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Re: [Discuss-gnuradio] USRP2 PPS and REF

From: Douglas Geiger
Subject: Re: [Discuss-gnuradio] USRP2 PPS and REF
Date: Tue, 10 Feb 2009 10:48:18 -0600
User-agent: Thunderbird (Windows/20081209)

Eric Blossom wrote:
> Hi Charles,
> You have to tell it to use them.
> Take a look in <usrp2/usrp2.h>:
>   config_mimo(MC_WE_LOCK_TO_SMA)
>   sync_to_pps()
> There are python bindings for these.
> (Oops, looks like we're missing the python binding for config_mimo...)
> Are you using this from Python?  If so, I'll fix this later on today.
> Eric

 On a related note. If I have two (or more) USRP2's locked onto my 10MHz
and 1PPS signal (calls to ->config_mimo(MC_WE_LOCK_TO_SMA) and
->sync_to_pps() return true, so I believe they are), do I need to do
anything else special?
 I'm working C++, based on the rx_streaming_samples.cc code - I have two
 usrp2 sptr's, u2a, and u2b (each created with a separate make() using
the specified mac address from the command line).
 Once I start streaming samples (making two calls:
u2a->start_rx_streaming(0), and u2b->start_rx_streaming(0)), and then
with two different handlers for receiving the samples:
 bool oka = u2a->rx_samples(0, handlera.get())
 bool okb = u2b->rx_samples(0, handlerb.get())
Where the handler is just writing to the specified files.

 I'm getting some odd results: both files typically end up with exactly
the sample results (i.e. in octave, subtracting the results of one from
the other results in all zeros). Since I've now tried this a few times
doing things like: removing the antenna from one (and not the other),
moving them far apart, etc. - I'm fairly certain this is a software
problem, and not the correct results.
 I can post my code if that would be helpful - I'm hoping I'm just
making some silly mistake with my calls to rx_samples, and the copy
handler or something similar. E.g., should I be using different channel
 I just updated the firmware on my USRP2's to r10377, and the fpga
bitstream to r10183.

Doug Geiger
Research Assistant
Communications and Signal Processing Lab
Oklahoma State University

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