[hpsdr] VMs and USB2

[Bob Cowdery]

Hi Graham

It must be turnround time, latency, pauses etc as the raw throughput is
more than enough. I don't understand the issues but I will do some
experimentation.

Bob


On Thu, 2009-02-05 at 17:00 -0600, Graham / KE9H wrote:
> Bob:
> 
> First, you have an I signal and a Q signal, so double your
> inbound data rates, then add something for overhead signalling.
> 
> But I suspect the bigger issue is latency/response time. 
> If your VM machine assigns the USB to Windows for a
> while, then goes away and does other things for a while,
> you could have full rate for one fourth of the time, and
> nothing for 3/4 of the time. If the nothing period is longer
> than a frame period, then the system will start dropping frames.
> 
> If PowerSDR is ready to process the next block of data,
> and it is not there, then it seems to substitute a silent frame,
> and keeps moving. Your ear interprets this as distortion.
> 
> So you have a quasi-real time process called PowerSDR,
> and an interrupted time sharing VM in between it and
> the HPSDR hardware.
> 
> Just my guess.
> 
> --- Graham
> 
> ==
> 
> Bob Cowdery wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > I should have done these very simple tests before I started but
> > hindsight is a wonderful thing.
> >
> > I copied a 288MB file from a USB stick to my hard drive. All systems are
> > reporting a USB device at 480Mbps (although it's hard to get info out of
> > XP).
> >
> > On my host Ubuntu system this takes 12 seconds.
> > On the VM's both Ubuntu and XP it took 45 seconds.
> >
> > This is 4 x slower so it should equate to about 120Mbps. In practise we
> > seem to be going about 1/2 speed anyway accounting for protocol, the
> > stick itself and disc write times I suppose that's reasonable.
> >
> > Why would this not be way more than is needed to transfer 48k at 24 bits
> > and 48k back at 16 bits. What am I missing here?
> >
> > 73
> > Bob
> > G3UKB
> >
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> >   
> 


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