Message-ID:	<D1FB30BBA491D1118E6D006097BCAE390C9912@Probe-nt-2a.Probe.co.uk>
From:	Shawn Hargreaves <ShawnH AT Probe DOT co DOT uk>
To:	djgpp AT delorie DOT com
Subject:	Re: Video Card IRQ
Date:	Thu, 19 Feb 1998 11:38:27 -0000
MIME-Version:	1.0

Lee Westlake writes:
> Could somebody please tell me whether or not most modern video 
> cards support a vertical retrace interrupt, 

Some do, but many do not. I don't know the exact figures, but at 
a guess it is probably supported on something like 60% or 70% of
modern hardware.

> and if so, what the standard IRQ is?

There is no such thing. This interrupt is usually disabled by 
default, and there is no standard method for enabling it, or even 
just detecting whether it is available.

> Could you also tell me whether or not the VBE 2.0 standard 
> supports the determination/allocation of this interrupt?

No, it doesn't. I think this is a great pity, but in the absence
of some such standard API it doesn't really seem useful to write 
code that uses the retrace interrupt, unless you only care about 
it working on specific hardware that you are able to support 
directly.

> If not, does anyone know a good source of information for 
> programming the most popular cards directly?

VGADOC (I think the latest is version 4b, which you can find
on x2ftp) is the most comprehensive that I have seen, but
I don't remember seeing much about retrace interrupts in
it...

	Shawn Hargreaves.

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