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Re: [Discuss-gnuradio] usrp_multi and the USRP2

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] usrp_multi and the USRP2
Date: Tue, 3 Feb 2009 13:23:28 -0800
User-agent: Mutt/1.5.18 (2008-05-17)

On Tue, Feb 03, 2009 at 02:33:15PM -0600, Douglas Geiger wrote:
>  Is there any code similar to usrp_multi.py to use multiple USRP2's
> already (or is it unnecessary)? As I understand it, with the USRP2, you
> either use the MIMO cable, or an external reference to synchronize the
> clocks - then on the host side you would still need to do the
> align_on_samplenumbers/deinterleaving, etc. business that usrp_multi.py
> took care of for the USRP1.
>  If nobody has code available to do this, should I expect any major
> hurdles in trying to convert the usrp_multi.py for use with the USRP2
> (besides converting the source create calls, removing the subdev calls,
> etc)?
>  If I'm using the MIMO cable, do I need to make any additional settings
> (e.g. sync_to_pps(True) or similar) to synchronize the master to slave?
> http://gnuradio.org/trac/wiki/USRP2GenFAQ says the VCXO locks on to the
> external reference, if one exists - which implies this is also the case
> for the MIMO cable, just wanted to verify that was true.
>  Looking at test_mimo_tx.cc in the u2-mimo-wip branch I see it is
> possible to setup one usrp2 interface, and send samples to different
> channels - is that accessible from python now - or is it still code
> that's in development? If that's the case, is it possible at all to get
> synchronized samples out of two usrp2's with a MIMO cable right now with
> python, or should I be writing something in C++ to do that for me?
>  Perhaps
>  Thanks,
>   Doug


There's currently no production code that supports using the USRP2 and
the MIMO cable.  We have test code that confirms that the h/w works as
we expect, but we're not going to sort this out until after "the great
reworking" of the host, firmware and on-the-wire spec as part of our
move toward VITA-49 (VITA Radio Transport), an emerging standard for
digital IF.

In the meanwhile, you can make this work by providing your own
star-distributed 10 MHz reference and PPS.  All USRP2's will be
coherent and will share the same timestamps.  You will have to invoke
config_mimo(MC_WE_LOCK_TO_SMA) and sync_to_pps() on each USRP2.


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