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Re: [Discuss-gnuradio] Run USRP at alternate clock frequency?

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Run USRP at alternate clock frequency?
Date: Fri, 10 Mar 2006 13:48:52 -0800
User-agent: Mutt/1.5.9i

On Fri, Mar 10, 2006 at 11:21:08AM -0500, Clark Pope wrote:
> I would like to run my USRP off a 44 MHz clock instead of the 64 MHz clock 
> that is currently used. A couple reasons:
> 1. the 64MHz rate exceeds the USB bandwidth even with byte-wide samples 
> (64*8 = 512 mbps)
> 2. 44 MHz works much better for the wlan signals I'm after
> So the questions are:
> 1. can I generate a 44Mhz clock from the 64 MHz or do I have to change the 
> crystal?

You need to change the crystal.
You'll also need to change the definition of 

   * \brief return frequency of master oscillator on USRP
  long  fpga_master_clock_freq () const { return 64000000; }

in usrp_basic.h  The rest of the code should follow, though I haven't
tested it.  YMMV, patches welcome ;)

> 2. If I change over to 44 MHz will everything else still work? Especially 
> the dbs and flex2400 boards?

Not sure about those.  Paging Matt Ettus, paging Matt Ettus...


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