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Re: [Discuss-gnuradio] Lost samples from RTL2832 dongle


From: CEL
Subject: Re: [Discuss-gnuradio] Lost samples from RTL2832 dongle
Date: Tue, 23 Jan 2018 12:44:14 +0000

Hi John,

my experience, indeed, is that USB passthrough support in VMs is
suboptimal. So, this could very well be a virtual USB host controller
problem.

I'd actually recommend circumventing the issue, e.g. by running rtl_tcp
on the host machine, and using the appropriate source string in the gr-
osmosdr source.

Best regards,
Marcus

On Tue, 2018-01-23 at 12:40 +0000, john cooper wrote:
> Hello GNU people, some help greatly appreciated.
> 
> I am a newbie to GNU Radio and have a lost samples problem,  lost from the 
> USB 2  RF device, seemingly not in the Flowgraph signal chain.
> 
> Although I have no hard evidence I am coming to the point of suspecting the 
> problem lies with the running of GNU under Oracle VM,  hosted by Win 10.
> 
> Physical RF device is a  DVB-T+DAB+FM USB dongle, with Realtek RTL2832U and 
> the R820 device.
> 
> System is GNU Radio ( latest version )  running as a guest under Oracle VM, 
> hosted by Win 10 Pro on a machine with significant system resources.
> 
> Oracle version is VM 5.2.6r
> 
> Problem is *always* dropped samples from a DVB-T+DAB+FM USB dongle, tens to 
> hundreds of lost samples.
> 
> I have done the following :-
> 
>     Added my name to the virtualbox users list.
> 
>     added the Virtual Box Extension Pack 5.2.6     to allow USB 2 support in 
> the VM
> 
>     Selected USB2 in the Oracle VM machine.
> 
>     Blacklisted the RTL2338 DVB-T  driver  via   
> /etc/modprobe.d/blacklist-rtl.conf    etc.
>     
>     Tested with rtl_test with sample speeds from 2.4e6 down to 0.25 e6
> 
>     Several Flowgraphs of various example FM broadcast receivers all have 
> choppy audio, believed to be due to lost sample from the RF device via USB2 
> and not seemingly due to mismatch of audio sing sample rates.
> 
> 
> Using only the RTL_SDR source block and Low Pass Filter, plus the WX GUI FFT 
> Sink and the WX GUI Scope Sink, in a FlowGraph produces spikes in the Audio 
> which coincide with the suggested sample losses from the physical dongle.
> 
> 
> Under any and all tests and sample rates the result of rtl_test when ran in 
> the terminal is a continual stream of lost samples.
> 
> 
> Other information;
> 
> running SDR# via the host system ( Win 10 Pro )  is faultless at 2.4e6 sample 
> speed and all lower speeds.
> 
> I have also  installed Gqrx in the VM and this system stalls with the 
> Terminal screen failing to enter the initial set up dialogue screen but does 
> list in the terminal screen the list of parameters, then hangs.
> 
> If anyone has input to the problem, I would be very pleased to hear back and 
> offer my thanks in advance.
> 
> John
> 
> 
>       Virus-free. www.avg.com
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> Discuss-gnuradio mailing list
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