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