Re: [Discuss-gnuradio] Changing frequency dynamically in benchmark_rx.py

[Jason Uher]

> I tried to locate the simple framer, but not able to find it. Greping for it
> takes me to the c code of gr_simple_framer but I am not able to make much
> sense of it. Can you please elaborate a bit more...? Where does the
> correlations takes place within the python code.

The framer sink is a block implemented in C, which is why there is no
python code for it, the actual correlating happens in
gr_correlate_access_code (also implemented in C), they are connected
together to do the demodulating in pkt.py, which is modulation
independent.

(from: 
http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/python/gnuradio/blks2impl/pkt.py)

141             self.correlator = gr.correlate_access_code_bb(access_code,
threshold)
142     
143             self.framer_sink = gr.framer_sink_1(self._rcvd_pktq)
144             self.connect(self, self._demodulator, self.correlator,
self.framer_sink)

correlate_access_code takes a stream of bits from the demodulator and
tries to find the code prepended to each packet, when it does it sets
the second LSB (because each demodulated bit is in the LSB and the
other 7 are 0).  The framer_sink_1 watches for this flag and blindly
collects the packet starting from that point.

If you want to get a better idea of what's happening and understand C
you can look here:

http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/lib/general/gr_correlate_access_code_bb.cc

http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/lib/general/gr_framer_sink_1.cc

(Note that if you have an old version of the trunk checked out you
might be better off looking at those files in your local repository)


Jason