[op25-dev] Control channel decoding

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Stephen ctx50026 at centurytel.net
Tue Jul 31 18:42:53 UTC 2012

There is a valve block that works like a switch. There is also a stream
selector block that can switch one or more inputs to one or more outputs.

You can find the stream selector block here


On 7/31/2012 3:09 AM, Dmitry Medvedev 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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