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Re: [Discuss-gnuradio] USRP I/O Buffering


From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] USRP I/O Buffering
Date: Sun, 07 Sep 2014 16:35:21 -0400
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On 09/07/2014 04:24 PM, Peter Witkowski wrote:
Hello,

I have a simple application written in Python using GNURadio.  All I am trying to accomplish is to have the USRP data be written to disk.  The application works fine when I dump data to /dev/null or run it at reduced sampling rates.  However, when I run at my desired sampling rate, I have a good amount of buffer overflows (a series of "O" characters get printed).

The host machine that I am working on should have no problems sampling at the higher rates, but I have found a curious issue in that not a whole lot of memory is used up by my GNURadio application.

As a result, I am wondering if there is any way to tell GNURadio to use larger buffers (on the order of a few GB) in order to prevent data from being dropped.  I noted that there seem to be several function calls available in the C++ API, but there seems to be a limited set of these calls in the Python wrappers.  Latency is a non-issue for me at the moment, but I need to capture all the data without dropping a large amount of data.  Note that I have the code running with "real-time" priorities in Linux.

Thanks for your help.  FYI I am running GNURadio on Ubuntu 14.04.  Also, I know that my RAID set-up is capable of writing to disk at twice the rate of data coming in per benchmarking the HDDs.

--
Peter Witkowski
address@hidden
_______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Adding buffering for long-term recording simply delays, by a few seconds, that point at which your system cannot keep up.


What sample rates are you trying to record?  What does your flow-graph look like?

Buffering is useful to allow you to "ride through" short-term shortfalls in the ability to handle samples.   It is useless for handling the situation
 where your long-term ability to keep up falls short of what you actually need.

Have you tried setting up a ramdisk, and writing to that?


-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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