QtSerialPort terminal example fails for me; how can the sample not work?

dabbler

I am using Qt 5.2 and when my app (which worked using QextSerialPort in v4.8.4) failed to communicate, I tried the example in ...\5.2.0\Src\qtserialport\examples\serialport\terminal. And that fails too.

I have a simple USB dongle that emulates a COM port. If I use RealTerm, I can send AT commands to it and get back OK just fine.

But the terminal example that comes with Qt does not communicate with it. I looked at an API snooper, and I am getting an unsuccessful return with error of "997:Overlapped I/O operation is in progress" for WaitCommEvent and WriteFile.

I am running it on Windows 7, and I copied the exe and DLLs over to a Windows 8 machine, and it failed there as well (though I admittedly didn't do the API snooping there).

Anyone have any ideas what to try? How can the unmodified example app just plain fail? I am befuddled.

kuzulis

What is model of your USB dongle? What is not work: data writting or data reading? Maybe it driver does not support overlapped mode, and I/O never completed.

Upd: you can try use the Free Serial Port Monitor to check a data transactions.

PleaseWait

Could you please provide some code? And your .pro file contents.

PleaseWait

I quickly checked out a small program I was working on a while ago. Its very basic. It pretty much assumes I only have one active serial port.

untitled.pro file
@
#-------------------------------------------------

Project created by QtCreator 2013-11-29T13:22:20

#-------------------------------------------------

QT += core serialport
QT -= gui

TARGET = untitled
CONFIG += console
CONFIG -= app_bundle

TEMPLATE = app

SOURCES += main.cpp
serialcomms.cpp

HEADERS +=
serialcomms.h
@

main.cpp
@
#include <QCoreApplication>
#include "serialcomms.h"

using namespace std;

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

serialComms comms;

return a.exec&#40;&#41;;

}
@

serialcomms.h
@
#ifndef SERIALCOMMS_H
#define SERIALCOMMS_H

#include <QObject>
#include <QtSerialPort/QSerialPort>
#include <QtSerialPort/QSerialPortInfo>

class serialComms : public QObject
{
Q_OBJECT
public:
explicit serialComms(QObject *parent = 0);
QSerialPort *serial;

signals:

public slots:
void readData();

};

#endif // SERIALCOMMS_H
@

serialcomms.cpp
@
#include "serialcomms.h"
#include <QDebug>

serialComms::serialComms(QObject *parent) :
QObject(parent)
{
serial = new QSerialPort(this);

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

serial->setPort(info);
serial->setBaudRate(QSerialPort::Baud19200);
serial->setDataBits(QSerialPort::Data8);
serial->setFlowControl(QSerialPort::NoFlowControl);
serial->setParity(QSerialPort::NoParity);
serial->setStopBits(QSerialPort::OneStop);
}

serial->open(QIODevice::ReadWrite);
serial->flush();
connect(serial, SIGNAL(readyRead()), this, SLOT(readData()));

}

void serialComms::readData() {
qDebug() << serial->readAll();
serial->flush();
}
@

I used this to get debugging output from an embedded linux module. So it basically just reads from the COM port. I built it using Qt5.1.1 in Windows 7.

Hope it helps!

PleaseWait

btw, check lines 10 to 12. If the application builds and runs, those lines should output the available serial devices you have connected.

kuzulis

2 PleaseWait,

please do not provide your code because your code is wrong.

The author used the Bluetooth dongle & Terminal example so it is enough for the start point..

2 dabbler,

please try the "casyncwriter" example (from the git) to check triggering of the bytesWritten() signal after writing data. It is important...

dabbler

I SOLVED the problem. So I'll mention it here in case it helps anyone. The bottom line is that I was trying to read data from the port synchronously... like this:
@
testPort.write( "AT\r", 3 );
Sleep( 200L );
QByteArray rsp = testPort.readAll();
@

But I learned that in order to receive data from the serial port, I need to mix in a call to processEvents()
or else the data won't arrive for me.
@
testPort.write( "AT\r", 3 );
Sleep( 200L );
QCoreApplication::processEvents( QEventLoop::AllEvents );
QByteArray rsp = testPort.readAll();
@
I suspect there are some signal/slot stuff that is required, even when I don't want to use signals/slots to receive the data.

In my case, my app normally uses signal/slots for the serial data. But to find the proper port, I found the code much more readable if I just sent an "AT\r" and looked for a response of "OK\r". But I found that after sending "AT\r" I needed to do a processEvents() call, and then I could do a readAll() to look for the "OK\r".

Now my app works fine.

I never went back to see why I had problems with the terminal sample code. Seems like that should have worked; but I guess I was having some different problem with that. Likely it was a problem between my chair and keyboard.

kuzulis

For your concrete problem is enough (something like it):

[code]
testPort.write( "AT\r", 3 );
if (!testPort.waitForBytesWritten(200L))
return;
QByteArray rsp;
while (testPort.waitForReadyRead(20L)) {
rsp += testPort.readAll();
if (rsp.size() == expectedSize)
break;
}

if (rsp.size() != expectedSize)
    return;

// parse rsp ...
...

[/code]