[op25-dev] Control channel decoding

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Matt Mills mmills at 2bn.net
Wed Aug 1 19:44:54 UTC 2012

FYI, some versions of libboost cause bugs/crashes in the valve.
Specifically (the last time I checked) the versions that come packaged with
ubuntu. Compiling from latest source does not have any issues (that I've
seen). Also, Stream-selector in place of a valve I've had less issues with.

On Wed, Aug 1, 2012 at 2:51 AM, Dmitry Medvedev <qaghqga at yahoo.com> wrote:

> 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,
> Dmitry
>   ------------------------------
> *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
> Dmitry,
> I'd suggest using a valve or stream selector for that. Do you have any
> interest in sharing your source code?
> Thanks,
> Matt.
> 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,
> Dmitry
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