[Discuss-gnuradio] dealing with framed data

[Matthieu Imbert]

Hi,

I'm currently trying to take the output of a fft block and pipe it in a 
tcp sink for (near) real-time processing outside of gnuradio.

My question is:

Assuming that I have vectors of n floats (the fft block outputs vectors 
of floats or complexes, so I may need to pipe it to a complex-to-mag2 
block to convert it to an array of floats, but that's not the main point 
of my question here), if I send them directly to the tcp sink, it will 
become a stream of bytes, and my code outside of gnuradio won't be able 
to detect the boundaries between vectors of n bytes. Actually it won't 
even be able to detect the boundaries between floats.

So I need to "frame" the data in a kind of basic protocol. For example: 
each vector of n floats, insert a m bytes header with a magic 
identifier, and perhaps a length and/or sequence number.

I'm confused about what technique to use to achieve this, between tagged 
streams, messages, pdus, packets:

- I tried using tagged stream (with "stream to tagged stream"), and 
piping it to "Packet Header Generator", but the output of the "packet 
header generator" seems to be only the packet header, and I don't know 
how to recombine it with the payload.

- I tried using "tagged stream to pdu", but then I don't know what to do 
of the pdu output, the only block I found which may input this data type 
is "Socket PDU" but I don't understand its purpose.

- Or should I use "simple framer"?

I'd appreciate some advice on the best / most simple way to achieve 
this. I'm new to gnuradio, so feel free to correct me on any errors (and 
accept my apologizes if my question seems trivial).

best,

--
Matthieu Imbert <address@hidden>
http://graal.ens-lyon.fr/~mimbert/
INRIA / LIP ENS-Lyon research engineer
http://www.inria.fr http://www.ens-lyon.fr/LIP
+33(0)472728149
Monod campus, room GN1 Nord 3.52
LIP ENS-Lyon, 46 allée d'Italie
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