Number of bytes receives not the same after each cycle

[Lesiok]

And this is good idea - create a frame with marker.
According to me it would look like this : AA AA id_0 id_1 d_0 d_1 d_2 d_3 d_4 d_5 d_6 d_7 d_8

[AUDI_ENG]

Foo::readyRead()
{
    static const int expectedPacketSize = 9; // your 9 bytes
    if (port->bytesAvailable() < expectedPacketSize)
        return; // do nothing
    QByteArray data = port->read(expectedPacketSize);
 
    // do domething processing of your packet
}

Foo::readyRead()
{
    static const int expectedPacketSize = 9; // your 9 bytes
    if (port->bytesAvailable() < expectedPacketSize)
        return; // do nothing
    QByteArray data = port->read(expectedPacketSize);
 
    // do domething processing of your packet
}

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Of course, I'm skip the parsing and synchronization of incoming packets from an incoming data stream.

the code works perfectly but I like to understand it deeply, can you explain me how it works, for exemple how it detects 9 bytes without losing data

Thank you

---

Added after 4 minutes:

And this is good idea - create a frame with marker.
According to me it would look like this : AA AA id_0 id_1 d_0 d_1 d_2 d_3 d_4 d_5 d_6 d_7 d_8

Thank you,

but why I want to repeat id_0 id_1 twice ? and you meaning that AA AA , id_0 8bytes , id_1 8bytes , id_2 8bytes...... ??

[Lesiok]

Thank you,
but why I want to repeat id_0 id_1 twice ? and you meaning that AA AA , id_0 8bytes , id_1 8bytes , id_2 8bytes...... ??

If id is one byte send only one of course. I thought that id is 2 bytes.
And NO, I mean : AA AA id_0 8 bytes, AA AA id_1 8 bytes.... Every packet starts with 2 bytes marker AA AA.

[AUDI_ENG]

If id is one byte send only one of course. I thought that id is 2 bytes.
And NO, I mean : AA AA id_0 8 bytes, AA AA id_1 8 bytes.... Every packet starts with 2 bytes marker AA AA.

Ok, i will try this : AA AA id_0 8 bytes , AA AA id_1 8 bytes ...
in Qt application I will change things in the code no when i read data?

[Lesiok]

As we said earlier : collect data into the buffer and then analyze them searching for frame start tag (bytes AA AA). Remember that the frame is 11 bytes no 9.

[AUDI_ENG]

As we said earlier : collect data into the buffer and then analyze them searching for frame start tag (bytes AA AA). Remember that the frame is 11 bytes no 9.

I used this code :

Foo::readyRead(){

static const int expectedPacketSize = 11; // your 11 bytes
if (port->bytesAvailable() < expectedPacketSize)
return; // do nothing

QByteArray data = port->read(expectedPacketSize); // do domething processing of your packet
}

so I have 11 bytes in the data buffer but how I can detect the start of the packet , in the same time when I read data ?
I can't analyse my packet for detecting data after reading, and if I collect all data in the same buffer, its very heavy for application

[Lesiok]

You should declar variable dataBuffer in class Foo and then do something like this :

Foo::readyRead(){
int frameLen = 11;
dataBuffer.append(port->readAll());
if( dataBuffer.size() < frameLen )
    return;// data to short
int indexOfFrame = dataBuffer.indexOf("\xAA\xAA");
if( indexOfFrame < 0)
    return;// frame marker not found
QByteArray oneFrame = dataBuffer.mid(indexOfFrame,frameLen);// we have one frame, do something with this
dataBuffer = dataBuffer.right(indexOfFrame,frameLen);//remove processed data from the buffer
}

Foo::readyRead(){
int frameLen = 11;
dataBuffer.append(port->readAll());
if( dataBuffer.size() < frameLen )
    return;// data to short
int indexOfFrame = dataBuffer.indexOf("\xAA\xAA");
if( indexOfFrame < 0)
    return;// frame marker not found
QByteArray oneFrame = dataBuffer.mid(indexOfFrame,frameLen);// we have one frame, do something with this
dataBuffer = dataBuffer.right(indexOfFrame,frameLen);//remove processed data from the buffer
}

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[AUDI_ENG]

I'm writing this code before your code, because with yours I'm losing data

if(Port->bytesAvailable() < lenFram){
 
      return; 
}
dataBuffer.append(port->read(lenFram)); // I change your line to this

if(Port->bytesAvailable() < lenFram){

      return; 
}
dataBuffer.append(port->read(lenFram)); // I change your line to this

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When I'm adding this before your code I have :

bytesreceives = "0aaaaa0c1209080a090908"
index TAG = 1
nb data read = 10 bytes = "aaaa0c1209080a090908"

bytesreceives = "0aaaaa0d0a09090a090909"
index TAG = 1
nb data read = 10 bytes = "aaaa0d0a09090a090909"

bytesreceives = "0aaaaa0e0e09080a080909"
index TAG = 1
nb data read = 10 bytes = "aaaa0e0e09080a080909"

_________________________________________________

with your code (with readAll() ) : I have this :

nb data read = 11 bytes = "aaaa070a09080a0908090a"
nb data read = 11 bytes = "aaaa080a08090a0909080a"
nb data read = 11 bytes = "aaaa0a1709090a0809090a"
nb data read = 11 bytes = "08090aaaaa0d0a08090a09" --> AA is not in the beginning
nb data read = 11 bytes = "09080aaaaa0f1709090a08" --> AA is not in the beginning
nb data read = 11 bytes = "09080aaaaa020a08090a09" --> AA is not in the beginning
nb data read = 11 bytes = "aaaa031209090a0908090a"
nb data read = 11 bytes = "aaaa041209090a0908090a" --> ID = 4
nb data read = 11 bytes = "08090aaaaa070e08090a09" --> AA is not in the beginning (ID = 7) ---> I miss data with ID = 5 and 6
nb data read = 11 bytes = "08090aaaaa091209080a09" --> AA is not in the beginning
nb data read = 11 bytes = "09090aaaaa0b0a09080a09" --> AA is not in the beginning



I have still the problem with the beginning of frames, sometimes, it is AAAA and sometimes other bytes of frames

[Lesiok]

Between lines 8 and 9 of my code should be :

if( (dataBuffer.size() - indexOfFrame) < frameLen )
    return; // frame is not complete

if( (dataBuffer.size() - indexOfFrame) < frameLen )
    return; // frame is not complete

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Line 10 sholud be :

dataBuffer = dataBuffer.right(indexOfFrame+frameLen);//remove processed data from the buffer

dataBuffer = dataBuffer.right(indexOfFrame+frameLen);//remove processed data from the buffer

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I have not tested my code. This is just an example of how something should look.

[AUDI_ENG]

Between lines 8 and 9 of my code should be :

if( (dataBuffer.size() - indexOfFrame) < frameLen )
    return; // frame is not complete

if( (dataBuffer.size() - indexOfFrame) < frameLen )
    return; // frame is not complete

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Line 10 sholud be :

dataBuffer = dataBuffer.right(indexOfFrame+frameLen);//remove processed data from the buffer

dataBuffer = dataBuffer.right(indexOfFrame+frameLen);//remove processed data from the buffer

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I have not tested my code. This is just an example of how something should look.

I have always 11 bytes and the beginning AAAA (working perfectly)
but I have still the problem about losing data, its normal to losing data (because somtimes the nombre of bytes availables is more then 22 for exemple --> so I lost one frame) ??

[Lesiok]

The amount of data in the buffer depends on how quickly you process them. Remember that the serial port operates completely asynchronously and it can happen that during the processing of one frame to the computer reaches a few more.

[AUDI_ENG]

Thank you so much for your replies, for your patience, for your ideas and your important information
I like your motivation to help all beginners
Thank you again