[op25-dev] Control channel decoding

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Dmitry Medvedev qaghqga at yahoo.com
Wed Aug 1 08:51:46 UTC 2012

Yes, valve is the block I was looking for. But, first try did not turn well: it works for a while, turning channels on and off, but after 10-100 switches something goes wrong and I get OOOOO. Experiments with dynamic reconfiguration gave me the same results (+memory leak, is there way to tell from python to release block memory after disconnect?). Maybe it's related to threading, as I turn valves on/off from separate thread. I'll try this again in some days.

Regarding the code: right not it's no more than a heap of proof-of-concept python code not tightly connected to gnuradio. Gnuradio part consists of application with multiple channels. Each channel is xlating fir -> quadrature demod -> symbol filter -> fsk4_demod -> slicer -> frame assembler --msg queue--> custom UDP sender (it adds frequency id to udp packet).
And there are standalone python program which receives UDP frames and stores it in db-like format. Further programs work on this files in pure python.
I'll release code in some days after I clean it up a little.

Best regards,

 From: Matt Mills <mmills at 2bn.net>
To: qaghqga at yahoo.com 
Sent: Tuesday, July 31, 2012 2:20 PM
Subject: Re: [op25-dev] Control channel decoding


I'd suggest using a valve or stream selector for that. Do you have any interest in sharing your source code?


On Tue, Jul 31, 2012 at 2:09 AM, Dmitry Medvedev <qaghqga at yahoo.com> wrote:

>I'm writing multichannel p25 recorder. It mostly works (thanks to op25 team and other contributors). Is there any open documentation on control channel messages, especially TSBK frames? I did trellis 
decoding and CRC algorithm (reverse engineered the later, as I couldn't 
find parameters). I understand structure of some messages, for example 
"Group Voice Channel Grant Update" (opcode 02, manufacturer id 00), but 
many opcodes remain unknown. Do you have any leads on this? 
>Also, I'm 
not very familiar with gnuradio, is there way to place some kind of 
"gate" in flowgraph so some parts of it can be switched on/off by 
external event? I want to use such feature to gate voice channels on/off and do not waste processor cycles on filtering channels that do not 
carry traffic at the moment.
>Best regards,
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