[ASM] Simple bootloader FASM

[Emily]

Hello guys,

Recently I've been making a simple bootloader in FASM. I want to improve my assembly and I want to start a simple DOS-OS.
I want to share my code and please review it!

start:
    mov ax, 07C0h
    add ax, 288    
    mov ss, ax
    mov sp, 4096
    mov ax, 07C0h
    mov ds, ax
    mov si, text_string
    call print_string    
    jmp $    
    text_string db 'I like dis shiz', 13, 10, 0

print_string:    
    mov ah, 0Eh

.repeat:
    lodsb    
    cmp al, 0
    je .done
    int 10h 
    jmp .repeat

.done:
    ret


    times 510-($-$$) db 0
    dw 0xAA55 

I KNOW it's not really good but I want a review!
I like to improve it a lot.

Thanks already. Have a good day.

[MentaL]

[Haku Douga]

Your sample starts bei setting the stack location & segments to hogwarts. Means, it uses some "magic".


You are using the BIOS interrupt call 10h, but you're not initializing the BX register. Depending on certain video modes, it wouldn't even work.


Performance tips:

1. Video mode setting
2. Pointing registers to the main memory location (shared with the video card)
3. Writing characters into the video memory

But don't worry, your sample is okay.
I'll expand my post soon, I haven't got much time for the moment.


// Some pretty useful resources:
http://wiki.osdev.org/Bootloader
http://wiki.osdev.org/Rolling_Your_Own_Bootloader

[Emily]

Your sample starts bei setting the stack location & segments to hogwarts. Means, it uses some "magic".


You are using the BIOS interrupt call 10h, but you're not initializing the BX register. Depending on certain video modes, it wouldn't even work.


Performance tips:

1. Video mode setting
2. Pointing registers to the main memory location (shared with the video card)
3. Writing characters into the video memory

But don't worry, your sample is okay.
I'll expand my post soon, I haven't got much time for the moment.


// Some pretty useful resources:
http://wiki.osdev.org/Bootloader
http://wiki.osdev.org/Rolling_Your_Own_Bootloader

Thanks for your review.
I know it's not the best but all this is for is just to learn. When I've learnt more in the future I might concider a real OS, but for now, just a simple, small one is enough.
Will take a look at the links you gave me.