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From: Timothy.Litton@comp.vuw.ac.nz (Tim Litton)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Accurate timing request
Message-ID: <1991Mar14.040625.13212@comp.vuw.ac.nz>
Date: 14 Mar 91 04:06:25 GMT
References: <1991Mar6.145414.8747@uwovax.uwo.ca> <1991Mar7.025205.9213@qualcomm.com>
Sender: tlitton@comp.vuw.ac.nz (Timothy Bruce Litton)
Organization: Computer Science, Victoria University, Wellington, NewZealand
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In article <1991Mar7.025205.9213@qualcomm.com>,
rdippold@maui.qualcomm.com (Ron Dippold) writes:
|> In article <1991Mar6.145414.8747@uwovax.uwo.ca>
|> bangarth@uwovax.uwo.ca writes:
|> >Researchers here are looking for some facility to measure time with
|> 1 ms. 
|> >or less accuracy on an AT or 386 machine. We currently with our
|> software 
|> >(in Turbo Pascal) can't get any better than about 3 ms. accuracy. I
|> have heard
|> 
|> I would suggest that you speed up the clock ticks.  Currently they
|> occur
|> 18.2 times a second, but you can speed it up so that they occur 1000
|> times
|> a second or more, as the timer is programmable.  Your interrupt
|> routine will
|> need to scale whatever timer value you use down to the expected value
|> and
|> pass that on to the old timer.  For example, if you speed up the
|> timer 128
|> times, you will need to call the old interrupt vector every 128
|> actual ticks.
|> You can get some great accuracy this way, just keep in mind that the
|> faster
|> you interrupt the processor, the more machine power it gobbles up.


Don't try this!!!

Your system clock is dependent on that timer, so are most of your I/O
devices for time outs!  Personally, I would put up the +/- 5ms
inaccuracy then try this!



Tim Litton.