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

David Taylor david-taylor at blueyonder.co.uk.invalid
Thu Aug 9 06:56:53 UTC 2012


On 08/08/2012 22:34, Rick Jones wrote:
[]
> 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.
[]
> Pointers to the fine manual for any of the above would be welcome.
>
> thanks,
>
> rick jones

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.
-- 
Cheers,
David
Web: http://www.satsignal.eu



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