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Re: [Discuss-gnuradio] Losing data during long collects


From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Losing data during long collects
Date: Tue, 3 Jun 2008 14:23:08 -0700
User-agent: Mutt/1.5.17 (2007-11-01)

On Tue, Jun 03, 2008 at 01:41:03PM -0700, Chris Stankevitz wrote:
> Hi,
>
> I'm using the USRP/DBSRX to record data for GPS.  GPS tracking demands a
> continuous stream of data -- dropped bits make tracking impossible.
> 4Msps of complex data supplies 16 MB/s -- within USB2 bandwidth and my 4
> disk RAID0 bandwidth.
>
> I record the data using my own c++ version of cfile.  I never get an
> error or overrun condition from usrp_standard::read so it appears that
> everything is working fine.  However, when I process the data it is
> clear that data is dropped -- approximately a few thousand samples every
> minute or two.  I typically record data for one hour at a time.


Bug in your code?  Are you double buffering or something?  Are you
properly handling locking between the producer and consumer?

> I read data from the USRP in batches of 8192 16 bit short samples.
>
> Anyone have any tips on tracking down why I am dropping data?
>
> Thanks,
>
> Chris

If you're running Linux and writing to an ext3 filesystem,  try
remounting it as an ext2 filesystem.  I've seen problems in the past
when the ext3 filesytem posts its journal, however they showed up as
overruns -- the filesystem wasn't keeping up.

Eric




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