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From: ALAN L HIGHTOWER <alh AT engr DOT engr DOT uark DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Help: Direct video/inline asm
Date: Sun, 1 Oct 1995 19:22:52 -0500
Organization: University of Arkansas
Lines: 47
References: <44iqr1$r6s AT kelly DOT teleport DOT com>
Nntp-Posting-Host: engr.engr.uark.edu
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Dj-Gateway: from newsgroup comp.os.msdos.djgpp



On 30 Sep 1995, Jonathan Nix wrote:

> 	This is rather premature, sorry. I'm sure theres a way, but when I;
> 
> 			char *vidmem=(char *)0xA0000000L;

All the information you need is in the FAQ, when puzzled, read it 
first... it's a pretty good source of information.

As to above problem, I'm not sure where you got 0xA0000000 from, other 
than in real mode vidmem is a000:0000, an entirely different thing.

In version 1.12 all of the VGA cards RAM is page mapped linearly at 
address 0xd0000000 and it performs the bank switches on the fly via
exception handling.  

In version 2.0, the linear mapping hack can't be done due to the way 
protection is handled under DPMI.  To access the video window you must 
reference it via offset 0xa0000 relative to the DOS low memory selector.  
(Which can be obtained through a DPMI call or the _go32_info_block).

> 	I can't figure out how to use an inline assembly block either, I 
> 	can do interrupt calls, but bios is waaaay too slow.

I would suggest looking at the as.tex that comes with DJGPP for the 
differences between GNU as and other assemblers.  Inline asm is done 
though the asm("") function.  Whatever is included between the quotes 
gets spewed out in the assembly stream when gcc finishes.  The long 
format is:

     asm( "  opword    opreands       \n\
             ....      ....           \n\
             opword    opreands       \n"
       : "=a" ( foo ), .... /* outputs: ax gets loaded into foo */
       : "d" ( bar ), ....  /* inputs: bar gets loaded into dx  */
       : "eax", "edx", .... /* clobbered regs: protects contents of eax, edx */
       );

as an example

> 		Any information would be much abliged, I will search the
>                 doc's, but I am so excited about programming in DOS for 
> 		both platforms.

good luck.