Serial Port configuration in RHEL

Nimika

How to configure serial port in Qt 5.7.0 version?
First of all I have installed Qt5.2.0 which was also not working so I downloaded the latest version thinking it might work but I am getting the same problem.
I am writing the same code which is there on web too but still not getting any solution. My code again and again showing Device not open while I am setting the port inside it.
Kindly help me out.
Is there anything to write inside version control or in kit option?

mrjj

Hi
As far as I know - you just use the class. ( in Qt5.7)
Please try the terminal sample and see if it will open port
http://doc.qt.io/qt-5/qtserialport-terminal-example.html
Its available to just open and run in creator.

Do you have a real comport on the machine or are you using SERIAL over USB plug?

Nimika

@mrjj Hey!
I am using a card having many RS 422 of my own to use COM ports. But I can't even open the system ports.
Is something there to configure system inside qt or while installing it?
Is there anything to write in git ? version control?

mrjj

@Nimika
Hi.
ok. With 5.7 it should just work if you have
QT += serialport in .pro file.

-Is there anything to write inside version control or in kit option?
No. Its just a c++ class.

Did you try the terminal sample?

Nimika

@mrjj
Hello
Thanks for reply.
I have added it in my pro file but still can't open it.

mrjj

@Nimika said in Serial Port configuration in RHEL:

still can't open it.

Well did u try the Terminal sample and try it there?
Can it list and see your ports?

Nimika

@mrjj yeah its working but not showing any serial port which I have installed using my card.
This is my program and its output----

#include <stdio.h>
#include <QObject>
#include <QtSerialPort/QSerialPort>
#include <QSerialPortInfo>
#include <string.h>
#include <QTextStream>
#include <QCoreApplication>
#include <QStringList>
#include <iostream>
#include <QDebug>

using namespace std;





QT_USE_NAMESPACE
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // Example use QSerialPortInfo
   foreach (const QSerialPortInfo &info, QSerialPortInfo::availablePorts()) {
        qDebug() << "Name : " << info.portName();
        qDebug() << "Description : " << info.description();
        qDebug() << "Manufacturer: " << info.manufacturer();

        // Example use QSerialPort
        QSerialPort serial;
        serial.setPortName("ttyM0");
        qDebug() << "Name:" << serial.portName();
       //serial.setPort(info);
       QIODevice::OpenMode mode = QIODevice::ReadOnly | QIODevice::Unbuffered;
       if(serial.open(mode))
           qDebug() << "port connected";
       if (serial.isOpen() && serial.isWritable())
       {
       qDebug() << "Serial is open";
       serial.close();
    }

    return a.exec();
}
}

output is:
Name : "ttyS0"
Description : ""
Manufacturer: ""
Name: "ttyM0"

``

SGaist

Hi and welcome to devnet,

Does your user have the rights to access that device ?

Call ls -la /dev/ttyS0 to see who can access it.

Your user is likely not in the group that can access the serial port. If that's indeed the case, add your user to that group and logout/login. You should then be able to access the device.

Nimika

how will I get to know wo is accessing that device?
how can I add the user to the group which you have specified.

jsulm

@Nimika The user using your application needs access right for /dev/ttyS0.
If you execute the command @SGaist provided you you will see who has access. Check which group is set for that device. Then add yourself to this group (see /etc/group file).

Nimika

@jsulm Hey thanks!
I am getting this after writing the calling function ls -la /dev/ttyS0:
crw-rw----. 1 root dialout 4, 64 Oct 7 10:35 /dev/ttyS0

What does it mean?

jsulm

@Nimika That means that user root and group dialout have read/write access, nobody else have any access.
So you either start your app as root, or (much better) add the user you're using (hopefully not root) to the group dialout.

SGaist

NEVER EVER use root like that. All the more when developing. It's bad practice and doing so you're opening a gaping security hole.

Add your normal user to the dialout group and be done with it.

Nimika

Thankyou both of you.
Please tell me how to add my normal user to the dialout group?
What is dialout group?

kuzulis

QIODevice::OpenMode mode = QIODevice::ReadOnly | QIODevice::Unbuffered;

Did you read documentation? QIODevice::Unbuffered it is unsupported mode.

Nimika

@kuzulis Yeah I made it as comment.

mrjj

@Nimika

Please tell me how to add my normal user to the dialout group?
sudo usermod -a -G dialout theuser
What is dialout group?
Its a predefined group found in many distros.
From old times it was used to allowed modems
to make connection etc. ( ie allow the user to connect to the internet :)

So often the system has this group and any user in it, have access to /dev/ttySX

jsulm

@Nimika You really should learn how user/groups and access rights management is working on UNIX/Linux.

Nimika

@jsulm Actually my system is Red Hat Enterprise Linux based so it is different to use its commands.

Nimika

@mrjj Thank you !! let me add it now and search whether it will work or not.....