Forum: GNU Radio Hier signal processing block in Python

Hi all,

Can somebody explain me a bit the difference between blocks written in
python in the way presented on the website and blocks like packet 
decoder,
packet encoder, gfsk modulator, etc. The latter blocks are written also 
in
Python, but they are different than the previous. Particularly I don't
understand why there are also thread classes stick to the blocks from 
the
second group.
And the most important thing is I would like to know how to make such 
block
out of tree.

Many thanks

On 01/24/2013 10:20 AM, Nemanja Savic wrote:
> Hi all,
>
> Can somebody explain me a bit the difference between blocks written in
> python in the way presented on the website and blocks like packet decoder,
> packet encoder, gfsk modulator, etc. The latter blocks are written also in
> Python, but they are different than the previous. Particularly I don't
> understand why there are also thread classes stick to the blocks from the
> second group.

Those old blocks are just hier blocks with some processing blocks from
gnuradio, where the python interface part is outside of the scheduler,
really just a python thread polling a message queue. The interface is a
python function call or something.

So, there are APIs to create blocks in python that actually use the
scheduler. For example, here is one that does the pkt framer/correlate
but presents a message interface. This block has inputs and outputs that
can be connected in a gnuradio flow graph.

https://github.com/guruofquality/grextras/blob/mas...

Then you can do cool things like this:
https://github.com/jmalsbury/pre-cog/wiki

> And the most important thing is I would like to know how to make such block
> out of tree.

Most of the feature above is in gnuradio master branch, but I dont think
there is a doc, so you will have to interpolate from this:

https://github.com/guruofquality/grextras/wiki/Blo...

-josh

Thank you Josh, I hope your answer will help.

The problem particularly with packet decoder block which could be found 
in
packet.py is that I can't figure out how messages goes from framer sink 
to
the message source.
Namely, framer sink sends message to the queue. There is a thread
responsible for reading message from the queue and for calculating crc.
After that, callback function is called and if message was OK, it will 
post
message again to the queue (Isn't there only one queue between two 
blocks
and both read from and write to that queue?).

By the way, do you think that message source sounds like block which
produces messages (that's what i was thinking at first glance, but maybe
cause I am not native speaker)?

Cheers