Use Qt to create your own serial port debugging assistant

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In my work, the thing I deal with most is probably serial port communication. Serial port is undoubtedly the simplest way to communicate data with the microcontroller. Today we use Qt to implement our own serial port debugging assistant.

Achieving goals

Write a Qt-based serial port debugging software by yourself to realize the communication between this software and the serial port assistant.

The data sent by the software is forwarded through the virtual serial port and can be correctly received in the serial port assistant;

The data sent by the serial port assistant can be displayed in the receiving text box of this software, thereby realizing two-way communication of serial port data.

Required tools and environment

• Virtual serial port software (used to create a pair of virtual serial ports)
• Qt Creator 4.10.1
• Qt 5.13.1
• XCOM V2.0 Serial Port Assistant
• My computer is Windows 10 64bit [version 10.0.19041.329]

Source code of this article

Reply to the keyword "Qt-COM" in the background to obtain the virtual serial port software and Qt project source code involved in this article.

Interface Design

Create a new Project using Qt Creator, select Application-->Qt Widgets Application as the template, and in the Class Information page of the wizard, select QMainWindow, QWidget, or QDialog as the Base class.

The project is created, and the specific design of the .ui file is as follows:

Specific implementation

Import serial communication module

Starting from Qt 5.1, Qt has its own serial communication class. Previous versions required the use of third-party serial communication classes.

To use the serial communication class, you need to add QT += serialport in the .pro file

Display all serial port numbers in the system

The serial port number list is displayed in a QComboBox control.

We call QSerialPortInfo::availablePorts() to get a QList. Each QSerialPortInfo in the List represents a serial port instance. This class stores information such as the port name, system location, description, and vendor of the existing serial ports in the system.

The implementation code for traversing all serial port names in the system is as follows:

 QStringList MainWindow::getPortNameList()
 {
    QStringList m_serialPortName;
    foreach(const QSerialPortInfo &info,QSerialPortInfo::availablePorts())
 {
        m_serialPortName << info.portName();
        qDebug()<< "serialPortName:" <<info.portName();
 }
 return m_serialPortName;
 }

Traverse the QList above and save the serial port name to the m_serialPortName variable, which is of QStringList type. Display the final result in the QComboBox:

 m_portNameList = getPortNameList(); 
     
 ui->comboBoxPortName->addItems(m_portNameList);

Open the serial port

Opening the serial port involves the following functions:

 // Check if the serial port is open
 bool QIODevice::isOpen() const
 // Clear the buffer
 bool QSerialPort::clear(QSerialPort::Directions directions = AllDirections)
 //Serial port closed
 [override virtual] void QSerialPort:: close ()
 //Set the serial port name to be opened
 void QSerialPort::setPortName(const QString & name )
 //Set the baud rate of serial communication
 bool QSerialPort::setBaudRate(qint32 baudRate, QSerialPort::Directions directions = AllDirections)
 //Set the data bit of serial communication, the data bit is usually 8 bits
 bool QSerialPort::setDataBits(QSerialPort::DataBits dataBits)
 //Set the flow control of serial communication, generally no flow control is required
 bool QSerialPort::setFlowControl(QSerialPort::FlowControl flowControl)
 //Set the parity check of serial communication, usually select "None"
 bool QSerialPort::setParity(QSerialPort::Parity parity)
 //Set the stop bit of serial communication, the stop bit is usually 1
 bool QSerialPort::setStopBits(QSerialPort::StopBits stopBits)

In the pop-up menu of right-clicking on the "Open Serial Port" button, select Go to Slot..., and in the clicked() event of the button, add the corresponding code for opening the serial port.

The communication process of the serial communication library basically requires the following steps, namely: open the serial port --> configure the serial port parameters (baud rate, data bits, stop bits, parity, flow control, etc.) --> send and receive data.

The specific implementation of serial port opening is as follows:

 void MainWindow::on_btnOpenCOM_clicked()
 {
 if (ui->btnOpenCOM->text()== "Open the serial port" )
 {
        if(m_serialPort->isOpen())
 {
            m_serialPort->clear();
            m_serialPort-> close ();
 } 
 
        m_serialPort->setPortName(m_portNameList[ui->comboBoxPortName->currentIndex()]); 
 
        if(!m_serialPort-> open (QIODevice::ReadWrite))
 {
 qDebug()<<m_portNameList[ui->comboBoxPortName->currentIndex()]<< "Open failed!" ;
 return ;
 } 
 
 //Open successfully
 m_serialPort->setBaudRate(ui->comboBoxBaudRate->currentText().toInt(),QSerialPort::AllDirections); //Set baud rate and read and write direction
 m_serialPort->setDataBits(QSerialPort::Data8); //The data bit is 8 bits
 m_serialPort->setFlowControl(QSerialPort::NoFlowControl); //No flow control
 m_serialPort->setParity(QSerialPort::NoParity); //No parity bit
 m_serialPort->setStopBits(QSerialPort::OneStop); //One stop bit 
 
 connect (m_serialPort,SIGNAL(readyRead()),this,SLOT(receiveInfo())); 
 
 ui->btnOpenCOM->setText( "Close serial port" );
 } else  
 {
        m_serialPort-> close ();
 ui->btnOpenCOM->setText( "Open serial port" );
 }
 }

Serial port sends data

The function of sending data through the serial port is:

 qint64 QIODevice::write(const char *data)

This function writes the data in the string ending with '\0' to the device (the data after '\0' is lost). It returns the number of bytes actually written, or -1 if an error occurs.

We determine whether the sent string is converted to hexadecimal based on whether the Hex send checkbox is checked in the interface, and then call the qint64 QIODevice::write(const char *data) function to send the QByteArray array to the device.

The specific implementation of the event after the send button is clicked is as follows:

 void MainWindow::on_btnSendData_clicked()
 {
    QString m_strSendData = ui->txtSend->text(); 
 
    if(ui->checkBoxHexSend->isChecked())
 {
        if (m_strSendData. contains ( " " ))
 {
 m_strSendData.replace ( QString ( " " ),QString( "" )); //Remove spaces
 } 
 
 QByteArray sendBuf; 
 
 convertStringToHex(m_strSendData, sendBuf); //Convert QString to hex 
 
        m_serialPort->write(sendBuf);
 }
 else  
 {
        m_serialPort->write(m_strSendData.toLocal8Bit());
 }
 }

Serial port receiving data

When serial port data is received in the buffer, the readyRead() signal will be emitted. We define a slot void receiveInfo() to parse the received data.

 connect (m_serialPort,SIGNAL(readyRead()),this,SLOT(receiveInfo()));

The following is the complete implementation of the receiving function. If you want to parse the data sent by the lower computer, implement the parsing of the data packet in this function.

 void MainWindow::receiveInfo()
 {
    qDebug()<< "receiveInfo()" ;
    QByteArray info = m_serialPort->readAll(); 
 
    QString strReceiveData = "" ;
    if(ui->checkBoxHexReceive->isChecked())
 {
        QByteArray hexData = info.toHex();
        strReceiveData = hexData.toUpper(); 
 
 qDebug()<< "Received serial port data: " <<strReceiveData; 
 
 for ( int i=0; i<strReceiveData. size (); i+=2+1)
            strReceiveData. insert (i, QLatin1String( " " ));
        strReceiveData.remove(0, 1); 
 
 qDebug()<< "Processed serial port data: " <<strReceiveData; 
 
        ui->txtReceiveData->append(strReceiveData);
 }
 else  
 {
        strReceiveData = info; 
 
 //Avoid Chinese garbled characters
        QTextCodec *tc = QTextCodec::codecForName( "GBK" );
        QString tmpQStr = tc->toUnicode(info); 
 
        ui->txtReceiveData->append(tmpQStr);
 } 
 
    //ui->txtReceiveData->append( "\r\n" );
 }

For detailed source code, please refer to the Qt project file.

Create a virtual serial port

To test whether our serial port assistant is correct, you can use a USB to TTL module, then short-circuit its sending and receiving pins, send and receive automatically, and see if the sent content can be received correctly.

Or use VSPD.exe software to create several pairs of virtual serial ports. The data sent from one serial port can be received by another serial port, and vice versa.

Results

Qt Tips

View online help documentation

Right-click a Qt built-in class, and then select Context-sensitive Help F1 in the right-click menu. The help document for this class will pop up on the right side of Qt Creator.

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