[ntp:questions] NTP.ORG MEINBERG KEEP TIME ACCURATE to 10MS

gbusenberg at yahoo.com gbusenberg at yahoo.com
Wed Nov 14 22:41:15 UTC 2012


On Tuesday, November 13, 2012 6:25:02 PM UTC-5, Dave Hart wrote:
> On Tue, Nov 13, 2012 at 9:24 PM, <gbusenberg at yahoo.com> wrote: > I am not sure if this is possible. I have a requirement from a customer that the time must be within 10ms of the parent server which is on the same LAN. I have tried several different things without an luck. NTP Time seems to get up to 400ms with defaults. > > I have tried to put the following within my ntp.conf file > > tinker panic 0 step .3 stepout 60 > driftfile <default> > server 10.1.126.204 iburst minpoll 5 > server 127.127.1.0 > fudge 127.127.1.0 stratum 12 > > If it is not possible to do 10ms, then I want to get the time as close as possible. I really don't know much about NTP. I have tried my best to search the web as much as possible however most people inclucding myself never use the tinker other than with panic 0. Since you mention Meinberg, I'm guessing you're using the Meinberg Windows ntpd installer? The latest version they offer is based on code that's quite a few years out of date, and in particular is missing a re-write of the Windows-specific clock interpolation that gives ntpd on Windows reasonable precision (as opposed to the native Windows clock precision which is often 15.6 msec). Assuming so, what version of Windows are you using it with? If it's Windows XP/2003 or earlier, you can likely improve the results you see by picking up a set of binaries for a more recent ntpd version from http://davehart.net/ntp/win/x86. Vista and later versions of Windows are more challenging if the system clock ticks more frequently than every 10 msec. Most of the systems running newer Windows default to ticking the system clock every 15.6 msec at startup, but may reduce that to every 1.0 or 0.5 msec by the time an interactive user runs certain timing-sensitive (audio/multimedia) programs or runtimes (e.g. Flash, Java). That has two deleterious effects -- first, the interpolation will not work (and is disabled in ntpd 4.2.6 and later if the problematic clock rate is in effect at its startup) so at best the precision is the same as the Windows clock, around 1 msec. Secondly and so far unresolved, the SetSystemTimeAdjustment API on Vista and later has a serious bug in that it silently rounds the requested change per tick as the API "pretends" the clock rate is fixed when starting with Vista it can change rate after startup. ntpd feeds small changes which get rounded away if the rate is increased, until the clock gets far enough off that the requested slew is big enough to not be rounded, by which point ntpd is overreacting and the clock discipline loop is destabilized. Fixing this would be easiest if Microsoft changes GetSystemTimeAdjustment from simply parroting what Set... was fed to reporting the effective value after rounding -- otherwise, ntpd is stuck trying to infer the effective clock tick size on an ongoing basis, so the rounding can be anticipated and worked around. Cheers, Dave Hart Cheers, Dave Hart

I tried downloading your binaries for 4.2.7p285.  I stopped the ntp servce, put the new .exe files in my NTP\bin directory and then started the service.  Seems to work however NTPQ may be corrupt. I can open the zip fine.  NTPQ.exe is 735,744 bytes.  When I execute this form the command line, windows opens a crash program box.

Problem signature:
  Problem Event Name:	APPCRASH
  Application Name:	ntpq.exe
  Application Version:	0.0.0.0
  Application Timestamp:	507465f1
  Fault Module Name:	ntpq.exe
  Fault Module Version:	0.0.0.0
  Fault Module Timestamp:	507465f1
  Exception Code:	c0000005
  Exception Offset:	000315a0
  OS Version:	6.1.7601.2.1.0.256.48
  Locale ID:	1033
  Additional Information 1:	0a9e
  Additional Information 2:	0a9e372d3b4ad19135b953a78882e789
  Additional Information 3:	0a9e
  Additional Information 4:	0a9e372d3b4ad19135b953a78882e789



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