[Discuss-gnuradio] Question about the USB of USRP1

[Sebastiaan Heunis]

Hi all

I've got a question about the bandwidth that the USRP1 can support
across the USB.  We have 32MB/s across the USB corresponding to 8Msps
for a single I-Q stream.  When we have two I-Q streams, this becomes
4Msps for each stream.

This means that when I have two I-Q sampled channels, I should be able
to set the decimation for each channel to 16.  This does however not
work.  With two I-Q channels, if I set decimation to 16, I get about
40 of those 'uO' s printed on my screen.  With a decimation of 32, I
get about 4.  With a decimation of 64, I get none.  So, currently I am
only able to support 8MB/s accross my USB without losing any samples.

I ran the usrp_benchmark_usb.py and got the following:

Testing 32MB/sec... usb_throughput = 32M
ntotal    = 16000000
nright    = 15999965
runlength = 15999965
delta     = 35
OK

So here I'm also losing 35 samples?

I have an HP Pavilion dv6500 laptop with a 1.5GHz Core2Duo CPU and 2GB
of RAM.  I'm also using a CPU frequency scaling utility to make sure
that my PC is running at full blast.  Might it be that the USB
controllers of laptops aren't that great, or is it normal to lose some
samples at 32MBps?

Thanks.

Sebastiaan

-- 
Sebastiaan Heunis
Radar and Remote Sensing Group, University of Cape Town, South Africa
Tel:  +27 83 305 5667