[ntp:questions] SetSystemTimeAdjustment() on Vista

Danny Mayer mayer at ntp.org
Sun May 31 17:47:04 UTC 2009


johumohu at yahoo.com wrote:
> Anybody ever tried to use SetSystemTimeAdjustment() on Vista?
> 

The NTP Reference Implementation uses it for controlling the system
clock. I'm not sure what you are really asking. Dave Hart added some
interpolation code to do a better job of it for Vista and seems to be
okay on earlier versions of Windows. Vista was showing a lot of jitter.

> I tested the accuracy ot the system time on my laptop. During about 6
> hours, the time gets about 1 second too fast. On the basis of the
> description of SetSystemTimeAdjustment(), the TimeAdjust should be
> changed from the default 156001 to 156008. But 156008 makes the time
> too slow. I tried 156002 and it is still too slow, it seems like
> 156001.5 would make it even but you cannot use fractions. In other
> words, the default value 156001 seems to be the best choice. The
> TimeIncrement is 156001. Any insight on this?
> 
> Also, one thing is not clear. The time adjustment is done at each
> interval identified by TimeIncrement which is fixed  15.6001
> millisecond. My question is what happens when the system time is
> updated every 1 millisecond, because on my laptop system time is
> updated mostly every 1 millisecond as long as there is some input
> activity at keyboard or mouse. Does it mean Vista waits until the full
> 15.6001 millisecond is reached when using TimeAdjust?

If you install the latest versions of the NTP reference implementation
you get much better control of the system clock.

Danny

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