Re: [Discuss-gnuradio] [USRP-users] Possible to use stream tagging features to implement RX sample bursts after a TX burst?

On Fri, Jun 24, 2011 at 4:54 AM, Tom Rondeau <trondeau1122@gmail.com> wrote:

On Thu, Jun 23, 2011 at 7:21 PM, Colby Boyer <colby.boyer@gmail.com> wrote:

On Thu, Jun 23, 2011 at 4:11 PM, Nick Foster <nick@ettus.com> wrote:

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> Where should I look for the API to tag samples on the USRP?

Tagging in this case has nothing to do with the USRP and everything to
do with Gnuradio. Take a look at the burst_tagger in
gnuradio-core/src/lib/general/gr_burst_tagger.cc for an example.

The Mode S decoder I wrote also uses tags throughout for preamble
tagging and framing, and can be found at
git://github.com/bistromath/gr-air-modes.git.

--n

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> --Colby

I think it does have something to do with the USRP. I need to know at what time my TX sampled got processed by the USRP, as this is the trigger for an RX burst.

--Colby

At one point, we looked into outfitting the UHD source block to read the packet metadata from the USRPs and send a tag when we saw a new time stamp. We took it out for efficiency reasons, but I think you could make another class like gr-uhd/lib/gr_uhd_source_tagged or something like that. Look at the metadata in the UHD packets, see if the timestamp is valid (there's a flag for that), and then you can extract the time and make it a new tag.

Tom

Maybe a better solution would be to use the UHD stream commands? Is it possible to issue a sequence of stream commands and have them executed serially by the USRP?

Example:
* Issue command to send Z samples at clock value M
* Issue command to receive X samples at clock value N
* Issue command to send Y samples immediately based on the decoded received samples

Thanks,
Colby