Xref: news2.mv.net comp.os.msdos.djgpp:3438
From: edoardo AT smartcom DOT it (Edo)
Newsgroups: comp.os.msdos.djgpp
Subject: Memory problem
Date: Fri, 03 May 1996 16:40:54 GMT
Organization: Smartcom S.r.l.
Lines: 98
Message-ID: <4mdcv7$2qgu@venere.inet.it>
Reply-To: edoardo AT smartcom DOT it
NNTP-Posting-Host: pc3.smartcom.it
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Hi!
Can anyone help me with this little piece of code? This program put a
pixel into a "virtual" screen and then copy the virtual screen into
the vga...but it doesn't work! I think that it is due to my low skill
with DJGPP programming (I have downloaded DJGPP only 3 days ago and
this is my first DJGPP proggy, but I've coded a mini 3d engine with
BorlandC ). When I run the prog, the following msg appears:

Page fault at eip=000015c2, error=0004
eax=00000039 ebx=0004c0a0 ecx=00003e80 edx=00006400 esi=00000000
edi=000a0000
ebp=00049cb0 esp=00049cae cs=00a7 ds=00af es=00bf fs=008f gs=00bf
ss=00af
Call frame traceback EIPs:
  0x000015c2
  0x00001658
  0x00001bc7

I think that the wrong instruction is:
  
  vr_addr=__dpmi_get_segment_base_address(vr_screen_sel,vr_screen);

because vr_addr is always 0 (but maybe I'm mistaking.....).
I got a 486dx2/80 with 8Mb RAM and I load DOS only with himem.sys.
Please help me!!!

#include <go32.h>
#include <dpmi.h>
#include <dos.h>
#include <malloc.h>

short vga_sel,vr_screen_sel,c;
int x,y;
long vr_addr;
unsigned long *vr_screen; 

/****************************************************************************/
void set_vga(short mode){
  __dpmi_regs r;
  r.x.ax=mode;
  __dpmi_int(0x10,&r);
}
/****************************************************************************/
void put_pixel(void){
  asm("  
  movw _vr_screen_sel,%es 
  movl _vr_addr,%edi         
  movw _y,%di                   
  movw %di,%dx                  
  shlw $6,%di                   
  shlw $8,%dx                   
  addw %dx,%di                  
  addw _x,%di                   
  movb _c,%al                   
  movb %al,%es:(%edi)         
  "); 
}
/****************************************************************************/
void screen_copy(void){
  asm("  
  pushw %ds                        
  movw  $16000,%cx              
  movl  $0xA0000,%edi     
  movl  _vr_addr,%esi     
  movw  _vr_screen_sel,%ds
  movw  _vga_sel,%es      
  rep;  movsl
  popw  %ds                        
  ");
}
/****************************************************************************/
void main()
{  
  vr_screen=(unsigned long *)malloc(320*200);
  set_vga(0x13);
  vga_sel=_dos_ds;
  vr_screen_sel=_go32_my_ds();
  vr_addr=__dpmi_get_segment_base_address(vr_screen_sel,vr_screen);
  vr_addr=vr_addr*16;
  x=160;
  y=100;
  c=57;
  put_pixel();
  screen_copy();
  getkey();
  set_vga(0x3);
  free(vr_screen);
}   


              _____    ____
             | ____|__/    \
       ____/ |  ___|  \ ||  | \____
           \ |     ||  |||  | /    
              \____||  |___/  
                 |____/   edoardo AT smartcom DOT it
                          VGAi RuLeZ!