kernel printing trash

[A32]

So, I am kinda new to this OS development, I got caught two months ago, and I was starting with the bare bones 1 kernel. I fitted in the boot sector fine. Then it grew and I needed a bootloader. I got none of the bootloader work, I got frustrated, and left OS dev behind. Now I am starting again, this I got a bootloader to work (MikeOS bootloder) but now my kernel is not working. I am simply tring to print "Hello world" to the screen, but instead, it prints some garbage ( looping over and over).
It is so frustrating. One possible theory is that MikeOS bootloader doesnt work with my kernel, but its the only working bootloader.

My kernel code:

Code: Select all

[BITS 16]

mov si,msgHello
call Print_string
hlt


Print_string:
lodsb
or al,al
jz .done
mov ah, 0x0E
mov bh, 0x00
mov bl, 0x07
int 0x10
jmp Print_string
.done:
ret

msgHello  db 0x0D, 0x0A, "Hello World", 0x0D, 0x0A, 0x00
TIMES 510-($-$$) DB 0

[gravaera]

Or you could try GrUB. Here is the Wiki article: http://wiki.osdev.org/GRUB

I don't use interrupts very much, and I've never used the BIOS printing interrupts before, but it seems like the problem is somewhere there. Maybe you could try checking that the right value are loaded into the registers?

[A32]

I changed it a little, its still printing trash, but atleast its printing different kind of trash.

[mnovotny]

Hi,

Are you sure you have your segment registers set up properly? Or use [ORG 0xXXXX] stuff.

[A32]

Hi,

Are you sure you have your segment registers set up properly? Or use [ORG 0xXXXX] stuff.

Oh yeah the segment registers. I fixed that, but... now it doesnt load... Maybe the bootloader has problems. But its the only working I have found, GRUB is too hard to configure.

[ahmedhalawa]

i think the problem in

Code: Select all

mov si,msgHello
call Print_string

to which where si point
in my opinion if wants to use this code with out any changes in it
try to add

Code: Select all

[org 0x07c0]

in your code

[A32]

i think the problem in

Code: Select all

mov si,msgHello
call Print_string

to which where si point
in my opinion if wants to use this code with out any changes in it
try to add

Code: Select all

[org 0x07c0]

in your code

Done everything, it still doesnt load. The new code:

Code: Select all

[BITS 16]
[org 0x07c0]


prepare:
mov ax, 0x07C0
mov ds, ax
mov es, ax

mov si,msgHello
call Print_string
hlt


Print_string:
.loop:
   lodsb
   or al, al
   jz .done
   mov ah, 0x0E
   int 0x10
   jmp .loop
 .done:
   ret

msgHello db "Hello World", 0

[mnovotny]

[org 0x07c0]

mov ax, 0x07C0
mov ds, ax
mov es, ax

I must ask: where does MikeOS bootloader load your kernel? Because that code is just nonsense from normal point of view.

[Combuster]

The bug:

hlt

"temporarily suspend execution" temporarily being until an (timer) interrupt happens.

[A32]

I... I Dont understand what you are saying MikeOS bootloader loads the kernel in RAM and jumps to position 2000h:0000h (whatever that is) in the loaded kernel. If the hello world program has errors, can you explain them to me with a OSdev-newbie language. Just learning.

Edit:

"temporarily suspend execution" temporarily being until an (timer) interrupt happens.

whats a timer interrupt?

[mnovotny]

Code: Select all

[BITS 16]

prepare:
mov ax, 0x2000             ; You said you're here
mov ds, ax
mov es, ax

mov si,msgHello
call Print_string

hang: jmp hang              ; Use instead of hlt


Print_string:
.loop:
   lodsb
   or al, al
   jz .done
   mov ah, 0x0E
   int 0x10
   jmp .loop
.done:
   ret

msgHello db "Hello World", 0

I'm in hurry and didn't test it, but try it.

[A32]

Thanks, that worked. I get that hang thingy but what really this

Code: Select all

mov ax, 0x2000
mov ds, ax
mov es, ax

does? I also get the mov parts but what is 0x2000?

[mnovotny]

http://wiki.osdev.org/Segmentation#Real_mode

MikeOS bootloader loads the kernel in RAM and jumps to position 2000h:0000h (whatever that is) in the loaded kernel.

[tantrikwizard]

I also get the mov parts but what is 0x2000?

You cannot expect to write an operating system if you lack the fundamental knowledge of the hardware you're trying to write an operating system for.

[Troy Martin]

whats a timer interrupt?

Oh dear lord...

I'd suggest you read the Intel manuals. And about half a dozen 16-bit assembly tutorials. Then, if you understand even a bit of your copy/pasted code, this might not happen again.