From:	"Rylan" <rylan AT intekom DOT co DOT za>
Newsgroups:	comp.lang.asm.x86,comp.os.msdos.djgpp
Subject:	How to generate a BIOS Int in inline AT&T
Date:	7 Aug 1998 20:08:29 GMT
Organization:	The South African Internet Exchange
Lines:	145
Approved:	<johnfine AT erols DOT com>
Message-ID:	<6qfmrt$9dr$1@winter.news.erols.com>
Reply-To:	"Rylan" <rylan AT inbtekom DOT co DOT za>
NNTP-Posting-Host:	207-172-240-142.s15.as3.bsd.erols.com
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi,

George Foot told me how to generate a BIOS int 16h (keyboard) in inline AT&T
assembler in DJGPP:

>__dpmi_int is just a function, so you pass parameters in the usual
>way.  For the parameters to __dpmi_int, which are nice parameters,
>you just push them onto the stack, four bytes each, right-to-left,
>and then do the (near) call:

>    movl   _regs, %eax     /* address of register block */
>   pushl  %eax
>    movl   $0x10, %eax     /* interrupt number (example) */
>    pushl  %eax
>    call   ___dpmi_int     /* (0x10, &regs) */
>    addl   $8, %esp        /* or popl twice */
>    /* now EAX is the return value */

>Since you're calling GCC-compiled code (or rather, code written to
>be called by GCC-compiled code) you must make sure the normal
>assumptions hold, e.g. ES=DS=CS=SS.  Also note that it can clobber
>ECX, EDX, FS and GS without restoring them; if you care about their
>values, save them (perhaps on the stack before pushing parameters).

My questions:

1) What are "nice parameters"?
2) How do I "make sure the normal assumptions hold"?
3) What kind of entry and exit code is needed if the "assumptionss do not
hold" e.g. if ES NOT egual to ES=DS=CS=SS in the routine I want to call the
int in?

My problem is that the code works 100% when in total isolation, but as soon
as I put it in my routine where I want to do the BIOS int (check for key
down during a loop to break the loop) it crashes the whole DOS box, dropping
me into W95.

Like this:

//D2 - Simple small fire with great smoke - quit with CTRL-BREAK
#include <stdio.h>
#include <conio.h>
#include <go32.h>
#include <dpmi.h>
#include <pc.h>

<-snip->

__dpmi_regs r;


<-snip->

void waitkey() Here it works fine - why?<--------------------------
{
 __asm__ __volatile__
 ("
   movw  $0x0,_r+28
   pushl $_r
   pushl $0x16
   call  ___dpmi_int
   addl $8,%esp
 ");
}

int main(void)
{

 __asm__ __volatile__
 ("
   pushw %%ds
   pushl %%ebp
   pushl %%esp

   movw %%ds,_dssave
   movl %%ebp,_ebpsave
   movl %%esp,_espsave

   movw _vid_descriptor,%%es
   movw _vid_descriptor,%%ds --------->Is this the problem?

   xorw %%bx,%%bx
  mainloop:
   movw $320,%%si
   movb $0x7d,%%ch

   pushw %%si
   pushw %%cx
  smoothloop:
   lodsb
   movb (%%esi),%%bl
   addw %%bx,%%ax
   movb 319(%%esi),%%bl
   addw %%bx,%%ax
   movb -2(%%esi),%%bl
   addw %%bx,%%ax

   shrw $2,%%ax
   movb %%al,-321(%%esi)
   loop smoothloop

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

-------->If i put it here it crashes totally - what kind of entry and exit
code is needed to
-------->be able to push parameters for __dpmi_int HERE and call __dpmi_int
HERE
-------->in this stack register context?
-------->I've tried restoring DS,ES,FS,GS before calling but __dpmi_int
still crashes
-------->I want the loop to exit on a keypress (i. e. int 16h func 01h, then
jz mainloop)
-------->but I can't execute the int, no matter what.

   jmp mainloop

  finish:
   popl %%esp
   popl %%ebp
   popw %%ds
 "
 :
 :
 : "ax","bx","cx","di","bp","sp","memory"
 );

 waitkey();
 unsetmode();
 exit(0);
}

Any help at all sincerely appreciated!

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

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