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[Discuss-gnuradio] Understanding flow control

From: Charles Irick
Subject: [Discuss-gnuradio] Understanding flow control
Date: Thu, 14 Jan 2010 14:13:01 -0500

I'm trying to understand the flow control between the USRP2 and host
machine. I assume that it needs to be worked out where the USRP2 will
always have a constant stream of uninterrupted radio data when sending
and receiving (unless a more complex radio is in place which allows
the signal to drop).

I have read that overruns are not really an issue, is this due to the
processing power/throughput of the spartan 3 vs the host processor?

I see that pause frames are used to help with flow control but I can
only see this being used if an overrun or full fifo has occured on the
USRP2, what happens if the fifo becomes empty?

I'm trying to catch the pause frames with tcp dump and i'm either
doing it wrong or they are not happening. I have tried usrp2_siggen
and usrp2_fft. I'm using the dev code from git on ubuntu 9.04 with
gnuradio 3.2.2

We are either overflowing, underflowing, or are perfectly in sync.
Only overflow with pause frames to control makes sense to me. If this
is not the case an explanation would be very much appreciated.


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