurred, this, [](QModbusDevice::Error error)->void{ qDebug() << error;});
          M Offline
          M Offline
          Mark81
          wrote on last edited by
          #11

          @J.Hilk You're right. Added and tried. Whenever the "hang" happens also this slot shows nothing, unfortunately.

          J.HilkJ 1 Reply Last reply
          0
          • M Mark81

            @J.Hilk You're right. Added and tried. Whenever the "hang" happens also this slot shows nothing, unfortunately.

            J.HilkJ Online
            J.HilkJ Online
            J.Hilk
            Moderators
            wrote on last edited by
            #12

            @Mark81 how much time passes between open and the first read request ?

            I noticed, on Windows, that when I call immediately after opening the device the first data , then most of the time nothing happens at all.

            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.

            M 1 Reply Last reply
            2
            • J.HilkJ J.Hilk

              @Mark81 how much time passes between open and the first read request ?

              I noticed, on Windows, that when I call immediately after opening the device the first data , then most of the time nothing happens at all.

              M Offline
              M Offline
              Mark81
              wrote on last edited by
              #13

              @J.Hilk adding a small delay seems to drastically improve the situation. Occasionally it still happens that the debug messages show a received answer but the slot is not called. That's weird because I can understand if some reasons the answer cannot be received, but this is not the case...

              1 Reply Last reply
              0
              • M Offline
                M Offline
                Mark81
                wrote on last edited by Mark81
                #14

                UPDATE

                I think (not sure, though) I noticed something interesting.
                When it works, the debug output from qt.modbus is like this:

                qt.modbus: (RTU client) Sent Serial PDU: 0x0304270001
qt.modbus.lowlevel: (RTU client) Sent Serial ADU: 0x0103042700013531
qt.modbus: (RTU client) Send successful: 0x0304270001
qt.modbus.lowlevel: (RTU client) Response buffer: "01030200017984"
qt.modbus: (RTU client) Received ADU: "01030200017984"

                and my slot is correctly called. Instead, when the problem arises the output is like the one reported in the first post or even this one:

                qt.modbus: (RTU client) Sent Serial PDU: 0x0304180002
qt.modbus.lowlevel: (RTU client) Sent Serial ADU: 0x010304180002453c
qt.modbus.lowlevel: (RTU client) Response buffer: "01030400004080ca53"
qt.modbus: (RTU client) Received ADU: "01030400004080ca53"
qt.modbus: (RTU client) Send successful: 0x0304180002
qt.modbus: (RTU client) Receive timeout: 0x0304180002
qt.modbus: (RTU client) Sent Serial PDU: 0x0304180002
qt.modbus.lowlevel: (RTU client) Sent Serial ADU: 0x010304180002453c
qt.modbus.lowlevel: (RTU client) Response buffer: "01030400004080ca53"
qt.modbus: (RTU client) Received ADU: "01030400004080ca53"
qt.modbus: (RTU client) Send successful: 0x0304180002
qt.modbus: (RTU client) Receive timeout: 0x0304180002

                Here my slot is not called.

                I see that every time this happens the "Response buffer" line comes before the "Send successful" one.
                I'm looking at the code but I don't understand if this might be a problem.

                (Sorry for the outdated link but I have difficult to find the actual source code of Qt5 - btw I'm using Qt5.11.1)

                aha_1980A 1 Reply Last reply
                0
                • M Offline
                  M Offline
                  Mark81
                  wrote on last edited by
                  #15

                  Perhaps I found it here https://code.woboq.org/qt5/qtserialbus/src/serialbus/qmodbusrtuserialmaster_p.h.html#154:

                  if (m_state != State::Receive) {
    qCDebug(QT_MODBUS) << "(RTU server) Ignoring response due to non receive state";
    return;
}

                  but https://code.woboq.org/qt5/qtserialbus/src/serialbus/qmodbusrtuserialmaster_p.h.html#351:

                  qCDebug(QT_MODBUS) << "(RTU client) Send successful:" << m_current.requestPdu;
m_state = Receive;

                  So if the state is not set to Receive it discard the response. Anyway I didn't see the debug output "Ignoring response...".

                  1 Reply Last reply
                  0
                  • M Mark81

                    UPDATE

                    I think (not sure, though) I noticed something interesting.
                    When it works, the debug output from qt.modbus is like this:

                    qt.modbus: (RTU client) Sent Serial PDU: 0x0304270001
qt.modbus.lowlevel: (RTU client) Sent Serial ADU: 0x0103042700013531
qt.modbus: (RTU client) Send successful: 0x0304270001
qt.modbus.lowlevel: (RTU client) Response buffer: "01030200017984"
qt.modbus: (RTU client) Received ADU: "01030200017984"

                    and my slot is correctly called. Instead, when the problem arises the output is like the one reported in the first post or even this one:

                    qt.modbus: (RTU client) Sent Serial PDU: 0x0304180002
qt.modbus.lowlevel: (RTU client) Sent Serial ADU: 0x010304180002453c
qt.modbus.lowlevel: (RTU client) Response buffer: "01030400004080ca53"
qt.modbus: (RTU client) Received ADU: "01030400004080ca53"
qt.modbus: (RTU client) Send successful: 0x0304180002
qt.modbus: (RTU client) Receive timeout: 0x0304180002
qt.modbus: (RTU client) Sent Serial PDU: 0x0304180002
qt.modbus.lowlevel: (RTU client) Sent Serial ADU: 0x010304180002453c
qt.modbus.lowlevel: (RTU client) Response buffer: "01030400004080ca53"
qt.modbus: (RTU client) Received ADU: "01030400004080ca53"
qt.modbus: (RTU client) Send successful: 0x0304180002
qt.modbus: (RTU client) Receive timeout: 0x0304180002

                    Here my slot is not called.

                    I see that every time this happens the "Response buffer" line comes before the "Send successful" one.
                    I'm looking at the code but I don't understand if this might be a problem.

                    (Sorry for the outdated link but I have difficult to find the actual source code of Qt5 - btw I'm using Qt5.11.1)

                    aha_1980A Offline
                    aha_1980A Offline
                    aha_1980
                    Lifetime Qt Champion
                    wrote on last edited by
                    #16

                    @Mark81 said in Modbus RTU: readyRead() not called:

                    (Sorry for the outdated link but I have difficult to find the actual source code of Qt5 - btw I'm using Qt5.11.1)

                    Then you should really test with a recent version 5.12.x. There has been quite some fixes last year.

                    Qt has to stay free or it will die.

                    1 Reply Last reply
                    0
                    • M Offline
                      M Offline
                      Mark81
                      wrote on last edited by
                      #17

                      Update to Qt5.12.2. Now with the very same code and data after a while it crashes with this error:

                      ASSERT failure in processQueue: "response timer active", file qmodbusrtuserialmaster_p.h, line 302

                      What should one do in such a case?

                      J.HilkJ 1 Reply Last reply
                      0
                      • M Mark81

                        Update to Qt5.12.2. Now with the very same code and data after a while it crashes with this error:

                        ASSERT failure in processQueue: "response timer active", file qmodbusrtuserialmaster_p.h, line 302

                        What should one do in such a case?

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

                        @Mark81 vote for the issue and pray, like I did

                        https://bugreports.qt.io/browse/QTBUG-73965

                        also leave a comment, it helps when people state that they have the same issue.

                        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.

                        M 1 Reply Last reply
                        3
                        • J.HilkJ J.Hilk

                          @Mark81 vote for the issue and pray, like I did

                          https://bugreports.qt.io/browse/QTBUG-73965

                          also leave a comment, it helps when people state that they have the same issue.

                          M Offline
                          M Offline
                          Mark81
                          wrote on last edited by
                          #19

                          @J.Hilk said in Modbus RTU: readyRead() not called:

                          @Mark81 vote for the issue and pray, like I did

                          I'll try to suggest to my customer to pray and wait a fix too.

                          J.HilkJ 1 Reply Last reply
                          0
                          • M Mark81

                            @J.Hilk said in Modbus RTU: readyRead() not called:

                            @Mark81 vote for the issue and pray, like I did

                            I'll try to suggest to my customer to pray and wait a fix too.

                            J.HilkJ Online
                            J.HilkJ Online
                            J.Hilk
                            Moderators
                            wrote on last edited by
                            #20

                            @Mark81
                            you can download the source code and in qmodbusrtumaster comment that line

                            QObject::connect(m_serialPort, &QSerialPort;::bytesWritten, q,
[this](qint64 bytes) {
m_current.bytesWritten += bytes;
if (m_state == Send && (m_current.bytesWritten ==m_current.adu.size()) && !m_current.reply.isNull()) {
       // the if conditions above are copied from processQueue()
        qCDebug(QT_MODBUS) << "(RTU client) Send successful(quick):" << m_current.requestPdu;
        m_state = Receive;
        m_sendTimer.stop();
//        m_responseTimer.start(m_responseTimeoutDuration); comment this line
}
});

                            thats the quick and dirty fix I made, fixes the unexpected state issue

                            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.

                            1 Reply Last reply
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