[solved] incomplete data read by qserialdevice

koahnig

[quote author="arianoo" date="1321504770"]it means that when i get notified that data is available on the port by ready read and call readAll immediately,it reads the data incorrectly while i see what there is on my port the function has changed it.what should i do?[/quote]

The readyRead signal is issued when some data ist available. This does not mean the sequence is already completed. As a matter of fact with low baud rates it might take considerable time to receive even short sequences.

As I understand your data is partially corrupted, but not completely. This does not sound like a wrong baud rate, but may be other settings as suggestesd above.

The question is what you are trying to achieve. If you want to communicate as in a dialog with a device, the approach with readAll may be feasible. Providing that the sequences send by the other device are reasonably short. You may wait some time after you have received readyRead and then start reading (e.g. readAll).

However, in my opinion this approach will be very fast at its limits. If you have varying length of information which cannot be determined beforehand. Especially, if you are doing some real-time communication with some sensor sending information at specific rate but different information length, you will run into trouble.

I would read the device in smaller chunks and store the data in a buffer myself. You may do this bytewise or in chunks based on the return of bytesAvailable.

arianoo

thank u all so much for considering my question and answering it. The settings of the port are all correct as i am able to communicate with devices by the commands i send to them and i also monitor the port by an interface device with the same settings and it works correctly and the problem is absolutely the way i read data from the port.
dear koahnig u have mentioned many points that can help me understand how serial ports work ,the bytesAvailable function always returns exactly the number of bytes that readAll would read and i have tried to read that size of data each time with read() function and it hasnt helped either.my problem with waiting is that for a good result and a high percentage of getting correct data i have to wait 3 seconds every time something is available on my port and it makes my program run too slow.i was using this approach up to last week but its really impossible to have this much delay. the way that has answered for me by now and is not yet reliable at all, is that i am opening the port in buffered mode and calling readall. most of the times it returns the exact data which is available on the port but this also has its own problems.
Im truely confused with this issue i have to work with two different devices through serial port and getting correct data from them is so important for me:(
ill be thankfull if u tell me the ideas that come to ur mind so that my problem gets fixed.
thanks alot for your attention

koahnig

dear arianoo
at first I like to mention two major differences. The experiences I collected on windows and wince. Futhermore, I had retrieved an old version of QExtSerialDevice. The project has been part of SourceForge at a time. Later I have found out that the project has been moved to google.
I just saw that you are refering to QSerialDevice. I do not know if the roots are the same. However, it seem to be newer than QExtSerialDevice.
I have a program reading data from a device in real-time. The information is of the form prefix-data-suffix. Initially the program used only TCP/IP for reading the data. It basically scans the input for the starting bytes of the prefix where also the also the complete record length can be found. This led to reading the input bytewise until the starting character found. The remainder will be read bytewise as well until bytesAvailable are read or the complete record has been received. The collected record will be processed immediately. Initially QExtSerialDevice could substitute the QTcpSocket since both are derived from QIODevice. The only difference was the opposite definition of atEnd() in QExtSerialDevice. Later I ported to WinCE where the API functions are completely different. Nevertheless, I maintained the bytewise copying process. A port to linux never happened and probably will never.
Since the information records are rather short, it was never an issue with TCP/IP. Depending on the baudrate it becomes an issue with serial comms. I personally would prefer the bytewise reading especialyl for my application. I need to buffer anyway, because half a record is a lost record.
I have no experience with QSerialDevice. Probably the readAll implementation is save, but I would be careful until I know. Only the developers working on it can tell what is happening during readAll and additional information is received. Or you have to dig into that yourself.

arianoo

hi Koahnig
I'm really thankful for your post i read it 10 days ago but didn't have time to answer.as your advice I started using buffered mode but I still have to add some delay before reading long data because if i read it immediately it gets damaged I also increased the time of setcharintervaltimeout which i don't know what exactly it does and i didn't realize if it changed anything.I want to thank u again cuz your ideas and information u wrote were truely helpful for me.
I also want to ask people who have worked with serial port about the best way to read data from it and about the meaning of setcharintervaltimeout and such settings.
thanks again
wish to get more answers from you;)

koahnig

Hi arianoo
out of curiosity what is the baud rate of your serial device?

arianoo

I'm connecting to two devices at the same time via 2 ports. one with baud rate 115200 which is most of the times w/o problems and the other one with baud rate 9600 that's killing me;) that device was a little different before and I had to communicate with it with 2400 baud and it was much more suffering but now with 9600 problems are less than before but still in getting long messages I'm having problem and haven't found any solutions so far.

koahnig

Higher baud rates seem to be easier to handle.
At first I used only fast baud rates. there was not an issue with reading a complete record at a time.
Suddenly another device provided "only" 9600 baud. That was the point when buffering was getting important.

arianoo

yeah you're right and I'm still looking for a reliable way for reading correct data from serial ports i really need it

koahnig

Are you doing the reading of the device in a separate thread?

arianoo

I'm reading it by events and also i stay in the current event to get my answer by waitforreadyread() do u think it might be a problem?

koahnig

I would have to know the implementation in detail to give a proper answer. And I do not. Also I am using a different implementation (QExtSerialDevice).
However, my application is reading from the serial port in a different thread.

arianoo

i think the event driven application im using is working the same as if it was on another thread and i think im aware of where my program is living while executing the problem is that sometimes the signal of the readyread event is raised before it truly ready i guess

koahnig

You might be right. I saw an implementation with different threads for reading and writing on the device. Since I have used it as a guideline, I have implemented in a separate thread as well. It could well be over-engineering, but it does not have the problems on lower baud rates. At least I do not know of such problems ;-)

abhijsj

Hi arianoo even i am using qserialdevice for serial data communication.
I am connecting two devices on two diff ports one is running at 19200 baud and another at 4800 baud.
but i am facing a serious problem ie when one port is open and at the same time if i am opening the other port it is unable to open it.
I have taken two different instances of abstractserial class but i am unable to open both the ports at the same time..
if i close the second port and then i am opening the other port then i am able to read the data successfully..
i just caunt get where i am stuck. if you could guide me then i would be able to sort this problem out..

arianoo

i am doing the same way also im openning two ports by two instances of qabstractserial and i have never had such problem maybe in some settings of your system there's a limitation for the number of open serial ports or maybe ur using the same name for both instances u create(???) or maybe something else is the problem because i never faced this issue u can also put a piece of ur program so that people on the forum see it maybe the answer will be found

abhijsj

Hey Arianoo i had already mailed a copy of my code to you you can check that out.

abhijsj

@
#include "dialog.h"
#include "ui_dialog.h"
#include <QDebug>
#include "qserialdevice_global.h"
#include "abstractserial.h"
QByteArray ba;
QByteArray ba1;
AbstractSerial *port;
AbstractSerial *port1;
Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{

timer = new QTimer(this);

// timer1 = new QTimer(this);
udpsocket = new QUdpSocket(this);
messageNo = 1;
ui->setupUi(this);
connect(ui->sstartButton, SIGNAL(clicked()), this, SLOT(startserialrecv()));
connect(ui->startButton, SIGNAL(clicked()), this, SLOT(startBroadcasting()));
connect(ui->sstartButton_2, SIGNAL(clicked()),this, SLOT(ttlopen()));
connect(ui->quitButton, SIGNAL(clicked()), this, SLOT(close()));
connect(ui->closebutton,SIGNAL(clicked()),this,SLOT(closeport()));
connect(ui->closebutton_2,SIGNAL(clicked()), this, SLOT(ttlclose()));
connect(timer, SIGNAL(timeout()), this, SLOT(broadcastDatagram()));
//connect(timer1, SIGNAL(timeout()), this, SLOT(startserialrecv()));

}
void Dialog::startBroadcasting()
{
ui->startButton->setEnabled(false);
timer->start(100);
}

void Dialog::startserialrecv()
{
port = new AbstractSerial(this);
connect( port, SIGNAL(readyRead()), this, SLOT(slotread()));
int rrto = 10;
int len = 100;
char *dn="/dev/ttyS0";
port->setDeviceName("/dev/ttyS0");
bool ret = port->open(AbstractSerial::ReadOnly);
if(ret)
{
qDebug("Port Opened Successfully");
if (!port->setBaudRate(AbstractSerial::BaudRate19200))
{
qDebug() << "Set baud rate " << AbstractSerial::BaudRate19200 << " error.";

   };

   if (!port->setDataBits(AbstractSerial::DataBits8))
   {
       qDebug() << "Set data bits " <<  AbstractSerial::DataBits8 << " error.";

   }

   if (!port->setParity(AbstractSerial::ParityEven))
   {
       qDebug() << "Set parity " <<  AbstractSerial::ParityEven << " error.";

   }

   if (!port->setStopBits(AbstractSerial::StopBits1))
   {
       qDebug() << "Set stop bits " <<  AbstractSerial::StopBits1 << " error.";

   }

   if (!port->setFlowControl(AbstractSerial::FlowControlOff))
   {
       qDebug() << "Set flow " <<  AbstractSerial::FlowControlOff << " error.";

   }
    if (port->waitForReadyRead(rrto))
        {
           /* ba = port->readAll();
            qDebug(ba);
            ui->textEdit1->setText(ba);
            ui->textEdit1->setText("Data Transmitted is: \"%1\"");
            qDebug(port->readAll());
         */}
         else
         {
                qDebug() << "Timeout read data in time : " << QTime::currentTime();
         }
     }
else
{
    qDebug("Serial Port Opening Failed");
}

}
void Dialog::slotread()
{
ba = port->readAll();
qDebug()<<"Data Rcvd :"<<ba;
ui->textEdit1->setText(ba);
qDebug() << "Readed is : " << ba.size() << " bytes";

}
void Dialog::closeport()
{
port->close();
qDebug() << "Serial device " << port->deviceName() << " is closed";
delete port;
port = 0;
}
void Dialog::ttlopen()
{
port1 = new AbstractSerial(this);
connect( port1, SIGNAL(readyRead()), this, SLOT(slotttlread()));

int rrto = 10;
int len = 100;
char *dn="/dev/ttyS1";
port1->setDeviceName("/dev/ttyS1");

// connect( port, SIGNAL(readyRead()), this, SLOT(readDataSlot()) );

//port->openMode(QIODevice::OpenMode);
bool ret = port1->open(AbstractSerial::ReadOnly);
   if(ret)
    {
   qDebug("Port Opened Successfully");

   //Here, the default current parameters (for example)
   if (!port1->setBaudRate(AbstractSerial::BaudRate115200))
       {
       qDebug() << "Set baud rate " <<  AbstractSerial::BaudRate115200 << " error.";

   };

   if (!port1->setDataBits(AbstractSerial::DataBits8))
   {
       qDebug() << "Set data bits " <<  AbstractSerial::DataBits8 << " error.";

   }

   if (!port1->setParity(AbstractSerial::ParityNone))
   {
       qDebug() << "Set parity " <<  AbstractSerial::ParityNone << " error.";

   }

   if (!port1->setStopBits(AbstractSerial::StopBits1))
   {
       qDebug() << "Set stop bits " <<  AbstractSerial::StopBits1 << " error.";

   }

   if (!port1->setFlowControl(AbstractSerial::FlowControlOff))
   {
       qDebug() << "Set flow " <<  AbstractSerial::FlowControlOff << " error.";

   }

   /* if (port1->waitForReadyRead(rrto))
        {
            ba = port->readAll();
            qDebug(ba);
            ui->textEdit1->setText(ba);
            ui->textEdit1->setText("Data Transmitted is: \"%1\"");
            qDebug(port->readAll());
         }
         else
         {
                qDebug() << "Timeout read data in time : " << QTime::currentTime();
         }*/
     }

else
{
    qDebug("Serial Port Opening Failed");
}

}
void Dialog::slotttlread()
{
ba1 = port1->readAll();
qDebug()<<"Data Rcvd :"<<ba1;
ui->textEdit1_2->setText(ba1);
qDebug() << "Readed is : " << ba1.size() << " bytes";
}

   void Dialog::ttlclose()
   {
       port1->close();
       qDebug() << "Serial device " << port1->deviceName() << " is closed";
       delete port1;
       port1 = 0;

   }

void Dialog::broadcastDatagram()
{

 QByteArray datagram = ba+ QByteArray::number(messageNo);
// QByteArray datagram = ba+ "123456";
 udpsocket->writeDatagram(datagram.data(), datagram.size(),
                          QHostAddress::Broadcast, 5000);
 ++messageNo;
 ui->textEdit->setText(tr("Sending data: \"%1\"").arg(datagram.data()));
 qDebug("Data is being transmitted");

}
@

[EDIT: code formatting, please wrap in @-tags, Volker]

koahnig

[quote author="abhijsj" date="1323510423"]Hey Arianoo i had already mailed a copy of my code to you you can check that out.
[/quote]

You need to use '@' as tag for starting and ending a section with source code. Otherwise it is not readable (see "here":http://developer.qt.nokia.com/wiki/ForumHelp#e3f82045ad0f480d3fb9e0ac2d58fb01 ) .

In addition it would have been better to start a new thread for your issue. This would attract more likely others to help you. Unfortunately, I cannot split threads.

abhijsj

@#include "dialog.h"
#include "ui_dialog.h"
#include <QDebug>
#include "qserialdevice_global.h"
#include "abstractserial.h"
QByteArray ba;
QByteArray ba1;
AbstractSerial *port;
AbstractSerial *port1;
Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{

timer = new QTimer(this);

// timer1 = new QTimer(this);
udpsocket = new QUdpSocket(this);
messageNo = 1;
ui->setupUi(this);
connect(ui->sstartButton, SIGNAL(clicked()), this, SLOT(startserialrecv()));
connect(ui->startButton, SIGNAL(clicked()), this, SLOT(startBroadcasting()));
connect(ui->sstartButton_2, SIGNAL(clicked()),this, SLOT(ttlopen()));
connect(ui->quitButton, SIGNAL(clicked()), this, SLOT(close()));
connect(ui->closebutton,SIGNAL(clicked()),this,SLOT(closeport()));
connect(ui->closebutton_2,SIGNAL(clicked()), this, SLOT(ttlclose()));
connect(timer, SIGNAL(timeout()), this, SLOT(broadcastDatagram()));
//connect(timer1, SIGNAL(timeout()), this, SLOT(startserialrecv()));