[hpsdr] VMs and USB2

[Graham / KE9H]

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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