1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Help needed to Write fist hello world operating system in pen drive.

Discussion in 'Assembly Language Programming (ALP) Forum' started by mohit_khanna, May 20, 2010.

  1. mohit_khanna

    mohit_khanna New Member

    Joined:
    May 20, 2010
    Messages:
    1
    Likes Received:
    0
    Trophy Points:
    0
    I am not much knew to assembly language. I worked on it in my college days. But now i am again starting it after a gap of two years. Lot of things are gone. Except the interest in the simplicity in assembly language. Now i am trying to make a very small operating system of simply printing hello world. I am using pen drive in place of floppy here. the program i am using is
    ;----------------------------------------------------------------------
    ; Simple boot program that prints the letter 'H'
    ; and then hangs
    ; Joel Gompert 2001
    ;
    ; Disclaimer: I am not responsible for any results of the use of the contents
    ; of this file
    ;----------------------------------------------------------------------
    org 0x7c ; This is where BIOS loads the bootloader


    ; Execution begins here
    entry:
    jmp short begin ; jump over the DOS boot record data


    ; ----------------------------------------------------------------------
    ; data portion of the "DOS BOOT RECORD"
    ; ----------------------------------------------------------------------
    brINT13Flag DB 90H ; 0002h - 0EH for INT13 AH=42 READ
    brOEM DB 'MSDOS5.0' ; 0003h - OEM name & DOS version (8 chars)
    brBPS DW 512 ; 000Bh - Bytes/sector
    brSPC DB 1 ; 000Dh - Sectors/cluster
    brResCount DW 1 ; 000Eh - Reserved (boot) sectors
    brFATs DB 2 ; 0010h - FAT copies
    brRootEntries DW 0E0H ; 0011h - Root directory entries
    brSectorCount DW 2880 ; 0013h - Sectors in volume, < 32MB
    brMedia DB 240 ; 0015h - Media descriptor
    brSPF DW 9 ; 0016h - Sectors per FAT
    brSPH DW 18 ; 0018h - Sectors per track
    brHPC DW 2 ; 001Ah - Number of Heads
    brHidden DD 0 ; 001Ch - Hidden sectors
    brSectors DD 0 ; 0020h - Total number of sectors
    DB 0 ; 0024h - Physical drive no.
    DB 0 ; 0025h - Reserved (FAT32)
    DB 29H ; 0026h - Extended boot record sig
    brSerialNum DD 404418EAH ; 0027h - Volume serial number (random)
    brLabel DB 'Joels disk ' ; 002Bh - Volume label (11 chars)
    brFSID DB 'FAT12 ' ; 0036h - File System ID (8 chars)
    ;------------------------------------------------------------------------


    ; --------------------------------------------
    ; Boot program code begins here
    ; --------------------------------------------
    ; boot code begins at 0x003E
    begin:
    mov ah, 0x0e ; Function to print a character to the screen
    mov al, 'H' ; Which character to print
    mov bl, 7 ; color/style to use for the character
    int 0x10 ; print the character

    hang:
    jmp hang ; just loop forever.

    ;---------------------------------------------

    size equ $ - entry
    %if size+2 > 512
    %error "code is too large for boot sector"
    %endif
    times (512 - size - 2) db 0

    db 0x55, 0xAA ;2 byte boot signature

    I save it in h.asm and then convert to bin file using nasm assembler by command
    nasm c:\h.asm -fbin -o c:\h.bin

    then i write it to my pendrive using debug by using the following commands
    debug c:\h.bin
    -l 0
    -n f:\h.bin
    -w 0


    Now everything works uptill now.

    When i reboot my pc making pen drive as priority boot device. Then i get the error
    Error reading disk
    Press any key to restart

    Then i get message-
    There is no boot data in your device.

    Where the things are going wrong. Please help.
     
  2. lionaneesh

    lionaneesh Active Member

    Joined:
    Mar 21, 2010
    Messages:
    848
    Likes Received:
    224
    Trophy Points:
    43
    Occupation:
    Student
    Location:
    India
    Firstly I'd like to Organize the code by using code tags and make it more readable..

    Code:
    ;----------------------------------------------------------------------
    ; Simple boot program that prints the letter 'H'
    ;  and then hangs
    ; Joel Gompert 2001
    ;
    ; Disclaimer: I am not responsible for any results of the use of the contents
    ;   of this file
    ;----------------------------------------------------------------------
        org 0x7c    ; This is where BIOS loads the bootloader
    
    
    ; Execution begins here
    entry:
        jmp short begin ; jump over the DOS boot record data
    
    
    ; ----------------------------------------------------------------------
    ; data portion of the "DOS BOOT RECORD"
    ; ----------------------------------------------------------------------
    brINT13Flag     DB      90H             ; 0002h - 0EH for INT13 AH=42 READ
    brOEM           DB      'MSDOS5.0'      ; 0003h - OEM name & DOS version (8 chars)
    brBPS           DW      512             ; 000Bh - Bytes/sector
    brSPC           DB      1               ; 000Dh - Sectors/cluster
    brResCount      DW      1               ; 000Eh - Reserved (boot) sectors
    brFATs          DB      2               ; 0010h - FAT copies
    brRootEntries   DW      0E0H        ; 0011h - Root directory entries
    brSectorCount   DW      2880        ; 0013h - Sectors in volume, < 32MB
    brMedia         DB      240        ; 0015h - Media descriptor
    brSPF           DW      9               ; 0016h - Sectors per FAT
    brSPH           DW      18              ; 0018h - Sectors per track
    brHPC           DW      2        ; 001Ah - Number of Heads
    brHidden        DD      0               ; 001Ch - Hidden sectors
    brSectors       DD      0            ; 0020h - Total number of sectors
            DB      0               ; 0024h - Physical drive no.
            DB      0               ; 0025h - Reserved (FAT32)
            DB      29H             ; 0026h - Extended boot record sig 
    brSerialNum     DD      404418EAH       ; 0027h - Volume serial number (random)
    brLabel         DB      'Joels disk '   ; 002Bh - Volume label  (11 chars)
    brFSID          DB      'FAT12   '      ; 0036h - File System ID (8 chars)
    ;------------------------------------------------------------------------
    
    
    ; --------------------------------------------
    ;  Boot program code begins here
    ; --------------------------------------------
    ; boot code begins at 0x003E
    begin:
        mov    ah, 0x0e    ; Function to print a character to the screen
        mov    al, 'H'        ; Which character to print
        mov    bl, 7        ; color/style to use for the character
        int    0x10        ; print the character
    
    hang:
        jmp    hang        ; just loop forever.
    
    ;---------------------------------------------
    
    size    equ    $ - entry
    %if size+2 > 512
      %error "code is too large for boot sector"
    %endif
        times    (512 - size - 2) db 0
    
        db    0x55, 0xAA        ;2  byte boot signature
    
    And I have started Learning OS Boot Kernel and HERE is a very good code resource..
     

Share This Page