Reading continuous data from Serial Port using QT C++

Question

I am new for QT C++ and am trying to write a program, which could continuous read data from Serial Port. My Program works sometimes smoothly but sometimes it read the wrong data. I have run debug and here is what I got:

"61\x00\x00"
"61\x00\x00"
"61\x00\x00"
"62\x00\x00"
"62\x00\x00"
"62\x00\x00"
"62\x00\x00"
"63\x00\x00"
"63\x00\x00"
"5"
"3\x00\x00"
"5"
"2\x00\x00"
"5"
"2\x00\x00"

"54\x00\x00"
"54\x00\x00"
"54\x00\x00"
"55\x00\x00"
"54\x00\x00"
"54\x00\x00"
"55\x00\x00"
"55\x00\x00"
"5"
"1\x00\x00"
"51"
"\x00\x00"
"5"
"2\x00\x00"
"5"
"1\x00\x00"
"5"
"1\x00\x00"

Someway QTSerialPort didn't read all data. And here is my code, where data should be read and display.

   if(serial->isOpen() && serial->isReadable()){
       QByteArray receivedData;
       receivedData = serial->readAll();
       qDebug()<<receivedData;
       ui->lcdDistance->display(receivedData.toInt());
    }else{
       QMessageBox::critical(this, tr("Error"), tr("Doesn't receive data"));
    }

I think the problem came from QT, not the microcontroller because I also run debug with my microcontroller and it worked very well.

Here is the code in my uC STM32

    while (1) {
    HAL_UART_Receive(&huart2, rxData, 1, 1000);

    if (rxData[0] == '1') { //RUN
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, SET);

        lcd_clear();
        lcd_put_cur(0, 0);
        lcd_send_string("LOADING...");

        HAL_Delay(1000);

        lcd_clear();

        int i = 40;

        //HAL_Delay(1000);

        while (i < 100) {
            htim2.Instance->CCR1 = i;
            sensor_time = hcsr04_read();
            distance = sensor_time * .034 / 2;

            sprintf(str_distance,"%lu", distance);

            lcd_clear();
            lcd_put_cur(1, 0);
            lcd_send_string(str_distance);

            sendDistanceStatus = HAL_UART_Transmit(&huart2, str_distance, sizeof(str_distance),
                    100);
            if (sendDistanceStatus == HAL_OK) {
                i++;
                HAL_Delay(300);
            }
        }

        HAL_Delay(1000);
    } else { //STOP
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, RESET);
        lcd_clear();
        lcd_put_cur(0, 0);
        lcd_send_string("STOP...");
    }

}

Please help me to solve this problem. Thanks in advance.

Answer 1

The problem is the synchronization of the information since it cannot be detected when the information starts and ends. A simple solution is to use a character like the endline( \n ):

sprintf(str_distance,"%lu\n", distance);

if(serial->isOpen() && serial->isReadable()){
    while(serial->canReadLine()){
        QByteArray ba = serial->readLine();
        ba = ba.replace('\0', QByteArray());
        qDebug() << ba;
        ui->lcdDistance->display(ba.toInt());
    }
}