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Re: [Discuss-gnuradio] Understanding flow control

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Understanding flow control
Date: Fri, 15 Jan 2010 10:12:49 -0800
User-agent: Mutt/1.5.20 (2009-08-17)

On Thu, Jan 14, 2010 at 10:11:38PM -0500, Tom Gross wrote:
> Following up on my previous email, thinking about this some more:
> I'm guessing that we are sending the USRP2 more data than it can
> handle, it is sending pause packets back, which when RX is ON, the
> ethernet card recognizes and slows down its output (not knowing
> anything about gig-e control flow but this sounds like x-on x-off),
> which causes our system to become unstable, BUT when we turn of RX on
> the ethernet device, it ignores the pause packets coming back from the
> USPR2, and keeps bombarding the USRP2 with transmitter data.
> so what happens if we ignore the pause packets? does the USRP2 drop
> packets on the floor and just output stuff as fast as it can?

Tom, are there any switches between the host and the USRP2?
If so, try removing them.  PAUSE frames and switches don't interact

I'm not sure I'm following the physical interconnection of the pieces.
Is this the set up?

  Does the host have two gig E ports?
  Is there a dedicated cable between eth<N> and USRP2 <1>?
  Is there a dedicated cable between eth<N+1> and USRP2 <2>?
  The two USRP2's are connected with a MIMO cable?


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