read data from serial port

[mrjj]

@JonB
Hi
I think the "s comes from qDebug and is not in the input. (looking at the sending code higher up)
It seems he reads the entire load in one go and closes port so that means he should be able to
read complete string and then split it. ( i hope )

[isan]

@mrjj said in read data from serial port:

@isan
Looking at the code, it seems to me you
send al data and thread will read it all. and then close serial.
so

while (serialDataAvail(fd) > -2) {
  //-------value format is int-------
  value = serialGetchar (fd) ;
  //--------vs format is QString------
  vs.push_back(value);  
 }
 serialClose(fd);
 
 // here u should have complete data and can use 
to get the values if data is complete
input would be vs

  QStringList lines = input.split("\\n\\r");
  for ( const QString& line : lines) {
    QStringList values = line.split(",");
    for ( const QString& valline : values ) {
      qDebug() << "val =" << valline.trimmed().toInt();
    }
  }
}

Data is always sent and It does not go out of while() and I can not wait for complete data
Upon receive, I must use the data in other classes
I should not miss any data, if I close the port, the data will be lost

[mrjj]

@isan
ok so it must be on the fly.

Then you need to use 2 buffers as not to parse already received data over and over.
so in pseudo code

Read char from serial
tempbuffer += char
if char is \n then
split tempbuffer
emit value
clear tempbuffer

//i assume u want to store all ?
Mainbuffer +=char

[isan]

@mrjj so the code is like:

void MyThread::run()
{

    qDebug("Thread id inside run %d",(int)QThread::currentThreadId());

    int fd ,x;
    
      
    if ((fd = serialOpen ("/dev/ttyACM0",230400)) < 0)
    {
        fprintf (stderr, "Unable to open serial device: %s\n", strerror (errno)) ;
    }

    while (serialDataAvail(fd)>-2)
    {
         //-------value format is int -------//
        value=serialGetchar (fd) ;
     //--------vs format is QString------//
         vs.push_back(value);
    //--------tempbuffer format is QString------//
   tempbuffer .append( vs);
   if (vs=="\n")
  //-------- values format is QStringList------//
     values = tempbuffer.split(",");
      x= values[0].toInt();
 msleep(1); 
       emit signalValueUpdated(x);
       tempbuffer.clear();
  
    }
    serialClose(fd); 
}

is it true?

[mrjj]

@isan
Hi
Almost, you need to clear tempbuffer as soon as you have used it.
And u need to check last read char (value) being the \n

void MyThread::run() {

  qDebug("Thread id inside run %d", (int)QThread::currentThreadId());

  int fd, x=0;


  if ((fd = serialOpen ("/dev/ttyACM0", 230400)) < 0) {
    fprintf (stderr, "Unable to open serial device: %s\n", strerror (errno)) ;
  }

  while (serialDataAvail(fd) > -2) {
    value = serialGetchar (fd) ;
    vs.push_back(value);
    tempbuffer += value;
    if (value == '\n') {
      values = tempbuffer.split(",");
      x = values[0].toInt();
      tempbuffer.clear();
    }
    msleep(1);
    emit signalValueUpdated(x);
    

  }
  serialClose(fd);
}

[JonB]

@mrjj , @isan
This code looks wrong. It doesn't help that we don't see the declarations of vs or tempbuffer. Comment:

//--------tempbuffer format is QStringList------//

No, it isn't, because later you go tempbuffer.split(",");. So it's probably a QString.

Then: you read 1 char, you append it to vs. Then you append vs to tempbuffer. If value is not \n, you pick up the next char, append that to vs (now 2 chars long), append that to tempBuffer (now 3 chars long)...

Hmm, vs must be a single char, not a QString like the comment says it is? Who knows....

Separate issue:

while (serialDataAvail(fd)>-2)

Nope. serialDataAvail(fd) returns -1 on error. The code accepts that as a legal. It also should therefore never exit the while loop. Further, if 0 bytes are available code goes into the value=serialGetchar (fd) call. After 10 seconds of no data that will return -1. At which point accepts that as the legal char received. Finally, if error opening device in the first place, the code writes a message and then continues into the loop, which makes no sense.

All this code really needs correcting....

Finally, have a think about the fact that sometimes you are using Qt & C++ functions, sometimes you are doing lowest-level C library calls. Do you really need to mix them?

[mrjj]

+@JonB
Thx, yes value should be added to tempbuffer.
Then i can learn not to edit code in forum directly :)
So something like this + all than @JonB said

while (serialDataAvail(fd) > -2) { // fix condition! 
    value = serialGetchar (fd) ;// read char
    vs.push_back(value); // store in ful buffer
    tempbuffer += value; // add to tempbuffer
    if (value == '\n') { // if we just read \n
      values = tempbuffer.split(","); // split on , to QStringList
      x = values[0].toInt(); // take first index and convert to int
      tempbuffer.clear(); // clear it for next 
    }
......

[J.Hilk]

I‘ve been following this thread for a while now, and you guy‘s doing a great job :-)

Just one thing that‘s been buging me from the beginning.

The call off split on the string. It‘s used for nothing but temporary storage to than turn the first entry into an INT.

I would highly recommand to at least use splitref.

[isan]

@mrjj Thanks for keep helping to solve my problem
It's work!

[mrjj]

@isan
Super :) \O/

[mrjj]

@J.Hilk
Yes i agree. but in this case we wanted to split very small sample so
i decided not to introduce new classes. (QVector/QStringRef)
as to focus on getting it running. But yes, much better to use normally as the speed gain is huge for large dataset. (more than i did imagine)