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Re: [Discuss-gnuradio] external ref

From: Brett L. Trotter
Subject: Re: [Discuss-gnuradio] external ref
Date: Fri, 12 Nov 2010 13:32:10 -0600
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On 11/09/2010 11:44 PM, Brett L. Trotter wrote:
> Does any alteration to code or firmware need to be made in order to get
> a USRP2 to lock to an external 10MHz reference?
I'm still looking for more information on this subject, and have some
additional information to add.

We're still in the non UHD realm, but looking into trying out the Python
method of telling the AD9510 to use the 10M refclock. In any case, I
wrote a new firmware that enabled the test output and told it to lock to
SMA, but I was unable to confirm based on the reported PPM drift in our
receiver or by scoping the test clock outs on both usrps at the same time.

The only conclusion we could come to by going back and forth between the
standard firmware and my ref sync firmware was that the test port was
being enabled but that the PPM generally stayed in the same range and
felt like either the clocks are good enough the oscillator wasn't
helping, they're syncing up with eachother by proximity effect, or we're
doing something wrong with the sync enable.

So the questions I have are:
1) I initially modified txrx.c
+   // trigger lock to SMA
+   clocks_mimo_config(MC_WE_LOCK_TO_SMA);
+   // enable debug clock
+   clocks_enable_test_clk(true, 1);

which definitely enabled the output port.
I later tried changing MC_WE_DONT_LOCK in clocks.c to MC_WE_LOCK_TO_SMA,
but saw no change which was generally expected. Am I doing the right
thing or is there something more we should be doing to properly enable
the ref sync?

2) the docs are saying the UHD firmware lights up LED E for ref sync,
but non UHD firmware has no indication. Is there a way to enable the
same light in the non UHD firmware?

3) just out of curiosity, what's involved in enabling J505 (the 2nd
output of the DS90CP22) just as it would give us one more place to prove
the clock is getting in to the USRP2.

All in all it seems UHD is the answer, but non-UHD is the more known
entity to us. If you have answers to any or all of these questions, any
thoughts or confirmation would be really handy.


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