Boot Script Problems

[James]

I am creating my boot script, but have come across a problem. I am using emu8086, to create/compile my script:

Code: Select all

#make_boot#
org 7c00h      ; set location counter.


; directive to create BOOT file:
#MAKE_BOOT#

; Boot record is loaded at 0000:7C00,
; so inform compiler to make required
; corrections:
ORG 7C00h

; load message address into SI register:
LEA SI, msg

; teletype function id:
MOV AH, 0Eh

print:   MOV AL, [SI]
         CMP AL, 0
         JZ done
         INT 10h   ; print using teletype.
         INC SI
         JMP print

; wait for 'any key':
done:      MOV AH, 0
           INT 16h

; store magic value at 0040h:0072h:
;   0000h - cold boot.
;   1234h - warm boot.
MOV     AX, 0040h
MOV     DS, AX
MOV     w.[0072h], 0000h ; cold boot.
JMP   0FFFFh:0000h    ; reboot!

new_line EQU 100, 10
msg DB  ' ------------------------------------ '
    DB  new_line, '|                                                  |'
    DB  new_line, '|             Trip OS                           |'
    DB  new_line, '|        (c)2006 Created by                |'
    DB  new_line, '|           James Brooks                     |'
    DB  new_line, '|           Dean Hassall                      |'
    DB  new_line, '|                                                  |'
    DB  new_line, ' ------------------------------------ '
    DB  new_line, 'Press any key to reboot', 0


INT 19h        ; reboot

Now, it works etc. But this bit:

Code: Select all

msg DB  ' ------------------------------------ '
    DB  new_line, '|                                                |'
    DB  new_line, '|             Trip OS                         |'
    DB  new_line, '|        (c)2006 Created by              |'
    DB  new_line, '|           James Brooks                   |'
    DB  new_line, '|           Dean Hassall                    |'
    DB  new_line, '|                                                |'
    DB  new_line, ' ----------------------------------- '
    DB  new_line, 'Press any key to reboot', 0

Will not come out as I want it to! When I test it, it has a 'd' after each line?

[James]

When I emulate my script on the program I use, it works fine. But when I just try it from booting.. It did nothing??
Evertime I try to boot from it I get this:

Code: Select all

boot17-12

Edit: I have sorted the problem with the 'd' appearing.

[James]

Why cant I boot that from floppy?

[Kemp]

I can think of two possibilities (assuming the code itself is correct).

First, your boot sector may be loaded at 07C0:0000 rather than 0000:7C00, in which case all the addressing will be off. Second, most BIOSes check for a magic value at the end of the sector to make sure it is valid and not just junk that happens to be on the disk. Your code is missing this.

[James]

Great so what do I need to add to it?

[Kemp]

The banner at the top of all the forum pages links to the OSFAQ, which has the following pages that you may want to read through:

Boot Sequence
Baby Step
Rolling Your Own Bootloader