I've written a tool which uses the QSerialPort to write to a serial device. It runs for a certain time until I get the following error message:
ASSERT: "bytesTransferred == writeChunkBuffer.size()" in file
qserialport_win.cpp, line 511
My sending function looks like this:
/**
* #brief Send text to device
* #param text
* #return Success/Fail
*/
bool Serial::send(QString text)
{
if (connectionStatus && qsp.isWritable()) {
QByteArray buffer = text.toLatin1();
if (buffer.size() != qsp.write(buffer))
qDebug() << "Send does not work";
qsp.flush();
msleep(15);
return true;
} else {
return false;
}
}
If I understand it correctly I write the text (which is around 20 chars) with flush to the device, wait 15ms and repeat it afterwards. I don't really understand why I get this message?
// EDIT:
After some time I figured out what the problem was. I forgot to mention, why I wait 15 ms. That was part of the documentation, to wait after I send the data. The biggest problem, related to sending data was, that I run QSerialPort in a separate thread. By using that I run in trouble. I moved it to the MainThread and use signal slot design by Qt.
Without knowing the API you're using or how it works, there is no inherent reason why a write() method should transfer all the data supplied, especially when it returns a write count: a clear signal that it may not transfer everything in one go.
The only problem is the assertion itself. You should loop until the data is written, not assume it is all written in a single write. Nor should you sleep between writes, in a vain attempt to outguess the device you're sending to. This is literally just a waste of time.
Related
I am trying to do communication from QT Application to Arduino. The flow is like this: QT Application sends a '1' and Arduino is expected to respond with some data(the data String length is huge, around 300). QT Application is sending '1' at the rate of around 5Hz(every 200ms).
The problem I am facing is, there is an accumulative delay between the Arduino to QT communication. That is, the data I receive from Arduino is not recent data but the frequency of data coming of Arduino is 5Hz only(which is as expected), just the data coming is not recent. This delay keeps on increasing with time. I believe there is some problem with buffer or something.
What I tried:
QSerialPort serialPort; is my device port
serialPort.clear()
serialPort.flush()
Increasing and decreasing Baud Rate from both ends.
Reduce character length from Arduino, here delay reduces significantly but the accumulated delay is observed after a long time.
to clear serial communication buffer, but the issue still persists.
Here is my code snippet:
connect(timer_getdat, SIGNAL(timeout()), this, SLOT(Rec()));
timer_getdat->start(200);
where Rec() is the function where I do communication part.
In Rec():
serialPort.write("1", 2);
// serialPort.waitForBytesWritten(100);
long long bytes_available = serialPort.bytesAvailable();
if (bytes_available >= 1)
{
serialPort.readLine(temp, 500);
serialPort.flush(); // no change
serialPort.clear(); // no change by .clear() also
}
I have been stuck on this issue for a quite long time. The above code snippet is what I think is necessary but if anyone needs more clarification, I may reveal more of the code.
I also encountered with the same issue, and yes QSerialPort.clear() and QSerialPort.flush() doesn't help. Try doing readAll()
So change the part in your Rec() function to something like this:
serialPort.write("1", 2);
long long bytes_available = serialPort.bytesAvailable();
if (bytes_available >= 1)
{
serialPort.readLine(temp, 500);
serialPort.readAll(); // This reads all the data in buffer at once and clears the queue.
}
Even on QT forums, I didn't find the answer to this, was playing with all functions available with QSerialPort class and readAll() seems to work.
About readAll(), Qt documentation says:
Reads all remaining data from the device, and returns it as a byte
array.
My explanation for the resolution is that readAll captures all of the data from the communication buffer and empties it.
This should be the job of clear() function but apparently readAll() seems to work.
In my application, done with Qt5, I would like to set a security system when I download data from internet. First of all, I want to check how many bytes I am downloading and abort if it is the case. I want to set a maximum limit of downloaded bytes, and abort if it is exceeded.
I am using QNetworkReply class.
First of all I checked the size() function, but at that point, I already received all the data (the request is completed), so that is not enough.
Second check, I looked into the signal downloadProgress(qint64 bytesReceived, qint64 bytesTotal). I though, I could check that and abort if bytesReceived are too big. But I am not sure for two motivations: first, as written in the documentation
Note that the values of both bytesReceived and bytesTotal may be different from size(), the total number of bytes obtained through read() or readAll(), or the value of the header(ContentLengthHeader). The reason for that is that there may be protocol overhead or the data may be compressed during the download.
Second, I don't know when I will receive this signal....maybe it will be too late...
Finally, I checked setReadBufferSize(qint64 size). It seems a good solution, but I am not sure about the following two lines in the documentation:
first,
QNetworkReply will try to stop reading from the network once this buffer is full (i.e., bytesAvailable() returns size or more)
What does it mean try? should I rely on that?
second,
Unlike QAbstractSocket::setReadBufferSize(), QNetworkReply cannot guarantee precision in the read buffer size. That is, bytesAvailable() can return more than size.
so, it seems I can not rely on a precise limit to be set.
Someone can suggest me the best way to implement it?
The best solution I found is to use the readyRead signal (QNetworkReply derives from QIODevice), and then implement the security check by myself in a slot:
void onReadyRead()
{
for (;;)
{
QByteArray currentDataRead = httpReply->read(100); // Just read some bytes
if ( currentDataRead.isEmpty() )
return;
myResponseBody.append(currentDataRead);
if (myResponseBody.size() > myMaxResponseSize) // check my limit
{
qDebug() << "Error: response size bigger than expected - aborting";
httpReply->abort();
}
}
}
Note: the inifite for(;;) loop and the check if ( currentDataRead.isEmpty() ) return; are needed in order to not leave some bytes out at the end, because we are inside onReadyRead that is a slot connected to readyRead and from the documentation:
readyRead() is not emitted recursively; if you reenter the event loop or call waitForReadyRead() inside a slot connected to the readyRead() signal, the signal will not be reemitted (although waitForReadyRead() may still return true).
--------------------
PS: I am still open to better solutions, possibly native in Qt
I want to implement a timeout mechanism such that if the arduino doesn't read the command within one second, it results in a timeout and the new command is discarded and the program runs fine.
But right now, the program hangs if any new command is sent during the execution of the old one.
This is the timeout section of my code:
QByteArray requestData = myRequest.toLocal8Bit();
serial.write(requestData);
if (serial.waitForBytesWritten(waitTime)) {
if (serial.waitForReadyRead(myWaitTimeout)) {
QByteArray responseData = serial.readAll();
while (serial.waitForReadyRead(10))
responseData += serial.readAll();
QString response(responseData);
emit this->response(response);
} else {
emit timeout(tr("Wait Read Request Timed Out %1")
.arg(QTime::currentTime().toString()));
}
} else {
emit timeout(tr("Wait Write Request Timed Out %1")
.arg(QTime::currentTime().toString()));
}
The timeout signal is connected to a slot that just prints the timeout message and does nothing.
How can I fix this so that I can achieve what I target?
You are using blocking approach to transmit data via serial port. Unless you are using threads I don't see possibility to send any additional data during execution of previous loop.
BTW: Your program, for example, will block indefinitely if Arduino manages to keep sending something within 10ms periods.
Add couple of QDebug() << "I'm here"; lines to check where your code gets stuck; it is possible that you are blocking somewhere outside code you pasted here. Alternative is to use debugger.
What if previous 'command' you tried to send is still in the buffer ? You'll end up filling output buffer. Check with QDebug how many bytes are in output buffer before writing more data to it. Buffer should be empty. (qint64 QIODevice::bytesToWrite() const).
How should QLocalSocket/QDataStream be read?
I have a program that communicates with another via named pipes using QLocalSocket and QDataStream. The recieveMessage() slot below is connected to the QLocalSocket's readyRead() signal.
void MySceneClient::receiveMessage()
{
qint32 msglength;
(*m_stream) >> msglength;
char* msgdata = new char[msglength];
int read = 0;
while (read < msglength) {
read += m_stream->readRawData(&msgdata[read], msglength - read);
}
...
}
I find that the application sometimes hangs on readRawData(). That is, it succesfully reads the 4 byte header, but then never returns from readRawData().
If I add...
if (m_socket->bytesAvailable() < 5)
return;
...to the start of this function, the application works fine (with the short test message).
I am guessing then (the documentation is very sparse) that there is some sort of deadlock occurring, and that I must use the bytesAvailable() signal to gradually build up the buffer rather than blocking.
Why is this? And what is the correct approach to reading from QLocalSocket?
Your loop blocks the event loop, so you will never get data if all did not arrive pn first read, is what causes your problem I think.
Correct approach is to use signals and slots, readyRead-signal here, and just read the available data in your slot, and if there's not enough, buffer it and return, and read more when you get the next signal.
Be careful with this alternative approach: If you are absolutely sure all the data you expect is going to arrive promptly (perhaps not unreasonable with a local socket where you control both client and server), or if the whole thing is in a thread which doesn nothing else, then it may be ok to use waitForReadyRead method. But the event loop will remain blocked until data arrives, freezing GUI for example (if in GUI thread), and generally troublesome.
I am trying to write really big files to serialport using QSerialPort (QT 5.3.1). The problem is - I keep sending more than device can handle.
Programm works like this (this function is called once in 50ms):
void MainWindow::sendNext()
{
if(sending && !paused && port.isWritable())
{
if(currentLine >= gcode.size()) //check if we are at the end of array
{
sending = false;
currentLine = 0;
ui->sendBtn->setText("Send");
ui->pauseBtn->setDisabled("true");
return;
}
if(sendLine(gcode.at(currentLine))) currentLine++; //check if this was written to a serial port
ui->filelines->setText(QString::number(gcode.size()) + QString("/") + QString::number(currentLine) + QString(" Lines"));
ui->progressBar->setValue(((float)currentLine/gcode.size()) * 100);
}
}
But it eventually gets flawed and hangs (on the device, not on the PC). If only I could check somehow if the device is ready or not for next line, but I cant find anything like it in the QSerial docs.
Any ideas?
You can use QSerialPort::waitForBytesWritten to ensure that the bytes are written. However this function would block the thread and it's recommended to use it in a new thread, otherwise your main thread would be blocked and your application freezes periodically.
The RS232 does have some flow control capabilities.
Check if Your device uses RTS/CTS and if so change the connection properties to use hardware flow control.
The QSerialPort also allows for checking the flow control lines manually with dataTerminalReady or requestToSend