Print string using INT 0x10 in bootsector

Question

I want to create printl function that allow me to print string in the ax register. I am in 16-bit real mode and I can not find any way to print a message. I using int 0x10 to print a single letter.

I try pass argument (string to print) in bx register, then in a loop print letter by letter and then go back using popa and ret. My code didn't really work -- either it created a infinite loop or printed a strange sign.

If you know more efficient way to do it then it's not a problem. I would also like to ask about comment your code if you gave any

This is my code

boot.asm:

start:
    mov bx, welcome    ;put argument to bx
    call printl        ;call printl function in sysf.asm
    hlt                ;halt cpu

welcome db 'Hello', 0

include 'sysf.asm'
times 510 - ($-$$) db 0

db 0x55
db 0xAA

sysf.asm:

;print function
; al is one letter argument (type Java:char)
;
print:
        pusha
        mov ah, 0x0e
        int 0x10
        popa
        ret              ; go back

;printl function
; bx is argument of type Java:String
;
printl:
        pusha
        jmp printl001
printl001:
        lodsb             ; I was working with si register but i would like to use bx register
        or al,al
        jz printl002
        mov ah, 0x0e
        int 0x10
        jmp printl001 
printl002:
        popa
        ret

Answer 1

The lodsb instruction loads the byte pointed to by the DS and SI registers but you haven't loaded either with a valid value. Since this a bootloader you also need to use the ORG directive, otherwise the assembler won't know where your code, and therefore the welcome message, gets loaded into memory. Try changing the start of of your program to:

ORG 0x7c00

start:
    push cs
    pop ds
    mov si, welcome