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Date:      Thu, 20 Feb 1997 23:34:43 +1100
From:      Bruce Evans <bde@zeta.org.au>
To:        bde@zeta.org.au, sos@ravenock.cybercity.dk
Cc:        brian@awfulhak.demon.co.uk, brian@utell.co.uk, hackers@freebsd.org
Subject:   Re: Screen flickering
Message-ID:  <199702201234.XAA00491@godzilla.zeta.org.au>

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>> 	1. Make the vertical retrace interrupt handler a "fast" interrupt
>> 	   handler so that it has a low latency and can't be interrupted.
>> 	   Don't use too many other "fast" interrupt handlers, or the
>> 	   interrupt latency might be too high.
>> 	2. Program the sparkly registers in the vertical retrace interrupt
>> 	   handler.  Do this in less than 20 usec or someone will complain
>> 	   that the interrupt latency is too high.
>
>I'd like to do it this way, but lots of the crappy VGA cards thats
>out there (and often its the same ones that produces most of
>the annoing jitter) doesn't support an interrupt, and some only
>allows using NMI.
>However it is quite easy to implement, so.....

It's not easy.  Multiple interrupts per driver are unusual and not
supported by config.  Fast interrupt handlers are unusual and must
be programmed carefully.

Bruce



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