Bug in split transactions on Raspberry Pi

Alan Stern stern at rowland.harvard.edu
Tue Jan 26 10:21:50 PST 2016

On Tue, 26 Jan 2016, Doug Anderson wrote:

> >> > Yes, but the software doesn't want to display individual SOF packets.
> >> > However I can see, for example, that 84 SOF packets were sent during a
> >> > 10.3-ms period.  Or 2048 were sent during a 256-ms period.  It seems
> >> > pretty regular.
> >>
> >> What analyzer are you using?
> >
> > The Total Phase Beagle 480, with their Data Center analysis software.
> Hrm.  I've got the Beagle 5000 Superspeed on my desk.  I can get it to
> show me individual SOFs, but maybe that's a feature of the new
> hardware?  I'm using Data Center v6.63.000
> I had to turn on lots of stuff to see all this and it eats up lots of
> memory quickly, but it works.  I've got:
> Capture Settings, USB
> -> Sequential
> -> Keep USB 2.0 Data-less Sequences
> In device settings I make sure it's not Filtering anything...

I had the wrong capture settings.  After changing them to match yours, 
I am now able to display the individual SOF packets.

The interval between SOFs is 125 us with a slight excess.  The excess
varies, sometimes 16 and sometimes 33 ns.  This probably represents the
resolution of the analyzer's hardware clock.  Either there's a slight
frequency mismatch between the analyzer and the controller clocks or
else the controller is letting each microframe run about 31 ns too
long.  Still, it seems to be quite regular.

Alan Stern

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