Mail Archives: djgpp/1999/04/13/14:15:10

Message-ID: <>
From: yjtseng <yjtseng AT micron DOT com>
To: djgpp AT delorie DOT com, salvador AT init DOT gov DOT ar
Cc: yjtseng AT micron DOT com
Subject: RE: cwsdpr0.exe 4/13/99
Date: Tue, 13 Apr 1999 12:14:51 -0600
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Reply-To: djgpp AT delorie DOT com

I thought that paging and virtual memory are the same, i.e. if paging is on
then virtual memory concept kicks in. And if virtual memory is disabled then
you are not supposed to have paging and in this case linear address is the
same as physical address. :-) 

What will happen if virtual memory is disabled (as is in cwsdpr0.exe),
paging is enabled (as shown in CR0 I read), and pages need to be swapped
out? Is this a legitimate scenario? Or, can you do paging without swapping
pages to/from disk storage?


	-----Original Message-----
	From:	Salvador Eduardo Tropea (SET) [SMTP:salvador AT inti DOT gov DOT ar]
	Sent:	April 13, 1999 5:11 AM
	To:	yjtseng; djgpp AT delorie DOT com
	Subject:	Re: cwsdpr0.exe

	yjtseng <yjtseng AT micron DOT com> asked:

	> I wrote inline assembly to access CR0. There was general
protection fault at
	> run time. After suggestions given by Salvador Eduardo Tropea and
	> Eldredge, I tried cwsdpr0.exe and it worked. I was able to access
	> Questions:
	> First:
	> Acording to cwsdpmi.doc, cwsdpr0.exe runs with virtual memory
disabled. But,
	> the value of CR0 that I read is 0x80000011 which means the paging
	> is on. Any idea anybody?

	Paging mechanism isn't virtual memory. If I remmember OK the EMM386
	uses it in DOS. It allows to remap the memory using pages, of course
	needed for virtula memory but not the reverse.
	There are a DPMI call to know if VM is available.
	> Second:
	> How can I pick cwsdpr0.exe as the DPMI host at compilation instead
of using 
	> 	stubedit  my.exe dpmi=cwsdpr0.exe
	> after the executable is generated?

	I think there is no easier way, you could tell the linker to use an
	stub file, but I think the stubedit step is easier.


	P.S. As you can see that's a priviledged instruction ;-) 
	------------------------------------ 0
	Visit my home page:
	Salvador Eduardo Tropea (SET). (Electronics Engineer)
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