[ntp:questions] is USB inherently evil, or only if something else is on the bus?

Chris Albertson albertson.chris at gmail.com
Thu Aug 9 01:29:17 UTC 2012


USB is always worse than a PPS directly attached to a serial port. there is
far less (orders of magnitude less) uncertainty in the interrupt latency
for USB

"Local" is not a good idea.  Something called "Orphan Mode" is developed to
handle the problem if s disconnected network.

If there were a FAQ these tow questions would be near the top of the list

Some place else on the list is "Which OS?"  I think now Linux is as good as
BSD, now that Linux has good PPS support.



On Wed, Aug 8, 2012 at 2:34 PM, Rick Jones <rick.jones2 at hp.com> wrote:

> I've scrounged a couple old Pentium M laptops (Hewlett-Packard nc6000s
> for the trivia-minded) with serial ports while entertaining the
> possibility of undertaking a project to do what so many others have
> done - connect-up a GPS receiver with PPS support.  That has me
> wondering about some of the previous discussion about USB and how it
> is perhaps not "evil" but considered quite sub-par for serving-up the
> PPS signal.
>
> Is that unsuitability inherent in USB, so it matters not whether there
> is anything else on the USB, or is it more a case of being "bad"
> generally only when other things are on the same USB?  I'm still
> looking to go serial, but was wondering.
>
> Also, speaking of things considered "bad" and drifting - fudging the
> LOCAL(0) is definitely frowned upon right?  If I happen to have say
> four servers in a location which might loose its connectivity to the
> outside world I probably don't want those servers to fall-back on
> LOCAL(0) right?  Would configuring each to have the other three as
> "peer" entities be the way to go?
>
> Pointers to the fine manual for any of the above would be welcome.
>
> thanks,
>
> rick jones
> --
> I don't interest myself in "why." I think more often in terms of
> "when," sometimes "where;" always "how much."  - Joubert
> these opinions are mine, all mine; HP might not want them anyway... :)
> feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...
>
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-- 

Chris Albertson
Redondo Beach, California


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