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"Team Ada: Ada Advocacy Issues (83 & 95)" <[log in to unmask]>
Tom Moran <[log in to unmask]>
Tue, 7 Nov 2000 09:39:29 +0100
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Tom Moran wrote:

> > Presumably DELAY UNTIL is
> > implemented with an
> > interrupt. Could there be an overhead of some 10 or more
> > microseconds
>   I would be astonished if Windows did short delays with interrupts.
> >From my timings, it takes 4.9 mics just to do the OS call etc for "T :=
> Ada.Calendar.Clock" (and since Gnat apparently uses the same (the only)
> clock for Real_Time and Calendar, that would be same). Most Windows
> calls specify times in milliseconds (though that is often misleading
> about actual precision).  The thing that ticks at .8 mics is accessed
> via a "QueryPerformanceCounter" call - I don't think they really think
> of it as a general purpose clock at all.
> > So would be surprising in a
> > realtime
> > operating system, though it is not surprising in a commercial
> > operating
> > system.
>   My timings are running on Windows 95, which is the latter.
> Does any version of Windows actually do timing and interrupts in 1
> microsecond?

in WIN NT/Win2K  BOOT.ini  file, this following variable is supposed to set
some interesting atomic beat.
  /TIMERES=  On the multiprocessor HAL (HALMPS.DLL) this option will set the
resolution of the system timer. The argument is a number interpreted in
100's of nanoseconds, but the rate will be set to the closest resolution the
HAL supports that is not larger than the one requested. The HAL supports the
following resolutions:
 100's of nanoseconds  =>   milliseconds
                9766                   .98
              19532                   2.0
              39063                   3.9
              78125                   7.8
 The default resolution is 7.8ms. The system timer resolution affects the
resolution of waitable timers. Example:   /TIMERES=9000 would set the timer
to a resolution of .98ms. (not better than Alsys many years ago (around

This information is available on
Anyone reached  this on windows based single processor machines ?


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