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Re: [Discuss-gnuradio] UHD GRC loopback glitches

From: Josh Blum
Subject: Re: [Discuss-gnuradio] UHD GRC loopback glitches
Date: Fri, 17 Sep 2010 13:44:42 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100826 Thunderbird/3.0.7

This could very well be underflow on the tx or overflow on the rx. Are you seeing Us and Os printed to stderr while running? I suggest:

1) reduce the sample rate to see of that fixes or reduces the problem
2) isolate the problem as either an rx or tx problem
3) if this in linux, make sure you have enabled a large rx buffer


On 09/17/2010 01:16 PM, Marc Epard wrote:
I have a simple GRC flowgraph that transmits a complex sine wave on a UHD USRP2
with a WBX, receives on a USRP2 with a DBSRX, and displays the output on a
scope. The two boxes are connected via a 30dB Mini-Circuits attenuator. Mostly
the output looks as I expected, but every 350 microseconds or so there's a
glitch that looks like the receiver stops and starts. You can see the effect in
the screen capture below (or in the PNG at https://public.me.com/mepard in the
gnuradio folder, where you'll also find the flowgraph).

I'm using current UHD and gnuradio code via git on a very capable machine
running Ubuntu 10.04. System Monitor shows one CPU at 100%, one at 25 - 40% and
the others blow 25%. Wireshark shows a lot of activity on the control port for
the receiver, but I haven't deciphered the packets (anyone have a UHD 

Any idea what is causing this or how I should troubleshoot it?



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