From: DavMac AT iname DOT com (Davin McCall) Newsgroups: comp.os.msdos.djgpp Subject: Re: Absolute addresses Date: Thu, 18 Nov 1999 01:52:55 GMT Organization: Monash Uni Lines: 37 Distribution: world Message-ID: <38335a66.1882882@newsserver.cc.monash.edu.au> References: NNTP-Posting-Host: damcc5.halls.monash.edu.au X-Trace: towncrier.cc.monash.edu.au 942889986 4239 130.194.198.138 (18 Nov 1999 01:53:06 GMT) X-Complaints-To: abuse AT monash DOT edu DOT au NNTP-Posting-Date: 18 Nov 1999 01:53:06 GMT X-Newsreader: Forte Free Agent 1.1/32.230 To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Reply-To: djgpp AT delorie DOT com You can't really do it very easily. You can only access logical addresses directly; to access a physical address you must perform a run-time calculation to convert the physical address into a logical address first. Normally, VGA memory is "out of bonds" of the range of memory that can normally be accessed. This means you have a couple of choices, one is called the "nearptr hack" and the other involves setting up a selector. Read the FAQ for more info. Incidentally, the whole point of protected mode is to remove the ability for programs to do stupid things like overwriting other programs memory space, and in some environments to stop them directly accessing devices (eg the VGA). The "method for using 32-bit memory addresses without using pm" is called "real big mode" or "unreal mode" (amongst other names) and is a royal pain, not to mention that it isn't supported by DJGPP, and can't be used under Windows or most memory managers. Davin. On Wed, 17 Nov 1999 10:04:42 +0100, "Ulf Wikström" wrote: >I'm using DJGPP with inline assembler, and I'm new on protected mode and >AT&T syntax. There's one thing I don't understand: >How do I specify an absolute memory adress using assembler??? I can't find >the answer anywhere, so it's all up to you proffesionals now :). I would >like to access vga-memory... (this whole idea of a protected mode seems a >little bit crazy to me, is there a method for using 32-bit memory adresses >without using pm?) __________________________________________________________ *** davmac - sharkin'!! davmac AT iname DOT com *** my programming page: http://yoyo.cc.monash.edu.au/~davmac/