[ntp:questions] Packet timestamps when using Windows-7/Vista
David J Taylor
david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid
Sat Dec 12 08:31:23 UTC 2009
"Dave Hart" <davehart at gmail.com> wrote in message
news:98c443b7-15b4-4472-b985-9c3e99788835 at j9g2000prh.googlegroups.com...
> On Dec 11, 6:31 pm, "David J Taylor" wrote:
>> I note that the line: "using Windows clock directly" appears in
>> and not Stamsund, and that "HZ 64.000 using 43 msec timer 23.256 Hz 64
>> deep" appears in Stamsund and not Gemini. Stamsund also has
>> "NTP_USER_INTERP_DANGEROUS=1" which must have been a hangover from our
>> earlier experiments.
> So it seems. You may be the only person to use that environment
> variable (though I'm pretty sure it's not spelled quite right there).
>> Perhaps this means I'm running Stamsund in a non-standard mode, without
>> having remembered I was, and what is the significance that it appears
>> work well as a reference server (although nothing like as well as on
>> Windows XP)?
> It's actually very interesting to me, and I'm glad you reminded me of
> it. It raises the question why is it interpolation is not horribly
> broken on this system with a 1ms resolution system clock, given that
> we know the scheduler resolution on all the known Windows versions is
> 1ms? I thought the problem that broke interpolation on Win7 and Vista
> systems with the system clock precision driven to 0.5 or 1ms was
> caused by the sampling of clock and counter pairs occurring in phase
> with the clock updates, because the interpolation scheme wants it
> samples well-distributed so there is always at least one sample in the
> last second or two that happened to be taken soon after the clock
> ticked to a new value.
> The fact that is working despite the 1ms system clock means I don't
> understand the breakage as well as I thought, and hints of a
> possibility interpolation could be made to work on more or all Vista/7
> Dave Hart
It isn't spelt correctly - I was walking from one system to another and
remembering the string in my head (a mistake!). It's actually:
on a second check (give or take more walking errors).
The major difference between the two systems is that one has a ref-clock
attached and the other doesn't. Plus, as you noted, HAL and hardware
I can test any 4.2.7 you want to pass me on both the LAN-synced Vista PC
(which has these apparent "server received after transmitted timestamps")
and the GPS-PPS-kernel-serial Windows-7 system, although I would prefer
not to have to reboot if at all possible. I could easily remove the
ref-clock from the Windows-7 system (Stamsund), and the lead might then
stretch to the Vista system (Gemini).
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