Re: [time-nuts] sync computer clock ticks

[Michael Di Domenico]

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 <[EMAIL PROTECTED]> 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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Re: [time-nuts] sync computer clock ticks

[John Ackermann N8UR]

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

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[time-nuts] Glenn Zorpette is out of the office.

[G . Zorpette]

I will be out of the office starting  01/04/2008 and will not return until
01/31/2008.

I will respond to your message when I return. If your matter is urgent, you
can try me at [EMAIL PROTECTED]


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[time-nuts] CPU frequency and NTP crazyness.

[Ryan]

I moved my NTP server to my old Athlon XP desktop running Windows XP
and quickly noticed the effect the CPU power save feature had on NTP.
Once the CPU started ramping down from 2GHz to wherever it lands when
it's done the NTP offsets would hit over a second. I installed
[EMAIL PROTECTED] and [EMAIL PROTECTED] to keep the processor frequency at the
maximum speed and everything has been just peachy with NTP. My
question is this, does anyone have a way to switch off the power save
feature the CPU is using so I don't have to run my machine full tilt?

Thanks all!
Ryan

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Re: [time-nuts] sync computer clock ticks

[michael taylor]

On Jan 4, 2008 12:03 PM, M. Warner Losh <[EMAIL PROTECTED]> 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
> ==
> *x.yy.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

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[time-nuts] FW: sync computer clock ticks

[David Moisan]

-Original Message-
From: David Moisan
Sent: Friday, January 04, 2008 11:43 AM
To: Discussion of precise time and frequency measurement
Subject: RE: [time-nuts] sync computer clock ticks

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Ackermann 
N8UR
Sent: Friday, January 04, 2008 9:17 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] sync computer clock ticks


>Challenges may be (a) in the Windows world, earlier versions (prior to
>some SP level of XP) have inherent limitations on timekeeping accuracy,

I have considerable experience with Windows networks.  Windows 2000 time 
clients are the worst, XP is better and Server 2003 best of all.  Vista and 
Windows 2008 are based on the 2003 code.  My workplace is a public access TV 
station and our biggest challenge is getting consistent time without being able 
to pay for nice things like IRIG displays or GPS clocks.  It doesn't help that 
our master controller is Windows 2000 based with a flaky CMOS clock that was 
caused by renovations in the room it was installed in.

Symmetricom has a app for Windows networks, LMCheck, that can check for 
variance.
http://dtdocs.ntp-systems.com/software/domaintime/instructions/tools/lmcheck.asp



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Re: [time-nuts] sync computer clock ticks

[Keith Payea]

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
[EMAIL PROTECTED]
www.bryantlabs.net
(707) 566-8935

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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 <[EMAIL PROTECTED]> 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.
>

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Re: [time-nuts] sync computer clock ticks

[M. Warner Losh]

In message: <[EMAIL PROTECTED]>
"Michael Di Domenico" <[EMAIL PROTECTED]> 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
==
*x.yy.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   # x.yyy.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

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Re: [time-nuts] FW: sync computer clock ticks

[Keith Payea]

The NTP built into Windows is very poor.  A couple of the versions are not
even compliant with the standard, and some servers will reject their
requests.  You have to use better client software, at least for your master
controller.

The CMOS clock only matters when you lose power.  NTP should only use it
once at start-up as a sanity check.

Keith

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of David Moisan
Sent: Friday, January 04, 2008 9:13 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] FW: sync computer clock ticks



-Original Message-
From: David Moisan
Sent: Friday, January 04, 2008 11:43 AM
To: Discussion of precise time and frequency measurement
Subject: RE: [time-nuts] sync computer clock ticks

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of John Ackermann N8UR
Sent: Friday, January 04, 2008 9:17 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] sync computer clock ticks


>Challenges may be (a) in the Windows world, earlier versions (prior to
>some SP level of XP) have inherent limitations on timekeeping accuracy,

I have considerable experience with Windows networks.  Windows 2000 time
clients are the worst, XP is better and Server 2003 best of all.  Vista and
Windows 2008 are based on the 2003 code.  My workplace is a public access TV
station and our biggest challenge is getting consistent time without being
able to pay for nice things like IRIG displays or GPS clocks.  It doesn't
help that our master controller is Windows 2000 based with a flaky CMOS
clock that was caused by renovations in the room it was installed in.

Symmetricom has a app for Windows networks, LMCheck, that can check for
variance.
http://dtdocs.ntp-systems.com/software/domaintime/instructions/tools/lmcheck
.asp



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Re: [time-nuts] sync computer clock ticks

[M. Warner Losh]

In message: <[EMAIL PROTECTED]>
"michael taylor" <[EMAIL PROTECTED]> writes:
: On Jan 4, 2008 12:03 PM, M. Warner Losh <[EMAIL PROTECTED]> 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
: > 
==
: > *x.yy.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


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Re: [time-nuts] FW: sync computer clock ticks

[Jack Hudler]

I use a Truetime NTS-100 for my NTP server.
Just scanned my network of Windows machines at home, all using MS NTP
Client. 3-Vista, 2-2003 Server, 1-XPSP2.
Worst 11 ms, average variance is 2ms.

Jack


-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Keith Payea
Sent: Friday, January 04, 2008 11:34 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] FW: sync computer clock ticks

The NTP built into Windows is very poor.  A couple of the versions are not
even compliant with the standard, and some servers will reject their
requests.  You have to use better client software, at least for your master
controller.

The CMOS clock only matters when you lose power.  NTP should only use it
once at start-up as a sanity check.

Keith

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of David Moisan
Sent: Friday, January 04, 2008 9:13 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] FW: sync computer clock ticks



-Original Message-
From: David Moisan
Sent: Friday, January 04, 2008 11:43 AM
To: Discussion of precise time and frequency measurement
Subject: RE: [time-nuts] sync computer clock ticks

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of John Ackermann N8UR
Sent: Friday, January 04, 2008 9:17 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] sync computer clock ticks


>Challenges may be (a) in the Windows world, earlier versions (prior to
>some SP level of XP) have inherent limitations on timekeeping accuracy,

I have considerable experience with Windows networks.  Windows 2000 time
clients are the worst, XP is better and Server 2003 best of all.  Vista and
Windows 2008 are based on the 2003 code.  My workplace is a public access TV
station and our biggest challenge is getting consistent time without being
able to pay for nice things like IRIG displays or GPS clocks.  It doesn't
help that our master controller is Windows 2000 based with a flaky CMOS
clock that was caused by renovations in the room it was installed in.

Symmetricom has a app for Windows networks, LMCheck, that can check for
variance.
http://dtdocs.ntp-systems.com/software/domaintime/instructions/tools/lmcheck
.asp



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Re: [time-nuts] sync computer clock ticks

[Christian Vogel]

I forgot two things!

(1) It's all Linux, with stock kernel.org kernels, see below.
(2) see comment about the application below.

Christian Vogel schrieb:
> 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
Kernel 2.6.21.3 SMP

> 
> 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 :-)
Kernel 2.6.22.1 PREEMP

And: We should not forget the original poster's question about if 1 usec 
precision can be achieved? I'd say that the most important thing about 
this question is, what application the precision is needed for.

For example, do you want to timestamp interrupts to synchronize 
machinery? Or just note down the timestamps of bittorrent downloads very 
precisely? Just synchronizing an otherwise idling computer is probably 
much easier than a machine that is doing a lot of additional work that 
can mess up the timekeeping by clogging the processor or just creating 
varying stress on the power-supply lines.

Scatterbrained,
Chris

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Re: [time-nuts] sync computer clock ticks

[M. Warner Losh]

In message: <[EMAIL PROTECTED]>
Christian Vogel <[EMAIL PROTECTED]> writes:
: For example, do you want to timestamp interrupts to synchronize 
: machinery? Or just note down the timestamps of bittorrent downloads very 
: precisely? Just synchronizing an otherwise idling computer is probably 
: much easier than a machine that is doing a lot of additional work that 
: can mess up the timekeeping by clogging the processor or just creating 
: varying stress on the power-supply lines.

That's the real question.  Like I said before, when you are down to
the microsecond level, what good is that?  The jitter from system
calls and such is going to be high enough to make that not completely
useful.  And if you are trying to do things to hardware with software
that requires that level of synchronization, you aren't going to get
it without timestamping done in hardware of some mutually observable
event (pps, packets on the network, etc).

Warner

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Re: [time-nuts] sync computer clock ticks

[Christian Vogel]

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

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Re: [time-nuts] CPU frequency and NTP crazyness.

[Christian Vogel]

Hi Ryan,

> maximum speed and everything has been just peachy with NTP. My
> question is this, does anyone have a way to switch off the power save
> feature the CPU is using so I don't have to run my machine full tilt?

you can do it by changing different power-schemes in Windows' 
Control-Panel Power Properties.

Download RMclock to watch your CPUs clocks and voltage/frequency 
settings while playing with the power-schemes.

If you select "Always On", your computer will not do any power-saving.

Chris

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Re: [time-nuts] CPU frequency and NTP crazyness.

[Eric Fort]

Two things come to mind here,  first most bios have a group of power
management features which are configurable, make sure those features are set
properly (disabled).  second, Your OS should have power management options
as well.  The features in windows seem a bit limited for directly addressing
cpu speed but under Linux the processor speed is directly settable.  The top
6 hits 
hereall
discuss this and give rather direct solutions.

Eric

On 1/4/08, Ryan <[EMAIL PROTECTED]> wrote:
>
> I moved my NTP server to my old Athlon XP desktop running Windows XP
> and quickly noticed the effect the CPU power save feature had on NTP.
> Once the CPU started ramping down from 2GHz to wherever it lands when
> it's done the NTP offsets would hit over a second. I installed
> [EMAIL PROTECTED] and [EMAIL PROTECTED] to keep the processor frequency at the
> maximum speed and everything has been just peachy with NTP. My
> question is this, does anyone have a way to switch off the power save
> feature the CPU is using so I don't have to run my machine full tilt?
>
> Thanks all!
> Ryan
>
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Re: [time-nuts] Syncing Computer to Datum 9700 Programmable Time System

[Darin R. Pfaff]

Howdy, all!

Since I retired from the Air Force a year ago, I've been intrigued with how
well my Datum 9700AT (going away present from my crew) keeps time compared
to all the computers and clocks in the house.  While it's not a cesium-based
standard, or even GPS-updated, it does pretty darned well over the course of
a year.  

I noticed all the wonderful outputs on the back, and I'd like to take the
1PPS signal and use it as a timing standard for my IBM workstation running
XP Pro SP2, thereby making it the home time server for the rest of our
computer network.  I'm assuming that it would have to go into one of the
available serial ports, but is there an off-the-shelf cable w/software to
enable this, or am I heading into uncharted territory?

Thanks for letting me pick the group's collective brains!

Darin R. Pfaff
Sun Prairie, WI

-Original Message-
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Behalf Of [EMAIL PROTECTED]
Sent: Friday, January 04, 2008 12:49 PM
To: time-nuts@febo.com
Subject: time-nuts Digest, Vol 42, Issue 9

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Today's Topics:

   1. Re: sync computer clock ticks (Keith Payea)
   2. Re: sync computer clock ticks (M. Warner Losh)
   3. FW:  sync computer clock ticks (David Moisan)
   4. Re: sync computer clock ticks (michael taylor)
   5. Re: sync computer clock ticks (M. Warner Losh)
   6. Re: FW:  sync computer clock ticks (Keith Payea)
   7. Re: FW:  sync computer clock ticks (Jack Hudler)
   8. Re: CPU frequency and NTP crazyness. (Christian Vogel)
   9. Re: sync computer clock ticks (Christian Vogel)


--

Message: 1
Date: Fri, 4 Jan 2008 09:01:14 -0800
From: "Keith Payea" <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] sync computer clock ticks
To: "'Discussion of precise time and frequency measurement'"

Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain;   charset="us-ascii"

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
[EMAIL PROTECTED]
www.bryantlabs.net
(707) 566-8935

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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 <[EMAIL PROTECTED]> 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 requir

Re: [time-nuts] sync computer clock ticks

[Bruce Griffiths]

M. Warner Losh wrote:
> In message: <[EMAIL PROTECTED]>
> Christian Vogel <[EMAIL PROTECTED]> writes:
> : For example, do you want to timestamp interrupts to synchronize 
> : machinery? Or just note down the timestamps of bittorrent downloads very 
> : precisely? Just synchronizing an otherwise idling computer is probably 
> : much easier than a machine that is doing a lot of additional work that 
> : can mess up the timekeeping by clogging the processor or just creating 
> : varying stress on the power-supply lines.
>
> That's the real question.  Like I said before, when you are down to
> the microsecond level, what good is that?  The jitter from system
> calls and such is going to be high enough to make that not completely
> useful.  And if you are trying to do things to hardware with software
> that requires that level of synchronization, you aren't going to get
> it without timestamping done in hardware of some mutually observable
> event (pps, packets on the network, etc).
>
> Warner
>   
PTP achieves submicrosecond synchronisation over small LANs without
network switches.
It uses hardware time stamping of LAN packets.
Someone has even implemented it in software (with degraded performance).
See:
http://ieee1588.nist.gov/

Bruce

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Re: [time-nuts] sync computer clock ticks

[M. Warner Losh]

In message: <[EMAIL PROTECTED]>
Bruce Griffiths <[EMAIL PROTECTED]> writes:
: M. Warner Losh wrote:
: > In message: <[EMAIL PROTECTED]>
: > Christian Vogel <[EMAIL PROTECTED]> writes:
: > : For example, do you want to timestamp interrupts to synchronize 
: > : machinery? Or just note down the timestamps of bittorrent downloads very 
: > : precisely? Just synchronizing an otherwise idling computer is probably 
: > : much easier than a machine that is doing a lot of additional work that 
: > : can mess up the timekeeping by clogging the processor or just creating 
: > : varying stress on the power-supply lines.
: >
: > That's the real question.  Like I said before, when you are down to
: > the microsecond level, what good is that?  The jitter from system
: > calls and such is going to be high enough to make that not completely
: > useful.  And if you are trying to do things to hardware with software
: > that requires that level of synchronization, you aren't going to get
: > it without timestamping done in hardware of some mutually observable
: > event (pps, packets on the network, etc).
: >
: > Warner
: >   
: PTP achieves submicrosecond synchronisation over small LANs without
: network switches.
: It uses hardware time stamping of LAN packets.

Right.  This is hardware time stamping of mutually observable events
(the two way time exchange).

One can measure down to nanosecond levels with custom hardware with
1588.  Sam Stein presented a paper at 2006 PITI that talked about an
average of 2.5ns with a standard deviation of 0.9ns in measuring clock
differences.

: Someone has even implemented it in software (with degraded performance).
: See:
: http://ieee1588.nist.gov/

Right, and the performance here is not much better than ntp, at least
in the tests that I've done.  The jitter is slightly better.

Warner

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Re: [time-nuts] sync computer clock ticks

[SAIDJACK]

In a message dated 1/4/2008 12:07:29 Pacific Standard Time, [EMAIL PROTECTED]  
writes:

>Right, and the performance here is not much better than ntp, at  least
>in the tests that I've done.  The jitter is slightly  better.

>Warner
Hi Warner, et. al.,
 
has anyone done any testing/evaluation of the typical performance the SNTP  
server built into GPSCon can achieve?
 
bye,
Said






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Re: [time-nuts] FW: sync computer clock ticks

[David Moisan]

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Keith Payea
Sent: Friday, January 04, 2008 11:34 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] FW: sync computer clock ticks

The NTP built into Windows is very poor.  A couple of the versions are not
even compliant with the standard, and some servers will reject their
requests.  You have to use better client software, at least for your master
controller.

I use ntpd on the controller PC;  it still has to yank it into sync every so 
often.

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Re: [time-nuts] sync computer clock ticks

[David I. Emery]

On Fri, Jan 04, 2008 at 10:28:33AM -0700, M. Warner Losh wrote:
> In message: <[EMAIL PROTECTED]>

> 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.

My experience in the late 90s with syncing Linux was based on
using serial port 1 PPS interrupts with custom code in the kernel to
optimize the serial port modem interrupt path.Time stamps of this
interrupt versus the hardware based microclock (based on an incrementing
counter in the CPU) were used to drive the NTP PLL which computed the
frequency error and time offset for the kernel PLL.

I found the microclock readings of time of day on the 1 PPS were
usually within 1 us (there were a few late ones due to interrupt off
intervals of course).   This was on fairly slow server class hardware
(Pentium Pro at 200 MHz).

On ethernet I would not expect that level of accuracy due to the
inherent CSMA/CD algorithm jitter... plus of course whatever the bridge
in the star hub introduces...

Obviously once one gets into the microsecond area one gets into
the world of software relativity where what one means by time of day
depends on where one is looking.   What I was using to judge performance
was what an interrupt level  call to microclock returned... but inside a
larger software system this will obviously be skewed by the various
calling delays to get to the kernel...

-- 
  Dave Emery N1PRE/AE, [EMAIL PROTECTED]  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."


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Re: [time-nuts] CPU frequency and NTP crazyness.

[Ryan]

I had an interesting result. I downloaded RMclock and with [EMAIL PROTECTED]
running the CPU was at full load and speed. I stopped Seti and the
load dropped to almost nothing but the speed stayed the same. After
about a minute the offset and jitter readings went through the roof.
My offsets were above half a second! There was no reduction in
anything CPU related while this happened. When I get access to the
machine I'll take a look at the bios settings to make sure I have the
power settings in an optimal configuration.

Unfortunately I'm stuck with Windows for the time being because the
EMWIN software I use is windows only. If I ran FreeBSD in a virtual
machine would I be saddled with the imperfections in the Windows
timing scheme?

On 1/4/08, Christian Vogel <[EMAIL PROTECTED]> wrote:
> Hi Ryan,
>
> > maximum speed and everything has been just peachy with NTP. My
> > question is this, does anyone have a way to switch off the power save
> > feature the CPU is using so I don't have to run my machine full tilt?
>
> you can do it by changing different power-schemes in Windows'
> Control-Panel Power Properties.
>
> Download RMclock to watch your CPUs clocks and voltage/frequency
> settings while playing with the power-schemes.
>
> If you select "Always On", your computer will not do any power-saving.
>
> Chris
>
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>

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Re: [time-nuts] sync computer clock ticks

[Michael Di Domenico]

> For example, do you want to timestamp interrupts to synchronize
> machinery? Or just note down the timestamps of bittorrent downloads very
> precisely? Just synchronizing an otherwise idling computer is probably
> much easier than a machine that is doing a lot of additional work that
> can mess up the timekeeping by clogging the processor or just creating
> varying stress on the power-supply lines.

The company i work for makes high performance interconnect solutions
for super computers.  i'm working on a demo where we're sending data
around a ring and i wanted to timestamp all the packets as it hits
each node of the ring.  the servers could be under some stress when
this is running.

i had a feeling what i wanted to do isn't possible, but i figured i'd
ask some experts before i give up.

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[time-nuts] 35601A as stand-in for 11848A ?

[BriMDavis]

Has anyone ever looked into the feasibility
of using a 35601a as a stand-in for the 11848a
in a 3048a phase noise system?

I've been attempting to piece together a 3048a for
low budget 'home project' use to do some two source
quadrature lock measurements.

The 35601a's are much cheaper as surplus, and at the
block diagram level appear similar, but without the
extra internal sources on the oscillator deck.

I presently have the service manual for the 11848a,
but not yet the 35601a, to see whether it has all the 
necessary signal paths for the 3048a calibration and 
quadrature lock process.

If similar enough, I was considering an attempt
at hacking up the 35601a HPIB interface to make it
appear to be an 11848a ( hoping that the evolutionary
path from 3047a -> 3048a left the two quite similar ).

Brian



**Start the year off right.  Easy ways to stay in shape. 
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Re: [time-nuts] 35601A as stand-in for 11848A ?

[John Miles]

I have a 35601A, although I've never done anything with it.  It seems to be
very much hardwired to work in a 3047A system, with the particular analyzer
model(s) and software controller that entails.  The 11848A is nicer but
still designed to work within a very specific system configuration.

My current thinking is that most people are better off with an 11729B/C, or
possibly just a homebrew quadrature-PLL implementation if they don't care
about microwave downconversion.  The 11729B/C plus an 8662A (or even an
8640B) has everything most people will ever need for PN measurement.

-- john, KE5FX

> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> Behalf Of [EMAIL PROTECTED]
> Sent: Friday, January 04, 2008 7:28 PM
> To: time-nuts@febo.com
> Subject: [time-nuts] 35601A as stand-in for 11848A ?
>
>
> Has anyone ever looked into the feasibility
> of using a 35601a as a stand-in for the 11848a
> in a 3048a phase noise system?
>
> I've been attempting to piece together a 3048a for
> low budget 'home project' use to do some two source
> quadrature lock measurements.
>
> The 35601a's are much cheaper as surplus, and at the
> block diagram level appear similar, but without the
> extra internal sources on the oscillator deck.
>
> I presently have the service manual for the 11848a,
> but not yet the 35601a, to see whether it has all the
> necessary signal paths for the 3048a calibration and
> quadrature lock process.
>
> If similar enough, I was considering an attempt
> at hacking up the 35601a HPIB interface to make it
> appear to be an 11848a ( hoping that the evolutionary
> path from 3047a -> 3048a left the two quite similar ).
>
> Brian
>
>


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Re: [time-nuts] sync computer clock ticks

[Bruce Griffiths]

Michael Di Domenico wrote:
>> For example, do you want to timestamp interrupts to synchronize
>> machinery? Or just note down the timestamps of bittorrent downloads very
>> precisely? Just synchronizing an otherwise idling computer is probably
>> much easier than a machine that is doing a lot of additional work that
>> can mess up the timekeeping by clogging the processor or just creating
>> varying stress on the power-supply lines.
>> 
>
> The company i work for makes high performance interconnect solutions
> for super computers.  i'm working on a demo where we're sending data
> around a ring and i wanted to timestamp all the packets as it hits
> each node of the ring.  the servers could be under some stress when
> this is running.
>
> i had a feeling what i wanted to do isn't possible, but i figured i'd
> ask some experts before i give up.
>
>   
Unless you use packet time stamping cards as used in network
characterisation.
Errors of around 120ns or so are typical, see:

http://nistboulder.net/Presentations/FCSEFTF2003(final).pdf


Suitable  PCI cards are available.

Bruce
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Re: [time-nuts] NLTL comb generators going away...

[John Miles]

Following up an earlier post:

> It appears that the 11729's 640-MHz PA can drive the 7123
> adequately, although the 12.16 GHz comb line is somewhat close to
> the spec limit of -20 dBm.  The 7113-110 is a better replacement
> for the 33004A in the 11729C, since it would actually be
> operating in spec.  They have several of those in stock (I just
> ordered 2 of the 8 they had left).

... and it turns out that their conversion efficiency when driven by the
11729C's 640 MHz PA is actually lower than the 7123's was.

So, contrary to what I posted earlier, it's necessary to modify the driver
for higher power output to use the NLTL multipliers that are still
available.  The 7103 looks like the best candidate, using a 3-dB pad at the
input, but I'm not sure if they have any of those left.

-- john, KE5FX



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