nasm-users — Discussion and help for Nasm users.

Re: [Nasm-users] can't write argv[0] on stdout - solved

[Holger H. <ha...@gm...>]

On Wed, 19 Aug 2009 13:11:49 -0400
Frank Kotler <fbk...@zy...> wrote:

> H. Peter Anvin wrote:
> > On 08/19/2009 01:48 AM, Holger Hanrath wrote:
> >> On Tue, 18 Aug 2009 21:19:21 +0200
> >> Holger Hanrath <ha...@gm...> wrote:
> >>
> >>
> >> here is the program what that does what i want in native x86_64:
> >>
> > 
> > Yes, but inefficient.
> > 
> >> ; write 3 bytes from argv[0] to stdout
> >> ; syscall numbers from asm/unistd_64.h
> >> stdout		equ	1
> >> write		equ	1
> >> exit		equ	60
> >> 	
> >> 	mov	rax,	write
> > 
> > Small number... you probably want "mov eax,..." instead.
> > 
> > etc.
> 
> Or even:
> 
> push write
> pop rax
> 
> Smaller, if that's the goal, but slower (I think), and it doesn't do 
> much for "readability", IMO.
> 
> There's a tutorial here:
> 
> <http://www.vikaskumar.org/wiki/index.php?title=X86-64_Tutorial>

good link wish i had it earlier

Holger

Re: [Nasm-users] can't write argv[0] on stdout - solved

[Holger H. <ha...@gm...>]

On Wed, 19 Aug 2009 09:50:17 -0700
"H. Peter Anvin" <hp...@zy...> wrote:

> On 08/19/2009 01:48 AM, Holger Hanrath wrote:
> > On Tue, 18 Aug 2009 21:19:21 +0200
> > Holger Hanrath <ha...@gm...> wrote:
> > 
> > 
> > here is the program what that does what i want in native x86_64:
> > 
> 
> Yes, but inefficient.

true 

> > ; write 3 bytes from argv[0] to stdout
> > ; syscall numbers from asm/unistd_64.h
> > stdout		equ	1
> > write		equ	1
> > exit		equ	60
> > 	
> > 	mov	rax,	write
> 
> Small number... you probably want "mov eax,..." instead.

from the AMD64 Abi:

"3. The number of the syscall has to be passed in register %rax."

Holger

Re: [Nasm-users] can't write argv[0] on stdout - solved

[Frank K. <fbk...@zy...>]

H. Peter Anvin wrote:
> On 08/19/2009 01:48 AM, Holger Hanrath wrote:
>> On Tue, 18 Aug 2009 21:19:21 +0200
>> Holger Hanrath <ha...@gm...> wrote:
>>
>>
>> here is the program what that does what i want in native x86_64:
>>
> 
> Yes, but inefficient.
> 
>> ; write 3 bytes from argv[0] to stdout
>> ; syscall numbers from asm/unistd_64.h
>> stdout		equ	1
>> write		equ	1
>> exit		equ	60
>> 	
>> 	mov	rax,	write
> 
> Small number... you probably want "mov eax,..." instead.
> 
> etc.

Or even:

push write
pop rax

Smaller, if that's the goal, but slower (I think), and it doesn't do 
much for "readability", IMO.

There's a tutorial here:

<http://www.vikaskumar.org/wiki/index.php?title=X86-64_Tutorial>

Might help...

Best,
Frank

Re: [Nasm-users] can't write argv[0] on stdout - solved

[H. P. A. <hp...@zy...>]

On 08/19/2009 01:48 AM, Holger Hanrath wrote:
> On Tue, 18 Aug 2009 21:19:21 +0200
> Holger Hanrath <ha...@gm...> wrote:
> 
> 
> here is the program what that does what i want in native x86_64:
> 

Yes, but inefficient.

> ; write 3 bytes from argv[0] to stdout
> ; syscall numbers from asm/unistd_64.h
> stdout		equ	1
> write		equ	1
> exit		equ	60
> 	
> 	mov	rax,	write

Small number... you probably want "mov eax,..." instead.

etc.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: [Nasm-users] can't write argv[0] on stdout - solved

[Holger H. <ha...@gm...>]

On Tue, 18 Aug 2009 21:19:21 +0200
Holger Hanrath <ha...@gm...> wrote:


here is the program what that does what i want in native x86_64:

; write 3 bytes from argv[0] to stdout
; syscall numbers from asm/unistd_64.h
stdout		equ	1
write		equ	1
exit		equ	60
	
section .text
     global _start

     _start:
	pop	rax		; rax = argc 
	pop	rax		; rax = argv[0]
	
         ; place the length of the string in RDX
	mov	rdx,	3	; write 3 bytes
	
	; print the string using write() system call
	mov     rsi, 	rax	; write needs the address of the string in rsi
        mov     rdi,	stdout	
	mov	rax,	write
        syscall

         ; exit from the application here
        xor     rdi,	rdi	; return 0
        mov     rax, 	exit
        syscall

Re: [Nasm-users] can't write argv[0] on stdout

[Holger H. <ha...@gm...>]

On Tue, 18 Aug 2009 23:33:46 -0700
"H. Peter Anvin" <hp...@zy...> wrote:

> On 08/18/2009 07:34 AM, Holger Hanrath wrote:
> > Hi all,
> > 
> > i want to write 3 bytes of argv[0] on stdout but it doesn't work. 
> > Return code -14 (EFAULT Bad address). Am i missing something here? 
> > 
> > System is archlinux 2009.08 x86_64 kernel 2.6.31-rc6 
> > nasm 2.05.01 Binutils 2.19.1.20090418
> > 
> > 
> > 
> > stdout	equ	1
> > write	equ	4
> > exit	equ	1
> > 
> > section .text
> > 	global	_start
> > _start:	
> > 	pop	rax		; rax = argc
> > 	pop	rax		; rax = argv[0]
> > 
> > 	mov	rdx,	3	; write 3 bytes
> > 	mov	rcx,	rax	; rcx = rax = argv[0]
> > 	mov	rbx,	stdout	
> > 	mov	rax,	write	
> > 	int	0x80
> > 	
> > 	mov	rbx,	0
> > 	mov	rax,	exit
> > 	int	0x80
> > 
> 
> int 0x80 is used for 32-bit system calls.  64 bits uses syscall, and
> entirely different system call numbers and a different calling convention.

i see that now thanks for pointing out

Holger

Re: [Nasm-users] can't write argv[0] on stdout

[H. P. A. <hp...@zy...>]

On 08/18/2009 07:34 AM, Holger Hanrath wrote:
> Hi all,
> 
> i want to write 3 bytes of argv[0] on stdout but it doesn't work. 
> Return code -14 (EFAULT Bad address). Am i missing something here? 
> 
> System is archlinux 2009.08 x86_64 kernel 2.6.31-rc6 
> nasm 2.05.01 Binutils 2.19.1.20090418
> 
> 
> 
> stdout	equ	1
> write	equ	4
> exit	equ	1
> 
> section .text
> 	global	_start
> _start:	
> 	pop	rax		; rax = argc
> 	pop	rax		; rax = argv[0]
> 
> 	mov	rdx,	3	; write 3 bytes
> 	mov	rcx,	rax	; rcx = rax = argv[0]
> 	mov	rbx,	stdout	
> 	mov	rax,	write	
> 	int	0x80
> 	
> 	mov	rbx,	0
> 	mov	rax,	exit
> 	int	0x80
> 

int 0x80 is used for 32-bit system calls.  64 bits uses syscall, and
entirely different system call numbers and a different calling convention.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: [Nasm-users] can't write argv[0] on stdout

[Holger H. <ha...@gm...>]

On Tue, 18 Aug 2009 13:22:01 -0400
Frank Kotler <fbk...@zy...> wrote:

> Holger Hanrath wrote:
> > Hi all,
> > 
> > i want to write 3 bytes of argv[0] on stdout but it doesn't work. 
> > Return code -14 (EFAULT Bad address). Am i missing something here? 
> > 
> > System is archlinux 2009.08 x86_64 kernel 2.6.31-rc6 
> > nasm 2.05.01 Binutils 2.19.1.20090418
> > 
> > 
> > 
> > stdout	equ	1
> > write	equ	4
> > exit	equ	1
> > 
> > section .text
> > 	global	_start
> > _start:	
> > 	pop	rax		; rax = argc
> > 	pop	rax		; rax = argv[0]
> > 
> > 	mov	rdx,	3	; write 3 bytes
> > 	mov	rcx,	rax	; rcx = rax = argv[0]
> > 	mov	rbx,	stdout	
> > 	mov	rax,	write	
> > 	int	0x80
> > 	
> > 	mov	rbx,	0
> > 	mov	rax,	exit
> > 	int	0x80
> 
> 64-bit does it a "bit" differently (from the late and sorely missed 
> Chuck Crayne:
> 
> section .data
>      string1 db  "Hello World!",10,0
> 
> section .text
>      global _start
> 
>      _start:
>          ; calculate the length of string
>          mov     rdi, string1
>          mov     rcx, -1
>          xor     al,al
>          cld
>          repnz scasb
> 
>          ; place the length of the string in RDX
>          mov     rdx, -2
>          sub     rdx, rcx
> 
>          ; print the string using write() system call
>          mov     rsi, string1
>          push    0x1
>          pop     rax
>          mov     rdi,rax
>          syscall
> 
>          ; exit from the application here
>          xor     rdi,rdi
>          push    0x3c
>          pop     rax
>          syscall
> 
> That won't do what you want, of course, but will give you an idea which 
> registers are used. (the push/pop is just shorter - probably want to use 
> "-Ox" to use it) I assume the stack is set up the same for 64-bit as for 
> 32-bit(?). Let us know how it works - 64-bit examples are in short 
> supply, still...
> 
> Best,
> Frank

Your example works fine thanks but i had no problems writing strings 
from the data section to stdout. I know that the rax register holds the 
right address after the second pop because i can copy the bytes i found there
into a string in the data section and then write it to stdout like this: 

;; copy argv[0] into str1 and write to stdout

stdout	equ 	1 
write  	equ 	4
exit   	equ 	1

section .data
str1		db    '#############',10,0
str1len		equ   $ - str1	
	
section .text

_copy:	cmp	BYTE [rax], 0 	    ; check if we reached the end of argv[0]
	je	_print		
	cmp	rcx, rbx	    ; check if argv[0] is not to long
	je	_print

 	mov	dl, [rax]	    ; move one byte into dl
	mov	BYTE [str1+rbx], dl ; move one byte into str1 at pos of rbx
	
	inc	rax		    ; move on in argv[0]
	inc	rbx		    ; move on in str1
	jmp	_copy


	global _start	
_start:
	pop	rax		; load argc
	pop	rax		; load argv[0]
	
	xor	rbx,rbx		; rbx = 0
	mov	rcx,str1len	; load str1len into rcx
	sub	rcx,2		; make sure we always wirte a new line
	xor	dl,dl		; dl = 0
	
	jmp	_copy
	
_print:	mov	rdx, str1len 	; message length
 	mov	rcx, str1	; message to write
	mov	rbx, 1		; file descriptor (stdout)
	mov	rax, 4		; system call number (sys_write)
	int	0x80		; call kernel	

	mov	rbx, 0		; return 0
	mov	rax, exit	; system call number (sys_exit)
	int	0x80		; call kernel
	

that works it's only when try to do the write with the memory address from 
the stack. I think i overlook something here but thanks for trying to 
help me.

Holger

Re: [Nasm-users] can't write argv[0] on stdout

[Frank K. <fbk...@zy...>]

Holger Hanrath wrote:
> Hi all,
> 
> i want to write 3 bytes of argv[0] on stdout but it doesn't work. 
> Return code -14 (EFAULT Bad address). Am i missing something here? 
> 
> System is archlinux 2009.08 x86_64 kernel 2.6.31-rc6 
> nasm 2.05.01 Binutils 2.19.1.20090418
> 
> 
> 
> stdout	equ	1
> write	equ	4
> exit	equ	1
> 
> section .text
> 	global	_start
> _start:	
> 	pop	rax		; rax = argc
> 	pop	rax		; rax = argv[0]
> 
> 	mov	rdx,	3	; write 3 bytes
> 	mov	rcx,	rax	; rcx = rax = argv[0]
> 	mov	rbx,	stdout	
> 	mov	rax,	write	
> 	int	0x80
> 	
> 	mov	rbx,	0
> 	mov	rax,	exit
> 	int	0x80

64-bit does it a "bit" differently (from the late and sorely missed 
Chuck Crayne:

section .data
     string1 db  "Hello World!",10,0

section .text
     global _start

     _start:
         ; calculate the length of string
         mov     rdi, string1
         mov     rcx, -1
         xor     al,al
         cld
         repnz scasb

         ; place the length of the string in RDX
         mov     rdx, -2
         sub     rdx, rcx

         ; print the string using write() system call
         mov     rsi, string1
         push    0x1
         pop     rax
         mov     rdi,rax
         syscall

         ; exit from the application here
         xor     rdi,rdi
         push    0x3c
         pop     rax
         syscall

That won't do what you want, of course, but will give you an idea which 
registers are used. (the push/pop is just shorter - probably want to use 
"-Ox" to use it) I assume the stack is set up the same for 64-bit as for 
32-bit(?). Let us know how it works - 64-bit examples are in short 
supply, still...

Best,
Frank

[Nasm-users] can't write argv[0] on stdout

[Holger H. <ha...@gm...>]

Hi all,

i want to write 3 bytes of argv[0] on stdout but it doesn't work. 
Return code -14 (EFAULT Bad address). Am i missing something here? 

System is archlinux 2009.08 x86_64 kernel 2.6.31-rc6 
nasm 2.05.01 Binutils 2.19.1.20090418



stdout	equ	1
write	equ	4
exit	equ	1

section .text
	global	_start
_start:	
	pop	rax		; rax = argc
	pop	rax		; rax = argv[0]

	mov	rdx,	3	; write 3 bytes
	mov	rcx,	rax	; rcx = rax = argv[0]
	mov	rbx,	stdout	
	mov	rax,	write	
	int	0x80
	
	mov	rbx,	0
	mov	rax,	exit
	int	0x80

Re: [Nasm-users] Setting/Clearing OF

[Robert A. <e.a...@st...>]

> Date: Tue, 11 Aug 2009 00:54:37 -0700
> From: hp...@zy...
> To: fbk...@zy...
> CC: e.a...@st...; nas...@li...
> Subject: Re: [Nasm-users] Setting/Clearing OF
> 
> On 08/10/2009 10:54 PM, Frank Kotler wrote:
>> 
>> "lahf" is only going to get the low 8 bits of the flags register, and OF 
>> is bit 11, so you'll have to resort to pushf, manipulate the dword on 
>> stack, and popf, I think. Something like this... (intended to be 
>> "portable")...
>> 
> 
> Another option is to perform an operation on the arithmetic flags that
> affects OF, and then use LAHF/SAHF to preserve the *other* AFs:
> 
> 	; Trashes AX
> clear_of:
> 	lahf
> 	xor al,al	; OF <- 0
> 	sahf
> 	ret
> 
> set_of:
> 	lahf
> 	mov al,127
> 	inc al		; OF <- 1
> 	sahf
> 	ret
> 
> -- 
> H. Peter Anvin, Intel Open Source Technology Center
> I work for Intel.  I don't speak on their behalf.
> 
> 
> 

Hi,

Thanks for the responses. I'll try both ways out to see which one works out the best for me.



Thanks again for your time,

Robert Alegrid

------------------------------------------------------------------------------
Robert Alegrid
RMIT University
Student #3164658
BP-079 Physics
BP-083 Mathematics

_________________________________________________________________
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Re: [Nasm-users] Setting/Clearing OF

[H. P. A. <hp...@zy...>]

On 08/10/2009 10:54 PM, Frank Kotler wrote:
> 
> "lahf" is only going to get the low 8 bits of the flags register, and OF 
> is bit 11, so you'll have to resort to pushf, manipulate the dword on 
> stack, and popf, I think. Something like this... (intended to be 
> "portable")...
> 

Another option is to perform an operation on the arithmetic flags that
affects OF, and then use LAHF/SAHF to preserve the *other* AFs:

	; Trashes AX
clear_of:
	lahf
	xor al,al	; OF <- 0
	sahf
	ret

set_of:
	lahf
	mov al,127
	inc al		; OF <- 1
	sahf
	ret

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: [Nasm-users] Setting/Clearing OF

[Frank K. <fbk...@zy...>]

Robert Alegrid wrote:
> Hi,
> 
> How do I set or clear the overflow flag? I can save it easily enough, but I don't know how to set or clear it. This is for part of a handler for animation scripts for a Win32 game.
> 
> ;-------------------------------------------------------------------------------
> ;    void __declspec(naked) __stdcall SetCurrentUnitExFlags(void) {
> SetCurrentUnitExFlags:
>     lahf

"lahf" is only going to get the low 8 bits of the flags register, and OF 
is bit 11, so you'll have to resort to pushf, manipulate the dword on 
stack, and popf, I think. Something like this... (intended to be 
"portable")...

Best,
Frank


; manipulate the overflow flag
;
; nasm -f elf flag.asm
; gcc -o flag flag.o
;
; Winders? untested.
; nasm -f win32 --prefix _ flag.asm
; gcc -o flag flag.obj


global main
extern puts

section .bss
     buffer resb 36 ; 32 characters + CR + LF + 0 ?

section .data
     flagstring db "                -NioODITSZ-A-P-C", 0

section .text
main:
     nop
     pusha
     mov al, 127
     add al, 1 ; set OF

     call showflags

; clear OF
     pushf
     and dword [esp], ~(1 << 11)
     popf

     call showflags

; set OF
     pushf
     or dword [esp], 1 << 11
     popf

     call showflags

     popa
     ret
;---------------

;---------------
showflags:
     pushf

     push flagstring
     call puts
     add esp, 4

     pop eax
     mov edi, buffer
     call eax2bin
     mov byte[edi], 0
     push buffer
     call puts
     add esp, 4

     ret
;----------------

;----------------
; ascii binary representation of eax -> string at edi
; returns edi = next position; eax, ecx, edx trashed
eax2bin:
     mov edx, eax
     mov ecx, 32
.top:
     mov al, '0'
     rcl edx, 1
     adc al, 0
     stosb
     loop .top
     ret
;---------------

[Nasm-users] Setting/Clearing OF

[Robert A. <e.a...@st...>]

Hi,

How do I set or clear the overflow flag? I can save it easily enough, but I don't know how to set or clear it. This is for part of a handler for animation scripts for a Win32 game.

;-------------------------------------------------------------------------------
;    void __declspec(naked) __stdcall SetCurrentUnitExFlags(void) {
SetCurrentUnitExFlags:
    lahf
    mov   CL, AH
 
    ; Bit 1 is already set, so if OF is set, do nothing
    jo    .SetConditionFlags
    ; Clear bit 1
    btr   CL, 1
.SetConditionFlags
    call  GetCurrentUnitID
    imul  EAX, UnitEx.Size
    mov   byte [ExtendedUnitNode + EAX + UnitEx.ConditionFlags], CL
    ret
;    }

;-------------------------------------------------------------------------------
;    void __declspec(naked) __stdcall GetCurrentUnitExFlags(void) {
GetCurrentUnitExFlags:
    call  GetCurrentUnitID
    imul  EAX, UnitEx.Size
    mov   AH, byte [ExtendedUnitNode + EAX + UnitEx.ConditionFlags]
    bts   AH, 1
    jnc   .BitNotSet
    
    ; How do I set OF?
    
    lahf
    ret
    
.BitNotSet:

    ; How do I clear OF?
    
    lahf
    ret
;    }


Thank you for your time
Robert

--------------------------------------------------------------------------------
Robert Alegrid
RMIT University
Student #3164658
BP-079 Physics
BP-083 Mathematics


_________________________________________________________________
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Re: [Nasm-users] Handling timer interrupt

[Frank K. <fbk...@zy...>]

Zulfi Khan wrote:
> I just tried to find the interrupt# in this topic and I got 1ch.

Yeah... 1Ch is supposed to be a "secondary timer interrupt", and it's 
supposed to be "safer" than hooking int 8 itself. However, I couldn't 
get anything to happen, using 1Ch. Maybe it has to be "enabled"(???). I 
switched to hooking int 8... and presto, my clock started working 
(sorta). I really should go back and retry with int 1Ch.

> I thought 8259 is irrelevant because its a separate IC.

It is a separate IC, but it controls which interrupts get sent to the 
CPU, and which don't. At the end of an interrupt routine, we need to 
tell the PIC we're done. Instead of dealing with that, I "chained" the 
original int 8. Grab the original address *before* installing the new 
routine, and jump into it at the end of the new routine. This is a 
common technique to take care of the "housekeeping" that needs to be 
done. Maybe that's not the way you want to do it. Lots to experiment with!

> Its prinnting garbage and F instaed of welcome kernel message.

Yeah... maybe going to an .exe was a mistake. I re-worked both the 
bootsector and the "kernel" code to jump to 7E4h:0, and made cs, ds, and 
es the same - something more like a .com file (but not exactly). This 
seems to be working. I'd like to be able to use separate "segment code" 
and "segment data" - maybe even "segment stack stack". So far, I haven't 
been able to load such a thing successfully, so I stick to "everything 
in one segment". At least I'm seeing the welcome message...

> I would try this again after reading what you have suggested.

The attached "mz2.zip" started out being your code... I altered it quite 
a bit. Made "add_isr" a subroutine, rather than your "install" macro, 
and added a "get_old_isr" to capture the original isr. "mz3.zip" is an 
attempt to integrate this into the more "modular" version. The idea is 
that the routines - add_isr, get_old_isr, write, getkey,... - are 
supposed to be "C callable". I haven't actually tried this - I don't 
"do" C - that's your department! :) I added "hours" - no way this puppy 
is going to run over a hour, but I figured I ought to handle the 
possibility...

I don't know if any of this crap will help you. It "sorta works", but 
isn't "right". The "clock" stays running in a "tight loop", but if I try 
to "getkey" for a delay, the whole thing locks up. So the only "command" 
that works is control-alt-delete. This indicates something seriously 
wrong with the way I've hooked the interrupt (I think). I haven't worked 
out what the problem is.

Takes a lot of rebooting! I downloaded Bochs, but couldn't get it to 
compile - some symbol "not defined in this scope". In a pinch, I'll mess 
with C to get it to compile when it won't, but C++ is beyond me 
completely. Trying to install from the RPM resulted in the usual cascade 
of errors. So I'm stuck with a "real reboot" from a "real floppy"... 
which I generally prefer, but it's time-consuming!

See of you can make anything out of it. Feel free to ask questions, but 
the answer will probably be "I dunno, that was the first thing that came 
into my head." :) Good Luck!

Best,
Frank

Re: [Nasm-users] Handling timer interrupt

[Frank K. <fbk...@zy...>]

zak100 wrote:
> Hi,
> I have changed the code but still I am getting garbage at kernel startup. I
> have got the macro definition at the beginning but the iret code at the end.
> I cant understand what ou mean by PIC.

What do you say to a student who hasn't done the assigned reading, Zulfi?

<http://www.arl.wustl.edu/~lockwood/class/cs306/books/artofasm/Chapter_17/CH17-3.html>

explains what I mean by PIC - Programmable Interrupt Controller - the 
8259 (or equivalent - I think modern hardware emulates this).

Might as well go to the original of this:

<http://homepage.mac.com/randyhyde/webster.cs.ucr.edu/www.artofasm.com/DOS/AoADosIndex.html>

You may want to read the whole thing.

> The new code is given below:
> ;Printing test mesg at kernel startup
> ;If I move macro at end , i get syntax error.
> %macro install 1 
>   push ax
>   mov ax, 0
>   mov word[%1*4],isr_add
>   mov word[%1*4+2],cs
>   pop ax
>  %endmacro

What's this supposed to do? It appears to overwrite your code. Why have 
you tried to make it a macro, when it loads the same "isr_add", no 
matter what the parameter?

>     mov ax, 7E0H
>     mov ds,ax
>     mov es,ax
>     mov si, msg
> 
>     mov ah, 0Eh
>     mov bx, 7
> top:
>     lodsb
>     cmp al, 0
>     jz blackhole1
>     int 10h
>     jmp short top

Are you seeing this message? If you aren't getting this far, it's 
useless to try to continue!

> blackhole1:install 01ch; calling macro

Okay... suppose we've got int 1Ch patched...

>      xor ax,ax; print the mesgA using int10h
>      mov ds,ax
>      mov es,ax

Why????????

>     mov si,msgA    ; "our dear string"
>     mov bx,7
>     mov ah,0Eh
> msgloop:
>   lodsb
>   or al,al
>   jz end44
>   int 10h       ; since we're still in RM, we can use bios.
>   jmp msgloop

I suppose you're going to print the time here? It'll still be 00:00, 
presumably...


>  end44: jmp end44
>  
> 
>         
> blackhole:   
>     hlt
>     jmp blackhole
> 
> msg db 'Welcome to the Kernel!', 0
> msgA db 'Total minutes elapsed since Kernel start is', 0AH, 0DH

Is this supposed to be zero-terminated?

> clkcounter db 0
> secs db 0
> mins db 0
> 
> 
> isr_add:
>   cli
>   inc byte [byte cs:clkcounter]
>   cmp byte [byte cs:clkcounter],18; if clkcounter is 18, it means 1 sec
>   jz handle_secs
>   sti
>   iret
> handle_secs:
>   mov byte [byte cs:clkcounter],0
>   inc byte [byte cs:secs]
>   cmp byte [byte cs:secs],60;if secs is 60, it means 1 min
>   jz handle_mins
>   sti
>   iret
> handle_mins:
>   mov byte [byte cs:secs],0
>   inc byte [byte cs:mins]; we are done, now print the number of minutes
> elapsed
>   sti 
>   iret
> 
> times 0x200-($-$$) db 0

18.2 ticks/second != 18 ticks/second - close enough to see if your isr 
is working, I guess, but your clock is going to be wildly fast!

>  Kindly somebody plz help me with the above code.

I'd have to "test" anything I'd suggest. Might take a while...

Best,
Frank

Re: [Nasm-users] Handling timer interrupt

[zak100 <zul...@ya...>]

Hi,
I have changed the code but still I am getting garbage at kernel startup. I
have got the macro definition at the beginning but the iret code at the end.
I cant understand what ou mean by PIC.

The new code is given below:
;Printing test mesg at kernel startup
;If I move macro at end , i get syntax error.
%macro install 1 
  push ax
  mov ax, 0
  mov word[%1*4],isr_add
  mov word[%1*4+2],cs
  pop ax
 %endmacro
 
 
    mov ax, 7E0H
    mov ds,ax
    mov es,ax
    mov si, msg

    mov ah, 0Eh
    mov bx, 7
top:
    lodsb
    cmp al, 0
    jz blackhole1
    int 10h
    jmp short top
    
blackhole1:install 01ch; calling macro
     xor ax,ax; print the mesgA using int10h
     mov ds,ax
     mov es,ax
    mov si,msgA    ; "our dear string"
    mov bx,7
    mov ah,0Eh
msgloop:
  lodsb
  or al,al
  jz end44
  int 10h       ; since we're still in RM, we can use bios.
  jmp msgloop
 end44: jmp end44
 

        
blackhole:   
    hlt
    jmp blackhole

msg db 'Welcome to the Kernel!', 0
msgA db 'Total minutes elapsed since Kernel start is', 0AH, 0DH
clkcounter db 0
secs db 0
mins db 0


isr_add:
  cli
  inc byte [byte cs:clkcounter]
  cmp byte [byte cs:clkcounter],18; if clkcounter is 18, it means 1 sec
  jz handle_secs
  sti
  iret
handle_secs:
  mov byte [byte cs:clkcounter],0
  inc byte [byte cs:secs]
  cmp byte [byte cs:secs],60;if secs is 60, it means 1 min
  jz handle_mins
  sti
  iret
handle_mins:
  mov byte [byte cs:secs],0
  inc byte [byte cs:mins]; we are done, now print the number of minutes
elapsed
  sti 
  iret

times 0x200-($-$$) db 0
  
 Kindly somebody plz help me with the above code.

Zulfi.


----------------------------------------------------------

zak100 wrote:
> 
> Hi,
> I am trying to handle timer interrupt in a OS like code. I have got a
> bootloader whose code is given below and is working (I am able to see the
> mesg at the start up):
> %define bootseg 0
> %define bootoff 7C00h
> 
> %define loadoff 7E00h
> 
> 
> 
> 
> ORG 7c00h      ;Because BIOS loades the OS at 
>                        ; address 0:7C00h so ORG 7C00h 
>                        ; makes that the refrence to date 
>                        ; are with the right offset (7c00h).
> 
> 
>                        
>    ; CS = 0 / IP = 7C00h // SS = ? / SP = ?
>    ; You are now at address 7c00.
> jmp start   ;Here we start the, BIOS gave us now the control.
> 
> 
> 
> ;///////////////////////////////////////////
> ;//Here goes all the data of the program.
> ;///////////////////////////////////////////
> 
> xCursor db 0
> yCursor db 0
> 
> 
> nSector db 0
> nTrack  db 0
> nSide   db 0
> nDrive  db 0
> 
> nTrays  db 0
> 
> ;
> szReady                db 'Are You Ready to start Loading the OS...',0
> szErrorReadingDrive    db 'Error Reading Drive, Press any Key to
> reboot...',0
> ;//Done Reading a track.
> szPlaceMarker          db  '~~~~',0
> szDone                 db  'Done',0
> 
> pOS                    dw   loadoff
> ;//Points to where to download the Operating System. 
> 
> ;/////////////////////////////////
> ;//Here the program starts.
> ;/////////////////////////////////
> 
> 
> start:
> 
>     CLI     ;Clear Interupt Flag so while setting 
>         ;up the stack any interrupt would not be fired.
> ;----------------STACK
>         mov AX,7B0h    ;lets have the stack start at 7c00h-256 = 7B00h
>         mov SS,ax      ;SS:SP = 7B0h:256 = 7B00h:256
>         mov SP,256     ;Lets make the stack 256 bytes.
>         
>         XOR AX,AX      ;Makes AX=0.
>         MOV ES,AX      ;Make ES=0
>         mov DS,ax
> 
> 
>     STI     ;Set Back the Interupt Flag after 
>         ;we finished setting a stack frame.
>        
>         Call ClearScreen       ;ClearScreen()
>         LEA AX,[szReady]         ;Get Address of szReady.
>         CALL PrintMessage      ;Call PrintfMessage()
>         CALL GetKey                    ;Call GetKey()
>         
>     mov bp, 1 ; sectors to load
>         CALL DownloadOS
> ;        CALL GetKey                    ;Call GetKey()
>         CALL GiveControlToOS  ;Give Control To OS.
> 
> ;/////////////////////////////////////
> ;//Prints a message to the screen.
> ;/////////////////////////////////////
> PrintMessage:
> 
>         mov DI,AX      ;AX holds the address of the string to Display.
>         Mov byte [xCursor],1  ;Column.
>         
> ContinuPrinting:
> 
>         cmp byte [DI],0    ;Did we get to the End of String.
>         JE EndPrintingMessage  ;if you get to the end of the string
> return.
>         
>         mov AH,2               ;Move Cursor
>         mov DH,[yCursor]         ;row.
>         mov DL,[xCursor]         ;column.
>         mov BH,0               ;page number.
>         INT 10h
>         INC byte [xCursor]
>         
>         mov AH,0Ah             ;Display Character Function.
>         mov AL,[DI]            ;character to display.
>         mov BH,0               ;page number.
>         mov CX,1               ;number of times to write character
>         INT 10h
>                
>         INC DI                 ;Go to next character.
>         
>         JMP ContinuPrinting    ;go to Print Next Character.
>                
> EndPrintingMessage:
>         
>         Inc byte [yCursor]            ;So Next time the message would
>                                ;be printed in the second line.
>         
>         cmp byte [yCursor],25
>         JNE dontMoveCorsurToBegin 
>         Mov byte [yCursor],0
>         
> dontMoveCorsurToBegin:
>         ret
>         
>                
> ;PrintMessage EndP 
> ;//////////////////////////////////////
> ;//Waits for the user to press a key.
> ;//////////////////////////////////////
> GetKey: ; PROC
> 
>         mov ah,0
>         int 16h ;Wait for a key press.
>         Ret
>         
> ;///////////////////////////////////////////
> ;//Gives Control To Second Part Loader.
> ;///////////////////////////////////////////
> GiveControlToOS:
> 
>         LEA AX,[szDone]
>         Call PrintMessage
>         CALL GetKey
> 
>         jmp 7E0h:40h
> 
> 	mov ax, [loadoff + 18h]
> 
> 	push 7E0h
> 	push ax
> 	retf
> 
> ;///////////////////////////////////
> ;//Clear Screen.
> ;///////////////////////////////////
> ClearScreen:
> 
>         mov ax,0600h   ;//Scroll All Screen UP to Clear Screen.
>         mov bh,07
>         mov cx,0
>         mov dx,184fh   
>         int 10h
>         
>         Mov byte [xCursor],0  ;//Set Cursor Position So next 
>                         ;//write would start in 
>                         ;//the beginning of screen.
>         Mov byte [yCursor],0
> 
>         Ret
>         
> ;/////////////////////////////////
> ;//PrintPlaceMarker.
> ;/////////////////////////////////
> PrintPlaceMarker:
> 
>         LEA AX,[szPlaceMarker]
>         CALL PrintMessage  ;Call PrintfMessage()
> ;        CALL GetKey        ;Call GetKey()
>         ret
>         
> ;///////////////////////////////////
> ;//DownloadOS
> ;///////////////////////////////////
> DownloadOS:
> 
>         mov byte [nDrive],0
>         mov byte [nSide],0
>         mov byte [nTrack],0
>         mov byte [nSector],1 ; desired sector - 1!
>         
> ContinueDownload:
>         
>         INC byte [nSector]            ;Read Next Sector.
>         cmp byte [nSector],19         ;Did we get to end of track.
>         JNE StayInTrack
> 
>         CALL PrintPlaceMarker  ;Print now '~~~~' so the user would 
>                                ;know that we finished reading a track
>         INC byte [nTrack]             ;If we get to end of track Move to
> next track.
>         mov byte [nSector],1          ;And Read Next Sector.
>         CMP byte [nTrack],5           ;Read 5 Tracks (Modify this value 
> 	                           ;to how much Tracks you want to read).
>         JE      EndDownloadingOS
>         
> StayInTrack:
>         
>         ;ReadSector();
>         Call ReadSector
>     dec bp
>     jz EndDownloadingOS
>         
>         
>         JMP     ContinueDownload
>         ;If didn't yet finish Loading OS.
>         
> EndDownloadingOS:
> 
>         ret
>         
> ;////////////////////////////////////////
> ;//Read Sector.
> ;////////////////////////////////////////
> ReadSector:
> 
>         mov byte [nTrays],0
>         
> TryAgain:
> 
>         mov AH,2               ;//Read Function.
>         mov AL,1               ;//1 Sector.
>         mov CH,[nTrack]
>         mov CL,[nSector]         ;//Remember: Sectors start with 1, not 0.
>         mov DH,[nSide]
>         mov DL,[nDrive]
>         Mov BX,[pOS]             ;//ES:BX points to the address 
>                                ;to were to store the sector.
>         INT 13h
>         
>     jnc EndReadSector
> 
>         mov AH,0               ;Else Reset Drive . And Try Again...
>         INT 13h
>         cmp byte [nTrays],3           ;Check if you tryed reading 
>                                ;more then 3 times.
>         
>         JE DisplayError        ; if tryed 3 Times Display Error.
>         
>         INC byte [nTrays]
>         
>         jmp TryAgain       ;Try Reading again.
>         
> DisplayError:
>         LEA AX,[szErrorReadingDrive]
>         Call PrintMessage
>         Call GetKey
>         mov AH,0                       ;Reboot Computer.
>         INT 19h
>         
> 
> EndReadSector:
>         ADD WORD [pOS],512  ;//Move the pointer 
>                                ;(ES:BX = ES:pOS = 0:pOS) 512 bytes.
>                                ;//Here you set the varible 
>                                ;pOS (pOS points to were BIOS 
>                                ;//Would load the Next Sector).
>         Ret
>         
> ;////////////////////////////////////
> ;//
> ;////////////////////////////////////
> 
> times 510 - ($ - $$) db 0
> db 55h, 0AAh
> ;-------------------
> 
> 
> 
> An then I have a kernel code which includes a file also:
> 
> %include "lib.inc"
>     mov ax, 7E0H
>     mov ds,ax
>     mov es,ax
>     mov si, msg
> 
>     mov ah, 0Eh
>     mov bx, 7
> top:
>     lodsb
>     cmp al, 0
>     jz blackhole1
>     int 10h
>     jmp short top
>     
> blackhole1:install 6
>     
> blackhole:   
>     hlt
>     jmp blackhole
> 
> msg db 'Welcome to the Kernel!', 0
> msgA db 'Total minutes elapsed since Kernel start is', 0AH, 0DH
> clkcounter db 0
> secs db 0
> mins db 0
> 
> times 0x200-($-$$) db 0
> 
> 
> The include file is given below:
> 
> %macro install 1
>   push ax
>   mov al,%1
>   mov ah, 0eh
>   int 10h
>   pop ax
>   ;push ds
>   ;mov ax, 0
>   ;mov word[%1*4],isr_add
>   ;mov word[%1*4+2],cs
>   ;pop ds
> %endmacro
> 
> isr_add:
>   cli
>   inc byte [byte cs:clkcounter]
>   cmp byte [byte cs:clkcounter],18
>   jz handle_secs
>   sti
>   iret
> handle_secs:
>   mov byte [byte cs:clkcounter],0
>   inc byte [byte cs:secs]
>   cmp byte [byte cs:secs],60
>   jz handle_mins
>   sti
>   iret
> handle_mins:
>   mov byte [byte cs:secs],0
>   inc byte [byte cs:mins]
>   push ds
>   push es
>   
>   xor ax,ax
>   mov ds,ax
>   mov es,ax
>   ; should probably set up a sane stack here, too.
>   mov si,msgA    ; "our dear string"
> 
>     ;mov bx,7
>   mov ah,0Eh
> msgloop:
>   lodsb
>   or al,al
>   jz end44
>   int 10h       ; since we're still in RM, we can use bios.
>   jmp msgloop
>  end44: pop es
>   pop ds
>   sti
>   iret
>   sti
>   iret
> 
> For compilation I am using following commands:
> nasm -f bin bootmz.asm -o boot.bin
> 
> nasm -f obj test_k.asm
> 
> 
> 
> alink -oEXE test_k.obj 
> 
> 
> copy /b boot.bin+test_k.exe image.bin
> partcopy image.bin 0 323 -f0
> 
> Can somebody plz help me with this?
> 
> Zulfi.
> 

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Re: [Nasm-users] Handling timer interrupt

[zak100 <zul...@ya...>]

Hi,
I want to print the time how long the kernel is in action at each timer
interrupt instance using mesgA. I am working on the information you have
provided and reply you soon. I want to handle interrupt 1C. I would check
this code again.

Zulfi.






zak100 wrote:
> 
> Hi,
> I am trying to handle timer interrupt in a OS like code. I have got a
> bootloader whose code is given below and is working (I am able to see the
> mesg at the start up):
> %define bootseg 0
> %define bootoff 7C00h
> 
> %define loadoff 7E00h
> 
> 
> 
> 
> ORG 7c00h      ;Because BIOS loades the OS at 
>                        ; address 0:7C00h so ORG 7C00h 
>                        ; makes that the refrence to date 
>                        ; are with the right offset (7c00h).
> 
> 
>                        
>    ; CS = 0 / IP = 7C00h // SS = ? / SP = ?
>    ; You are now at address 7c00.
> jmp start   ;Here we start the, BIOS gave us now the control.
> 
> 
> 
> ;///////////////////////////////////////////
> ;//Here goes all the data of the program.
> ;///////////////////////////////////////////
> 
> xCursor db 0
> yCursor db 0
> 
> 
> nSector db 0
> nTrack  db 0
> nSide   db 0
> nDrive  db 0
> 
> nTrays  db 0
> 
> ;
> szReady                db 'Are You Ready to start Loading the OS...',0
> szErrorReadingDrive    db 'Error Reading Drive, Press any Key to
> reboot...',0
> ;//Done Reading a track.
> szPlaceMarker          db  '~~~~',0
> szDone                 db  'Done',0
> 
> pOS                    dw   loadoff
> ;//Points to where to download the Operating System. 
> 
> ;/////////////////////////////////
> ;//Here the program starts.
> ;/////////////////////////////////
> 
> 
> start:
> 
>     CLI     ;Clear Interupt Flag so while setting 
>         ;up the stack any interrupt would not be fired.
> ;----------------STACK
>         mov AX,7B0h    ;lets have the stack start at 7c00h-256 = 7B00h
>         mov SS,ax      ;SS:SP = 7B0h:256 = 7B00h:256
>         mov SP,256     ;Lets make the stack 256 bytes.
>         
>         XOR AX,AX      ;Makes AX=0.
>         MOV ES,AX      ;Make ES=0
>         mov DS,ax
> 
> 
>     STI     ;Set Back the Interupt Flag after 
>         ;we finished setting a stack frame.
>        
>         Call ClearScreen       ;ClearScreen()
>         LEA AX,[szReady]         ;Get Address of szReady.
>         CALL PrintMessage      ;Call PrintfMessage()
>         CALL GetKey                    ;Call GetKey()
>         
>     mov bp, 1 ; sectors to load
>         CALL DownloadOS
> ;        CALL GetKey                    ;Call GetKey()
>         CALL GiveControlToOS  ;Give Control To OS.
> 
> ;/////////////////////////////////////
> ;//Prints a message to the screen.
> ;/////////////////////////////////////
> PrintMessage:
> 
>         mov DI,AX      ;AX holds the address of the string to Display.
>         Mov byte [xCursor],1  ;Column.
>         
> ContinuPrinting:
> 
>         cmp byte [DI],0    ;Did we get to the End of String.
>         JE EndPrintingMessage  ;if you get to the end of the string
> return.
>         
>         mov AH,2               ;Move Cursor
>         mov DH,[yCursor]         ;row.
>         mov DL,[xCursor]         ;column.
>         mov BH,0               ;page number.
>         INT 10h
>         INC byte [xCursor]
>         
>         mov AH,0Ah             ;Display Character Function.
>         mov AL,[DI]            ;character to display.
>         mov BH,0               ;page number.
>         mov CX,1               ;number of times to write character
>         INT 10h
>                
>         INC DI                 ;Go to next character.
>         
>         JMP ContinuPrinting    ;go to Print Next Character.
>                
> EndPrintingMessage:
>         
>         Inc byte [yCursor]            ;So Next time the message would
>                                ;be printed in the second line.
>         
>         cmp byte [yCursor],25
>         JNE dontMoveCorsurToBegin 
>         Mov byte [yCursor],0
>         
> dontMoveCorsurToBegin:
>         ret
>         
>                
> ;PrintMessage EndP 
> ;//////////////////////////////////////
> ;//Waits for the user to press a key.
> ;//////////////////////////////////////
> GetKey: ; PROC
> 
>         mov ah,0
>         int 16h ;Wait for a key press.
>         Ret
>         
> ;///////////////////////////////////////////
> ;//Gives Control To Second Part Loader.
> ;///////////////////////////////////////////
> GiveControlToOS:
> 
>         LEA AX,[szDone]
>         Call PrintMessage
>         CALL GetKey
> 
>         jmp 7E0h:40h
> 
> 	mov ax, [loadoff + 18h]
> 
> 	push 7E0h
> 	push ax
> 	retf
> 
> ;///////////////////////////////////
> ;//Clear Screen.
> ;///////////////////////////////////
> ClearScreen:
> 
>         mov ax,0600h   ;//Scroll All Screen UP to Clear Screen.
>         mov bh,07
>         mov cx,0
>         mov dx,184fh   
>         int 10h
>         
>         Mov byte [xCursor],0  ;//Set Cursor Position So next 
>                         ;//write would start in 
>                         ;//the beginning of screen.
>         Mov byte [yCursor],0
> 
>         Ret
>         
> ;/////////////////////////////////
> ;//PrintPlaceMarker.
> ;/////////////////////////////////
> PrintPlaceMarker:
> 
>         LEA AX,[szPlaceMarker]
>         CALL PrintMessage  ;Call PrintfMessage()
> ;        CALL GetKey        ;Call GetKey()
>         ret
>         
> ;///////////////////////////////////
> ;//DownloadOS
> ;///////////////////////////////////
> DownloadOS:
> 
>         mov byte [nDrive],0
>         mov byte [nSide],0
>         mov byte [nTrack],0
>         mov byte [nSector],1 ; desired sector - 1!
>         
> ContinueDownload:
>         
>         INC byte [nSector]            ;Read Next Sector.
>         cmp byte [nSector],19         ;Did we get to end of track.
>         JNE StayInTrack
> 
>         CALL PrintPlaceMarker  ;Print now '~~~~' so the user would 
>                                ;know that we finished reading a track
>         INC byte [nTrack]             ;If we get to end of track Move to
> next track.
>         mov byte [nSector],1          ;And Read Next Sector.
>         CMP byte [nTrack],5           ;Read 5 Tracks (Modify this value 
> 	                           ;to how much Tracks you want to read).
>         JE      EndDownloadingOS
>         
> StayInTrack:
>         
>         ;ReadSector();
>         Call ReadSector
>     dec bp
>     jz EndDownloadingOS
>         
>         
>         JMP     ContinueDownload
>         ;If didn't yet finish Loading OS.
>         
> EndDownloadingOS:
> 
>         ret
>         
> ;////////////////////////////////////////
> ;//Read Sector.
> ;////////////////////////////////////////
> ReadSector:
> 
>         mov byte [nTrays],0
>         
> TryAgain:
> 
>         mov AH,2               ;//Read Function.
>         mov AL,1               ;//1 Sector.
>         mov CH,[nTrack]
>         mov CL,[nSector]         ;//Remember: Sectors start with 1, not 0.
>         mov DH,[nSide]
>         mov DL,[nDrive]
>         Mov BX,[pOS]             ;//ES:BX points to the address 
>                                ;to were to store the sector.
>         INT 13h
>         
>     jnc EndReadSector
> 
>         mov AH,0               ;Else Reset Drive . And Try Again...
>         INT 13h
>         cmp byte [nTrays],3           ;Check if you tryed reading 
>                                ;more then 3 times.
>         
>         JE DisplayError        ; if tryed 3 Times Display Error.
>         
>         INC byte [nTrays]
>         
>         jmp TryAgain       ;Try Reading again.
>         
> DisplayError:
>         LEA AX,[szErrorReadingDrive]
>         Call PrintMessage
>         Call GetKey
>         mov AH,0                       ;Reboot Computer.
>         INT 19h
>         
> 
> EndReadSector:
>         ADD WORD [pOS],512  ;//Move the pointer 
>                                ;(ES:BX = ES:pOS = 0:pOS) 512 bytes.
>                                ;//Here you set the varible 
>                                ;pOS (pOS points to were BIOS 
>                                ;//Would load the Next Sector).
>         Ret
>         
> ;////////////////////////////////////
> ;//
> ;////////////////////////////////////
> 
> times 510 - ($ - $$) db 0
> db 55h, 0AAh
> ;-------------------
> 
> 
> 
> An then I have a kernel code which includes a file also:
> 
> %include "lib.inc"
>     mov ax, 7E0H
>     mov ds,ax
>     mov es,ax
>     mov si, msg
> 
>     mov ah, 0Eh
>     mov bx, 7
> top:
>     lodsb
>     cmp al, 0
>     jz blackhole1
>     int 10h
>     jmp short top
>     
> blackhole1:install 6
>     
> blackhole:   
>     hlt
>     jmp blackhole
> 
> msg db 'Welcome to the Kernel!', 0
> msgA db 'Total minutes elapsed since Kernel start is', 0AH, 0DH
> clkcounter db 0
> secs db 0
> mins db 0
> 
> times 0x200-($-$$) db 0
> 
> 
> The include file is given below:
> 
> %macro install 1
>   push ax
>   mov al,%1
>   mov ah, 0eh
>   int 10h
>   pop ax
>   ;push ds
>   ;mov ax, 0
>   ;mov word[%1*4],isr_add
>   ;mov word[%1*4+2],cs
>   ;pop ds
> %endmacro
> 
> isr_add:
>   cli
>   inc byte [byte cs:clkcounter]
>   cmp byte [byte cs:clkcounter],18
>   jz handle_secs
>   sti
>   iret
> handle_secs:
>   mov byte [byte cs:clkcounter],0
>   inc byte [byte cs:secs]
>   cmp byte [byte cs:secs],60
>   jz handle_mins
>   sti
>   iret
> handle_mins:
>   mov byte [byte cs:secs],0
>   inc byte [byte cs:mins]
>   push ds
>   push es
>   
>   xor ax,ax
>   mov ds,ax
>   mov es,ax
>   ; should probably set up a sane stack here, too.
>   mov si,msgA    ; "our dear string"
> 
>     ;mov bx,7
>   mov ah,0Eh
> msgloop:
>   lodsb
>   or al,al
>   jz end44
>   int 10h       ; since we're still in RM, we can use bios.
>   jmp msgloop
>  end44: pop es
>   pop ds
>   sti
>   iret
>   sti
>   iret
> 
> For compilation I am using following commands:
> nasm -f bin bootmz.asm -o boot.bin
> 
> nasm -f obj test_k.asm
> 
> 
> 
> alink -oEXE test_k.obj 
> 
> 
> copy /b boot.bin+test_k.exe image.bin
> partcopy image.bin 0 323 -f0
> 
> Can somebody plz help me with this?
> 
> Zulfi.
> 

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Re: [Nasm-users] Handling timer interrupt

[Frank K. <fbk...@zy...>]

zak100 wrote:

...
> An then I have a kernel code which includes a file also:
> 
> %include "lib.inc"

This is equivalent to cut-and-pasting the include file here. The macro 
shouldn't be a problem (won't emit anything here) but the isr code is 
going to be placed here, and will be the first thing executed. When it 
gets to "iret", the game is over!


>     mov ax, 7E0H
>     mov ds,ax
>     mov es,ax
>     mov si, msg
> 
>     mov ah, 0Eh
>     mov bx, 7
> top:
>     lodsb
>     cmp al, 0
>     jz blackhole1
>     int 10h
>     jmp short top
>     
> blackhole1:install 6

6 ??? I should think you'd want 8. Or better yet, 1Ch... Int 6 is the 
invalid opcode handler, I think...

> blackhole:   
>     hlt
>     jmp blackhole
> 
> msg db 'Welcome to the Kernel!', 0
> msgA db 'Total minutes elapsed since Kernel start is', 0AH, 0DH
> clkcounter db 0
> secs db 0
> mins db 0
> 
> times 0x200-($-$$) db 0
> 
> 
> The include file is given below:
> 
> %macro install 1
>   push ax
>   mov al,%1
>   mov ah, 0eh
>   int 10h
>   pop ax
>   ;push ds
>   ;mov ax, 0

mov ds, ax ; ?

>   ;mov word[%1*4],isr_add
>   ;mov word[%1*4+2],cs
>   ;pop ds
> %endmacro
> 

You don't want this code at the beginning of your kernel! Move it 
elsewhere, or jump over it, or something.

> isr_add:
>   cli
>   inc byte [byte cs:clkcounter]
>   cmp byte [byte cs:clkcounter],18
>   jz handle_secs
>   sti

I think you need to acknowledge the interrupt to the PIC before you 
"iret", or you'll never get another interrupt.

>   iret
> handle_secs:
>   mov byte [byte cs:clkcounter],0
>   inc byte [byte cs:secs]
>   cmp byte [byte cs:secs],60
>   jz handle_mins
>   sti
>   iret
> handle_mins:
>   mov byte [byte cs:secs],0
>   inc byte [byte cs:mins]
>   push ds
>   push es
>   
>   xor ax,ax
>   mov ds,ax
>   mov es,ax

What are you doing here? "msgA" is at 7E0h:something, isn't it?

>   ; should probably set up a sane stack here, too.
>   mov si,msgA    ; "our dear string"
> 
>     ;mov bx,7
>   mov ah,0Eh
> msgloop:
>   lodsb
>   or al,al
>   jz end44
>   int 10h       ; since we're still in RM, we can use bios.

Yeah, but we're in the middle of an interrupt handler. Doing an 
interrupt in the middle of another interrupt can be tricky! What happens 
if the timer interrupt fires in the middle of the int 10h? This might 
work, or might hang - I'm not really sure (and haven't tested it).

>   jmp msgloop
>  end44: pop es
>   pop ds
>   sti
>   iret
>   sti
>   iret
> 
> For compilation I am using following commands:
> nasm -f bin bootmz.asm -o boot.bin
> 
> nasm -f obj test_k.asm
> 
> 
> 
> alink -oEXE test_k.obj 
> 
> 
> copy /b boot.bin+test_k.exe image.bin
> partcopy image.bin 0 323 -f0
> 
> Can somebody plz help me with this?

Looks like some good information here:

<http://www.arl.wustl.edu/~lockwood/class/cs306/books/artofasm/Chapter_17/CH17-3.html>

Mostly what I find searching around assumes you want to do 32-bit Pmode 
interrupt handling... The old Rmode stuff must be around somewhere...

Best,
Frank

[Nasm-users] Handling timer interrupt

[zak100 <zul...@ya...>]

Hi,
I am trying to handle timer interrupt in a OS like code. I have got a
bootloader whose code is given below and is working (I am able to see the
mesg at the start up):
%define bootseg 0
%define bootoff 7C00h

%define loadoff 7E00h




ORG 7c00h      ;Because BIOS loades the OS at 
                       ; address 0:7C00h so ORG 7C00h 
                       ; makes that the refrence to date 
                       ; are with the right offset (7c00h).


                       
   ; CS = 0 / IP = 7C00h // SS = ? / SP = ?
   ; You are now at address 7c00.
jmp start   ;Here we start the, BIOS gave us now the control.



;///////////////////////////////////////////
;//Here goes all the data of the program.
;///////////////////////////////////////////

xCursor db 0
yCursor db 0


nSector db 0
nTrack  db 0
nSide   db 0
nDrive  db 0

nTrays  db 0

;
szReady                db 'Are You Ready to start Loading the OS...',0
szErrorReadingDrive    db 'Error Reading Drive, Press any Key to
reboot...',0
;//Done Reading a track.
szPlaceMarker          db  '~~~~',0
szDone                 db  'Done',0

pOS                    dw   loadoff
;//Points to where to download the Operating System. 

;/////////////////////////////////
;//Here the program starts.
;/////////////////////////////////


start:

    CLI     ;Clear Interupt Flag so while setting 
        ;up the stack any interrupt would not be fired.
;----------------STACK
        mov AX,7B0h    ;lets have the stack start at 7c00h-256 = 7B00h
        mov SS,ax      ;SS:SP = 7B0h:256 = 7B00h:256
        mov SP,256     ;Lets make the stack 256 bytes.
        
        XOR AX,AX      ;Makes AX=0.
        MOV ES,AX      ;Make ES=0
        mov DS,ax


    STI     ;Set Back the Interupt Flag after 
        ;we finished setting a stack frame.
       
        Call ClearScreen       ;ClearScreen()
        LEA AX,[szReady]         ;Get Address of szReady.
        CALL PrintMessage      ;Call PrintfMessage()
        CALL GetKey                    ;Call GetKey()
        
    mov bp, 1 ; sectors to load
        CALL DownloadOS
;        CALL GetKey                    ;Call GetKey()
        CALL GiveControlToOS  ;Give Control To OS.

;/////////////////////////////////////
;//Prints a message to the screen.
;/////////////////////////////////////
PrintMessage:

        mov DI,AX      ;AX holds the address of the string to Display.
        Mov byte [xCursor],1  ;Column.
        
ContinuPrinting:

        cmp byte [DI],0    ;Did we get to the End of String.
        JE EndPrintingMessage  ;if you get to the end of the string return.
        
        mov AH,2               ;Move Cursor
        mov DH,[yCursor]         ;row.
        mov DL,[xCursor]         ;column.
        mov BH,0               ;page number.
        INT 10h
        INC byte [xCursor]
        
        mov AH,0Ah             ;Display Character Function.
        mov AL,[DI]            ;character to display.
        mov BH,0               ;page number.
        mov CX,1               ;number of times to write character
        INT 10h
               
        INC DI                 ;Go to next character.
        
        JMP ContinuPrinting    ;go to Print Next Character.
               
EndPrintingMessage:
        
        Inc byte [yCursor]            ;So Next time the message would
                               ;be printed in the second line.
        
        cmp byte [yCursor],25
        JNE dontMoveCorsurToBegin 
        Mov byte [yCursor],0
        
dontMoveCorsurToBegin:
        ret
        
               
;PrintMessage EndP 
;//////////////////////////////////////
;//Waits for the user to press a key.
;//////////////////////////////////////
GetKey: ; PROC

        mov ah,0
        int 16h ;Wait for a key press.
        Ret
        
;///////////////////////////////////////////
;//Gives Control To Second Part Loader.
;///////////////////////////////////////////
GiveControlToOS:

        LEA AX,[szDone]
        Call PrintMessage
        CALL GetKey

        jmp 7E0h:40h

	mov ax, [loadoff + 18h]

	push 7E0h
	push ax
	retf

;///////////////////////////////////
;//Clear Screen.
;///////////////////////////////////
ClearScreen:

        mov ax,0600h   ;//Scroll All Screen UP to Clear Screen.
        mov bh,07
        mov cx,0
        mov dx,184fh   
        int 10h
        
        Mov byte [xCursor],0  ;//Set Cursor Position So next 
                        ;//write would start in 
                        ;//the beginning of screen.
        Mov byte [yCursor],0

        Ret
        
;/////////////////////////////////
;//PrintPlaceMarker.
;/////////////////////////////////
PrintPlaceMarker:

        LEA AX,[szPlaceMarker]
        CALL PrintMessage  ;Call PrintfMessage()
;        CALL GetKey        ;Call GetKey()
        ret
        
;///////////////////////////////////
;//DownloadOS
;///////////////////////////////////
DownloadOS:

        mov byte [nDrive],0
        mov byte [nSide],0
        mov byte [nTrack],0
        mov byte [nSector],1 ; desired sector - 1!
        
ContinueDownload:
        
        INC byte [nSector]            ;Read Next Sector.
        cmp byte [nSector],19         ;Did we get to end of track.
        JNE StayInTrack

        CALL PrintPlaceMarker  ;Print now '~~~~' so the user would 
                               ;know that we finished reading a track
        INC byte [nTrack]             ;If we get to end of track Move to
next track.
        mov byte [nSector],1          ;And Read Next Sector.
        CMP byte [nTrack],5           ;Read 5 Tracks (Modify this value 
	                           ;to how much Tracks you want to read).
        JE      EndDownloadingOS
        
StayInTrack:
        
        ;ReadSector();
        Call ReadSector
    dec bp
    jz EndDownloadingOS
        
        
        JMP     ContinueDownload
        ;If didn't yet finish Loading OS.
        
EndDownloadingOS:

        ret
        
;////////////////////////////////////////
;//Read Sector.
;////////////////////////////////////////
ReadSector:

        mov byte [nTrays],0
        
TryAgain:

        mov AH,2               ;//Read Function.
        mov AL,1               ;//1 Sector.
        mov CH,[nTrack]
        mov CL,[nSector]         ;//Remember: Sectors start with 1, not 0.
        mov DH,[nSide]
        mov DL,[nDrive]
        Mov BX,[pOS]             ;//ES:BX points to the address 
                               ;to were to store the sector.
        INT 13h
        
    jnc EndReadSector

        mov AH,0               ;Else Reset Drive . And Try Again...
        INT 13h
        cmp byte [nTrays],3           ;Check if you tryed reading 
                               ;more then 3 times.
        
        JE DisplayError        ; if tryed 3 Times Display Error.
        
        INC byte [nTrays]
        
        jmp TryAgain       ;Try Reading again.
        
DisplayError:
        LEA AX,[szErrorReadingDrive]
        Call PrintMessage
        Call GetKey
        mov AH,0                       ;Reboot Computer.
        INT 19h
        

EndReadSector:
        ADD WORD [pOS],512  ;//Move the pointer 
                               ;(ES:BX = ES:pOS = 0:pOS) 512 bytes.
                               ;//Here you set the varible 
                               ;pOS (pOS points to were BIOS 
                               ;//Would load the Next Sector).
        Ret
        
;////////////////////////////////////
;//
;////////////////////////////////////

times 510 - ($ - $$) db 0
db 55h, 0AAh
;-------------------



An then I have a kernel code which includes a file also:

%include "lib.inc"
    mov ax, 7E0H
    mov ds,ax
    mov es,ax
    mov si, msg

    mov ah, 0Eh
    mov bx, 7
top:
    lodsb
    cmp al, 0
    jz blackhole1
    int 10h
    jmp short top
    
blackhole1:install 6
    
blackhole:   
    hlt
    jmp blackhole

msg db 'Welcome to the Kernel!', 0
msgA db 'Total minutes elapsed since Kernel start is', 0AH, 0DH
clkcounter db 0
secs db 0
mins db 0

times 0x200-($-$$) db 0


The include file is given below:

%macro install 1
  push ax
  mov al,%1
  mov ah, 0eh
  int 10h
  pop ax
  ;push ds
  ;mov ax, 0
  ;mov word[%1*4],isr_add
  ;mov word[%1*4+2],cs
  ;pop ds
%endmacro

isr_add:
  cli
  inc byte [byte cs:clkcounter]
  cmp byte [byte cs:clkcounter],18
  jz handle_secs
  sti
  iret
handle_secs:
  mov byte [byte cs:clkcounter],0
  inc byte [byte cs:secs]
  cmp byte [byte cs:secs],60
  jz handle_mins
  sti
  iret
handle_mins:
  mov byte [byte cs:secs],0
  inc byte [byte cs:mins]
  push ds
  push es
  
  xor ax,ax
  mov ds,ax
  mov es,ax
  ; should probably set up a sane stack here, too.
  mov si,msgA    ; "our dear string"

    ;mov bx,7
  mov ah,0Eh
msgloop:
  lodsb
  or al,al
  jz end44
  int 10h       ; since we're still in RM, we can use bios.
  jmp msgloop
 end44: pop es
  pop ds
  sti
  iret
  sti
  iret

For compilation I am using following commands:
nasm -f bin bootmz.asm -o boot.bin

nasm -f obj test_k.asm



alink -oEXE test_k.obj 


copy /b boot.bin+test_k.exe image.bin
partcopy image.bin 0 323 -f0

Can somebody plz help me with this?

Zulfi.
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[Nasm-users] Documentation for RDOFF2

[René K. <sh...@go...>]

Hi,

I'm considering the RDOFF2 format for usage in one of my projects.
The biggest drawback so far is the flack (almost non-existent) 
documentation. The file rdoff.texi in the nasm trunk contains
mostly a skeleton without real documentation and the NASM manual
has only outdated information about RDOFF1.

I bit of searching turned up 
http://thor.prohosting.com/~walles/rfc00220.htm which seems to be a 
documentation for the binary format.
But unfortunately RDOFF2 seems to add some extensions to directives
like SEGMENT which in turn are documented nowhere..

Can someone point me at a valid, current documentation for RDOFF2?

Cheers,
René

Re: [Nasm-users] calling 'C' functions

[zak100 <zul...@ya...>]

Its working now. Thanks for your time, commands, description and for your
effort.

Zulfi.


Frank Kotler-3 wrote:
> 
> zak100 wrote:
>> Hi,
>> Thanks for your help. 
>>  
>> 
>> I have received your mz folder. It has two binaries: boot and image.
>> 'boot'
>> is fine
>> but when i tried to load image to sector 2 it didnt work. Maybe I am
>> doing
>> something 
>> wrong.
> 
> What *I* do is to combine "boot.bin" plus "mzt1.exe"(!) into 
> "image.bin", and load the whole thing, starting at sector 1. You could 
> use "image.bin", loading it to sector 1 - "writeit" won't do (only does 
> 512 bytes), but "partcopy" ought to - "partcopy image.bin 0 323 -f0", I 
> think would do it. (I create "image.bin" with "cat", but you could use 
> "copy /b boot.bin+mzt1.exe image bin", I think)
> 
> Alternatively, you could write them separately - "boot.bin" with 
> "writeit" or "partcopy", and "partcopy" for "mzt1.exe". The idea is 
> simply to eliminate the "exe2bin" step, and load an MZ executable.
> 
>> However, I didnt find any 'C' files.
> 
> Heh! No, I'm not taking the course, so I don't have to follow the rules.
> :)
> 
> I don't "do" C, unless absolutely necessary - haven't got a 16-bit 
> compiler, in any case. If you look at "kmain.asm", "write.asm" and 
> "getkey.asm", you'll see that they're "fake C" - you "should" be able to 
> replace them with "real C" equivalents... if I've done it right (big 
> if). "mzt1.asm" serves the purpose (approximately) of "crt0" or whatever 
> your compiler calls the "startup code" that calls "main" - "kmain", in 
> this case.
> 
> I've modified your bootsector (the one we "translated" from Tasmese) - 
> among other things, I altered it to read just one sector (reading 5 
> tracks wasn't working for me, for some reason). My "mzt1.exe" is well 
> under that, so far, but when it gets more extensive, the bootsector is 
> going to have to change. I mention this because, in my experience, C 
> tends to produce "bloated" code, compared to asm, and if you go over 512 
> bytes, it's going to mysteriously quit working.
> 
> Another way I haven't "followed the assignment" is that I used int 10h 
> for "write()". I'm confident I can write a string to B800:????, if I can 
> find the string! The purpose of this step of the exercise, for me, is to 
> be able to find my data! I figure if I can find the string, I can find 
> "cursor_x" and "cursor_y", and I know how to find the "screen". This 
> seems to "work"... as long as I put code and data in the same segment. 
> So far, my attempts to declare a "proper stack" and put "data" in 
> "segment data" have failed. What I'm seeing in the executable header 
> doesn't match what I "expect" to see. If and when I figure out how to 
> deal with that, and with far calls and far data, I won't be stuck in a 
> single 64k segment! (plus, it's not nice to teach beginners to ignore 
> the warning about "no stack"! :)
> 
> I don't know what compiler you're using, or what you're telling it. Are 
> you sticking to "model tiny"? I'm not sure what a compiler (and Alink) 
> will emit, from the code you posted. If you want to send me some 
> "output" - either before or after "exe2bin", or both, I'll try to figure 
> out how we might load it (if you're still having trouble with that). No 
> guarantee - I can't always figure out how to load my own stuff. :) "Post 
> exe2bin" should be "easier"... maybe...
> 
> Sorry I wasn't clearer about how to use that example. I was pretty tired 
> when I posted. ("try this *one* more thing and test it and then I'm 
> going to bed!"...) I should have mentioned that while "build" won't work 
> in dos (a bash script), it has some clues to how to put the thing
> together.
> 
> Lemme see if I remember how to write a dos batch file...
> 
> call nasm -f bin bootmz.asm -o boot.bin
> 
> call nasm -f obj mzt1.asm
> call nasm -f obj kmain.asm
> call nasm -f obj write.asm
> call nasm -f obj getkey.asm
> 
> call alink -oEXE mzt1.obj kmain.obj write.obj getkey.obj
> 
> call copy /b boot.bin+mzt1.exe image.bin
> call partcopy image.bin 0 323 -f0
> echo done
> 
> That's totally untested (and doesn't check returned errorlevels). Good
> luck!
> 
> Best,
> Frank
> 
> 
> ------------------------------------------------------------------------------
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Re: [Nasm-users] calling 'C' functions

[H. P. A. <hp...@zy...>]

Frank Kotler wrote:
> I don't "do" C, unless absolutely necessary - haven't got a 16-bit 
> compiler, in any case.

If you need one, OpenWatcom is quite good and free.

	-hpa

Re: [Nasm-users] calling 'C' functions

[Frank K. <fbk...@zy...>]

zak100 wrote:
> Hi,
> Thanks for your help. 
>  
> 
> I have received your mz folder. It has two binaries: boot and image. 'boot'
> is fine
> but when i tried to load image to sector 2 it didnt work. Maybe I am doing
> something 
> wrong.

What *I* do is to combine "boot.bin" plus "mzt1.exe"(!) into 
"image.bin", and load the whole thing, starting at sector 1. You could 
use "image.bin", loading it to sector 1 - "writeit" won't do (only does 
512 bytes), but "partcopy" ought to - "partcopy image.bin 0 323 -f0", I 
think would do it. (I create "image.bin" with "cat", but you could use 
"copy /b boot.bin+mzt1.exe image bin", I think)

Alternatively, you could write them separately - "boot.bin" with 
"writeit" or "partcopy", and "partcopy" for "mzt1.exe". The idea is 
simply to eliminate the "exe2bin" step, and load an MZ executable.

> However, I didnt find any 'C' files.

Heh! No, I'm not taking the course, so I don't have to follow the rules. :)

I don't "do" C, unless absolutely necessary - haven't got a 16-bit 
compiler, in any case. If you look at "kmain.asm", "write.asm" and 
"getkey.asm", you'll see that they're "fake C" - you "should" be able to 
replace them with "real C" equivalents... if I've done it right (big 
if). "mzt1.asm" serves the purpose (approximately) of "crt0" or whatever 
your compiler calls the "startup code" that calls "main" - "kmain", in 
this case.

I've modified your bootsector (the one we "translated" from Tasmese) - 
among other things, I altered it to read just one sector (reading 5 
tracks wasn't working for me, for some reason). My "mzt1.exe" is well 
under that, so far, but when it gets more extensive, the bootsector is 
going to have to change. I mention this because, in my experience, C 
tends to produce "bloated" code, compared to asm, and if you go over 512 
bytes, it's going to mysteriously quit working.

Another way I haven't "followed the assignment" is that I used int 10h 
for "write()". I'm confident I can write a string to B800:????, if I can 
find the string! The purpose of this step of the exercise, for me, is to 
be able to find my data! I figure if I can find the string, I can find 
"cursor_x" and "cursor_y", and I know how to find the "screen". This 
seems to "work"... as long as I put code and data in the same segment. 
So far, my attempts to declare a "proper stack" and put "data" in 
"segment data" have failed. What I'm seeing in the executable header 
doesn't match what I "expect" to see. If and when I figure out how to 
deal with that, and with far calls and far data, I won't be stuck in a 
single 64k segment! (plus, it's not nice to teach beginners to ignore 
the warning about "no stack"! :)

I don't know what compiler you're using, or what you're telling it. Are 
you sticking to "model tiny"? I'm not sure what a compiler (and Alink) 
will emit, from the code you posted. If you want to send me some 
"output" - either before or after "exe2bin", or both, I'll try to figure 
out how we might load it (if you're still having trouble with that). No 
guarantee - I can't always figure out how to load my own stuff. :) "Post 
exe2bin" should be "easier"... maybe...

Sorry I wasn't clearer about how to use that example. I was pretty tired 
when I posted. ("try this *one* more thing and test it and then I'm 
going to bed!"...) I should have mentioned that while "build" won't work 
in dos (a bash script), it has some clues to how to put the thing together.

Lemme see if I remember how to write a dos batch file...

call nasm -f bin bootmz.asm -o boot.bin

call nasm -f obj mzt1.asm
call nasm -f obj kmain.asm
call nasm -f obj write.asm
call nasm -f obj getkey.asm

call alink -oEXE mzt1.obj kmain.obj write.obj getkey.obj

call copy /b boot.bin+mzt1.exe image.bin
call partcopy image.bin 0 323 -f0
echo done

That's totally untested (and doesn't check returned errorlevels). Good luck!

Best,
Frank

Re: [Nasm-users] calling 'C' functions

[zak100 <zul...@ya...>]

Hi,
Thanks for your help. 
 

I have received your mz folder. It has two binaries: boot and image. 'boot'
is fine
but when i tried to load image to sector 2 it didnt work. Maybe I am doing
something 
wrong. However, I didnt find any 'C' files. Still waiting for your response
in this 
regard.

Zulfi.

Frank Kotler-3 wrote:
> 
> zak100 wrote:
>> Hi,
>> I am trying to call 'C" functions from my tiny kernel code. Can somebody
>> plz
>> help me with this?
>> ; call c function
>> extern [_K_main]
>> ;--- test kernel.bin---
>> 
>> ;    push cs
>> ;    push cs
>> ;    pop ds
>> ;    pop es
>>     mov ax, 7E0H
>>     mov ds,ax
>>     mov es,ax
>>     mov si, msg
>> 
>>     mov ah, 0Eh
>>     mov bx, 7
>> top:
>>     lodsb
>>     cmp al, 0
>>     jz blackhole
>>     int 10h
>>     jmp short top
>> 
>> blackhole:
>>     
>>     mov cx,1000
>>     Delay: Loop Delay
>>     call _K_main; this is in main.c
>>     hlt
>>     jmp blackhole
>> 
>> msg db 'Welcome to the Kernel!', 0
>> 
>> times 0x200-($-$$) db 0
>>         
>> 
>> I am getting following error mesg:
>> D:\nasm prog>nasm -f bin -o boot.bin test_kernel2.asm
>> test_kernel2.asm:5: error: label or instruction expected at start of line
> 
> Hi Zulfi,
> 
> Removing the brackets will at least give you correct syntax (extern 
> _K_main), but binary format still doesn't know about external 
> references. What format is your proposed _K_main in? OMF probably, for 
> 16-bit code(???).
> 
> Try assembling with "nasm -f obj test_kernel2.asm" this will produce 
> "test_kernel2.obj", by default. If your linker won't handle long file 
> names, you can shorten it with the "-o" switch, but your linker is 
> probably going to be happier with ".obj" than ".bin" (maybe not?).
> 
> Then... your linker is probably going to want to produce an MZ 
> executable by default. I don't think it's too hard to write a loader for 
> MZ, but it might be easier to persuade your linker to produce a .com 
> file. I believe ld (for 32-bit Linux - won't help you) can be coerced to 
> produce a flat binary, explicitly specifying origins for the various 
> sections (if you know how - I don't). If your linker will do that, 
> you're in luck. Failing that... I dunno.
> 
> Make sure your compiler isn't producing any "dosisms" in your C code, of 
> course.
> 
> The OS-development guys may have better advice on this.
> 
> Best,
> Frank
> 
> P.S. Thanks for asking here, rather than nasm-devel, Zulfi! :)
> 
> 
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