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Re: [Discuss-gnuradio] Using Header/Payload Demux


From: Martin Braun
Subject: Re: [Discuss-gnuradio] Using Header/Payload Demux
Date: Mon, 27 Jan 2014 09:12:24 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0

On 01/25/2014 09:30 PM, chris 0 wrote:
> Tag Debug: Rx Bytes
> Input Stream: 00
>   Offset: 0  Source: n/a     Key: packet_len   Value: 14
>   Offset: 0  Source: n/a     Key: packet_num   Value: 0
>   Offset: 1  Source: n/a     Key: packet_num   Value: 1
>   Offset: 1  Source: n/a     Key: packet_len   Value: 112
>   Offset: 3  Source: n/a     Key: packet_num   Value: 2
>   Offset: 3  Source: n/a     Key: packet_len   Value: 112
>   Offset: 5  Source: n/a     Key: packet_num   Value: 3
>   Offset: 5  Source: n/a     Key: packet_len   Value: 112
>   Offset: 7  Source: n/a     Key: packet_num   Value: 4
>   Offset: 7  Source: n/a     Key: packet_len   Value: 112
>   Offset: 8  Source: n/a     Key: packet_num   Value: 5
>   Offset: 8  Source: n/a     Key: packet_len   Value: 112
>   Offset: 10  Source: n/a     Key: packet_num   Value: 6
>   Offset: 10  Source: n/a     Key: packet_len   Value: 112
>   Offset: 12  Source: n/a     Key: packet_num   Value: 7
>   Offset: 12  Source: n/a     Key: packet_len   Value: 112
> 
> For some reason the first packet_len is still 14, rather than 112, which
> is confusing me.

Hi Chris,

this is, in fact, correct behaviour.
HPD -> All lengths are 14
Multiply tag -> All lengths are 112
Repacker -> Finds first tag, uses that for processing and scales it
back. You can test this by adding more tag debugs.

An easy solution would be to pipe the OUTPUT of the initial repacker
into both the header generator and the payload modulator. This way the
number of symbols gets coded into the header. Note that this length is
also used in the HPD to slice the payload out of the rx'd stream.

See: http://i.imgur.com/1ciVDjM.png

I'm beginning to realize that maybe the default header generator needs a
scaling value as well. *sigh*

MB



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