Bjorn Gabrielsson wrote:
"Richard B. Gilbert" <[EMAIL PROTECTED]> writes:
K wrote:
I know about NTP v3 and v4 and use it on some systems. I need a time
accuracy of < 1 ms.
I know that the linux os is compiled for something like 1 ms precision
?
So it can be done. I think that the Motorola GPS has a great deal to
do with it.
The motorola should carry you down towards 1us, but K was only asking
for a thousand times less accuracy... :-)
clock would be much less stable. 10 ms is about the best accuracy I
would expect from a client synchronized to a server that synchronized
over the internet.
Even with a DSL-line - if its not overloaded - sub 1ms is easily
attained with good internet servers. Looking at a machine with four
external servers, I get see,
/usr/sbin/ntpq -c pe
remote refid st t when poll reach delay offset jitter
==============================================================================
LOCAL(0) 73.78.73.84 5 l 25 64 377 0.000 0.000 0.001
xxx .PPS. 1 u 219 256 377 11.476 -0.235 0.779
xxx .PPS. 1 u 102 256 377 17.818 -0.140 75.660
xxx .PPS. 1 u 217 256 377 21.575 0.203 0.235
xxx .PPS. 1 u 192 256 377 20.889 0.385 0.142
This machine usually have two GPS-refclocks and they show no
systematic offsets wrt the Internet servers.
--
Björn
Either your internet connection, your internet servers, or both are far
better than mine. I have broadband cable. My NTP server, Sunblok, uses
five internet servers in addition to the Motorola GPS reference clock.
The internet servers show systematic offsets with respect to GPS of +1
to +5 ms. There are also seemingly random spikes in the time received
from the internet servers of +/- 5 to 20 ms. When the GPS is not
running, ntpd tends to synchronize with a different server every few
minutes which does nothing for the stability of the clock.
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