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Re: [Discuss-gnuradio] Daughterboard clocking on USRP2

From: John Orlando
Subject: Re: [Discuss-gnuradio] Daughterboard clocking on USRP2
Date: Tue, 16 Mar 2010 18:52:02 -0500

> On Tue, Mar 16, 2010 at 04:34:44PM -0500, John Orlando wrote:
>> Hi all,
>> Just looking through the WBX daughterboard code in the latest git repo
>> for adding support for the USRP2 (which can be found at
>> usrp2/firmware/lib/).  I noticed that in adf4350.c, there is a #define
>> for INPUT_REF_FREQ that is defined as 50e6 (50 MHz), which is then
>> used in all of the follow-on calculations for determining register
>> settings.  I had thought that the USRP2 only provided a 100 MHz ref
>> clock for use by the daughterboards on the clock_rx_p line, but I must
>> be missing a divide by 2 some place.  Can anyone confirm A) if the WBX
>> runs off of 50 or 100 MHz, and B) if it is 50 MHz, how the clk div 2
>> occurs on the USRP2?
> The adf4350 has a ref clock doubler and ref clock divider bit, in
> addition to the R divider setting.  In the case of WBX on USRP2, we use
> the ref clock divider bit (adf4350_regs.c, line 34, adf4350_regs_rdiv2),
> hence the 100M clock is divided to 50M on the adf4350 before the R
> divider.
Ahh...gotcha.  Makes sense now.
> I could have written the INPUT_REF_FREQ more clearly, my apologies for
> the confusion.
No worries.  I just wanted to make sure I wasn't missing something.
Thanks for the quick response Jason.

John Orlando
CEO/System Architect
Epiq Solutions

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