[ntp:questions] Timekeeping broken on Windows XP with multimedia timer enabled (-M option)

David J Taylor david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid
Wed Jan 20 19:37:31 UTC 2010

"Alan" <greigaln at netscape.net> wrote in message 
news:Z9I5n.58805$Q36.5787 at newsfe19.ams2...
> Would like to get to the bottom of this as well. Using 4.4.6-o with -M , 
> I get "Frequency error 3030 PPM exceeds tolerance 500 PPM". Considering 
> that without =M the frequency modification is only about 5 PPM then 
> obvioulsy something very strange is going on. It seems that even if the 
> timer precision is increased by another program then time immediately 
> starts to drift rapidly by hundreds of milliseconds.


Our experience was that the switching between normal and high-resolution 
timers caused steps of many milliseconds (I don't recall the exact figure) 
which really messed up NTP.  So either run with no MM timers at all, or 
run with the MM timers permanently enabled, and NTP recognises that 
change, and adjusts accordingly.  Have NTP start the MM timers was one 
solution, and hence the -M option.

It might be helpful to know what the event log says with both sets of 
startup parameters, as there may be a clue there which Dave Hart, the 
person closest to this code, can interpret.

I must confess to having nagging doubts about AMD (but with no good 
reason), about whether you have another program setting the time (check 
that w32time.exe is not running - Show Processes from all users), and 
perhaps something in the BIOS.  One final idea (which there was no option 
on my test system) might be to start with just one CPU active in the BIOS.


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