QtSerialPort problem (C++) (QML)

MonoFox

Hello,
I'am trying to read frames from USB CAN UCCB Converter which sends data in hex to the COM port. I have created a counter and a primitive code, which is supposed to read data from the COM port. I have a problem with this, I can send data to the port but when downloading data I have simply '0'
https://scr.hu/L22RyAZ

Main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlComponent>
#include <QTextStream>
#include <QDebug>

#include <QSerialPort>
#include <QSerialPortInfo>

#include <QDataStream>
#include <QQmlProperty>
#include <QTextStream>

#include <iostream>
namespace  {
 QSerialPort serialPort;

}


 void Read_Data();
int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

        QGuiApplication app(argc, argv);

        // Load gauge UI.
        QQmlEngine engine;
        QQmlComponent component(&engine, "qrc:/main.qml");
        QObject *object = component.create();

      object->setProperty("fuel_frame", 31);
       object->setProperty("kph_frame", "150");
        object->setProperty("rpm_frame", "3000");

          object->setProperty("rpm_arc", 300);
            object->setProperty("kph_arc", 150);



        serialPort.setPortName("COM2");
        serialPort.setBaudRate(QSerialPort::Baud9600);
        serialPort.setDataBits(QSerialPort::Data8);
                 serialPort.setParity(QSerialPort::NoParity);
                 serialPort.setStopBits(QSerialPort::OneStop);
                 serialPort.setFlowControl(QSerialPort::NoFlowControl);
         serialPort.open(QIODevice::ReadWrite);
        if(serialPort.isOpen())
                 {

                     qDebug() << "Port is open: " << serialPort.portName();
                     // Connect framesRecieved signal to slot function for reading frames.

                    Read_Data();

                 }
                 else
                 {
                     qDebug() << "Port is closed";
                 }

    return app.exec();
}

void Read_Data()
{

    long receive_num = 0;
    bool flag_showInHex = true;
    QByteArray buf;
    buf = serialPort.readAll();
    receive_num += buf.count();
    qDebug() << "R:" + QString::number(receive_num);
    if(!buf.isEmpty())
    {
        if(flag_showInHex == true){
            qDebug() << "buf.count: " << buf.count();
            int i = 0;
            QString str_buf;
            for(i = 0; i < buf.count(); i++){
                QString s;
                s.sprintf("%02X ", (unsigned char)buf.at(i));
                str_buf += s;
            }
            qDebug() << str_buf;



        }else{

        }

    }
    buf.clear();
}

SGaist

Hi,

Are you really connecting Read_Data or just calling it as in the code you provided ? If the later, then that's normal, a serial port is not a text file that you open and read. Data must have flown to it before you can read something.

MonoFox

@SGaist
Thanks for answer.
I just calling Read_Data when SerialPort is open.
To testing i've create com bridge COM2<>COM3 : https://scr.hu/L22Rl8y

if(serialPort.isOpen())
{

            qDebug() << "Port is open: " << serialPort.portName();
            
            if(serialPort.bytesAvailable()){
    
               Read_Data();
               
            }else{
                qDebug() << "Null";
            }

            
             }
             else
             {
                 qDebug() << "Port is closed";
             }

SGaist

As written before, it's not how serial ports are working.

You should take advantage of Qt's asynchronous capabilities like shown in the Terminal example.