[Discuss-gnuradio] USB transfers speeds with USRP 1

Can anyone please help me with something?

I have an application using 2 tv tuner modules that I need to capture
samples from.  The code that explains what the setup follows.

self.u = usrp.source_c(decim_rate = options.decim, nchan = 2)

self.skiphead0 = gr.skiphead(gr.sizeof_gr_complex, 1000)
self.skiphead1 = gr.skiphead(gr.sizeof_gr_complex, 1000)
self.head0 = gr.head(gr.sizeof_gr_complex, int(options.nsamples ))
self.head1 = gr.head(gr.sizeof_gr_complex, int(options.nsamples ))
                
self.di = gr.deinterleave(gr.sizeof_gr_complex)
self.dst0 = gr.file_sink(gr.sizeof_gr_complex, filename0)
self.dst1 = gr.file_sink(gr.sizeof_gr_complex, filename1)
                
self.connect(self.u, self.di)
                
self.connect((self.di,0), self.skiphead0, self.head0, self.dst0)
self.connect((self.di,1), self.skiphead1, self.head1, self.dst1)

self.u.set_mux(gru.hexint(0xf2f0f2f0))

After this I set the gains of the tv tuners and the ddc and tuner
frequencies.  When I use a decimation of 16 (resulting in two IQ
channels at 4Msps each) and try to capture 10seconds of data, I get a
lot of 'uO' messages on the console.  When I use a decimation of 32, I
still get some 'uO' messages on the console.  Only when using a
decimation of 64 (two 1Msps IQ channels) do I not get any 'uO'
messages when capturing 10s of data.

Now, the funny thing is that when I run test_usrp_standard_rx in
/usrp/host/apps using sudo ./test_usrp_standard_rx -D 8 -M 900, I get
noverruns=0.  So with my PC and USRP I can actually get a transfer
rate of 32MB/s which leads me to believe that something in the setup
of my application might cause the problems with the USB transfer rate.

Does anyone have any ideas to what might be happening?

Thank you in advance.

Sebastiaan

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


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