Qt Forum

    • Login
    • Search
    • Categories
    • Recent
    • Tags
    • Popular
    • Users
    • Groups
    • Search
    • Unsolved

    Call for Presentations - Qt World Summit

    Solved read data from serial port

    General and Desktop
    4
    29
    2924
    Loading More Posts
    • Oldest to Newest
    • Newest to Oldest
    • Most Votes
    Reply
    • Reply as topic
    Log in to reply
    This topic has been deleted. Only users with topic management privileges can see it.
    • mrjj
      mrjj Lifetime Qt Champion @isan last edited by

      @isan
      hmm
      maybe input is not as you expect then.
      try qDebug() << values;
      to see what it has

      I 1 Reply Last reply Reply Quote 0
      • I
        isan @mrjj last edited by

        @mrjj said in read data from serial port:

        qDebug() << values;

        return :
        \n191", "2018/8/3", "23:28:55 \r\n187", "2018/8/3", "23:28:55 \r\n185", "2018/8/3", "23:28:55 \r\n164", "2018/8/3", "23:28:55 \r\n131", "2018/8/3", "23:28:55 \r\n103", "2018/8/3", "23:28:55 \r\n....................................

        1 Reply Last reply Reply Quote 0
        • mrjj
          mrjj Lifetime Qt Champion last edited by mrjj

          Ok so when we only split at ","
          We get \n\r on some/all of the values.
          Using something Like ReadLine might be easier.
          but you seem to use native serial comm and not Qt version?
          but you can try
          for ( const QString& valline : values ) {
          qDebug() << "val =" << valline.trimmed().toInt();
          }
          Trimmed() should remove the \n\r
          http://doc.qt.io/qt-5/qstring.html#trimmed

          ah. wait.
          it looks like some of the values are in same index as timestamp
          "23:28:55 \r\n187"

          1 Reply Last reply Reply Quote 1
          • mrjj
            mrjj Lifetime Qt Champion last edited by mrjj

            Hi
            Im not really sure what is happening.
            Seems to not to be structured as we think/needs more splitting

            QString input{"85,2018/8/3,17:21:3\\n\\r85,2018/8/3,17:21:3\\n\\r95,2018/8/3,17:21:3"};
              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();
                }
              }
            

            val = 85
            val = 0
            val = 0
            val = 85
            val = 0
            val = 0
            val = 95
            val = 0
            val = 0

            when do you start processing the input ?
            After it all have been read or how do u know that input is ready ?

            I 1 Reply Last reply Reply Quote 1
            • I
              isan @mrjj last edited by isan

              @mrjj it's return zero and sometimes 2018

              when do you start processing the input ?
              After it all have been read or how do u know that input is ready ?

              I'm not sure what you mean?
              read from serial port in thread and thread start in other class constructor.
              so it's start when program run!
              data send from arduino that connected to raspberry pi with USB port

              mrjj 1 Reply Last reply Reply Quote 0
              • mrjj
                mrjj Lifetime Qt Champion @isan last edited by

                @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();
                    }
                  }
                }
                
                JonB I 2 Replies Last reply Reply Quote 1
                • JonB
                  JonB @mrjj last edited by JonB

                  @mrjj
                  I have no idea of the implications, but you have pasted code for OP as:

                    QStringList lines = input.split("\\n\\r");
                  

                  If he is supposed to be copying this, shouldn't he be using

                    QStringList lines = input.split("\r\n");
                  

                  Or, from his qDebug(), does it mean that the input literally has the 4-character sequence \r\n in it, and not CR-LF? In which case he would want

                  QStringList lines = input.split("\\r\\n");
                  
                  
                  mrjj 1 Reply Last reply Reply Quote 3
                  • mrjj
                    mrjj Lifetime Qt Champion @JonB last edited by

                    @JonB
                    Thank you , yes u are right its \r\n :) (of cause)
                    or \r\n when escaped.

                    1 Reply Last reply Reply Quote 2
                    • JonB
                      JonB last edited by JonB

                      Now, going back to where @isan wrote:

                      return :
                       \n191", "2018/8/3", "23:28:55 \r\n187", "2018/8/3", "23:28:55 \r\n185", "2018/8/3", "23:28:55 \r\n164", "2018/8/3", "23:28:55 \r\n131", "2018/8/3", "23:28:55 \r\n103", "2018/8/3", "23:28:55 \r\n....................................
                      

                      So if that's really right, after first splitting on "\r\n" (not even certain about that if the input really starts as shown with just \n and not \r\n, I'll just assume it's really \r\n), he then needs to split on "\",\"", not just plain ,. Then at the end of that you have 3 clean tokens per line.

                      I have to say the input looks a bit oddly tokenized/quoted, but that's what corresponds to the input he shows. If you're not careful and leave " characters in, you'll get toInt() returning 0 where you don't expect.

                      mrjj 1 Reply Last reply Reply Quote 2
                      • mrjj
                        mrjj Lifetime Qt Champion @JonB last edited by

                        @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 )

                        1 Reply Last reply Reply Quote 2
                        • I
                          isan @mrjj last edited by 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 1 Reply Last reply Reply Quote 0
                          • mrjj
                            mrjj Lifetime Qt Champion @isan last edited by

                            @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

                            I 1 Reply Last reply Reply Quote 1
                            • I
                              isan @mrjj last edited by 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 1 Reply Last reply Reply Quote 0
                              • mrjj
                                mrjj Lifetime Qt Champion @isan last edited by 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 1 Reply Last reply Reply Quote 1
                                • JonB
                                  JonB @mrjj last edited by 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 1 Reply Last reply Reply Quote 2
                                  • mrjj
                                    mrjj Lifetime Qt Champion @JonB last edited by 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 
                                        }
                                    ......
                                    
                                    I 1 Reply Last reply Reply Quote 1
                                    • J.Hilk
                                      J.Hilk Moderators last edited by

                                      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.

                                      Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct

                                      Qt Needs YOUR vote: https://bugreports.qt.io/browse/QTQAINFRA-4121


                                      Q: What's that?
                                      A: It's blue light.
                                      Q: What does it do?
                                      A: It turns blue.

                                      mrjj 1 Reply Last reply Reply Quote 3
                                      • I
                                        isan @mrjj last edited by isan

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

                                        mrjj 1 Reply Last reply Reply Quote 2
                                        • mrjj
                                          mrjj Lifetime Qt Champion @isan last edited by

                                          @isan
                                          Super :) \O/

                                          1 Reply Last reply Reply Quote 0
                                          • mrjj
                                            mrjj Lifetime Qt Champion @J.Hilk last edited by

                                            @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)

                                            1 Reply Last reply Reply Quote 1
                                            • First post
                                              Last post