From: jerry AT eteklabs DOT nospam DOT com (Jerry Lawrence)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: far pointers using djgpp
Date: Wed, 17 Jun 1998 17:28:50 -0400
Message-ID: <MPG.ff1ff203d4e5e319896ce@gateway>
References: <Pine DOT SOL DOT 3 DOT 95 DOT 980617000723 DOT 17603A-100000 AT tiger DOT vut DOT edu DOT au> <35881d34 DOT 2869157 AT news DOT unisys DOT com DOT br>
Organization: e-Tek Labs
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To: djgpp AT delorie DOT com
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In article <35881d34 DOT 2869157 AT news DOT unisys DOT com DOT br>, brunobg AT geocities DOT com 
says...
> On Tue, 16 Jun 1998 14:12:23 GMT, Butler Owen scm2211 <s9708172 AT tiger DOT vut DOT edu DOT au>
> wrote:
> 
> >I would like to create a pointer to my VGA cards memory.  I know this
> >starts at 0xA000,0000 
> >in another compiler I would use:
> >char far *screen= (char far *) MK_FP(0xa000,0);
> >problems arise:
> >1. djgpp does not support the "far" keyword
> >2. the implementation of "dos.h" that comes with djgpp does not contain
> >MK_FP()
> >if I try this:
> >char * screen = (char *) 0xa0000000;
> >it compiles fine, then crashes at the point I try and set anything through
> >this pointer.
> >Any suggestions?
> 
> You need to use the _far* functions... Here is a little tutorial I wrote. It's
> basic, but once you understand far pointers in DJGPP it's easy to go deeper. Hope
> it helps, any questions, please email me.
> 
> -----------cut----------
>                            Far pointers and DJGPP
> 


Or, you could do this: (can't remember where i got the info from)

1) store a local ram buffer of the screen buffer; do all screen
   operations to this buffer.
2) in your graphics init function, use this right after you change
   screen mode:
	__djgpp_nearptr_enable();
3) in your graphics deinit function, use this:
	__djgpp_nearptr_disable();

4) when a full screen buffer is ready to be displayed:

	memcpy( (unsigned char *) (0xa0000+__djgpp_conventional_base), 
			(buff),320*200);

where "buff" is a 64k buffer (assuming 320x200x256 color)

i think i got this info from a link off the djgpp homepage
	-j