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Re: [Discuss-gnuradio] Problem with USRP2 continuous transmission at >10

From: Christoph Thein
Subject: Re: [Discuss-gnuradio] Problem with USRP2 continuous transmission at >10MHz
Date: Mon, 12 Oct 2009 16:03:43 +0200
User-agent: KMail/1.11.2 (Linux/2.6.28-15-generic; KDE/4.2.2; i686; ; )

Hi Matt,

thanks for the advice. We connected the serial port and couldn't observe the 
underrun message and we enabled the realtime scheduling but there was no 
improvement. Strangely enough after that the program only works without 
interrupts  if it is started as su in a shell and if this shell window is put 
in the background of the desktop (meaning that another window is the one we 
are working in right at that moment). 

We are using Ubuntu 9.04 with the latest trunk version of gnuradio but don't 
know enough about the OS realtime scheduling issue to explain it. Does anybody 
have more knowledge about ubuntu  and realtime to explain this behaviour? 


Hanwen and Christoph

> hanwen wrote:
> > Hi,
> >
> > We use tx_samples.cc to transmit a file with 16bit-short complex samples
> > at 10MHz and 20MHz. We use another USRP2 to receive the signal and store
> > on disk. We observed there are some unexpected gaps in the received
> > samples. Using usrp2_fft.py with the osiliscope view, we also observed
> > such kind of gaps.
> > We guess this might be caused by underrun at the transmitter side. We
> > use the delievered ethernet cable, so this shouldn't be the problem of
> > bad cable.
> > Anyway, how can we transmit samples contineously and stably without
> > underrun at 20MSamples/s??
> 1 -- Make sure you have realtime scheduling enabled
> 2 -- Use a very fast computer
> are you sure you are seeing underruns?  Have you connected to the debug
> serial port on the USRP2 and seen it send "U"?
> Matt
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