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To: Christopher Masto <chris@netmonger.net>
cc: hackers@FreeBSD.ORG, yokota@zodiac.mech.utsunomiya-u.ac.jp
Subject: Re: Some curiosity about syscons 
In-reply-to: Your message of "Mon, 26 Oct 1998 23:02:08 EST."
             <19981026230208.A8159@netmonger.net> 
References: <19981026230208.A8159@netmonger.net> 
Date: Sun, 01 Nov 1998 20:31:24 +0900
From: Kazutaka YOKOTA <yokota@zodiac.mech.utsunomiya-u.ac.jp>
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[...]
>Rather than back up and start over with a different approach, I added
>a tiny ioctl to syscons to call scrn_update().  With that and some
>fudging, I actually have the damned thing working.

Um, scrn_update() can be called on certain conditions.  See scrn_timer()
for correct timing.

All in all, it is very difficult to guarantee that the screen is
update at precisely 60Hz.

>If anyone is still following this, and particularly if you Know From
>Experience, perhaps you can comment on some of these architectural
>issues.  I need a 60Hz vertical refresh rate, and I need to be able to
>display 18 lines of text every frame.  This needs to happen during the
>vertical retrace interval, as a single glitched frame will cause a
>failure.  Ideally I would like the cursor not to be present, but it
>isn't actually a problem if I can make sure it is always at the top or
>bottom of the screen.

You have to poll a CRTC status port for vertical retrace period.

As Mike has already suggested, it is probably best to do this sort of
things as a screen saver LKM.  The screen saver can do whatever
it wants (just like DOS programs... :-)

The tricky thing is that syscons will instantly deactivate the 
screen saver LKM as soon as a key is pressed (or mouse is moved).

Kazu


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