Modbus RTU: readyRead() not called
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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?
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What is the parent class of your ModbusMaster implementation? What does it derive from?
readyRead is a signal. You are implementing it as a slot. You should probalby connect the modbus readyRead signal to a reader slot in your constructor. I don't believe you want to overide readyRead, but only use it to cause a reader slot to be executed.
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@Mark81 You should connect a slot to https://doc.qt.io/qt-5/qmodbusreply.html#errorOccurred and see whether this one is emitted and if so what the error is.
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@Kent-Dorfman No, reply is https://doc.qt.io/qt-5/qmodbusreply.html, it does not have readyRead signal, but it has finished() signal.
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@Kent-Dorfman the parent class is
QObject
.readyRead()
is my own slot asjsulm
said. The signal isfinished()
.@jsulm unfortunately there are no errors:
QModbusDataUnit req(type, startAddress, count); if (auto *reply = _modbus->sendReadRequest(req, _id)) { connect(reply, &QModbusReply::errorOccurred, this, [reply]() { qDebug() << reply->errorString(); }); if (!reply->isFinished()) connect(reply, &QModbusReply::finished, this, &ModbusMaster::readReady); // ...
but the output is the same.
After a lot of trials I noticed that, seldom, the slot is called. But it's about 1 to 10.
Given that the hardware is ok because other Modbus master applications work fine, what I don't understand is why if the answer is received (Received ADU
is correct) the signal/slot mechanism doesn't work. This code seems very similar to the Qt5 example. The only code that is not shown here (but I've commented out to try it) is aQTimer
that after 5000 ms fires a timeout if no answers were received. -
@jsulm said in Modbus RTU: readyRead() not called:
@Mark81 You should connect a slot to https://doc.qt.io/qt-5/qmodbusreply.html#errorOccurred and see whether this one is emitted and if so what the error is.
Actually, there's no need to connect to that slot. According to the documentation:
void QModbusReply::finished() This signal is emitted when the reply has finished processing. The reply may still have returned with an error. [...]
Because I check for errors in my slot it should make no difference at all.
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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.
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@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.
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@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.
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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;});
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@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...
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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)
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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...". -
@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.
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@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.
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@Mark81
you can download the source code and in qmodbusrtumaster comment that lineQObject::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