From: Andrea Martino <amartino AT iiic DOT ethz DOT ch>
Newsgroups: comp.os.msdos.djgpp
Subject: Memory protection & graphic device under DJGPP
Date: Mon, 30 Jun 1997 12:38:53 +0200
Organization: Swiss Federal Institute of Technology (ETHZ)
Lines: 43
Message-ID: <33B78CBD.320@iiic.ethz.ch>
NNTP-Posting-Host: slab136.ethz.ch
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

Hy,
   I have a question about memory protection & graphic_device under
djgpp...

I have written an application that uses some VBE2 features like the most
popular linear frame buffer...

---

I have seen in some examples that we have to map the linear frame buffer
address with the

   __dpmi_physical_address_mapping(&info);

command for accessing the display with a variable like

   char *video = (char *) (info.address + __djgpp_conventional_base);

---

My problems are the following:

- Why I *MUST* turn off the memory protection with

   __djgpp_nearptr_enable()

when I want to write at my (char *) video??? How can I do this without
disable the memory protection and without using "far" (without make
another descriptor)???


- When I turn off the protection I, the program works fine without
mapping the address too, why???

Thanx

		Andrea Martino
		amartino AT iiic DOT ethz DOT ch

P.S.: I cannot read the news everyday, so it`s possible to recive the
answer with a mail too???

P.S.S.: Please, don`t write things like "try Allegro..."