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

From: Juha Vierinen
Subject: Re: [Discuss-gnuradio] Losing data during long collects
Date: Wed, 4 Jun 2008 20:04:16 +0300

I have sampled continuously for many hours without problems. I had a
setup with USRP syncronized to an external clock. I have then measured
a constant frequency sinusoid derived out of the same clock and
verified that the ratio of consecutive complex samples was always
constant (up to a certain error term). I have also measured carefully
timed pulses that are derived out of the same clock, and they appear
exactly in the correct place even after many hours of sampling.

However, I never managed to get the normal filesink working without
dropping samples (even though others haven't had any problems). I
suspect that the filesystem was the reason. I have only tried sampling
with ext3 and mainly XFS.  Since I didn't know any better, I wrote my
own double buffered filesink block, which is available here:


There is also an example sampler.py application that can be used for
sampling data. The program saves the samples as big endian short
integers. It also conveniently chops up the data into small
processable constant length files.


On Tue, Jun 3, 2008 at 11:41 PM, Chris Stankevitz <address@hidden> 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.
> 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
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