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From: ast@botter.UUCP
Newsgroups: comp.os.minix
Subject: Request for help with EGA board fix posted by Der-Ru Sheu
Message-ID: <1207@botter.cs.vu.nl>
Date: Wed, 10-Jun-87 16:45:44 EDT
Article-I.D.: botter.1207
Posted: Wed Jun 10 16:45:44 1987
Date-Received: Sun, 14-Jun-87 20:40:50 EDT
Reply-To: ast@cs.vu.nl (Andy Tanenbaum)
Distribution: world
Organization: VU Informatica, Amsterdam
Lines: 24

A while back sheu@gitpyr.UUCP (Der-Ru Sheu) posted the following fix
to make the EGA board work:

 > Following is a brief explanation.  There is a register inside the EGA 
 > sequencer, to tell 'Extended Memory' (those beyond 64K, or 16K in fact, 
 > since 4 color planes share the same memory space) is installed or not.  
 > By cheating the hardware no extended memory installed, it will perform
 > exactly like a CGA (but with a much better resolution, of course).
 > 
 > I added the following three lines into 'main.c' (at the very begin).
 > I believe this modification won't cause any problem with mono or CGA cards, 
 > since those I/O addresses are not used anywhere else.  However, I don't have 
 > the hardware to test it with.
 > 
 >   port_out(0x3c4, 4);   /* Select register inside the sequencer     */
 >   port_out(0x3c5, 1);   /* No extended memory, take my word for it. */
 >   /*  That's all!  Just as I said, it's simpler.  (Optional, :-) )  */
 > 
We finally tried it here and it didn't quite work.  However, we tried it on a
Zenith Z-248 EGA card, which may be different from IBM's.  Since it is
such a simple and elegant fix, I would like to hack it into shape.  Has
anyone else tried it, and if so, please post your findings.

Andy Tanenbaum (ast@cs.vu.nl).