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Re: [Discuss-gnuradio] USRP2 and external clock (from GPS receiver)

From: Douglas Geiger
Subject: Re: [Discuss-gnuradio] USRP2 and external clock (from GPS receiver)
Date: Fri, 20 Feb 2009 11:37:44 -0600
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Matt Ettus wrote:
> Douglas Geiger wrote:
>> I'm at svn revision 10441 - with both the firmware and fpga code built
>> from that (using Xilinx ISE 10.1 to make the fpga). I've just modified
>> the txrx.c code - adding:
>> clocks_enable_test_clk(true, 2);
>> clocks_mimo_config(MC_WE_LOCK_TO_SMA);
>> just before the while(1) loop
>> My rx_mimo.cc code also calls ->config_mimo(MC_WE_LOCK_TO_SMA), but
>> right now I've stepped back to just getting one USRP2 synchronized to my
>> external source - which in this case is a function generator with a
>> 10MHz sine with 2V P-P.
>> Is it possible some of the hardware on my USRP2's isn't working?
> Unlikely, since it was tested before shipping.
> I will send you code to run in a separate email.
> Matt

 Ok - now that I've discovered I had some bad cabling - specifically a
bad T-splitter: the side going to my O-scope worked, the side going to
my USRP2's did *not* - which I suppose can be chalked up to user error.
I am now able to synchronize the clocks - both with the firmware/fpga
code you sent, and the version I had built locally.
 However - once I start running my code on the host PC, the clock loses
sync. I have to power down, and re-power-up the USRP2 for the clock to
lock onto my external source again. This is with the firmware/fpga from
svn r10441, and my host code. I've tried calling ->config_mimo and
- ->sync_to_pps() as soon as I create my USRP2 objects, but that didn't
seem to help.

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