How implement serial delay

bask185

I have a send function and now I need a delay of 2 ms after I send a byte. If I send quicker than these 2 ms the receiving end will miss the data.

void MainWindow::send(QString c)
{
    serial->write(c.toLatin1());
    QString cAsHex = QString("%1").arg(c, 0, 16);
    qDebug()  << cAsHex << " >>";
}

I was wondering what the most efficient way would be to do this. I don't know whether I can use some fancy serial function of which I don't know about yet or if I should pause the entire application using a QThread delay.

It is not big deal if the program freezes temporarily.

jsulm

@bask185 Just use QTimer

mrjj

And what ever you do, please dont use QThread delay. :)

bask185

@jsulm said in How implement serial delay:

@bask185 Just use QTimer

Thank you. I will try it out ;)

@mrjj said in How implement serial delay:

And what ever you do, please dont use QThread delay. :)

You cannot say something like that if you don't provide the 'why' argument with it. This is just like saying: "never use global variables" or "always use 'private' and 'public'".

If I say: "jump in the ditch", how likely will it be that you will actually do it? But if I say: "Jump in the ditch, because there is a person drowning in it" than it is more likely that you will actually jump in the ditch. I said in the OP that it would not be a big deal if my program would freeze temporarily during a data transfer so I am not even remotely getting why I should not use a QThread delay??? If my push buttons would be disabled, it would actually be better because no user can accidently send a 'false' byte.

bask185

This

void MainWindow::send(QString c)
{
  QTimer::singleShot(2, this, SLOT(timeOut()));
  timer = true;

  serial->write(c.toLatin1());
  QString cAsHex = QString("%1").arg(c, 0, 16);
  qDebug()  << cAsHex << " >>";
  while (timer == true) {;}
}

void MainWindow::timeOut()
{
    timer = false;
}

is not working. The idea is that timeOut gets called 2ms after a byte has been send so the program can escape the while loop.

Why is this not working??

EDIT:
does not matter I used a different approach with a timer object and ->start(2) and -> stop() functions. This works ;)

mrjj

@bask185

Fair enough, please don't use QThread delay for any kind of pausing in a main thread as it also strangulate the
event/signal processing and can lead to all sort of odd behaviors. Its simply a wrong solution to the requirements.

Your buttons are not really disabled, they simply not getting the click event ( or some might) so using
delay is just bad design in 99% of all cases in regards to the main thread.
To disable, there is a function for just that.

jsulm

@bask185 Well, this just cannot work as your while loop blocks the event loop which breaks signals/slots.
Why did you put the loop there?

void MainWindow::send(QString c)
{
  QTimer::singleShot(2, this, SLOT(timeOut()));
  serial->write(c.toLatin1());
  QString cAsHex = QString("%1").arg(c, 0, 16);
  qDebug()  << cAsHex << " >>";
}

void MainWindow::timeOut()
{
    // Here send the rest of the data
}

J.Hilk

I would suggest something like this:

//Member variables:
QTimer *timer;
QList<QString> dataToSend;

/*Timer event*/
timer = new QTimer(this);
connect(timer, &QTimer::timeout, timer, [=]{
     if(dataToSend.size() > 0){
         send(dataToSend.first());
         dataToSend.removeFirst();
    }
    if(dataToSend.isEmpty())
        timer->stop();
});

/*Start send*/
...
dataToSend.append(newData);
if(!timer->isRunning())
    timer->start(2);

bask185

I now use:

void MainWindow::send(QString c)
{

  timer->start(2);

  serial->write(c.toLatin1());
  QString cAsHex = QString("%1").arg(c, 0, 16);
  qDebug()  << cAsHex << " >>";
  while (Timer == true) {;}
}

void MainWindow::timeOut()
{
    Timer = false;
    timer->stop();
}

and it works like a charm