Date: Wed, 15 May 1996 08:00:23 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: John Fortin <fortin44 AT eelab DOT newpaltz DOT edu>
Cc: djgpp AT delorie DOT com
Subject: Re: 0xa0000 and dpmi_segment_to_descriptor
In-Reply-To: <3198B45B.316C@eelab.newpaltz.edu>
Message-Id: <Pine.SUN.3.91.960515075616.2056C-100000@is>
Mime-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII


On Tue, 14 May 1996, John Fortin wrote:

> mail archives in order to understand why we must use near or far pointers
> to gain access to the video buffer.  

Far pointers are required to access portions of memory that aren't in the 
application's address space.  Near pointer method just makes all the 
memory be inside your address space, which is bad memory-protection-wise, 
but required if you need the speediest access.  Without these methods, 
you'd get GPF if you try to access those addresses.

> I don't understand why we can't use a function such as 
> dpmi_segment_to_descriptor to map this to a linear address without
> the disadvantages of the 'fat ds' method.  What am I missing here??

They get linear address, yes, but is that linear address inside your 
program's address space?  I think not.