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Re: [Discuss-gnuradio] usrp2 tune two different frequencies

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] usrp2 tune two different frequencies
Date: Mon, 20 Apr 2009 09:42:30 -0700
User-agent: Mutt/1.5.18 (2008-05-17)

On Mon, Apr 20, 2009 at 11:32:42AM -0400, address@hidden wrote:
> On Mon, 20 Apr 2009, Johnathan Corgan wrote:
>> On Mon, Apr 20, 2009 at 7:59 AM,  <address@hidden> wrote:
>>> Is there any reason why the situation could not be the same as with the
>>> USPR1, with which I can program 2 DDC's on 1 LFRX daughterboard (with the
>>> appropriate mux) to tune in two separate frequencies?
>> Yes, the USRP2 only has one DDC in the FPGA code.
>> Johnathan
> I guess I was just curious why there is only one DDC in the FPGA, and if  
> it's possible in future that more than one will be made available.
> thanks,
> eric

Eric, this will probably all change as part of the VRT (VITA-49 work).
A big part of that design work is a strategy for naming all of the
things that you might want to control, and how they're arranged.  For
example, on the USRP1 you have up to 4 DDCs, but they are all run at
the same decimation rate.

The current working concept is that we'll have a hierarchy something like this:

  Physical Unit (e.g., mimo interconnected USRP2s)
    Pipeline (everthing in the pipeline is running at the same sample rate)
      Signal (would handle multiple DDCs in a given pipeline)

We'd like to come up with a control protocol that gives us reasonable
flexibility.  That is, users can build custom FPGA images without
having to hack up a bunch of host and/or firmware to make the new FPGA
image work.  Our current on-the-wire protocol is quite fragile.  It
was originally cooked up to facilitate quick testing of the USRP2, but
then the USRP2's shipped with it...  The VRT work will be much better
thought out, and will support ease of use, flexibility, and extensibility.


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