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

Rick Jones rick.jones2 at hp.com
Thu Aug 9 16:55:01 UTC 2012

David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> Rick, judge for yourself.  I made a simple comparison between pure LAN 
> sync, and PPS over USB sync here:

>    http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html#usb


> The minimum average jitter value was 110 - 140 µs with the LAN
> connection, and 45 µs with the USB/PPS connection.  So a USB/PPS
> connection may be better than a LAN connection, and most likely much
> better than a WAN or Wi-Fi connection.  Direct serial/PPS is much
> better than USB, though.

WRT LAN, I'll refer back to previous discussions about interrupt
coalescing/avoidance algorithms for LAN cards.  I think unruh did some
experimentation there.

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