From:	Johan Karlsson <k AT sm DOT luth DOT se>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Disabling cache?
Date:	Tue, 08 Jul 1997 12:21:02 +0200
Organization:	Luleå University of Technology
Lines:	37
Message-ID:	<33C2148E.3F54BC7E@sm.luth.se>
NNTP-Posting-Host:	my21.sm.luth.se
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hello,
I need to be able to turn the cache off for a specific memory area.
The memory board I'm using is a bit special, when I write to a specific
address I will affect all other addresses on the board. Therefor when I
read from the board a value stored in cache will not be valid.

Is there any way of turning the caching of for a specific address area?

I have found a way using asm to invalidate the cache but this costs to
much (15 cycles)
__asm__("invd\n")

I need an efficent way to do this.
I don't want to turn the cache off completely, since this will slow
other parts of the program to down much.

Some background info.

I'm using a PC 486 with an ISA Bus, msdos 6.20, dpmi version 0.9

So far I have with help from this group written a program that reads the
board. Using:

allocate an LDT descriptor (Int 31h/AX=0); 
map selector to physical address (Int 31h/AX=0800h); 
lock linear address (Int 31h/AX=0600h); 
set segment base address (Int 31h/AX=7); 
set segment limit (Int 31h/AX=8). 
and farptr

I'm thankful for all help I can get.

MVH
Johan Karlsson
mailto:k AT sm DOT luth DOT se
Department of Computer Science and Electrical Engineering
Luleå University of Technology, SWEDEN

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