QSerialPort cannot read Asynchronously

[Afif Zaki]

Hi,
I just tried a simple qt console program (in Qt 5.9.5) which is only reading data from virtual serial port with command socat -d -d pty,raw,echo=0 pty,raw,echo=0 in my bash terminal. So the input portName is "/dev/pts/1" (for writing data) and output is "/dev/pts/2" (for reading data).

The program is totally same with QSerialPort Example: Command Line Reader Async Example. However, I changed several codes for the input so that I can manually configure the port inside the program.

This is a the constructor of serialportreader class:

#include "serialportreader.h"
SerialPortReader::SerialPortReader(QSerialPort *serialPort, QObject *parent) :
    QObject(parent),
    m_serialPort(serialPort),
    qtout(stdout)
{
    qtout << m_serialPort->isOpen() << endl;
    connect(m_serialPort, &QSerialPort::readyRead, this, &SerialPortReader::ReadHandler);
    connect(m_serialPort, &QSerialPort::errorOccurred, this, &SerialPortReader::ErrorHandler);
    connect(&timer, &QTimer::timeout, this, &SerialPortReader::TimeOutHandler);
    timer.start(5000);
}

That program cannot reading / receiving the data I sent even serial.isOpen() && serial.isReadable is always true. And i found the problem is at line connect(m_serialPort, &QSerialPort::readyRead, this, &SerialPortReader::ReadHandler); which signal readyRead cannot emitted while data is already sent to reader. The reason I used that is I want to reading data from serial port asyncronously which is more comfortable for receiving data from many serial port simultaneously.

Here my writer program:

#include <QCoreApplication>
#include <QTextStream>
#include <QtSerialPort/QSerialPort>
#include <QByteArray>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QTextStream qtin(stdin);
    QTextStream qtout(stdout);

    QSerialPort *serialPort;
    serialPort = new QSerialPort("/dev/pts/1");

    serialPort->setBaudRate(QSerialPort::Baud9600);
    serialPort->setFlowControl(QSerialPort::NoFlowControl);
    serialPort->setParity(QSerialPort::NoParity);
    serialPort->setDataBits(QSerialPort::Data8);
    serialPort->setStopBits(QSerialPort::OneStop);

    serialPort->open(QIODevice::WriteOnly);

    if (serialPort->isOpen() && serialPort->isWritable())
        qtout << "Port is Available" << endl;
    else
        qtout << "Port is Not Available" << endl;

    // Write Data //
    qtout << "Writting Message..." << endl;
    serialPort->write("asd");
    //serialPort->flush();
    serialPort->waitForBytesWritten(10000);
    qtout << "Finished" << endl;

    serialPort->close();
    a.exit(1);
    //return a.exec();
}

What should I do? or Do you have any advice for my problem? (sorry for my bad English)

[aha_1980]

@Afif-Zaki

The program is totally same with QSerialPort Example: Command Line Reader Async Example, but only I changed the input so that I can configure the port inside the program.

does that mean, the Command Line Reader Example does also not work?

I'm not sure these kind of virtual ports are supported, @kuzulis can say more to this topic

[kuzulis]

Just use tty0tty as a kernel module, instead of socat.

PS: I'm don't care about pseudo terminals, as it is not a serial ports.

[Afif Zaki]

Hi @kuzulis,
I just tried using tty0tty with /dev/tnt0 as input and /dev/tnt1 as output. Still, the reader program cannot read/receive data.

So, the readyRead signal won't able to emitted if data sent from the virtual port?

[kuzulis]

@Afif-Zaki said in QSerialPort cannot read Asynchronously:

So, the readyRead signal won't able to emitted if data sent from the virtual port?

No, this means, that you something doing wrong.

[Afif Zaki]

Hi @kuzulis,
Thank you very much for suggesting me using tty0tty instead of socat.
My program won't read serial data because I accidentally close port after I declare the SerialRead class.