Dennis Laczny of RACEAMERICA Timing Systems states:
<<<John's point of having to reset the PC time-of-day is right on. A PC
is
driven by an interrupt system and the I/O ports where sensors are
connected
and the internal time-of-day clock are the lowest priorities due to the
slow data rates (compared to what is going on inside the PC at 200Mhz +)
and this lower priority causes the time-of-day clock (and the .001
second
requirement) to vary slightly.
All of the software timing solutions are cost effective (if you don't
count
the cost of the PC) and offer the driver registration and scoring, some
offer the timing also. Software timing will vary slightly from one PC
to
another based on what's in the PC, so comparing results from one region
to
another would not be accurate to .001 seconds. Comparing results from
one
event to another would require using the same PC hardware for both
events,
but even then, that would not guarantee .001 second accuracy for both
events.>>>
Sorry but this is total BS. The fact that the PC clock is inaccurate
under Windows or MSDOS has nothing to do with what the hardware is
capable of doing given the proper realtime programming. I agree there is
no Win32 API call that will give you millisecond accuracy, but there a
loads of realtime OSes for the PC that will give you much greater
accuracy than that - I'd be willing to guess at the microsecond level.
The real time clock inaccuracies can be circumvented in a number of
ways. Probably the best way would be to purchase a programmable interval
timer that would provide hardware interrupts on a regular basis. A
device driver would have to be written to make the results available to
a PC based application but this isn't rocket science...
Paul Foster
25 years of realtime programming...
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