[time-nuts] Symmetricom TS2100-GPS - 1PPS has 10uS offset
tn1ajb at nic.fi
Sun May 12 04:34:44 EDT 2013
Jason Rabel kirjoitti:
> I think nobody ever really bothered to fix anything since the NTP time was
> "good enough".
Yes - definitely... If it's only used for NTP then the 10 usec error is
totally insignificiant. NTP solution seems to be quite inaccurate, if I
poll my server from http://support.ntp.org/ntpq.php the results can vary
couple of milliseconds every time. However the offset shown by test page
is always less than 10 milliseconds. Maybe this is because the route is
too long: delay is more than 230 ms - the test site is far side of the
world for me... It' the nature of the TCP/IP and Internet that the
delays are quite random.
Same result if I set up "software" NTP server which polls many NTP
servers from the net. The results are always vayring many milliseconds
and the server will constantly change the "best" server to follow. I
think the multitasking operating system will also add some errors to the
ntp server operation, since the internal system delays will always
change as well.
> The hidden "eng" menu does have some interesting stuff. I've tweaked
> the offset to bring time in sync with my other NTP servers,
> usually around -4000 does the trick since the TS2100 doesn't
> use a true NTP implementation (I think it is more SNTP).
According to manual it should support both protocols, but maybe this NTP
vs SNTP is more like client side difference? I understood that NTP polls
many servers to get kind of "averaged" timing, when SNTP uses only one
server. For example Windows has SNTP only, you can define only one time
server to use at time. Well of course TS2100 doesn't poll any servers
and uses only one time source, GPS.
> I have seen different offset settings in units, so I would think there
> would be *some* way to save the setting, but like you have
> not found out a way to do it yet. :(
Yes! That's now the only question...
If this will remain unknown, then maybe I will setup a microcontroller
connected to the console port and set it to follow somehow, when TS2100
is restarted. Then it could send the "eng tim offset..." command via
serial port to restore the offset setting automatically every time when
needed. This is quite stupid way to "store" the setting, but it might be
the only way if the offical way to store the settings will remain unknown.
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