From owner-freebsd-hackers  Thu Jul  2 03:20:03 1998
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Subject: Re: Console driver (was: Problems with irq 9(2)?)
In-Reply-To: <rx4af6s4p4n.fsf@oslo.geco-prakla.slb.com> from =?ISO-8859-1?Q?Dag=2DErling_Coidan_Sm=F8rgrav?= at "Jul 2, 98 10:46:00 am"
To: smoergrd@oslo.geco-prakla.slb.com (Dag-Erling Coidan Smørgrav)
Date: Thu, 2 Jul 1998 03:19:57 -0700 (PDT)
Cc: nick.hibma@jrc.it, hackers@FreeBSD.ORG
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In reply to Dag-Erling Coidan Smørgrav who wrote:
> Nick Hibma <nick.hibma@jrc.it> writes:
> > Isn't there a way to check in which vertical line the graphical
> > processor is working and then do a tsleep until it arrives at line
> > number max-2 and _then_ start to do this idle loop?
> 
> No. The vertical retrace period is the time during which the electron
> beam is being repositioned from the bottom right to the top left of
> the screen. Synchronizing with the vertical retrace is not a trivial
> task, as any demo coder will tell you.
> 
> However, no VGA board that I know of will exhibit snow while in text
> mode, so waiting for vertical retrace is not necessary. It should not
> be removed, though, as older CGA and MDA boards require it; but it
> could be turned into a kernel option. If you feel very strongly about
> this, cut'n'paste this article into send-pr and somebody will get
> around to it.

Well you dont know much then :), most modern videocards will
"snow" when you muck with the font generator, you probably
confuses this with writing to the screen buffer, which works
on all VGA's etc etc...
No idea in makeing a PR on this, I'm aware of the problem,
but there really is no good solution to it I'm afraid..

> > Or, much better, use an int routine called by the vertical retrace that
> > is mentioned in the message below.
> 
> No. Modern graphics adapters do not have that functionality.
> 

Well, most VGA comaptibles do have it, but there is enough cards
outthere that doesn't, so its not a soluiton.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Soren Schmidt             (sos@FreeBSD.org)             FreeBSD Core Team
               So much code to hack -- so little time.

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