QSerialPort readLine () is extremely slow compared to readAll ()

Question

The data that I read from the serial port (in Qt, using QtSerialPort / QSerialPort) is separated by the newline characters '\ n' and return '\ r', which I am going to look at it for analysis, the line length can be very strong, but very Easily extract data from each row format.

//signal/slot connection on readyRead() is as follows: connect(serial, SIGNAL(readyRead()), this, SLOT(readData())); 

where readData () is defined as:

 void MainWindow::readData() { //As mentioned below, which I will reiterate, I have already tried the addition of // canReadLine(): if (serial->canReadLine()){ QByteArray data = serial->readLine(); //QByteArray allData = serial->readAll(); parseSerialBytes(data); //console->putData(data); //console->putData(alldata); } } 

However, the QIODevice::readLine() function is extremely slow and explicitly blocks receiving data at full frequency compared to QIODevice :: readAll ()

Can someone explain how to use the readLine() function correctly, so I don't have to go through readAll() in QByteArray to parse each line? I used the Qt Widgets “Terminal” example to create this asynchronous serialport read function.

Thanks in advance - this seems to be a common problem that I have not seen here yet.

Answer 1

This is a common mistake. readData is called only once per piece of data , not necessarily once per line .

You need to continue reading rows until data is available. This is also a poor design for reading lines in a widget class. Move it to a separate object.

 class Receiver : public QObject { Q_OBJECT QSerialPort m_port; QByteArray m_buffer; void processLine(const QByteArray & line) { ... } Q_SLOT void readData() { // IMPORTANT: That a *while*, not an *if*! while (m_port.canReadLine()) processLine(m_port.readLine()); } public: Receiver(QObject * receiver = 0) : QObject(parent) { connect(&m_port, &QIODevice::readyRead, this, &Receiver::readData); ... } } 

Your mistake was to implement readData as shown below. Such code reads only one line, regardless of how many lines are available for reading. It will seem “slow” because with each call, more and more data is accumulated that remains unread. In the end, he will run out of heaps.

 void readData() { // WRONG! if (m_port.canReadLine()) processLine(m_port.readLine()); }