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

unruh unruh at invalid.ca
Thu Aug 9 15:09:06 UTC 2012

On 2012-08-08, 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.

It has no interrupt line which he software can use to accurately
register when the PPS came in. Everything comes over the serial line and
must wait until the line is clear to send the 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?

Not really. Try "orphan" mode instead.

> Pointers to the fine manual for any of the above would be welcome.
> thanks,
> rick jones

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