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]
