Re: [Discuss-gnuradio] File sink causes "S" errors

[Marcus D. Leech]

On 10/05/2010 09:35 PM, Thomas Hobiger wrote:
> Hi everybody,
>
> I am running a USRP2 with a DBSRX and talking to the hardware via raw
> ethernet. Running GRC goes well (e.g. doing a real-time FFT spectrum),
> but when I start recording on disc I get many "S" messages ("2
> successive packets which do not have 2 successive sequence numbers")
> after about 10 seconds. I am currently sampling with a decimation of
> 4, but the problem remains with other decimation factors as wekk, just
> the messages show up slightly delayed. I think the HD itself is not
> the reason as I am recording to a 80 GB SSD, which has EXT4 and is
> mounted in a quite fast mode (I have benchmarked the I/O giving me
> much more bandwidth than what streams in from the USRP2).
> I have started to modify parts of the GNURADIO code, but changing
> buffer sizes does not help much.
>
> Is there anybody who experienced similar troubles?
>
> Regards,
>   Thomas Hobiger
>
You might try converting your samples to a more-compact format prior to
recording them.

If you're trying to record complex-float at 25Msps, you'll run out of
disk-io throughput pretty
  quickly.

If the dynamic range of your data can be represented in bytes, for
example, then you only
  need to sustain sps x 2 bytes per second for complex signals.  If you
can get away with
  real-only signals, then you're looking at sps x 1 bytes per second of
required write performance.


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