Date: Thu, 30 Mar 1995 12:29:07 -0600 (CST)
From: Scott McCaskill <jmccaski AT CS DOT Trinity DOT Edu>
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: accessing video memory


In one of the the on-line faqs at dj's web site, I found the following:

   When I use 0xD0000000 as the starting address to access the video RAM
   in graphics mode, nothing appears on the screen. What am I doing
   wrong?

   You have to call GrSetMode() function to initialize the 0xD0000000
   area manager which takes care of the mapping described above.

Where can I find more information on this "area manager"?  What source 
file(s) is it in?  Is it in (or called from) GrSetMode?  The reason I ask is 
that I'm tying to port some mode X routines that were written for watcom, 
and the following causes a segmentation fault:

memset((unsigned char *)(0xD000 << 4), 0x00, 0x00010000);

In the original code, the first arg was 0xA000 << 4, but from I've read 
in various documents about libgr, apparently go32 mapss this address to 
0xd0000000.  Obviously, I'm no expert on these things--I just have some 
nice mode x graphics routines that I'd like to be able to use with djgpp.

I've even tried calling GrSetMode(GR_320_200_graphics) and then the mode 
x setmode routines, but it still dies at the memset.

thanks,
Scott

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Scott McCaskill
(jmccaski AT cs DOT trinity DOT edu)              http://www.cs.trinity.edu/~jmccaski/