hello.
I want to write a program that will open the port and read data (in continuous mode, loop).

According to the algorithm:

Start ->
1.Try open port
a) if opened then read data
b) if not opened it wait 30 seconds and try to raise open port (jump to 1)

Qt Code: 
  1. #include "mainwindow.h"
  2. #include "ui_mainwindow.h"
  3.  
  4.  
  5. MainWindow::MainWindow(QWidget *parent) :
  6.     QMainWindow(parent),
  7.     ui(new Ui::MainWindow)
  8. {
  9.     ui->setupUi(this);
  10.     port = new QextSerialPort("/dev/ttyUSB0");
  11.     port->setBaudRate(BAUD9600);
  12.     port->setFlowControl(FLOW_OFF);
  13.     port->setParity(PAR_NONE);
  14.     port->setDataBits(DATA_8);
  15.     port->setStopBits(STOP_1);
  16.  
  17.     port->setTimeout(500);
  18.     reading();
  19.  
  20. }
  21.  
  22. MainWindow::~MainWindow()
  23. {
  24.     delete ui;
  25. }
  26.  
  27.  
  28.  
  29. void MainWindow::reading()
  30. {
  31.  
  32.  
  33.     qDebug() << port->open(QIODevice::ReadWrite);
  34.  
  35.     if (port->isOpen()==false)
  36.     {
  37.         port->flush();
  38.  
  39.         port->startTimer(30000);
  40.         qDebug() << "its it reading";
  41.         //port->waitForReadyRead(1000);
  42.         reading();
  43.     }
  44.     else
  45.     {
  46.         connect(port, SIGNAL(readyRead()), this, SLOT(onDataAvailable()));
  47.     }
  48. }
  49.  
  50. void MainWindow::onDataAvailable()
  51. {
  52.  
  53.     if (port->isOpen())
  54.     {
  55.     QByteArray mdata = port->readAll();
  56.     qDebug() << "\n";
  57.  
  58.     qDebug() << mdata.toHex(); // hex data
  59.     qDebug() << mdata;  //  ascii data
  60.  
  61.  
  62.  
  63.     ui->lineEdit->clear();
  64.     ui->lineEdit->setText(mdata);
  65.     }
  66.     else
  67.     {
  68.  
  69.         reading();
  70.         qDebug() << "error 2 port is not open";
  71.     }
  72.    // port->close();
  73. }
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