[DMDX] Re: DMDX 2.x timing At 03:40 PM 8/10/00 -0700, you wrote:
>Given the previous discussion about differences in refresh intervals 
>estimated by different versions of DMDX, I think it is worth making the 
>following points.
>
>1.  On my machines, at least, the two versions give the same results.  So 
>it is possible that the discrepancies are limited to particular graphics 
>cards and/or CPUs.

   Guaranteed.


>2.  If you are worried about whether your refresh interval is really what 
>DMDX reports, there is a very simple test.  Write an item file that asks 
>for a frame to be displayed for 10000 ticks, and then time the display 
>with a stopwatch to see whether you get the right value.  Do this 20 times 
>and average the results, and then divide by 10000, and you will have a 
>very precise measurement of the refresh interval.

   I'm not entirely sure that method would work if DMDX was told that the 
retrace interval was 8.5ms when it was in fact 11.5ms.  Such a method 
certainly worked in the days of yore when we had a retrace interrupt with 
DM and DMTG, however I'm pretty sure it won't work now as DMDX will be 
working to make the retrace interval 8.5ms.  The only sure way (short of 
using photosensitive test equipment) is to read the documentation in TimeDX 
on timing the retrace interval and to look closely at the results printed 
in that window.  If the interval was 11.5ms when the parameters specified 
8.5ms there would be an enormous number of timed out retraces (75% or more 
would be my guess) and while DMDX operates just dandy missing upwards of 
50% of them when it's timing parameters are correct you will find that the 
times that it finds two retraces in a row at are exactly the retrace 
interval, it's likely that in the above scenario that it would never find 
two retraces in a row, if it did the intervals would be all over the place.


-jonathan (j.c.f.)

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