Booting Issue!

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rhyno_dagreat

Joined: 31 Jul 2006
Posts: 487
Location: Maryland, Unol Daleithiau

rhyno_dagreat

Hello! I just started using FASM and in my humble opinion, it rocks! I find it more appealing than NASM and other assemblers for some odd reason. Razz

But anyways, back to the issue at hand...
I just decided I was gonna try to write an OS in ASM, and right now I'm working on the bootsector and trying to load up another sector right after it. Now so far the bootsector program loads up, but it doesn't load the second sector into memory. I was hoping someone could help me here.

This is the loader itself...

Code:

;BOOTSTART
org 7C00h

message db 'Loading RhynOS...',13,10,0

start:
        xor ax, ax
        mov ds, ax

        mov si, message
        call bios_print

load_os:
        mov ax, 0060h
        mov es, ax
        mov bx, 0000h
        mov ah, 02h
        mov al, 1
        mov ch, 0
        mov cl, 2
        mov dh, 0
        mov dl, 0
        int 13h
        jmp 0060h:0000h

bios_print:
        lodsb
        or al, al
        jz done
        mov ah, 0x0E
        int 0x10
        jmp bios_print

done:
        call load_os

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

And this is what it's loading...

Code:

org 0000h
use16

welcome db 'Welcome to RhynOS!', 13, 10, 0

start:
        mov ax, 0060h
        mov ds, ax
        mov si, welcome

ch_loop:
        lodsb
        or al, al
        jz return
        mov ah, 0x0E
        int 0x10
        jmp ch_loop

return:
        ret


        times 512-($-$$) db 0

Some input/help would be greatly appreciated! Thanks!

P.S. - This is the first time I've really used int 13h, and I might be doing something wrong with that, so could someone give me a good explaination on it? I've looked at Ralph Brown's Interrupt list, and it didn't help much.

Thanks!

-Rhyno

31 Jul 2006, 16:20

zhak

Joined: 12 Apr 2005
Posts: 490
Location: Belarus

zhak

first of all, you should place your message after code, or issue jmp start command before it, because BIOS redirects execution flow on 0:7C00 and your text is interpreted as commands and executed. that's why nothing works.
also, it's better to use BIOS Drive Number that is returned by BIOS in DL register when you call INT 13h, but not set it hardcoded as you've done (mov dl, 0).

31 Jul 2006, 21:25

rhyno_dagreat

Joined: 31 Jul 2006
Posts: 487
Location: Maryland, Unol Daleithiau

rhyno_dagreat

Thanks zhak! That did it! And it was something so trivial... Anyways, I'm wondering about what you just said about the BIOS returning the drive number? How does it do that, if you don't mind my asking?

31 Jul 2006, 23:10

Kenneth

Joined: 16 Nov 2005
Posts: 38
Location: United States of America

Kenneth

When it starts up the drive number is already in dl.

01 Aug 2006, 00:37

rhyno_dagreat

Joined: 31 Jul 2006
Posts: 487
Location: Maryland, Unol Daleithiau

rhyno_dagreat

Ah... I see... thanks! BTW... I recall a while ago there was a bunch of FASM programming tutorials out there... does anyone know any weblinks to them?

01 Aug 2006, 02:53

zhak

Joined: 12 Apr 2005
Posts: 490
Location: Belarus

zhak

http://www.phoenix.com/NR/rdonlyres/56E38DE2-3E6F-4743-835F-B4A53726ABED/0/specsbbs101.pdf
This is BIOS Boot Specification. Take a look at this document. It's useful for a boot loader writer.

01 Aug 2006, 10:43

rhyno_dagreat

Joined: 31 Jul 2006
Posts: 487
Location: Maryland, Unol Daleithiau

rhyno_dagreat

Thanks!

01 Aug 2006, 18:34

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