Qt - serial communication - receiving

Damian7546

I solved my problem by creating a slot for readyRead() signal. Solution/problem is described here:

https://stackoverflow.com/a/44693193/11766659

Damian7546

I have next problem. When I was very short cable RS485 the frame was received all in one shot . now in long cable the frame recive is byte by bytes, so my code doesn't works.
Like I said I use slot "recive()" for readyRead() signal.

void SerialWorker::recive()
{
        QByteArray buffer_checksum;
        quint8 inByte;
        quint8 checksum_temp;
        int numByte = 0;
        int receiverStatus = RCV_ST_IDLE;
        Frame *m_inFrame = nullptr;
        int dataLength = 0;
        QByteArray receivedData = m_Serial->readAll();


qDebug()<<receivedData;

        while(receivedData.count() > 0)
        {

          ...................
          .................
       }
}

How I should wait for all bytes in frame in my slot ?

Christian Ehrlicher

@Damian7546 said in Qt - serial communication - receiving:

How I should wait for all bytes in frame in my slot ?

You must not wait but read the data into a custom buffer (e.g. QByteArray) and parse the data later on.

Damian7546

So, I changed my slot "recive()" in this way:

void SerialWorker::recive()
{
        receivedData = receivedData + m_Serial->readAll();
        if(!receivedData.isEmpty())
        {
            timeoutReciveData(this, SLOT(parseRecivedData()), 1000);
        }
}

But something is wrong with singleshot , because doesn't work:

void SerialWorker::parseRecivedData()
{
     qDebug() << receivedData ;
         /* parse should be here */

}
void SerialWorker::timeoutReciveData(const QObject *obj, const char *signalOrSlot, int msDelay)
{
     QTimer::singleShot(msDelay, obj, signalOrSlot);
}

Any idea ?

Christian Ehrlicher

@Damian7546 said in Qt - serial communication - receiving:

But something is wrong with singleshot , because doesn't work:

does not work? What does this mean? Why do you not directly call parseRecivedData or QTimer::singleShot()?

yinhao.qian

This post is deleted!

Damian7546

@Christian-Ehrlicher said in Qt - serial communication - receiving:

Why do you not directly call parseRecivedData

Because I do not know when my frame will be completed, so I give the some time by timeoutReciveData and next go to parseRecivedData().
I expect such a frame:
DevAddres,LengthFrame,Command,Data1...n,CRCH,CRCL

@Christian-Ehrlicher said in Qt - serial communication - receiving:

does not work? What does this mean?

The parseRecivedData() slot does not start even though buffer "receivedData" are not empty .

Christian Ehrlicher

@Damian7546 said in Qt - serial communication - receiving:

Because I do not know when my frame will be completed, so I give the some time by timeoutReciveData and next go to parseRecivedData().

And why should it be finished in 1000ms? It does not help at all.
Parse your buffer directly.

Damian7546

Ok,
thank for your suggestion. I must rewrite my parseRecivedData() function.

Damian7546

I wrote again my "recive()" function like you said, it works, but I have several doubt.

void SerialWorker::recive()
{
        QByteArray buff2CalcChecksum;
        Frame *m_inFrame = nullptr;
        receivedData_raw = receivedData_raw + m_Serial->readAll();
        if(!receivedData_raw.isEmpty())
        {
            for(int i=0; i <  receivedData_raw.count(); i++)
            {
                buff2CalcChecksum = buff2CalcChecksum + receivedData_raw[i];
                if ((((m_inFrame->CalculateCRC2_in(buff2CalcChecksum)) & 0xFF) == buff2CalcChecksum[i+2])  &&
                    (((m_inFrame->CalculateCRC2_in(buff2CalcChecksum) >> 8) & 0xFF) == buff2CalcChecksum[i+1]))
                {
                    qDebug() << "We have the correct frame";
                    receivedData = receivedData_raw;
                    receivedData_raw.clear();
                    parseRecivedData();
                }

                if (receivedData_raw.count() > 20 ) receivedData_raw.clear();  /// it is not a good idea...
             }
         }
}

How to protect code when too long no CRC sums ?
It is a good idea that from first byte, calculate CRC sum to recognize my whole frame?

Christian Ehrlicher

I don't think your code will ever work - the data comes in as a stream so you first have to figure out the start and end of your frame. For this a lot of protocols use a start and end-marker so you know when a frame starts and ends.

Damian7546

This protocol do not have marker start and end of frame. This is a frame:

Christian Ehrlicher

Then I don't know how you will ever find the start of a frame... they must have at least e.g. an end marker ('\r' or '\n' for example) where you can start from.