Number of bytes receives not the same after each cycle

[AUDI_ENG]

This is normal symptom for each data stream device (serial port, TCP socket etc.). 9 characters in packet is your private assumption. Data stream device do not know about it. You should read stream of data, analyze it and divide for logical packets.
By the way your protocol is very weak. How do you know that for example 01 is the number of the next packet and not its content ?

Thank you for your reply,

my protocol is :
_ID________ |______ Data______
01_______________8 bytes_____ (always)
02_______________8 bytes_____
03_______________8 bytes_____
04_______________8 bytes_____
05_______________8 bytes_____
06_______________8 bytes_____
..

Work with a local buffer.

All data that comes in is appended to the buffer.
Then you loop over the combined buffer, take chunks of 9 bytes until that is no longer possible.

Cheers,
_

thanks for your reply

what do you mean about local buffer ?

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
}

To copy to clipboard, switch view to plain text mode 

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

Thanks for your reply

I will try this monday,
with this code, i will lose some packets no ?