From: "Rylan" <rylan AT intekom DOT co DOT za>
Newsgroups: comp.os.msdos.djgpp
Subject: Real Mode Intel to Protected Mode AT&T
Date: Tue, 4 Aug 1998 19:03:25 +0200
Organization: The South African Internet Exchange
Lines: 139
Message-ID: <6q7f86$dh5$1@news2.saix.net>
Reply-To: "Rylan" <rylan AT inbtekom DOT co DOT za>
NNTP-Posting-Host: pc25-01-p15.saix.net
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

Hi!

I'm trying to do an interesting little experiment to convert a small real
mode assembler demo to protected mode inline AT&T syntax for DJGPP.

It is a small "fire" demo of gray smoke moving upward from the middle of the
screen with a very realistic smoke effect.

Here is the Intel program that does the effect (looks like TASM):


.MODEL TINY
.386

.CODE
.STARTUP

 push 0a000h
 pop   es
 push  es
 pop ds

 mov   al,13h
 int   10h

 mov     dx,3c8h
 xor     ax,ax
 out     dx,al
 inc     dx
 DAC_loop:
 out dx,al
 out dx,al
 out dx,al
 inc ax
 jnz DAC_loop

MainLoop:
 mov     si,320
 mov     ch,7dh ; cx=0, 320*100=0x7D00, so ch=0x7D
 push si  ; to be re-cycled later
 push cx

smoothloop:
 lodsb   ; thanx to Chaos for reminding me this!
 mov     bl,[si]
 add     ax,bx
 mov     bl,[si+319]
 add     ax,bx
 mov     bl,[si-2]
 add     ax,bx
 shr     ax,2
 mov   [si-321],al
 loop   smoothloop

 pop   di  ; re-cycle time!
 pop   cx
randline:
 mul word ptr [di] ; what a way to make random numbers!
 inc ax        ; why is 'inc ah' 2bytes but 'inc ax' 1byte??
 stosw
 dec di             ; must try to get rid of this byte...
 loop randline

 MOV     AH,1
 INT     16h ; key-press test
 Jz MainLoop
;|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Bye:
 mov     ax,3
 int     10h
 ret
 END

The AT&T & C equivalent works fine (including setting up the palette) but
then something goes wrong. I only get a stationary line of fire in the
middle of the screen. I do not include the whole program (for reasons of
brevity) since the rest of it works fine (a selector for video ram, etc.
etc.) The problem must lie here  somewhere: (The mainloop section)

 __asm__ __volatile__
 ("
   movw _global_selector,%%es
   movw _global_selector,%%fs
   movl $0xA0000,%%edi
   movl $0aA0000,%%esi

  mainloop:
   movw $320,%%si
   movb $0x7d,%%ch
   pushw %%si
   pushw %%cx
  smoothloop:
   lodsb
   movb %%fs:(%%esi),%%bl
   addw %%ax,%%bx
   movb %%fs:319(%%esi),%%bl
   addw %%ax,%%bx
   movb %%fs:-2(%%esi),%%bl
   addw %%ax,%%bx
   shrw $2,%%ax
   movb %%fs:-321(%%esi),%%al
  loop smoothloop

   popw %%di
   popw %%cx
  randline:
   mulw (%%edi)
   incw %%ax
   stosw
   decw %%di
   loop randline

   jmp  mainloop
 "
 :
 :
 : "ax","bx","cx","memory"
 );

Note that I use FS as an override, since trying to use DS GPF's me out each
time.
FS then references as FS:ESI (instead of DS:ESI) and EDI of course
automatically references ES:EDI (the video selector for video RAM).
Can anybody tell me where I made a mistake? Some selector:offset mistake
somewhere? Any help will be gladly appreciated - please reply by mail if at
all possible.

Anybody else interested in this kind of conversion stuff?

(BTW - I did this with NASM (Real TASM to Prot NASM) and it worked fine -
just interested in the AT&T side of things)

Again, fanx!

--
Spawned By Rylan
Is truth beauty or beauty truth?