[SOLVED]QEMU not running my OS from Real Mode Assembly
Posted: Sat Aug 09, 2014 7:23 pm
Hello, I am very new to operating system development (this is the first time I have ever tried it) and I am having problems with running my OS in QEMU. I am running Linux Mate (a Ubuntu distro), and I have followed the Real Mode Assembly tutorial and ran these commands to load my OS to a floppy. Then I ran this command to run it on QEMU: Yes, I was in the corrected directory, I triple checked. The QEMU window popped up, but after some time it returned me with an error saying no bootable device. Of coarse, there is no boot loader in this tutorial, the author said there should be no need for one. Here is my code, which I copied directly from the tutorial :
Please, if anyone knows what I am doing wrong please let me know, or if this question has been asked before, please refer me to the link. If I have done something extremely stupid please also let me know(I do some very stupid things while programming user space stuff sometimes). I would not be surprised if I am missing something obvious, and if one of you could point it out, I would be grateful. Thank you. [edit] I changed "know" to "knows" [edit]
Code: Select all
nasm kernel.asm -f bin -o kernel.bin
dd if=kernel.bin of=/dev/fd0 Code: Select all
qemu-system-x86_64 -cdrom fd0 Code: Select all
mov ax, 0x07C0 ; set up segments
mov ds, ax
mov es, ax
mov si, welcome
call print_string
mainloop:
mov si, prompt
call print_string
mov di, buffer
call get_string
mov si, buffer
cmp byte [si], 0 ; blank line?
je mainloop ; yes, ignore it
mov si, buffer
mov di, cmd_hi ; "hi" command
call strcmp
jc .helloworld
mov si, buffer
mov di, cmd_help ; "help" command
call strcmp
jc .help
mov si,badcommand
call print_string
jmp mainloop
.helloworld:
mov si, msg_helloworld
call print_string
jmp mainloop
.help:
mov si, msg_help
call print_string
jmp mainloop
welcome db 'Welcome to My OS!', 0x0D, 0x0A, 0
msg_helloworld db 'Hello OSDev World!', 0x0D, 0x0A, 0
badcommand db 'Bad command entered.', 0x0D, 0x0A, 0
prompt db '>', 0
cmd_hi db 'hi', 0
cmd_help db 'help', 0
msg_help db 'My OS: Commands: hi, help', 0x0D, 0x0A, 0
buffer times 64 db 0
; ================
; calls start here
; ================
print_string:
lodsb ; grab a byte from SI
or al, al ; logical or AL by itself
jz .done ; if the result is zero, get out
mov ah, 0x0E
int 0x10 ; otherwise, print out the character!
jmp print_string
.done:
ret
get_string:
xor cl, cl
.loop:
mov ah, 0
int 0x16 ; wait for keypress
cmp al, 0x08 ; backspace pressed?
je .backspace ; yes, handle it
cmp al, 0x0D ; enter pressed?
je .done ; yes, we're done
cmp cl, 0x3F ; 63 chars inputted?
je .loop ; yes, only let in backspace and enter
mov ah, 0x0E
int 0x10 ; print out character
stosb ; put character in buffer
inc cl
jmp .loop
.backspace:
cmp cl, 0 ; beginning of string?
je .loop ; yes, ignore the key
dec di
mov byte [di], 0 ; delete character
dec cl ; decrement counter as well
mov ah, 0x0E
mov al, 0x08
int 10h ; backspace on the screen
mov al, ' '
int 10h ; blank character out
mov al, 0x08
int 10h ; backspace again
jmp .loop ; go to the main loop
.done:
mov al, 0 ; null terminator
stosb
mov ah, 0x0E
mov al, 0x0D
int 0x10
mov al, 0x0A
int 0x10 ; newline
ret
strcmp:
.loop:
mov al, [si] ; grab a byte from SI
mov bl, [di] ; grab a byte from DI
cmp al, bl ; are they equal?
jne .notequal ; nope, we're done.
cmp al, 0 ; are both bytes (they were equal before) null?
je .done ; yes, we're done.
inc di ; increment DI
inc si ; increment SI
jmp .loop ; loop!
.notequal:
clc ; not equal, clear the carry flag
ret
.done:
stc ; equal, set the carry flag
ret
times 510-($-$$) db 0
dw 0AA55h ; some BIOSes require this signature Please, if anyone knows what I am doing wrong please let me know, or if this question has been asked before, please refer me to the link. If I have done something extremely stupid please also let me know(I do some very stupid things while programming user space stuff sometimes). I would not be surprised if I am missing something obvious, and if one of you could point it out, I would be grateful. Thank you. [edit] I changed "know" to "knows" [edit]