John Ackermann N8UR wrote:
Hal Murray said the following on 04/05/2006 03:08 PM:
As a practcal matter, the best is probably the one that's that most
reliable. Or the one that's most convenient. Or the one with the
fastest CPU or best network connection.
The last few nano/micro seconds won't make much difference
after a network hop.
You're probably right, but my problem (if you can call having too many
time sources a problem!) is that it's not intuitively clear which one of
the servers is the best, other than that the WWVB server is
significantly worse than the GPS and Cs ones. But the GPS and Cs ones
have very similar performance. To the outside world it doesn't matter
because the internet and even my firewall performance will mask
differences at this level, but as an academic exercise, and on the local
wire, I'd like to see if I can wring the best possible performance out
of the system.
I'm probably asking NTP to perform at a level it's not really designed
for, and that perhaps the OS/hardware can't even support (in terms of
system clock stability and time resolution -- though a longer term goal
is to replace the mobo clock with a source derived from the Cs to solve
at least one problem).
The latter is the PHK way: Use a frequency synthesizer to generate the
required input frequency for your chosen motherboard, using the 10 MHz
(or whatever) Cs output as the source.
The next step is to build a 10 MHz (or faster!) counter which will reset
on each PPS signal, then count until latched by a read signal from the
NTP server. This allows you to get rid of the variable interrupt latency
problem.
Terje
--
- <[EMAIL PROTECTED]>
"almost all programming can be viewed as an exercise in caching"
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