How can I load the next file from bootloader ?? Please HELP

[KiBOrG]

How can I load the next file from bootloader ?? Please HELP ME, I?m Newbie

I want write my bootloader to FDD and when i have a lot of lines in bootloader i wand load next file ??

Is it really ?

How Can I do ??

Help me, please

KiBOrG

[Pype.Clicker]

you need a second stage, most probably. Since you're only allowed to have 512 bytes in the bootsector, your first task is to load more things (for instance the next sectors, or some file from FAT12, depending on what's on your floppy) using the BIOS INT13h

[Dex4u]

This also may help, it let you load a bin or com or exe from the floppy disk, its call "bootprog" you can get it here come with wel commented code, so that may help too.
http://alexfru.chat.ru/epm.html#bootprog

[aladdin]

I found a method to load two files from the bootsector without the need of a secod stage loader ...

i did it by storing both filenames in two variables and the respecting loading adresses in two other variables,

the i wrote some routines to load a file from a fat12 floppy, after calling this routine i test if i just loaded the first or the second file, if it is the first one, i load the second else i continue :
the folowing pseudo code can help you understand how i did it :

Code: Select all

var first_file = "setup.bin"
var second_file = "kernel.bin"

var first_addr = 0x9200
var second_addr = 0x1000

var current_file_to_load = @first_file
var current_addr = first_addr;


/*do something*/
 ...

.loading :
routine_to_load_file ( current_file_to_load, current_addr)


if (current_addr == first_addr) then
    current_addr=second_addr;
    current_file_to_load=@second_file;
    goto .loading


/* do something else */
/* jump to start code ... if you want */

Note1: if you want to use fat12 filesystem, you have to write the fat header in your bootsector, doing this you will anly have 410byte to write all your code
Note2: this pseudo-code is very simple compared to what you should really do in asm but it gives you an idea about how you can do it ...
Note3: even if i consider my code very optimised, i have too few comments (some characters)


Note4: here is my bootsector code
http://xos.freezee.org/beta/boot.asm
but it is commented in french

[slash]

Well here is a sample bootloader that boots and loads the file that is just after it:

Code: Select all

    [ORG 0] ;starts here

            jmp 07C0h:start     ; Goto segment 07C0

    start:
            ; Update the segment registers
            mov ax, cs
            mov ds, ax
            mov es, ax


    reset:                      ; Reset the floppy drive
            mov ax, 0           ;
            mov dl, 0           ; drive 0 means the A:\ drive, 1 = B:\
            int 13h             ;
            jc reset            ; if ther was error then try again


    read:
            mov ax, 1000h       ; ES:BX = 1000:0000
            mov es, ax          ;
            mov bx, 0           ;

            mov ah, 2           ; Load disk data to ES:BX
            mov al, 5           ; Load 5 sectors
            mov ch, 0           ; Cylinder
            mov cl, 2           ; Sector
            mov dh, 0           ; Head
            mov dl, 0           ; Drive 0=A:\ , 1 = B:\
            int 13h             ; start reading

            jc read             ; try again if there was error


            jmp 1000h:0000      ; Jump to the program


    times 510-($-$$) db 0
    dw 0AA55h ;Ends here

To compile the bootstrap, use this command:
nasm boot.asm -o boot.bin

And write the resulting "boot.bin" to sector 0 on floppy disk.
Well if you understand asm then you can see that boot code lasts just 1 sector on the floppy after that you have your other file to load.Your other file must fit into 5 sectors [5 sectors = 5 KB] of floppy but you can change that by changing line 32 to "mov cl,[no# of sectors to read]".

[KiBOrG]

Very thanks for all. ;D ;D ;D

Thank,

KiBOrG