Re: [Discuss-gnuradio] CC1101 GFSK packet decode with variable length

[Daniel Estévez]

Hi,

Besides using the Header Payload Demuxer as Julian suggested, a simple
trick when the packet size is unknown but limited to a (not very large)
maximum size is to cut a PDU with the maximum packet size and then throw
away everything you don't need.

I have a CC1101 decoder in gr-satellites that does variable length
packets using this trick. See
https://destevez.net/2018/12/decoding-reaktor-hello-world/

Best regards,

Daniel.

El 31/12/18 a las 01:28, Julian Arnold escribió:
> Hey Bob,
> 
> there is plenty of documentation on this topic you can check out under
> [1,2].
> Especially, the Header Payload Demuxer (HPD) [3] should be worth a look
> if you are dealing with packetized variable length data.
> 
> Hope those pointer can get you started. If you have further questions
> after going through those pages, let me know.
> 
> Cheers,
> Julian
> 
> [1] https://www.gnuradio.org/doc/doxygen/page_packet_data.html
> [2] https://www.gnuradio.org/doc/doxygen/page_packet_comms.html
> [3]
> https://www.gnuradio.org/doc/doxygen/classgr_1_1digital_1_1header__payload__demux.html
> 
> 
> On 31.12.18 01:00, Alban Meffre wrote:
>> Hi
>> I would like to decode a simple GFSK packet
>>
>> here is the packet structure :
>> preamble : AAh x 4
>> sync word : D391h
>> length byte : 1 byte
>> payload : 1 to 64 bytes
>> CRC : 2 bytes
>>
>> TX : arduino + CC1101 module, 2GFSK, 100kbps, excursion 50kHz, carrier
>> 433 MHz
>> RX : RTLSDR
>>
>> until now i was able to demodulate the signal and add a "sync" tag
>> using the correlate access code.
>>
>> my goal is to extract the payload and send it to a file or a socket.
>> is there a simple way to do that without writing my own block ?
>>
>> i can't go further, because i do not manage to find the info i need
>> i do not know where to start : stream, tagged stream, PDU, messages,
>> etc..
>> i do not figure out how to use these tag for variable length. nothing
>> clear in the doc
>>
>> i'd be glad if someone helps me
>> best regards
>> bob
>>
>>
>>
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