sync computer clock ticks
This has probably been asked many times before, but i am unable to
find any documentation to point me in the right direction. And yes i
am a newbie with clocks...
I'd like to synchronize the clock ticks on 16 different computers
running linux, down to the 1usec area. Is this even possible from a
computer hardware standpoint?
If so, can someone point me towards some documentation that explains
how to wire up 16 computers to a reference clock source and override
the computer internal clocks?
I found the Symetricom website, but it seems light on details on
exactly how a solution like this all connects together and they're
products are likely outside my budget.
Ideally, I'd like to use the serial port on each of these 16 servers
to connect to some device to get the synchronization signal from a
reference. Even if this was possible, i don't think it would get me
to 1usec though.
Thanks
- Michael
On Thu, Jan 03, 2008 at 10:14:01PM -0500, Michael Di Domenico wrote:
I'd like to synchronize the clock ticks on 16 different computers
running linux, down to the 1usec area. Is this even possible from a
computer hardware standpoint?
Ideally, I'd like to use the serial port on each of these 16 servers
to connect to some device to get the synchronization signal from a
reference. Even if this was possible, i don't think it would get me
to 1usec though.
I've had ntp sync of the microsecond/nanosecond time of day
counter on Linux in the 1 us area using serial port timing with custom
mods to the kernel (years ago, I think this is standard now)...
This of course DOES NOT sync the actual clock tick interrupts,
it only syncs the microclock stuff...
The only way I know to sync clock interrupts is to use a common
clock oscillator and even then the actual interrupt times will not be
synced... unless one does some hardware modifications to the motherboards
But it certainly IS possible to get multiple machines to see the
same time of day to with around a microsecond or two...
--
Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
Michael Di Domenico wrote:
This has probably been asked many times before, but i am unable to
find any documentation to point me in the right direction. And yes i
am a newbie with clocks...
I'd like to synchronize the clock ticks on 16 different computers
running linux, down to the 1usec area. Is this even possible from a
computer hardware standpoint?
If so, can someone point me towards some documentation that explains
how to wire up 16 computers to a reference clock source and override
the computer internal clocks?
I found the Symetricom website, but it seems light on details on
exactly how a solution like this all connects together and they're
products are likely outside my budget.
Ideally, I'd like to use the serial port on each of these 16 servers
to connect to some device to get the synchronization signal from a
reference. Even if this was possible, i don't think it would get me
to 1usec though.
Thanks
- Michael
Michael
Google ntp.
It is unlikely that you will synchronise the computer clocks to within
1us with ntp unless the computer hardware and operating system is
suitably modified.
This can be done cheaply (one machine needs to be setup as a dedicated
stratum 1 ntp server synchronised to a good time source like a M12M gps
timing receiver or equivalent device).
NTP broadcasts the required info as LAN packets.
If you really need that precisionyou may need to use ptp with suitable
hardware (National Instruments and others have suitable boards)
NIST has a webpage on PTP.
Bruce
I've used NTP for years, but i was under the impression that it is not
able to synchonize the clocks below 1 or 2 seconds. Can you point me
towards a specific article that speaks about the configuration
parameters to get ntp sync'd that low?
On Jan 3, 2008 10:25 PM, Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
Michael Di Domenico wrote:
This has probably been asked many times before, but i am unable to
find any documentation to point me in the right direction. And yes i
am a newbie with clocks...
I'd like to synchronize the clock ticks on 16 different computers
running linux, down to the 1usec area. Is this even possible from a
computer hardware standpoint?
If so, can someone point me towards some documentation that explains
how to wire up 16 computers to a reference clock source and override
the computer internal clocks?
I found the Symetricom website, but it seems light on details on
exactly how a solution like this all connects together and they're
products are likely outside my budget.
Ideally, I'd like to use the serial port on each of these 16 servers
to connect to some device to get the synchronization signal from a
reference. Even if this was possible, i don't think it would get me
to 1usec though.
Thanks
- Michael
Michael
Google ntp.
It is unlikely that you will synchronise the computer clocks to within
1us with ntp unless the computer hardware and operating system is
suitably modified.
This can be done cheaply (one machine needs to be setup as a dedicated
stratum 1 ntp server synchronised to a good time source like a M12M gps
timing receiver or equivalent device).
NTP broadcasts the required info as LAN packets.
If you really need that precisionyou may need to use ptp with suitable
hardware (National Instruments and others have suitable boards)
NIST has a webpage on PTP.
Bruce
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Michael Di Domenico wrote:
I've used NTP for years, but i was under the impression that it is not
able to synchonize the clocks below 1 or 2 seconds. Can you point me
towards a specific article that speaks about the configuration
parameters to get ntp sync'd that low?
Hi Michael --
PC hardware and operating systems can put some limits on NTP
performance, though with some attention to detail getting ~1 microsecond
with an attached hardware reference clock is fairly straightforward. On
a lightly loaded LAN, machines can be sync'd to a server on the same LAN
to a few hundred microseconds.
Challenges may be (a) in the Windows world, earlier versions (prior to
some SP level of XP) have inherent limitations on timekeeping accuracy,
and (b) Linux does not directly support high accuracy timekeeping with
hardware clocks that provide a PPS signal. For various (mainly
political, it seems) reasons you need to do a kernel patch to enable use
of the PPS signal.
I have a bunch of statistics showing NTP performance at
http://www.febo.com/time-freq/ntp/stats/index.html. There, you can see
how a group of very high performance stratum 1 servers (with directly
connected reference clocks) look across the local LAN, as well as how
some local stratum 2 and external stratum 2 servers look. There's also
a link there to a page that describes what is probably the most accurate
hardware available for an NTP server (and which costs less than $300 to
implement).
John
Michael:
What NTP software are you using? Many are intended just to keep the clock
within a second, and don't work very hard at it.
The best is to get a port of the "real" NTP from the source at
http://www.ntp.org/ They have ports for most major OS's. You should be
able to maintain better than 10 milliseconds to UTC once it has settled for
a while.
Also be sure to check out the NTP server pool project at
http://www.pool.ntp.org/. It's an effort to spread out the load on major
NTP servers.
Keith
Keith Payea
Bryant Labs
kpayea@bryantlabs.net
www.bryantlabs.net
(707) 566-8935
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Michael Di Domenico
Sent: Friday, January 04, 2008 6:00 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] sync computer clock ticks
I've used NTP for years, but i was under the impression that it is not
able to synchonize the clocks below 1 or 2 seconds. Can you point me
towards a specific article that speaks about the configuration
parameters to get ntp sync'd that low?
On Jan 3, 2008 10:25 PM, Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
Michael Di Domenico wrote:
This has probably been asked many times before, but i am unable to
find any documentation to point me in the right direction. And yes i
am a newbie with clocks...
I'd like to synchronize the clock ticks on 16 different computers
running linux, down to the 1usec area. Is this even possible from a
computer hardware standpoint?
If so, can someone point me towards some documentation that explains
how to wire up 16 computers to a reference clock source and override
the computer internal clocks?
I found the Symetricom website, but it seems light on details on
exactly how a solution like this all connects together and they're
products are likely outside my budget.
Ideally, I'd like to use the serial port on each of these 16 servers
to connect to some device to get the synchronization signal from a
reference. Even if this was possible, i don't think it would get me
to 1usec though.
Thanks
- Michael
Michael
Google ntp.
It is unlikely that you will synchronise the computer clocks to within
1us with ntp unless the computer hardware and operating system is
suitably modified.
This can be done cheaply (one machine needs to be setup as a dedicated
stratum 1 ntp server synchronised to a good time source like a M12M gps
timing receiver or equivalent device).
NTP broadcasts the required info as LAN packets.
If you really need that precisionyou may need to use ptp with suitable
hardware (National Instruments and others have suitable boards)
NIST has a webpage on PTP.
Bruce
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
In message: 97a7c7ed0801040600x5d2781cfl40e31dd70731492c@mail.gmail.com
"Michael Di Domenico" mdidomenico@gmail.com writes:
: I've used NTP for years, but i was under the impression that it is not
: able to synchonize the clocks below 1 or 2 seconds. Can you point me
: towards a specific article that speaks about the configuration
: parameters to get ntp sync'd that low?
I don't know about other people, but out of the box I get sub 20ms
synchronization. Right now, it is sitting at about 12.5ms:
remote refid st t when poll reach delay offset jitter
---============
*xxxxx.yyyyyy.co 10.7.1.1 2 u 965 1024 377 64.176 -12.570 0.508
My config file is just a simple:
server 1.2.3.4 # xxxxx.yyyyyyy.com
driftfile /mod/etc/ntp.drift
restrict default notrust nomodify
restrict 127.0.0.1
restrict 1.2.3.4
restrict 10.0.0.6
restrict 10.0.0.0 mask 255.255.0.0 notrust
On Jan 4, 2008 12:03 PM, M. Warner Losh imp@bsdimp.com wrote:
I don't know about other people, but out of the box I get sub 20ms
synchronization. Right now, it is sitting at about 12.5ms:
remote refid st t when poll reach delay offset jitter
---============
*xxxxx.yyyyyy.co 10.7.1.1 2 u 965 1024 377 64.176 -12.570 0.508
That's a 12 ms offset from UTC, as far as I understand the original
poster only needs <= 1 microsecond synchronization on his local
network.
-Michael
In message: 25630a120801040918x2203daebs7eb0de5f00ffc56c@mail.gmail.com
"michael taylor" mctylr@gmail.com writes:
: On Jan 4, 2008 12:03 PM, M. Warner Losh imp@bsdimp.com wrote:
: >
: > I don't know about other people, but out of the box I get sub 20ms
: > synchronization. Right now, it is sitting at about 12.5ms:
: >
: > remote refid st t when poll reach delay offset jitter
: >
---============
: > *xxxxx.yyyyyy.co 10.7.1.1 2 u 965 1024 377 64.176 -12.570 0.508
: >
:
: That's a 12 ms offset from UTC, as far as I understand the original
: poster only needs <= 1 microsecond synchronization on his local
: network.
I have no experience with gige networks, but the best I've been able
to do on 100baseT networks is 50us. I'm unsure what <1us
synchronization really means, since that's starting to get below the
level of system calls on fast machines.
Warner
Hi Michael,
I've used NTP for years, but i was under the impression that it is not
able to synchonize the clocks below 1 or 2 seconds. Can you point me
towards a specific article that speaks about the configuration
parameters to get ntp sync'd that low?
at work, I use it to sync all servers and workstations to 4 stratum 1
NTP-servers. I get ~100us offset usually. Without special hardware I'd
say that 1usec is not possible.
Server, Gig-Ethernet, 4 hops (>=Gigabit) to ntp:
*ntp2-rz.rrze.un .GPS. 1 u 758 1024 377 1.225 -0.179 0.068
(HP DL380-G3, Dual 3.2 GHz P4, no powersaving)
-> Temperature fluctuates +/- 3 Deg-Celsius every 20sec due to HVAC
Client, 100Mbit, 5 hops (last 4 are better than Gigabit):
*ntp2-rz.rrze.un .GPS. 1 u 987 1024 377 1.577 -0.111 0.091
(P4-Celeron, 2.4 GHz, currently throttled to 300 MHz)
-> Temperature currently stable and possibly very cool, have not
been in my office for a week :-)
My main problem is probably that ntp switches between three equally good
servers quite frequently (it just did).
Chris