Volk machine

When running with a USRP source at 25M and a low pass filter down to
10MHz,
I get something saying “Using Volk machine: sse4_a_64”, and my file sink
only records a couple seconds of data. I ran the volk_profile script,
but
still get the same result. The script returned something other than
“sse4_a_64” as the best volk to use. My GNU Radio seems to have trouble
reading configuration files, so is there a way to manually point to the
volk parameter to use when I load GNU Radio?

Paul B. Huter

Your file sink only records a few seconds of data because your hard
drive
can’t keep up, not because of any problem with Volk. The Volk machine
being
used does not indicate which particular architecture is used for each
kernel – that isn’t printed at runtime.

–n

I agree with Nick: that VOLK stuff is all expected behavior. If you’re
trying to write to a file at high rates you should look in to using a
ramdisk/tmpfs. You’ll be limited by how much RAM you have rather than
IO speed.

However, based on your other threads I wonder if you’ve taken Tom’s
recent suggestion to just lower your input sampling rate? If you’re
only interested in ~1MHz bandwidth you shouldn’t be sampling at 50
MHz.

-nathan

Paul,

30MHz is a big chunk of data to be streaming to anything. A 4GB ramdisk
will be full in 30 seconds at this rate. Do you really not know a
priori
where
in the whole 0-30MHz spectrum your signal will be?

I notice now in your first post that you’re streaming 25Msps with a
low-pass filter to 10MHz – if this is the case, why use a 25Msps rate
in
the first place? You can make the USRP work for you by asking for 10Msps
(or less, if you know you need less bandwidth) – it’ll handle the
downsampling and filtering.

–n

I finally got around to trying writing to RAM, and the result is worse -
my
replay FFT is static.

I am trying to record a chunk of spectrum (in this case the shortwave
chunk, 0-30MHz) and then go back and look at small pieces to find my
specific data. If someone can provide insight into how to do this, I
would
appreciate it.

Thank you all for all the assistance to date.

Paul B. Huter

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