From: Si <vecktor AT vecktorlite DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Correct Memory Mapping
Date: Thu, 29 Jan 1998 10:30:12 -0800
Organization: BT Labs, Martlesham Heath, Ipswich, UK
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To: djgpp AT delorie DOT com
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Hello , I am relatively new to protected mode programming, and am having
a few memory problems. I am using a VESA 2.0 linear frame buffer
in various resolutions (256 cols only), when setting the mode I use
nearptrs to directly access the frame buffer( I know this disables mem
protection, but its what I want to use) I use code as described in
Charles Sandmanns vbetest.c demo (downloaded from brennans page) to
get the correct address of the buffer

if(__dpmi_physical_address_mapping(&info) == -1) {
   printf("Physical mapping of address 0x%x failed!\n",mb->PhysBasePtr);
   exit(2);
}

then I add the __djgpp_conventional_base 

the problem comes when I malloc some mem the address always is illegal
when I try to access that memory how do I calc the correct address, I
tried afew things and on thing that did work was to add
__djgpp_conventional_base to the malloced address before I used it
that seemed to sort of work but not always??? also what does
sbrk() have to do with things, I know It may change some addresses,
but which ones, what does it affect, what do I need to watch out for
when using nearptrs.
Any help will be greatly appreciated,, thanks in advance
Si....