[time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

Ruslan Nabioullin rnabioullin at gmail.com
Thu Feb 16 01:30:37 EST 2017

On 02/15/2017 01:17 PM, Chris Albertson wrote:
> Why set up a dedicated NTP server if you only have two computers
> that will use it?    Your server will be accurate to a few
> microseconds but your two computers will only by good to a few
> milliseconds because ethernet is not nearly as good as PPS.

Well Ethernet can be *extremely* accurate if PTP is used (a whitepaper 
specifies <= 100 ns accuracy if the LAN is optimized for it).

Well, the assumption here is that one would render this service 
available to the public, registering the server(s) with the NTP website 
and/or the NTP Pool Project; n.b. this is still possible for connections 
lacking a static IP address, by means of an IPv6 tunnel, available at no 
cost from at least one vendor.  Otherwise yes, by some perspectives it 
can be considered quite pointless and wasteful to operate dedicated 
servers, standards, receivers, etc. with no means of time transfer to 

 > NTP is almost zero load on the CPU and the best thing is the NTP
 > accuracy is not effected by CPU load  SO you can run other service
 > without degrading the NTP server.

Well n.b. TVB's hardware PPS timestamping post.  Also WWV and CHU 
decoding by NTP's modules can be problematic, as well as the obvious 
case of the server being overloaded.  Finally note that based on others' 
experimentation, the motherboard's XO temperature is nontrivially-highly 
correlated with CPU load, so for better motherboard XO-based holdover 
performance, once must create an ersatz oven utilizing the CPU(s), by 
running them at full utilization (obviously with proper scheduling 
priority), so typically volunteer distributed computing project(s) such 
as BOINC (SETI at home, etc.), Folding at Home, etc.  Of course then power 
consumption becomes problematic.


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