*BSD News Article 28647


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From: hasty@netcom.com (Amancio Hasty Jr)
Subject: Re: DOOM for X
Message-ID: <hastyCMnA5y.Mpw@netcom.com>
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
References: <2lo4m0$sdt@bosnia.pop.psu.edu> <SJA.94Mar12174713@gamma.hut.fi> <2m0h7a$3ck@u.cc.utah.edu>
Distribution: inet
Date: Mon, 14 Mar 1994 07:58:45 GMT
Lines: 32

In article <2m0h7a$3ck@u.cc.utah.edu> terry@cs.weber.edu (Terry Lambert) writes:
>In article <SJA.94Mar12174713@gamma.hut.fi> sja@snakemail.hut.fi (Sakari Jalovaara) writes:

>(1)	You can't necessarily map memory from the display adapter
>	directly.  There is often a "window" which you must use to
>	communicate with display memory that would be used instead.
>
Not sure what the above means. It is almost correct. 
In the case of svga, most cards support the concept of banking,
so that a program can map the vga's memory into the user space.
Some support 64k banking or 128k banking at a time. Full addressing
of the card is done by specifying a "vga bank" and the offset
into the start of the vga mapped address. BTW: vga banking 
is not really a standard so it varies from svga implementation
to svga implementation.

The S3 801/982/864/928 as well as a few other vga cards are fully
capable of mapping their entire video ram into the user space;hence,
there is no need for "vga banking". The S3 cards have registers 
which tell the card where to map the video memory to. 

Amancio





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