[op25-dev] Control channel decoding

Dmitry Medvedev qaghqga at yahoo.com
Tue Jul 31 08:09:51 UTC 2012


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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