newbie question on gnu 'as'

newbie question on gnu 'as'

[Anticipating a Reply]

Hi Everybody,

        I have got a small piece of Assembly code ,
which writes a character "A" on the screen .

  The below program is compiled and written 
to the boot sector of a floppy. It compiles
using the command :

	as86 boot.s -o boot.o
	ld86 -d boot.o -o boot 

   I want to rewrite it in AT&T syntax and
want to use GNU "as" assembler to compile it .
I tried doing it ,but with no success .

  Can anybody please help me rewite the
below code in AT&T syntax and tell me how
to compile & link it ?

   Thanks in Advance .

With Best Regards


THE CODE :
------------


entry start 

start: 
       mov ax,#0xb800 ; Video Memory address is 0xb800
  
       mov es,ax      ; Video Memory is made as Extra
Segment
       seg es         ; Makes next instruction execute
wrt Extra Segment 
       mov [0],#0x41  ; ASCII value of the Character
to be displayed 
                      ;  in 1-row & 1-column
       seg es         ; Makes next instruction execute
wrt Extra Segment 
       mov [1],#0x1f  ; Attribute of the Character to
be displayed
                      ;  in 1-row & 1-column
                      ; 0x1f represents White
Character on a Blue Background
loop1: 
       jmp loop1


________________________________________________________________________
Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
       visit http://in.autos.yahoo.com

Re: newbie question on gnu 'as'

[Bruno N. F. Pacheco]

Just read the comments..

/*
 * letter.S
 *
 * % as letter.S -o letter.o
 * % ld -s letter.o
 * % a.out
 *
 * by live <brunonfp@fastmail.fm>
 */

    .data
buffer:
    .byte 65

    .text
    .globl _start
    .align 4

_start:
    movl $4, %eax       # write() syscall
    movl $1, %ebx       # stdout
    leal buffer, %ecx   # buff pointer
    movl $1, %edx       # number of characters to write
    int $0x80           # call kernel
        /* Ignoring erros */

.loop:
    jmp .loop


	-- Bruno N. F. Pacheco

On Tue, 30 Jul 2002, [iso-8859-1] Anticipating a Reply wrote:

> Hi Everybody,
>
>         I have got a small piece of Assembly code ,
> which writes a character "A" on the screen .
>
>   The below program is compiled and written
> to the boot sector of a floppy. It compiles
> using the command :
>
> 	as86 boot.s -o boot.o
> 	ld86 -d boot.o -o boot
>
>    I want to rewrite it in AT&T syntax and
> want to use GNU "as" assembler to compile it .
> I tried doing it ,but with no success .
>
>   Can anybody please help me rewite the
> below code in AT&T syntax and tell me how
> to compile & link it ?
>
>    Thanks in Advance .
>
> With Best Regards
>
>
> THE CODE :
> ------------
>
>
> entry start
>
> start:
>        mov ax,#0xb800 ; Video Memory address is 0xb800
>
>        mov es,ax      ; Video Memory is made as Extra
> Segment
>        seg es         ; Makes next instruction execute
> wrt Extra Segment
>        mov [0],#0x41  ; ASCII value of the Character
> to be displayed
>                       ;  in 1-row & 1-column
>        seg es         ; Makes next instruction execute
> wrt Extra Segment
>        mov [1],#0x1f  ; Attribute of the Character to
> be displayed
>                       ;  in 1-row & 1-column
>                       ; 0x1f represents White
> Character on a Blue Background
> loop1:
>        jmp loop1
>
>
> ________________________________________________________________________
> Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
>        visit http://in.autos.yahoo.com
> -
> To unsubscribe from this list: send the line "unsubscribe linux-assembly" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>

Re: newbie question on gnu 'as'

[Emanuele Altieri]

[-- Attachment #1: Type: text/plain, Size: 2357 bytes --]

I'm assuming that you want to keep your code as a boot program:

           .code16               # needed for booting
           .global _start
   _start:
           movw    $0xB800, %ax
           movw    %ax, %es
           movb    $0x41, %es:0  
           movb    $0x1f, %es:1
   loop1:  jmp     loop1


To assembly and link the program:

   as -o boot.o boot.s
   ld -s -oformat binary -Ttext 0x0 -o boot boot.o

The last command creates the "boot" file that is ready to be 
installed in the first sector of the floppy disk:

   dd seek=0 if=boot of=/dev/fd0


Hope this helps

  -Emanuele


On Tue, 2002-07-30 at 07:59, Anticipating a Reply wrote:
> Hi Everybody,
> 
>         I have got a small piece of Assembly code ,
> which writes a character "A" on the screen .
> 
>   The below program is compiled and written 
> to the boot sector of a floppy. It compiles
> using the command :
> 
> 	as86 boot.s -o boot.o
> 	ld86 -d boot.o -o boot 
> 
>    I want to rewrite it in AT&T syntax and
> want to use GNU "as" assembler to compile it .
> I tried doing it ,but with no success .
> 
>   Can anybody please help me rewite the
> below code in AT&T syntax and tell me how
> to compile & link it ?
> 
>    Thanks in Advance .
> 
> With Best Regards
> 
> 
> THE CODE :
> ------------
> 
> 
> entry start 
> 
> start: 
>        mov ax,#0xb800 ; Video Memory address is 0xb800
>   
>        mov es,ax      ; Video Memory is made as Extra
> Segment
>        seg es         ; Makes next instruction execute
> wrt Extra Segment 
>        mov [0],#0x41  ; ASCII value of the Character
> to be displayed 
>                       ;  in 1-row & 1-column
>        seg es         ; Makes next instruction execute
> wrt Extra Segment 
>        mov [1],#0x1f  ; Attribute of the Character to
> be displayed
>                       ;  in 1-row & 1-column
>                       ; 0x1f represents White
> Character on a Blue Background
> loop1: 
>        jmp loop1
> 
> 
> ________________________________________________________________________
> Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
>        visit http://in.autos.yahoo.com
> -
> To unsubscribe from this list: send the line "unsubscribe linux-assembly" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html



[-- Attachment #2: boot.s --]
[-- Type: text/plain, Size: 416 bytes --]

# boot.s
#
# To assembly and link as a **boot** program:
#
#    as boot.s -o boot.o
#    ld -s -oformat binary -Ttext 0x0 -o boot boot.o
#
# To copy it to the boot sector of a floppy disk:
#
#    dd seek=0 if=boot of=/dev/fd0
#
# ---
# Emanuele (ealtieri@hampshire.edu)
	
	.code16
	.global _start
_start:
	movw	$0xB800, %ax
	movw	%ax, %es
	movb	$0x41, %es:0
	movb	$0x1f, %es:1
loop1:	jmp	loop1

Re: newbie question on gnu 'as'

[Anticipating a Reply]

Hello Emanuele ,

   Thank you for the below code 
you sent . It works perfectly and
will help me learn more of assembly .

   Can you please help me figure 
out where I'am wrong in the code below,
which I have witten for the same 
functionality .

.code16

.globl _start 

_start: 
       movw $0xb800,%bx  # Video Memory address   
       movb $0x41,(%bx)  # ASCII value to be displayed


       movw $0xb801,%bx  # Video Memory address    
       movb $0x1f,(%bx)  # Attribute of the Character 
loop1: 
       jmp loop1


    Thanks once again .

With Best Regards

 --- Emanuele Altieri <ealtieri@hampshire.edu> wrote:
> I'm assuming that you want to keep your code as a
> boot program:
> 
>            .code16               # needed for
> booting
>            .global _start
>    _start:
>            movw    $0xB800, %ax
>            movw    %ax, %es
>            movb    $0x41, %es:0  
>            movb    $0x1f, %es:1
>    loop1:  jmp     loop1
> 
> 
> To assembly and link the program:
> 
>    as -o boot.o boot.s
>    ld -s -oformat binary -Ttext 0x0 -o boot boot.o
> 
> The last command creates the "boot" file that is
> ready to be 
> installed in the first sector of the floppy disk:
> 
>    dd seek=0 if=boot of=/dev/fd0
> 
> 
> Hope this helps
> 
>   -Emanuele
> 
> 
> On Tue, 2002-07-30 at 07:59, Anticipating a Reply
> wrote:
> > Hi Everybody,
> > 
> >         I have got a small piece of Assembly code
> ,
> > which writes a character "A" on the screen .
> > 
> >   The below program is compiled and written 
> > to the boot sector of a floppy. It compiles
> > using the command :
> > 
> > 	as86 boot.s -o boot.o
> > 	ld86 -d boot.o -o boot 
> > 
> >    I want to rewrite it in AT&T syntax and
> > want to use GNU "as" assembler to compile it .
> > I tried doing it ,but with no success .
> > 
> >   Can anybody please help me rewite the
> > below code in AT&T syntax and tell me how
> > to compile & link it ?
> > 
> >    Thanks in Advance .
> > 
> > With Best Regards
> > 
> > 
> > THE CODE :
> > ------------
> > 
> > 
> > entry start 
> > 
> > start: 
> >        mov ax,#0xb800 ; Video Memory address is
> 0xb800
> >   
> >        mov es,ax      ; Video Memory is made as
> Extra
> > Segment
> >        seg es         ; Makes next instruction
> execute
> > wrt Extra Segment 
> >        mov [0],#0x41  ; ASCII value of the
> Character
> > to be displayed 
> >                       ;  in 1-row & 1-column
> >        seg es         ; Makes next instruction
> execute
> > wrt Extra Segment 
> >        mov [1],#0x1f  ; Attribute of the Character
> to
> > be displayed
> >                       ;  in 1-row & 1-column
> >                       ; 0x1f represents White
> > Character on a Blue Background
> > loop1: 
> >        jmp loop1
> > 
> > 
> >
>
________________________________________________________________________
> > Want to sell your car? advertise on Yahoo Autos
> Classifieds. It's Free!!
> >        visit http://in.autos.yahoo.com
> > -
> > To unsubscribe from this list: send the line
> "unsubscribe linux-assembly" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at 
> http://vger.kernel.org/majordomo-info.html
> 
> 
> > # boot.s
> #
> # To assembly and link as a **boot** program:
> #
> #    as boot.s -o boot.o
> #    ld -s -oformat binary -Ttext 0x0 -o boot boot.o
> #
> # To copy it to the boot sector of a floppy disk:
> #
> #    dd seek=0 if=boot of=/dev/fd0
> #
> # ---
> # Emanuele (ealtieri@hampshire.edu)
> 	
> 	.code16
> 	.global _start
> _start:
> 	movw	$0xB800, %ax
> 	movw	%ax, %es
> 	movb	$0x41, %es:0
> 	movb	$0x1f, %es:1
> loop1:	jmp	loop1
>  

________________________________________________________________________
Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
       visit http://in.autos.yahoo.com

Re: newbie question on gnu 'as' => explaination about the why (for really newbie ;-))

[Frederic Marmond]

Hi,

Here are some explainations you may want to know.

When your PC boots, it is in real mode.
This mode (!= protected mode) manage memory in this way:
segment+offset
The segment is a 64ko range , step by 16 bytes.
So, if you want to write to b8000 (video memory start in text mode), you 
may set your segment at 0xb800 (=> 0xb800 * 16 = 0xb8000)
Then, you can adress this segment of 65536 bytes with an offset of 16bits.
(that's why in real mode you can only see the first 1Mo of your memory: 
0xFFFF*16 = 0xFFFF0  ~= 1024*1024  (in fact, a little bit more than 1Mo, 
because of the offset of 0xffff max))
For your problem, in pseudo code:
mov 0x411f to 0xb800:0    (write 0x411f to the corner high-left)
mov 0x411f to 0xb800:(80*2 *10+ 20*2)    (write 0x411f to the 10th line 
(80*2 *10= 80(charPerLine) *2(1char=ascii+attribut) *10(10th line)) and 
20th char)

in assembly, segments are stored in special registers: ds (Data 
Segment), CS(Code Segment), Es,Fs,Gs (Extra Segments), SS(Stack Segment)
Offset may be any of the followings (Ax,Bx,Cx,Dx,Si,Di,Sp). (and, in 
32bits mode: eAx,eBx,eCx....)

So, the pseudo code may be write like that ((in intel syntax, which I 
prefer, and that compile with nasm):
mov    ax,0xb800
mov    es,ax                ; we cannot affect directly value to seg 
register (cannot write mov es,0xb800)
mov    bx,0x0            ; start of the segment
mov     [es:bx],0x411f    ;the compilator will assume automaticaly movw 
(mov word => 16 bits)

That is what Emanuele wrote you (in At&t syntax):

           movw    $0xB800, %ax
           movw    %ax, %es			; affect the start adress to the segment
           movb    $0x41, %es:0  			; store value in the video memory
           movb    $0x1f, %es:1					; these 2 lines may be = to movw $0x411f,%es:0


hope it helps!

Fred

Anticipating a Reply wrote:

>Hello Emanuele ,
>
>   Thank you for the below code 
>you sent . It works perfectly and
>will help me learn more of assembly .
>
>   Can you please help me figure 
>out where I'am wrong in the code below,
>which I have witten for the same 
>functionality .
>
>.code16
>
>.globl _start 
>
>_start: 
>       movw $0xb800,%bx  # Video Memory address   
>       movb $0x41,(%bx)  # ASCII value to be displayed
>
>
>       movw $0xb801,%bx  # Video Memory address    
>       movb $0x1f,(%bx)  # Attribute of the Character 
>loop1: 
>       jmp loop1
>
>
>    Thanks once again .
>
>With Best Regards
>
> --- Emanuele Altieri <ealtieri@hampshire.edu> wrote:
>  
>
>>I'm assuming that you want to keep your code as a
>>boot program:
>>
>>           .code16               # needed for
>>booting
>>           .global _start
>>   _start:
>>           movw    $0xB800, %ax
>>           movw    %ax, %es
>>           movb    $0x41, %es:0  
>>           movb    $0x1f, %es:1
>>   loop1:  jmp     loop1
>>
>>
>>To assembly and link the program:
>>
>>   as -o boot.o boot.s
>>   ld -s -oformat binary -Ttext 0x0 -o boot boot.o
>>
>>The last command creates the "boot" file that is
>>ready to be 
>>installed in the first sector of the floppy disk:
>>
>>   dd seek=0 if=boot of=/dev/fd0
>>
>>
>>Hope this helps
>>
>>  -Emanuele
>>
>>
>>On Tue, 2002-07-30 at 07:59, Anticipating a Reply
>>wrote:
>>    
>>
>>>Hi Everybody,
>>>
>>>        I have got a small piece of Assembly code
>>>      
>>>
>>,
>>    
>>
>>>which writes a character "A" on the screen .
>>>
>>>  The below program is compiled and written 
>>>to the boot sector of a floppy. It compiles
>>>using the command :
>>>
>>>	as86 boot.s -o boot.o
>>>	ld86 -d boot.o -o boot 
>>>
>>>   I want to rewrite it in AT&T syntax and
>>>want to use GNU "as" assembler to compile it .
>>>I tried doing it ,but with no success .
>>>
>>>  Can anybody please help me rewite the
>>>below code in AT&T syntax and tell me how
>>>to compile & link it ?
>>>
>>>   Thanks in Advance .
>>>
>>>With Best Regards
>>>
>>>
>>>THE CODE :
>>>------------
>>>
>>>
>>>entry start 
>>>
>>>start: 
>>>       mov ax,#0xb800 ; Video Memory address is
>>>      
>>>
>>0xb800
>>    
>>
>>>  
>>>       mov es,ax      ; Video Memory is made as
>>>      
>>>
>>Extra
>>    
>>
>>>Segment
>>>       seg es         ; Makes next instruction
>>>      
>>>
>>execute
>>    
>>
>>>wrt Extra Segment 
>>>       mov [0],#0x41  ; ASCII value of the
>>>      
>>>
>>Character
>>    
>>
>>>to be displayed 
>>>                      ;  in 1-row & 1-column
>>>       seg es         ; Makes next instruction
>>>      
>>>
>>execute
>>    
>>
>>>wrt Extra Segment 
>>>       mov [1],#0x1f  ; Attribute of the Character
>>>      
>>>
>>to
>>    
>>
>>>be displayed
>>>                      ;  in 1-row & 1-column
>>>                      ; 0x1f represents White
>>>Character on a Blue Background
>>>loop1: 
>>>       jmp loop1
>>>
>>>
>>>
>>>      
>>>
>________________________________________________________________________
>  
>
>>>Want to sell your car? advertise on Yahoo Autos
>>>      
>>>
>>Classifieds. It's Free!!
>>    
>>
>>>       visit http://in.autos.yahoo.com
>>>-
>>>To unsubscribe from this list: send the line
>>>      
>>>
>>"unsubscribe linux-assembly" in
>>    
>>
>>>the body of a message to majordomo@vger.kernel.org
>>>More majordomo info at 
>>>      
>>>
>>http://vger.kernel.org/majordomo-info.html
>>
>>
>>    
>>
>>># boot.s
>>>      
>>>
>>#
>># To assembly and link as a **boot** program:
>>#
>>#    as boot.s -o boot.o
>>#    ld -s -oformat binary -Ttext 0x0 -o boot boot.o
>>#
>># To copy it to the boot sector of a floppy disk:
>>#
>>#    dd seek=0 if=boot of=/dev/fd0
>>#
>># ---
>># Emanuele (ealtieri@hampshire.edu)
>>	
>>	.code16
>>	.global _start
>>_start:
>>	movw	$0xB800, %ax
>>	movw	%ax, %es
>>	movb	$0x41, %es:0
>>	movb	$0x1f, %es:1
>>loop1:	jmp	loop1
>> 
>>    
>>
>
>________________________________________________________________________
>Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
>       visit http://in.autos.yahoo.com
>-
>To unsubscribe from this list: send the line "unsubscribe linux-assembly" in
>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>  
>

Re: newbie question on gnu 'as' => explaination about the why (for really newbie ;-))

[Anticipating a Reply]

Hi Frederic ,

   Thank you very much for all the 
explanation you have given about the 
addressing in 16-bit real mode .

   From this explanation , I think 
I was wrong in line number 7 , 
which had 0xb800 acting as an 
offset to the Data Segment .

   That is,if I'am not wrong we 
always need to specify the addresses 
in the below format -

    seg_reg:offset 
----
 OR
----    
   if given as 
  
   movb $xxx , ( %seg_reg )

then the contents of "seg_reg"
will be considered as an Offset 
with respect to the Data Segment.
     

1> .code16
2>
3> .globl _start 
4>
5> _start: 
6>       movw $0xb800,%bx  # Video Memory address   
7>       movb $0x41,(%bx)  # ASCII value to 
8>       movw $0xb801,%bx  # Video Memory address    
9>       movb $0x1f,(%bx)  # Attribute of the  
10> loop1: 
11>       jmp loop1


Hope I have got the concept correctly .

  Thanking you all for bearing my basic
doubts and clearing them too.

With best Regards


 --- Frederic Marmond <fmarmond@eprocess.fr> wrote: >
Hi,
> 
> Here are some explainations you may want to know.
> 
> When your PC boots, it is in real mode.
> This mode (!= protected mode) manage memory in this
> way:
> segment+offset
> The segment is a 64ko range , step by 16 bytes.
> So, if you want to write to b8000 (video memory
> start in text mode), you 
> may set your segment at 0xb800 (=> 0xb800 * 16 =
> 0xb8000)
> Then, you can adress this segment of 65536 bytes
> with an offset of 16bits.
> (that's why in real mode you can only see the first
> 1Mo of your memory: 
> 0xFFFF*16 = 0xFFFF0  ~= 1024*1024  (in fact, a
> little bit more than 1Mo, 
> because of the offset of 0xffff max))
> For your problem, in pseudo code:
> mov 0x411f to 0xb800:0    (write 0x411f to the
> corner high-left)
> mov 0x411f to 0xb800:(80*2 *10+ 20*2)    (write
> 0x411f to the 10th line 
> (80*2 *10= 80(charPerLine) *2(1char=ascii+attribut)
> *10(10th line)) and 
> 20th char)
> 
> in assembly, segments are stored in special
> registers: ds (Data 
> Segment), CS(Code Segment), Es,Fs,Gs (Extra
> Segments), SS(Stack Segment)
> Offset may be any of the followings
> (Ax,Bx,Cx,Dx,Si,Di,Sp). (and, in 
> 32bits mode: eAx,eBx,eCx....)
> 
> So, the pseudo code may be write like that ((in
> intel syntax, which I 
> prefer, and that compile with nasm):
> mov    ax,0xb800
> mov    es,ax                ; we cannot affect
> directly value to seg 
> register (cannot write mov es,0xb800)
> mov    bx,0x0            ; start of the segment
> mov     [es:bx],0x411f    ;the compilator will
> assume automaticaly movw 
> (mov word => 16 bits)
> 
> That is what Emanuele wrote you (in At&t syntax):
> 
>            movw    $0xB800, %ax
>            movw    %ax, %es			; affect the start
> adress to the segment
>            movb    $0x41, %es:0  			; store value in
> the video memory
>            movb    $0x1f, %es:1					; these 2 lines
> may be = to movw $0x411f,%es:0
> 
> 
> hope it helps!
> 
> Fred
> 
> Anticipating a Reply wrote:
> 
> >Hello Emanuele ,
> >
> >   Thank you for the below code 
> >you sent . It works perfectly and
> >will help me learn more of assembly .
> >
> >   Can you please help me figure 
> >out where I'am wrong in the code below,
> >which I have witten for the same 
> >functionality .
> >
> >.code16
> >
> >.globl _start 
> >
> >_start: 
> >       movw $0xb800,%bx  # Video Memory address   
> >       movb $0x41,(%bx)  # ASCII value to be
> displayed
> >
> >
> >       movw $0xb801,%bx  # Video Memory address    
> >       movb $0x1f,(%bx)  # Attribute of the
> Character 
> >loop1: 
> >       jmp loop1
> >
> >
> >    Thanks once again .
> >
> >With Best Regards
> >
> > --- Emanuele Altieri <ealtieri@hampshire.edu>
> wrote:
> >  
> >
> >>I'm assuming that you want to keep your code as a
> >>boot program:
> >>
> >>           .code16               # needed for
> >>booting
> >>           .global _start
> >>   _start:
> >>           movw    $0xB800, %ax
> >>           movw    %ax, %es
> >>           movb    $0x41, %es:0  
> >>           movb    $0x1f, %es:1
> >>   loop1:  jmp     loop1
> >>
> >>
> >>To assembly and link the program:
> >>
> >>   as -o boot.o boot.s
> >>   ld -s -oformat binary -Ttext 0x0 -o boot boot.o
> >>
> >>The last command creates the "boot" file that is
> >>ready to be 
> >>installed in the first sector of the floppy disk:
> >>
> >>   dd seek=0 if=boot of=/dev/fd0
> >>
> >>
> >>Hope this helps
> >>
> >>  -Emanuele
> >>
> >>
> >>On Tue, 2002-07-30 at 07:59, Anticipating a Reply
> >>wrote:
> >>    
> >>
> >>>Hi Everybody,
> >>>
> >>>        I have got a small piece of Assembly code
> >>>      
> >>>
> >>,
> >>    
> >>
> >>>which writes a character "A" on the screen .
> >>>
> >>>  The below program is compiled and written 
> >>>to the boot sector of a floppy. It compiles
> >>>using the command :
> >>>
> >>>	as86 boot.s -o boot.o
> >>>	ld86 -d boot.o -o boot 
> >>>
> >>>   I want to rewrite it in AT&T syntax and
> >>>want to use GNU "as" assembler to compile it .
> >>>I tried doing it ,but with no success .
> >>>
> >>>  Can anybody please help me rewite the
> >>>below code in AT&T syntax and tell me how
> >>>to compile & link it ?
> >>>
> >>>   Thanks in Advance .
> >>>
> >>>With Best Regards
> >>>
> >>>
> >>>THE CODE :
> >>>------------
> >>>
> >>>
> >>>entry start 
> >>>
> >>>start: 
> >>>       mov ax,#0xb800 ; Video Memory address is
> >>>      
> >>>
> >>0xb800
> >>    
> >>
> >>>  
> >>>       mov es,ax      ; Video Memory is made as
> >>>      
> >>>
> >>Extra
> >>    
> >>
> >>>Segment
> >>>       seg es         ; Makes next instruction
> >>>      
> >>>
> >>execute
> >>    
> >>
> >>>wrt Extra Segment 
> >>>       mov [0],#0x41  ; ASCII value of the
> >>>      
> >>>
> >>Character
> >>    
> >>
> >>>to be displayed 
> >>>                      ;  in 1-row & 1-column
> >>>       seg es         ; Makes next instruction
> >>>      
> >>>
> >>execute
> >>    
> >>
> >>>wrt Extra Segment 
> >>>       mov [1],#0x1f  ; Attribute of the
> Character
> >>>      
> >>>
> >>to
> >>    
> >>
> >>>be displayed
> >>>                      ;  in 1-row & 1-column
> >>>                      ; 0x1f represents White
> >>>Character on a Blue Background
> >>>loop1: 
> >>>       jmp loop1
> >>>
> >>>
> >>>
> >>>      
> >>>
>
>________________________________________________________________________
> >  
> >
> >>>Want to sell your car? advertise on Yahoo Autos
> >>>      
> >>>
> >>Classifieds. It's Free!!
> >>    
> >>
> >>>       visit http://in.autos.yahoo.com
> >>>-
> >>>To unsubscribe from this list: send the line
> >>>      
> >>>
> >>"unsubscribe linux-assembly" in
> >>    
> >>
> >>>the body of a message to
> majordomo@vger.kernel.org
> >>>More majordomo info at 
> >>>      
> >>>
> >>http://vger.kernel.org/majordomo-info.html
> >>
> >>
> >>    
> >>
> >>># boot.s
> >>>      
> >>>
> >>#
> >># To assembly and link as a **boot** program:
> >>#
> >>#    as boot.s -o boot.o
> >>#    ld -s -oformat binary -Ttext 0x0 -o boot
> boot.o
> >>#
> >># To copy it to the boot sector of a floppy disk:
> >>#
> >>#    dd seek=0 if=boot of=/dev/fd0
> >>#
> >># ---
> >># Emanuele (ealtieri@hampshire.edu)
> >>	
> >>	.code16
> >>	.global _start
> >>_start:
> >>	movw	$0xB800, %ax
> >>	movw	%ax, %es
> >>	movb	$0x41, %es:0
> >>	movb	$0x1f, %es:1
> >>loop1:	jmp	loop1
> >> 
> >>    
> >>
> >
>
>________________________________________________________________________
> >Want to sell your car? advertise on Yahoo Autos
> Classifieds. It's Free!!
> >       visit http://in.autos.yahoo.com
> >-
> >To unsubscribe from this list: send the line
> "unsubscribe linux-assembly" in
> >the body of a message to majordomo@vger.kernel.org
> >More majordomo info at 
> http://vger.kernel.org/majordomo-info.html
> >
> >  
> >
> 
> 
> 
> -
> To unsubscribe from this list: send the line
> "unsubscribe linux-assembly" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at 
http://vger.kernel.org/majordomo-info.html 

________________________________________________________________________
Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
       visit http://in.autos.yahoo.com

Re: newbie question on gnu 'as' => explaination about the why (for really newbie ;-))

[Frederic Marmond]

  hum, well...
I don't use the AT&T syntax, so, I may be wrong, but I think your code 
is not right again:
you don't specify any segment! (only the bx register)
So, how do you think the CPU will know where to put your 0x411f ?
You have to specify the segment after having fill it with a value.
movw 0xb800,%bx
movw %bx,%ds
movw $0x411f,(%bx)        <= I'm not sure (perhapse a AT&T guru may help us)
                                            Here, we assume that DS is 
the default segment token by the as compiler

if I take your origin-code:

       mov ax,#0xb800 ; Video Memory address is 0xb800
       mov es,ax      ; Video Memory is made as Extra Segment
       seg es         ; Makes next instruction execute wrt Extra Segment 
       mov [0],#0x41  ; ASCII value of the Character to be displayed 
                      ;  in 1-row & 1-column
       seg es         ; Makes next instruction execute wrt Extra Segment 
       mov [1],#0x1f  ; Attribute of the Character to be displayed
                      ;  in 1-row & 1-column
                      ; 0x1f represents White


The "seg es" lines are what we need.
I think that by default, 'ds' is used, so, my 3 lines of code may work.


in this:

6>       movw $0xb800,%bx  # Video Memory address   
7>       movb $0x41,(%bx)  # ASCII value to 
8>       movw $0xb801,%bx  # Video Memory address    
9>       movb $0x1f,(%bx)  # Attribute of the  

you will put 0x411f at [ds:0xb800], which is somewhere around your 
program code... it will surely erase something you may need (perhapse 
your code!)



Anticipating a Reply wrote:

>Hi Frederic ,
>
>   Thank you very much for all the 
>explanation you have given about the 
>addressing in 16-bit real mode .
>
>   From this explanation , I think 
>I was wrong in line number 7 , 
>which had 0xb800 acting as an 
>offset to the Data Segment .
>
>   That is,if I'am not wrong we 
>always need to specify the addresses 
>in the below format -
>
>    seg_reg:offset 
>----
> OR
>----    
>   if given as 
>  
>   movb $xxx , ( %seg_reg )
>
>then the contents of "seg_reg"
>will be considered as an Offset 
>with respect to the Data Segment.
>     
>
>1> .code16
>2>
>3> .globl _start 
>4>
>5> _start: 
>6>       movw $0xb800,%bx  # Video Memory address   
>7>       movb $0x41,(%bx)  # ASCII value to 
>8>       movw $0xb801,%bx  # Video Memory address    
>9>       movb $0x1f,(%bx)  # Attribute of the  
>10> loop1: 
>11>       jmp loop1
>
>
>Hope I have got the concept correctly .
>
>  Thanking you all for bearing my basic
>doubts and clearing them too.
>
>With best Regards
>
>
> --- Frederic Marmond <fmarmond@eprocess.fr> wrote: >
>Hi,
>  
>
>>Here are some explainations you may want to know.
>>
>>When your PC boots, it is in real mode.
>>This mode (!= protected mode) manage memory in this
>>way:
>>segment+offset
>>The segment is a 64ko range , step by 16 bytes.
>>So, if you want to write to b8000 (video memory
>>start in text mode), you 
>>may set your segment at 0xb800 (=> 0xb800 * 16 =
>>0xb8000)
>>Then, you can adress this segment of 65536 bytes
>>with an offset of 16bits.
>>(that's why in real mode you can only see the first
>>1Mo of your memory: 
>>0xFFFF*16 = 0xFFFF0  ~= 1024*1024  (in fact, a
>>little bit more than 1Mo, 
>>because of the offset of 0xffff max))
>>For your problem, in pseudo code:
>>mov 0x411f to 0xb800:0    (write 0x411f to the
>>corner high-left)
>>mov 0x411f to 0xb800:(80*2 *10+ 20*2)    (write
>>0x411f to the 10th line 
>>(80*2 *10= 80(charPerLine) *2(1char=ascii+attribut)
>>*10(10th line)) and 
>>20th char)
>>
>>in assembly, segments are stored in special
>>registers: ds (Data 
>>Segment), CS(Code Segment), Es,Fs,Gs (Extra
>>Segments), SS(Stack Segment)
>>Offset may be any of the followings
>>(Ax,Bx,Cx,Dx,Si,Di,Sp). (and, in 
>>32bits mode: eAx,eBx,eCx....)
>>
>>So, the pseudo code may be write like that ((in
>>intel syntax, which I 
>>prefer, and that compile with nasm):
>>mov    ax,0xb800
>>mov    es,ax                ; we cannot affect
>>directly value to seg 
>>register (cannot write mov es,0xb800)
>>mov    bx,0x0            ; start of the segment
>>mov     [es:bx],0x411f    ;the compilator will
>>assume automaticaly movw 
>>(mov word => 16 bits)
>>
>>That is what Emanuele wrote you (in At&t syntax):
>>
>>           movw    $0xB800, %ax
>>           movw    %ax, %es			; affect the start
>>adress to the segment
>>           movb    $0x41, %es:0  			; store value in
>>the video memory
>>           movb    $0x1f, %es:1					; these 2 lines
>>may be = to movw $0x411f,%es:0
>>
>>
>>hope it helps!
>>
>>Fred
>>
>>Anticipating a Reply wrote:
>>
>>    
>>
>>>Hello Emanuele ,
>>>
>>>  Thank you for the below code 
>>>you sent . It works perfectly and
>>>will help me learn more of assembly .
>>>
>>>  Can you please help me figure 
>>>out where I'am wrong in the code below,
>>>which I have witten for the same 
>>>functionality .
>>>
>>>.code16
>>>
>>>.globl _start 
>>>
>>>_start: 
>>>      movw $0xb800,%bx  # Video Memory address   
>>>      movb $0x41,(%bx)  # ASCII value to be
>>>      
>>>
>>displayed
>>    
>>
>>>      movw $0xb801,%bx  # Video Memory address    
>>>      movb $0x1f,(%bx)  # Attribute of the
>>>      
>>>
>>Character 
>>    
>>
>>>loop1: 
>>>      jmp loop1
>>>
>>>
>>>   Thanks once again .
>>>
>>>With Best Regards
>>>
>>>--- Emanuele Altieri <ealtieri@hampshire.edu>
>>>      
>>>
>>wrote:
>>    
>>
>>> 
>>>
>>>      
>>>
>>>>I'm assuming that you want to keep your code as a
>>>>boot program:
>>>>
>>>>          .code16               # needed for
>>>>booting
>>>>          .global _start
>>>>  _start:
>>>>          movw    $0xB800, %ax
>>>>          movw    %ax, %es
>>>>          movb    $0x41, %es:0  
>>>>          movb    $0x1f, %es:1
>>>>  loop1:  jmp     loop1
>>>>
>>>>
>>>>To assembly and link the program:
>>>>
>>>>  as -o boot.o boot.s
>>>>  ld -s -oformat binary -Ttext 0x0 -o boot boot.o
>>>>
>>>>The last command creates the "boot" file that is
>>>>ready to be 
>>>>installed in the first sector of the floppy disk:
>>>>
>>>>  dd seek=0 if=boot of=/dev/fd0
>>>>
>>>>
>>>>Hope this helps
>>>>
>>>> -Emanuele
>>>>
>>>>
>>>>On Tue, 2002-07-30 at 07:59, Anticipating a Reply
>>>>wrote:
>>>>   
>>>>
>>>>        
>>>>
>>>>>Hi Everybody,
>>>>>
>>>>>       I have got a small piece of Assembly code
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>,
>>>>   
>>>>
>>>>        
>>>>
>>>>>which writes a character "A" on the screen .
>>>>>
>>>>> The below program is compiled and written 
>>>>>to the boot sector of a floppy. It compiles
>>>>>using the command :
>>>>>
>>>>>	as86 boot.s -o boot.o
>>>>>	ld86 -d boot.o -o boot 
>>>>>
>>>>>  I want to rewrite it in AT&T syntax and
>>>>>want to use GNU "as" assembler to compile it .
>>>>>I tried doing it ,but with no success .
>>>>>
>>>>> Can anybody please help me rewite the
>>>>>below code in AT&T syntax and tell me how
>>>>>to compile & link it ?
>>>>>
>>>>>  Thanks in Advance .
>>>>>
>>>>>With Best Regards
>>>>>
>>>>>
>>>>>THE CODE :
>>>>>------------
>>>>>
>>>>>
>>>>>entry start 
>>>>>
>>>>>start: 
>>>>>      mov ax,#0xb800 ; Video Memory address is
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>0xb800
>>>>   
>>>>
>>>>        
>>>>
>>>>> 
>>>>>      mov es,ax      ; Video Memory is made as
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>Extra
>>>>   
>>>>
>>>>        
>>>>
>>>>>Segment
>>>>>      seg es         ; Makes next instruction
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>execute
>>>>   
>>>>
>>>>        
>>>>
>>>>>wrt Extra Segment 
>>>>>      mov [0],#0x41  ; ASCII value of the
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>Character
>>>>   
>>>>
>>>>        
>>>>
>>>>>to be displayed 
>>>>>                     ;  in 1-row & 1-column
>>>>>      seg es         ; Makes next instruction
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>execute
>>>>   
>>>>
>>>>        
>>>>
>>>>>wrt Extra Segment 
>>>>>      mov [1],#0x1f  ; Attribute of the
>>>>>          
>>>>>
>>Character
>>    
>>
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>to
>>>>   
>>>>
>>>>        
>>>>
>>>>>be displayed
>>>>>                     ;  in 1-row & 1-column
>>>>>                     ; 0x1f represents White
>>>>>Character on a Blue Background
>>>>>loop1: 
>>>>>      jmp loop1
>>>>>
>>>>>
>>>>>
>>>>>     
>>>>>
>>>>>          
>>>>>
>>________________________________________________________________________
>>    
>>
>>> 
>>>
>>>      
>>>
>>>>>Want to sell your car? advertise on Yahoo Autos
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>Classifieds. It's Free!!
>>>>   
>>>>
>>>>        
>>>>
>>>>>      visit http://in.autos.yahoo.com
>>>>>-
>>>>>To unsubscribe from this list: send the line
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>"unsubscribe linux-assembly" in
>>>>   
>>>>
>>>>        
>>>>
>>>>>the body of a message to
>>>>>          
>>>>>
>>majordomo@vger.kernel.org
>>    
>>
>>>>>More majordomo info at 
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>http://vger.kernel.org/majordomo-info.html
>>>>
>>>>
>>>>   
>>>>
>>>>        
>>>>
>>>>># boot.s
>>>>>     
>>>>>
>>>>>          
>>>>>
>>>>#
>>>># To assembly and link as a **boot** program:
>>>>#
>>>>#    as boot.s -o boot.o
>>>>#    ld -s -oformat binary -Ttext 0x0 -o boot
>>>>        
>>>>
>>boot.o
>>    
>>
>>>>#
>>>># To copy it to the boot sector of a floppy disk:
>>>>#
>>>>#    dd seek=0 if=boot of=/dev/fd0
>>>>#
>>>># ---
>>>># Emanuele (ealtieri@hampshire.edu)
>>>>	
>>>>	.code16
>>>>	.global _start
>>>>_start:
>>>>	movw	$0xB800, %ax
>>>>	movw	%ax, %es
>>>>	movb	$0x41, %es:0
>>>>	movb	$0x1f, %es:1
>>>>loop1:	jmp	loop1
>>>>
>>>>   
>>>>
>>>>        
>>>>
>>________________________________________________________________________
>>    
>>
>>>Want to sell your car? advertise on Yahoo Autos
>>>      
>>>
>>Classifieds. It's Free!!
>>    
>>
>>>      visit http://in.autos.yahoo.com
>>>-
>>>To unsubscribe from this list: send the line
>>>      
>>>
>>"unsubscribe linux-assembly" in
>>    
>>
>>>the body of a message to majordomo@vger.kernel.org
>>>More majordomo info at 
>>>      
>>>
>>http://vger.kernel.org/majordomo-info.html
>>    
>>
>>> 
>>>
>>>      
>>>
>>
>>-
>>To unsubscribe from this list: send the line
>>"unsubscribe linux-assembly" in
>>the body of a message to majordomo@vger.kernel.org
>>More majordomo info at 
>>    
>>
>http://vger.kernel.org/majordomo-info.html 
>
>________________________________________________________________________
>Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
>       visit http://in.autos.yahoo.com
>
>  
>

Re: newbie question on gnu 'as' => explaination about the why (for really newbie ;-))

[Anticipating a Reply]

Hi Frederic ,

  Thanks again .

  Let me do some more investigation and 
study before I ask anymore questions on 
AT&T syntax and Assembly .

With Best Regards

 --- Frederic Marmond <fmarmond@eprocess.fr> wrote: >
hum, well...
> I don't use the AT&T syntax, so, I may be wrong, but
> I think your code 
> is not right again:
> you don't specify any segment! (only the bx
> register)
> So, how do you think the CPU will know where to put
> your 0x411f ?
> You have to specify the segment after having fill it
> with a value.
> movw 0xb800,%bx
> movw %bx,%ds
> movw $0x411f,(%bx)        <= I'm not sure (perhapse
> a AT&T guru may help us)
>                                             Here, we
> assume that DS is 
> the default segment token by the as compiler
> 
> if I take your origin-code:
> 
>        mov ax,#0xb800 ; Video Memory address is
> 0xb800
>        mov es,ax      ; Video Memory is made as
> Extra Segment
>        seg es         ; Makes next instruction
> execute wrt Extra Segment 
>        mov [0],#0x41  ; ASCII value of the Character
> to be displayed 
>                       ;  in 1-row & 1-column
>        seg es         ; Makes next instruction
> execute wrt Extra Segment 
>        mov [1],#0x1f  ; Attribute of the Character
> to be displayed
>                       ;  in 1-row & 1-column
>                       ; 0x1f represents White
> 
> 
> The "seg es" lines are what we need.
> I think that by default, 'ds' is used, so, my 3
> lines of code may work.
> 
> 
> in this:
> 
> 6>       movw $0xb800,%bx  # Video Memory address   
> 7>       movb $0x41,(%bx)  # ASCII value to 
> 8>       movw $0xb801,%bx  # Video Memory address   
> 
> 9>       movb $0x1f,(%bx)  # Attribute of the  
> 
> you will put 0x411f at [ds:0xb800], which is
> somewhere around your 
> program code... it will surely erase something you
> may need (perhapse 
> your code!)
> 
> 
> 
> 
> Anticipating a Reply wrote:
> 
> >Hi Frederic ,
> >
> >   Thank you very much for all the 
> >explanation you have given about the 
> >addressing in 16-bit real mode .
> >
> >   From this explanation , I think 
> >I was wrong in line number 7 , 
> >which had 0xb800 acting as an 
> >offset to the Data Segment .
> >
> >   That is,if I'am not wrong we 
> >always need to specify the addresses 
> >in the below format -
> >
> >    seg_reg:offset 
> >----
> > OR
> >----    
> >   if given as 
> >  
> >   movb $xxx , ( %seg_reg )
> >
> >then the contents of "seg_reg"
> >will be considered as an Offset 
> >with respect to the Data Segment.
> >     
> >
> >1> .code16
> >2>
> >3> .globl _start 
> >4>
> >5> _start: 
> >6>       movw $0xb800,%bx  # Video Memory address  
> 
> >7>       movb $0x41,(%bx)  # ASCII value to 
> >8>       movw $0xb801,%bx  # Video Memory address  
>  
> >9>       movb $0x1f,(%bx)  # Attribute of the  
> >10> loop1: 
> >11>       jmp loop1
> >
> >
> >Hope I have got the concept correctly .
> >
> >  Thanking you all for bearing my basic
> >doubts and clearing them too.
> >
> >With best Regards
> >
> >
> > --- Frederic Marmond <fmarmond@eprocess.fr> wrote:
> >
> >Hi,
> >  
> >
> >>Here are some explainations you may want to know.
> >>
> >>When your PC boots, it is in real mode.
> >>This mode (!= protected mode) manage memory in
> this
> >>way:
> >>segment+offset
> >>The segment is a 64ko range , step by 16 bytes.
> >>So, if you want to write to b8000 (video memory
> >>start in text mode), you 
> >>may set your segment at 0xb800 (=> 0xb800 * 16 =
> >>0xb8000)
> >>Then, you can adress this segment of 65536 bytes
> >>with an offset of 16bits.
> >>(that's why in real mode you can only see the
> first
> >>1Mo of your memory: 
> >>0xFFFF*16 = 0xFFFF0  ~= 1024*1024  (in fact, a
> >>little bit more than 1Mo, 
> >>because of the offset of 0xffff max))
> >>For your problem, in pseudo code:
> >>mov 0x411f to 0xb800:0    (write 0x411f to the
> >>corner high-left)
> >>mov 0x411f to 0xb800:(80*2 *10+ 20*2)    (write
> >>0x411f to the 10th line 
> >>(80*2 *10= 80(charPerLine)
> *2(1char=ascii+attribut)
> >>*10(10th line)) and 
> >>20th char)
> >>
> >>in assembly, segments are stored in special
> >>registers: ds (Data 
> >>Segment), CS(Code Segment), Es,Fs,Gs (Extra
> >>Segments), SS(Stack Segment)
> >>Offset may be any of the followings
> >>(Ax,Bx,Cx,Dx,Si,Di,Sp). (and, in 
> >>32bits mode: eAx,eBx,eCx....)
> >>
> >>So, the pseudo code may be write like that ((in
> >>intel syntax, which I 
> >>prefer, and that compile with nasm):
> >>mov    ax,0xb800
> >>mov    es,ax                ; we cannot affect
> >>directly value to seg 
> >>register (cannot write mov es,0xb800)
> >>mov    bx,0x0            ; start of the segment
> >>mov     [es:bx],0x411f    ;the compilator will
> >>assume automaticaly movw 
> >>(mov word => 16 bits)
> >>
> >>That is what Emanuele wrote you (in At&t syntax):
> >>
> >>           movw    $0xB800, %ax
> >>           movw    %ax, %es			; affect the start
> >>adress to the segment
> >>           movb    $0x41, %es:0  			; store value
> in
> >>the video memory
> >>           movb    $0x1f, %es:1					; these 2
> lines
> >>may be = to movw $0x411f,%es:0
> >>
> >>
> >>hope it helps!
> >>
> >>Fred
> >>
> >>Anticipating a Reply wrote:
> >>
> >>    
> >>
> >>>Hello Emanuele ,
> >>>
> >>>  Thank you for the below code 
> >>>you sent . It works perfectly and
> >>>will help me learn more of assembly .
> >>>
> >>>  Can you please help me figure 
> >>>out where I'am wrong in the code below,
> >>>which I have witten for the same 
> >>>functionality .
> >>>
> >>>.code16
> >>>
> >>>.globl _start 
> >>>
> >>>_start: 
> >>>      movw $0xb800,%bx  # Video Memory address   
> >>>      movb $0x41,(%bx)  # ASCII value to be
> >>>      
> >>>
> >>displayed
> >>    
> >>
> >>>      movw $0xb801,%bx  # Video Memory address   
> 
> >>>      movb $0x1f,(%bx)  # Attribute of the
> >>>      
> >>>
> >>Character 
> >>    
> >>
> >>>loop1: 
> >>>      jmp loop1
> >>>
> >>>
> >>>   Thanks once again .
> >>>
> >>>With Best Regards
> >>>
> >>>--- Emanuele Altieri <ealtieri@hampshire.edu>
> >>>      
> >>>
> >>wrote:
> >>    
> >>
> >>> 
> >>>
> >>>      
> >>>
> >>>>I'm assuming that you want to keep your code as
> a
> >>>>boot program:
> >>>>
> >>>>          .code16               # needed for
> >>>>booting
> >>>>          .global _start
> >>>>  _start:
> >>>>          movw    $0xB800, %ax
> >>>>          movw    %ax, %es
> >>>>          movb    $0x41, %es:0  
> >>>>          movb    $0x1f, %es:1
> >>>>  loop1:  jmp     loop1
> >>>>
> >>>>
> >>>>To assembly and link the program:
> >>>>
> >>>>  as -o boot.o boot.s
> >>>>  ld -s -oformat binary -Ttext 0x0 -o boot
> boot.o
> >>>>
> >>>>The last command creates the "boot" file that is
> >>>>ready to be 
> >>>>installed in the first sector of the floppy
> disk:
> >>>>
> >>>>  dd seek=0 if=boot of=/dev/fd0
> >>>>
> >>>>
> >>>>Hope this helps
> >>>>
> >>>> -Emanuele
> >>>>
> >>>>
> >>>>On Tue, 2002-07-30 at 07:59, Anticipating a
> Reply
> >>>>wrote:
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>Hi Everybody,
> >>>>>
> >>>>>       I have got a small piece of Assembly
> code
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>,
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>which writes a character "A" on the screen .
> >>>>>
> >>>>> The below program is compiled and written 
> >>>>>to the boot sector of a floppy. It compiles
> >>>>>using the command :
> >>>>>
> >>>>>	as86 boot.s -o boot.o
> >>>>>	ld86 -d boot.o -o boot 
> >>>>>
> >>>>>  I want to rewrite it in AT&T syntax and
> >>>>>want to use GNU "as" assembler to compile it .
> >>>>>I tried doing it ,but with no success .
> >>>>>
> >>>>> Can anybody please help me rewite the
> >>>>>below code in AT&T syntax and tell me how
> >>>>>to compile & link it ?
> >>>>>
> >>>>>  Thanks in Advance .
> >>>>>
> >>>>>With Best Regards
> >>>>>
> >>>>>
> >>>>>THE CODE :
> >>>>>------------
> >>>>>
> >>>>>
> >>>>>entry start 
> >>>>>
> >>>>>start: 
> >>>>>      mov ax,#0xb800 ; Video Memory address is
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>0xb800
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>> 
> >>>>>      mov es,ax      ; Video Memory is made as
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>Extra
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>Segment
> >>>>>      seg es         ; Makes next instruction
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>execute
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>wrt Extra Segment 
> >>>>>      mov [0],#0x41  ; ASCII value of the
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>Character
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>to be displayed 
> >>>>>                     ;  in 1-row & 1-column
> >>>>>      seg es         ; Makes next instruction
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>execute
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>wrt Extra Segment 
> >>>>>      mov [1],#0x1f  ; Attribute of the
> >>>>>          
> >>>>>
> >>Character
> >>    
> >>
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>to
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>be displayed
> >>>>>                     ;  in 1-row & 1-column
> >>>>>                     ; 0x1f represents White
> >>>>>Character on a Blue Background
> >>>>>loop1: 
> >>>>>      jmp loop1
> >>>>>
> >>>>>
> >>>>>
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
>
>>________________________________________________________________________
> >>    
> >>
> >>> 
> >>>
> >>>      
> >>>
> >>>>>Want to sell your car? advertise on Yahoo Autos
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>Classifieds. It's Free!!
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>      visit http://in.autos.yahoo.com
> >>>>>-
> >>>>>To unsubscribe from this list: send the line
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>"unsubscribe linux-assembly" in
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>>the body of a message to
> >>>>>          
> >>>>>
> >>majordomo@vger.kernel.org
> >>    
> >>
> >>>>>More majordomo info at 
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>http://vger.kernel.org/majordomo-info.html
> >>>>
> >>>>
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>>>># boot.s
> >>>>>     
> >>>>>
> >>>>>          
> >>>>>
> >>>>#
> >>>># To assembly and link as a **boot** program:
> >>>>#
> >>>>#    as boot.s -o boot.o
> >>>>#    ld -s -oformat binary -Ttext 0x0 -o boot
> >>>>        
> >>>>
> >>boot.o
> >>    
> >>
> >>>>#
> >>>># To copy it to the boot sector of a floppy
> disk:
> >>>>#
> >>>>#    dd seek=0 if=boot of=/dev/fd0
> >>>>#
> >>>># ---
> >>>># Emanuele (ealtieri@hampshire.edu)
> >>>>	
> >>>>	.code16
> >>>>	.global _start
> >>>>_start:
> >>>>	movw	$0xB800, %ax
> >>>>	movw	%ax, %es
> >>>>	movb	$0x41, %es:0
> >>>>	movb	$0x1f, %es:1
> >>>>loop1:	jmp	loop1
> >>>>
> >>>>   
> >>>>
> >>>>        
> >>>>
>
>>________________________________________________________________________
> >>    
> >>
> >>>Want to sell your car? advertise on Yahoo Autos
> >>>      
> >>>
> >>Classifieds. It's Free!!
> >>    
> >>
> >>>      visit http://in.autos.yahoo.com
> >>>-
> >>>To unsubscribe from this list: send the line
> >>>      
> >>>
> >>"unsubscribe linux-assembly" in
> >>    
> >>
> >>>the body of a message to
> majordomo@vger.kernel.org
> >>>More majordomo info at 
> >>>      
> >>>
> >>http://vger.kernel.org/majordomo-info.html
> >>    
> >>
> >>> 
> >>>
> >>>      
> >>>
> >>
> >>-
> >>To unsubscribe from this list: send the line
> >>"unsubscribe linux-assembly" in
> >>the body of a message to majordomo@vger.kernel.org
> >>More majordomo info at 
> >>    
> >>
> >http://vger.kernel.org/majordomo-info.html 
> >
>
>________________________________________________________________________
> >Want to sell your car? advertise on Yahoo Autos
> Classifieds. It's Free!!
> >       visit http://in.autos.yahoo.com
> >
> >  
> >
> 
> 
>  

________________________________________________________________________
Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
       visit http://in.autos.yahoo.com

Re: newbie question on gnu 'as' => explaination about the why (for really newbie ;-))

[Anticipating a Reply]

Hello Emanuele ,

    Thank you very much for the explanation
given by you , which has cleared my doubt 
about 16-bit mode addressing totally .

    Actually , I was fooled by the Video
memory address 0xb800 which is loaded into
the segment register in the orignal code . 

    Now I understand that its lower 4 bits
are left-shifted & the offset is added to 
produce the 20 bit address . 

    Thanks again for the help .

With Best Regards

 --- Emanuele Altieri <ealtieri@hampshire.edu> wrote:
> Hi,
> 
> My reply comes a bit late. I hope it is still
> helpful. 
> This is the code that you wrote:
> 
>  .code16
>  .globl _start 
>  _start: 
>          movw $0xb800,%bx  # Video Memory address   
>          movb $0x41,(%bx)  # ASCII value to be
> displayed
>          movw $0xb801,%bx  # Video Memory address   
>          movb $0x1f,(%bx)  # Attribute of the
>  loop1:  jmp loop1
> 
> The problem with the code above is that it is
> writing to memory address
> 0xB800 rather than 0xB8000 (notice the extra zero),
> where video memory
> is actually located. The (%bx) notation means write
> to (or read from)
> memory at the address specified in %bx, and in %bx
> we have 0xB800.
> 
> Now, how can we make it write to 0xB8000 instead?
> The problem with this
> address is that we can't make it fit in a real-mode
> register, such as
> %bx, because the register can only hold two bytes of
> data.
> To overcome this limitation, Intel provides us with
> segment registers
> (es, ds, fs, gs). You can address memory by
> combining one of these
> registers with %bx. For example:
> 
>          mov $SOME_VALUE, %es:(%bx)
> 
> The memory address to write to is calculated by
> multiplying %es by 16
> and adding %bx to it. So, if we have
> 
>          # %es = $0xB800
>          # %bx = $0
>          mov $SOME_VALUE, %es:(%bx)    # write to
> 0xB8000
> 
> the final address is calculated as following:
> 
>         B800          (value in %es * 16)
>       +  0000         (value in %bx     )
>         =====
>         B8000
> 
> that is the address that we want.
> 
> You can learn more on real-mode addressing and
> segmentation from the
> 16-bit edition of the Art Of Assembly Language,
> section 4.3. Follow the
> link below:
> 
>
http://webster.cs.ucr.edu/Page_asm/ArtofAssembly/ch04/CH04-1.html#HEADING1-64
> 
> The whole chapter 4 is very interesting.
> 
> If you want to find out more about the AT&T's
> addressing modes, there
> are many tutorials on the linuxassembly.org site,
> such as this:
> 
> http://www.linuxassembly.org/linasm.html
> 
> 
> Take care
> 
>   -Emanuele
> 
> 
> 
> On Thu, 2002-08-01 at 00:43, Anticipating a Reply
> wrote:
> > Hi Frederic ,
> > 
> >   Thanks again .
> > 
> >   Let me do some more investigation and 
> > study before I ask anymore questions on 
> > AT&T syntax and Assembly .
> > 
> > With Best Regards
> > 
> >  --- Frederic Marmond <fmarmond@eprocess.fr>
> wrote: >
> > hum, well...
> > > I don't use the AT&T syntax, so, I may be wrong,
> but
> > > I think your code 
> > > is not right again:
> > > you don't specify any segment! (only the bx
> > > register)
> > > So, how do you think the CPU will know where to
> put
> > > your 0x411f ?
> > > You have to specify the segment after having
> fill it
> > > with a value.
> > > movw 0xb800,%bx
> > > movw %bx,%ds
> > > movw $0x411f,(%bx)        <= I'm not sure
> (perhapse
> > > a AT&T guru may help us)
> > >                                            
> Here, we
> > > assume that DS is 
> > > the default segment token by the as compiler
> > > 
> > > if I take your origin-code:
> > > 
> > >        mov ax,#0xb800 ; Video Memory address is
> > > 0xb800
> > >        mov es,ax      ; Video Memory is made as
> > > Extra Segment
> > >        seg es         ; Makes next instruction
> > > execute wrt Extra Segment 
> > >        mov [0],#0x41  ; ASCII value of the
> Character
> > > to be displayed 
> > >                       ;  in 1-row & 1-column
> > >        seg es         ; Makes next instruction
> > > execute wrt Extra Segment 
> > >        mov [1],#0x1f  ; Attribute of the
> Character
> > > to be displayed
> > >                       ;  in 1-row & 1-column
> > >                       ; 0x1f represents White
> > > 
> > > 
> > > The "seg es" lines are what we need.
> > > I think that by default, 'ds' is used, so, my 3
> > > lines of code may work.
> > > 
> > > 
> > > in this:
> > > 
> > > 6>       movw $0xb800,%bx  # Video Memory
> address   
> > > 7>       movb $0x41,(%bx)  # ASCII value to 
> > > 8>       movw $0xb801,%bx  # Video Memory
> address   
> > > 
> > > 9>       movb $0x1f,(%bx)  # Attribute of the  
> > > 
> > > you will put 0x411f at [ds:0xb800], which is
> > > somewhere around your 
> > > program code... it will surely erase something
> you
> > > may need (perhapse 
> > > your code!)
> > > 
> > > 
> > > 
> > > 
> > > Anticipating a Reply wrote:
> > > 
> > > >Hi Frederic ,
> > > >
> > > >   Thank you very much for all the 
> > > >explanation you have given about the 
> > > >addressing in 16-bit real mode .
> > > >
> > > >   From this explanation , I think 
> > > >I was wrong in line number 7 , 
> > > >which had 0xb800 acting as an 
> > > >offset to the Data Segment .
> > > >
> > > >   That is,if I'am not wrong we 
> > > >always need to specify the addresses 
> > > >in the below format -
> > > >
> > > >    seg_reg:offset 
> > > >----
> > > > OR
> > > >----    
> > > >   if given as 
> > > >  
> > > >   movb $xxx , ( %seg_reg )
> > > >
> > > >then the contents of "seg_reg"
> > > >will be considered as an Offset 
> > > >with respect to the Data Segment.
> > > >     
> > > >
> > > >1> .code16
> > > >2>
> > > >3> .globl _start 
> > > >4>
> > > >5> _start: 
> > > >6>       movw $0xb800,%bx  # Video Memory
> address  
> > > 
> > > >7>       movb $0x41,(%bx)  # ASCII value to 
> > > >8>       movw $0xb801,%bx  # Video Memory
> address  
> > >  
> > > >9>       movb $0x1f,(%bx)  # Attribute of the  
> > > >10> loop1: 
> > > >11>       jmp loop1
> > > >
> > > >
> > > >Hope I have got the concept correctly .
> > > >
> > > >  Thanking you all for bearing my basic
> > > >doubts and clearing them too.
> > > >
> > > >With best Regards
> > > >
> > > >
> > > > --- Frederic Marmond <fmarmond@eprocess.fr>
> wrote:
> > > >
> > > >Hi,
> > > >  
> > > >
> > > >>Here are some explainations you may want to
> know.
> > > >>
> > > >>When your PC boots, it is in real mode.
> > > >>This mode (!= protected mode) manage memory in
> > > this
> > > >>way:
> > > >>segment+offset
> > > >>The segment is a 64ko range , step by 16
> bytes.
> > > >>So, if you want to write to b8000 (video
> memory
> > > >>start in text mode), you 
> > > >>may set your segment at 0xb800 (=> 0xb800 * 16
> =
> > > >>0xb8000)
> > > >>Then, you can adress this segment of 65536
> bytes
> > > >>with an offset of 16bits.
> > > >>(that's why in real mode you can only see the
> > > first
> > > >>1Mo of your memory: 
> > > >>0xFFFF*16 = 0xFFFF0  ~= 1024*1024  (in fact, a
> > > >>little bit more than 1Mo, 
> > > >>because of the offset of 0xffff max))
> > > >>For your problem, in pseudo code:
> > > >>mov 0x411f to 0xb800:0    (write 0x411f to the
> > > >>corner high-left)
> > > >>mov 0x411f to 0xb800:(80*2 *10+ 20*2)   
> (write
> > > >>0x411f to the 10th line 
> > > >>(80*2 *10= 80(charPerLine)
> > > *2(1char=ascii+attribut)
> > > >>*10(10th line)) and 
> > > >>20th char)
> > > >>
> > > >>in assembly, segments are stored in special
> > > >>registers: ds (Data 
> > > >>Segment), CS(Code Segment), Es,Fs,Gs (Extra
> > > >>Segments), SS(Stack Segment)
> > > >>Offset may be any of the followings
> > > >>(Ax,Bx,Cx,Dx,Si,Di,Sp). (and, in 
> > > >>32bits mode: eAx,eBx,eCx....)
> > > >>
> > > >>So, the pseudo code may be write like that
> ((in
> > > >>intel syntax, which I 
> > > >>prefer, and that compile with nasm):
> > > >>mov    ax,0xb800
> > > >>mov    es,ax                ; we cannot affect
> > > >>directly value to seg 
> > > >>register (cannot write mov es,0xb800)
> > > >>mov    bx,0x0            ; start of the
> segment
> > > >>mov     [es:bx],0x411f    ;the compilator will
> > > >>assume automaticaly movw 
> > > >>(mov word => 16 bits)
> > > >>
> > > >>That is what Emanuele wrote you (in At&t
> syntax):
> > > >>
> > > >>           movw    $0xB800, %ax
> > > >>           movw    %ax, %es			; affect the
> start
> > > >>adress to the segment
> > > >>           movb    $0x41, %es:0  			; store
> value
> > > in
> > > >>the video memory
> > > >>           movb    $0x1f, %es:1					; these 2
> > > lines
> > > >>may be = to movw $0x411f,%es:0
> > > >>
> > > >>
> > > >>hope it helps!
> > > >>
> > > >>Fred
> > > >>
> > > >>Anticipating a Reply wrote:
> > > >>
> > > >>    
> > > >>
> > > >>>Hello Emanuele ,
> > > >>>
> > > >>>  Thank you for the below code 
> > > >>>you sent . It works perfectly and
> > > >>>will help me learn more of assembly .
> > > >>>
> > > >>>  Can you please help me figure 
> > > >>>out where I'am wrong in the code below,
> > > >>>which I have witten for the same 
> > > >>>functionality .
> > > >>>
> > > >>>.code16
> > > >>>
> > > >>>.globl _start 
> > > >>>
> > > >>>_start: 
> > > >>>      movw $0xb800,%bx  # Video Memory
> address   
> > > >>>      movb $0x41,(%bx)  # ASCII value to be
> > > >>>      
> > > >>>
> > > >>displayed
> > > >>    
> > > >>
> > > >>>      movw $0xb801,%bx  # Video Memory
> address   
> > > 
> > > >>>      movb $0x1f,(%bx)  # Attribute of the
> > > >>>      
> > > >>>
> > > >>Character 
> > > >>    
> > > >>
> > > >>>loop1: 
> > > >>>      jmp loop1
> > > >>>
> > > >>>
> > > >>>   Thanks once again .
> > > >>>
> > > >>>With Best Regards
> > > >>>
> > > >>>--- Emanuele Altieri <ealtieri@hampshire.edu>
> > > >>>      
> > > >>>
> > > >>wrote:
> > > >>    
> > > >>
> > > >>> 
> > > >>>
> > > >>>      
> > > >>>
> > > >>>>I'm assuming that you want to keep your code
> as
> > > a
> > > >>>>boot program:
> > > >>>>
> > > >>>>          .code16               # needed for
> > > >>>>booting
> > > >>>>          .global _start
> > > >>>>  _start:
> > > >>>>          movw    $0xB800, %ax
> > > >>>>          movw    %ax, %es
> > > >>>>          movb    $0x41, %es:0  
> > > >>>>          movb    $0x1f, %es:1
> > > >>>>  loop1:  jmp     loop1
> > > >>>>
> > > >>>>
> > > >>>>To assembly and link the program:
> > > >>>>
> > > >>>>  as -o boot.o boot.s
> > > >>>>  ld -s -oformat binary -Ttext 0x0 -o boot
> > > boot.o
> > > >>>>
> > > >>>>The last command creates the "boot" file
> that is
> > > >>>>ready to be 
> > > >>>>installed in the first sector of the floppy
> > > disk:
> > > >>>>
> > > >>>>  dd seek=0 if=boot of=/dev/fd0
> > > >>>>
> > > >>>>
> > > >>>>Hope this helps
> > > >>>>
> > > >>>> -Emanuele
> > > >>>>
> > > >>>>
> > > >>>>On Tue, 2002-07-30 at 07:59, Anticipating a
> > > Reply
> > > >>>>wrote:
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>Hi Everybody,
> > > >>>>>
> > > >>>>>       I have got a small piece of Assembly
> > > code
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>,
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>which writes a character "A" on the screen
> .
> > > >>>>>
> > > >>>>> The below program is compiled and written 
> > > >>>>>to the boot sector of a floppy. It compiles
> > > >>>>>using the command :
> > > >>>>>
> > > >>>>>	as86 boot.s -o boot.o
> > > >>>>>	ld86 -d boot.o -o boot 
> > > >>>>>
> > > >>>>>  I want to rewrite it in AT&T syntax and
> > > >>>>>want to use GNU "as" assembler to compile
> it .
> > > >>>>>I tried doing it ,but with no success .
> > > >>>>>
> > > >>>>> Can anybody please help me rewite the
> > > >>>>>below code in AT&T syntax and tell me how
> > > >>>>>to compile & link it ?
> > > >>>>>
> > > >>>>>  Thanks in Advance .
> > > >>>>>
> > > >>>>>With Best Regards
> > > >>>>>
> > > >>>>>
> > > >>>>>THE CODE :
> > > >>>>>------------
> > > >>>>>
> > > >>>>>
> > > >>>>>entry start 
> > > >>>>>
> > > >>>>>start: 
> > > >>>>>      mov ax,#0xb800 ; Video Memory address
> is
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>0xb800
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>> 
> > > >>>>>      mov es,ax      ; Video Memory is made
> as
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>Extra
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>Segment
> > > >>>>>      seg es         ; Makes next
> instruction
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>execute
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>wrt Extra Segment 
> > > >>>>>      mov [0],#0x41  ; ASCII value of the
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>Character
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>to be displayed 
> > > >>>>>                     ;  in 1-row & 1-column
> > > >>>>>      seg es         ; Makes next
> instruction
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>execute
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>wrt Extra Segment 
> > > >>>>>      mov [1],#0x1f  ; Attribute of the
> > > >>>>>          
> > > >>>>>
> > > >>Character
> > > >>    
> > > >>
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>to
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>be displayed
> > > >>>>>                     ;  in 1-row & 1-column
> > > >>>>>                     ; 0x1f represents
> White
> > > >>>>>Character on a Blue Background
> > > >>>>>loop1: 
> > > >>>>>      jmp loop1
> > > >>>>>
> > > >>>>>
> > > >>>>>
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > >
> >
>
>>________________________________________________________________________
> > > >>    
> > > >>
> > > >>> 
> > > >>>
> > > >>>      
> > > >>>
> > > >>>>>Want to sell your car? advertise on Yahoo
> Autos
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>Classifieds. It's Free!!
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>      visit http://in.autos.yahoo.com
> > > >>>>>-
> > > >>>>>To unsubscribe from this list: send the
> line
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>"unsubscribe linux-assembly" in
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>>the body of a message to
> > > >>>>>          
> > > >>>>>
> > > >>majordomo@vger.kernel.org
> > > >>    
> > > >>
> > > >>>>>More majordomo info at 
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>http://vger.kernel.org/majordomo-info.html
> > > >>>>
> > > >>>>
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > > >>>>># boot.s
> > > >>>>>     
> > > >>>>>
> > > >>>>>          
> > > >>>>>
> > > >>>>#
> > > >>>># To assembly and link as a **boot**
> program:
> > > >>>>#
> > > >>>>#    as boot.s -o boot.o
> > > >>>>#    ld -s -oformat binary -Ttext 0x0 -o
> boot
> > > >>>>        
> > > >>>>
> > > >>boot.o
> > > >>    
> > > >>
> > > >>>>#
> > > >>>># To copy it to the boot sector of a floppy
> > > disk:
> > > >>>>#
> > > >>>>#    dd seek=0 if=boot of=/dev/fd0
> > > >>>>#
> > > >>>># ---
> > > >>>># Emanuele (ealtieri@hampshire.edu)
> > > >>>>	
> > > >>>>	.code16
> > > >>>>	.global _start
> > > >>>>_start:
> > > >>>>	movw	$0xB800, %ax
> > > >>>>	movw	%ax, %es
> > > >>>>	movb	$0x41, %es:0
> > > >>>>	movb	$0x1f, %es:1
> > > >>>>loop1:	jmp	loop1
> > > >>>>
> > > >>>>   
> > > >>>>
> > > >>>>        
> > > >>>>
> > >
> >
>
>>________________________________________________________________________
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> > > >
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> > > >
> > > 
> > > 
> > >  
> > 
> >
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________________________________________________________________________
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> Classifieds. It's Free!!
> >        visit http://in.autos.yahoo.com
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________________________________________________________________________
Want to sell your car? advertise on Yahoo Autos Classifieds. It's Free!!
       visit http://in.autos.yahoo.com