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Re: [Discuss-gnuradio] Question about "extra" header

From: Bennett, David S. (Scott)
Subject: Re: [Discuss-gnuradio] Question about "extra" header
Date: Fri, 11 Oct 2013 09:28:58 -0400

> The extra_dict argument to the constructor is just a way to add more data to
> the extra part of the header; any more data you want to add that wouldn't
> be in there normally.
> The extra part of the header collects any tags observed, so the USRP will
> generate tags like rx_freq that will go into the header.
> The metadata section of the manual has a pretty good explanation of how it
> works:
> http://gnuradio.org/doc/doxygen/page_metadata.html
> Tom


Thanks for the note.  As a kind of "hack" programmer, stuff like that isn't 
always clear to me on the first (or second, or third, or etc.) time through 
reading it - usually it's because I don't know exactly what I'm looking for.  
But I was able this morning to add the additional tags (at least a test of them 
with the same data types) to the usrp_source_impl.cc source code, and it looks 
like, when I read the metadata with the gr_read_file_metadata.py script, I can 
read out what I wrote in.  So that's progress.  I guess the extra tags as 
sourced from the USRP are handled by the parser because the expected header 
length is different from where the actual data starts (from the 'strt' tag), 
and the script interprets that additional information as extra header.

I appreciate your help.


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