From: "Max Erhard" <erhard AT banstead DOT u-net DOT com>
Newsgroups: comp.os.msdos.djgpp
References: <dMOe2.122$14 DOT 362 AT newsr2 DOT u-net DOT net>
Subject: Re: beginner mode13 question
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Date: Sat, 19 Dec 1998 15:06:19 -0000
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I have now found the nearptr.h file, I had an old djdev.zip file. I would
still be pleased for any general help etc.

Max Erhard wrote in message ...
>I am having trouble getting mode13 programs to work. Plotting pixels using
>bios interupts works OK. But as soon as I try to directly address the video
>memory, I start to get horrible GPFs. I have tried A000, A0000 and A0000000
>as the address for video memory but no luck. I have read about special
>commands for near pointers or something but they need <sys/nearptr.h> and I
>do not have this file in my /include/sys folder, only farptr.h. Also is
>there a memory model setting for gcc that I need to know about.
>
>Errors look like this:-
>
>General Protection Fault at eip=211
>eax=00000001 ebx=00051d00 ecx=000a0141 edx=000a0141 esi=00000000
>edi=00000000
>ebp=00051d50 esp=00051d4c cs=bf ds=b7 es=b7 fs=b7 gs=b7 ss=c7 cr2=00001fec
>Call frame traceback EIPs:
>  0x00000211
>  0x00000285
>
>My code is:- (which should make a rainbow of all of the 256 colours on
>screen.)
>
>#include <stdio.h>
>#include <bios.h>
>#include <dos.h>
>
>int a;
>int dx;
>int dy;
>unsigned char *VGA=(unsigned char *)0xA0000L;
>
>void set_mode13()
>{
> union REGS regs;
> regs.h.ah = 0x00;
> regs.h.al = 0x13;
> int86(0x10,&regs,&regs);
>}
>
>void set_textmode()
>{
> union REGS regs;
> regs.h.ah = 0x00;
> regs.h.al = 0x03;
> int86(0x10,&regs,&regs);
>}
>
>void plot_pixel(int x, int y, int colour)
>{
> VGA[y*320+x]=colour;
>}
>
>void main ()
>{
> set_mode13();
> for(a=0;a<=256;a+1)
> {
>  for(dx=1;dx<=320;dx++)
>  {
>   for(dy=1;dy<=200;dy++)
>   {
>    plot_pixel(dx,dy,a);
>   }
>  }
> }
> set_textmode();
>}
>
>
>