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Re: [Discuss-gnuradio] Selecting specific USB ports for USRP

From: Jeffrey Ung
Subject: Re: [Discuss-gnuradio] Selecting specific USB ports for USRP
Date: Thu, 9 Aug 2007 11:31:54 -0700


Thanks for the speedy response.

Is there any way I could use one USRP to both transmit and receive a signal?  That is, I want to use benchmark_tx.py to send out a dbpsk modulated signal and use benchmark_rx.py to receive this same signal.  Would this be possible?  I'm using a FLEX400 daughterboard.  I actually have two of them.


On 8/9/07, Johnathan Corgan <address@hidden> wrote:
Jeffrey Ung wrote:

> I installed GNU Radio on an Intel OSX machine (with the help of
> Michael Dickens (THANKS!)) and now I was wondering if it were
> possible to specify which USB port the computer should use when
> looking for the USRP.  I ask because I want to connect two USRPs to
> the same computer and run on as a TX for dbpsk and the other as a RX
> for dbpsk.  Is this even possible?  If so, how would I go about it?

It is possible to plug two USRPs in to the USB.

If you are writing your own software, you'll need to add the 'which'
parameter to usrp.source_c() and usrp.sink_c():

src1 = usrp.source_c(which=0)
src2 = usrp.source_c(which=1)

Unfortunately, many of the example programs are written to assume there
is only one USRP, including the digital 'tunnel' program.  So you'll
need to modify these to accept a new command line parameter.

Now which USRP gets assigned #0 and #1 is dependent on the order they
enumerate on the USB, first by bus, then by device.  This may be
affected by which one is plugged in first or turned on first.

It's possible, when writing your own code, to retrieve the serial number
from the source_c object and use that to determine which actual hardware
unit you've grabbed.

The other caveat is that most motherboards share a single USB controller
for all their ports.  So you're sharing the same 32 MB/s bandwidth
across two USRPs now, effectively halving the maximum RF bandwidth you
can work with if both USRPs are using the USB equally.

Johnathan Corgan
Corgan Enterprises LLC

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