🚀 go-pugleaf

In article <4284@news.duke.edu> kds@phy.duke.edu (Stokes Kevin) writes:
>  I think the original posting was about the user of the VGA Card's hardware
>interrupt, not the timer chip.  The timer chip wouldn't stay in phase with the
>video retrace, and therefore wouldn't help.

Actually, you can do this.  If you look at the source code for REND386
(FTP from sunee.uwaterloo.ca) you see a method.  I find the time period of 
the vertical frame, then set the timer up to be some small amount (i.e
200 uS) shorter.  You sync the timer with the vertical retrace by reloading
it, then wait 5 frames and repeat.  The total delay at each resync is 
about 500 uS, and that is the maximum drift too.  Works fine with Sega
glasses.  Only drawback: you must keep interrupt disables shorter than 300 uS
or so, else the glasses start showing banding at the bottom of the screen.
Of course, this would happen with the vertical interrupt as well.



--------------------------------------------------------------------------
| My life is Hardware,                    |                              | 
| my destiny is Software,                 |         Dave Stampe          |
| my CPU is Wetware...                    |                              | 
| Anybody got a SDB I can borrow?         | dstamp@watserv1.uwaterloo.ca |
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