Start from scratch, boot02 (convert the print string function into a function)

Bind the function of printing strings on the screen as a function. For future use.
; Helloworld. ASM

Org 07c00h
; Setup stack. Setup stack at most top of 640 K
Start: mov ax, 0x0fc0
MoV SS, ax
MoV ax, 0x0400
MoV sp, ax

MoV BX, msg1
Push BX
Call dumpstr
Pop BX
JMP $

Dumpstr:
; Backup used registor
PUSH AX
Push BX
Push CX
Push DX
Push BP

; Get Parameter
MoV bp, SP
Add bp, 12
MoV BX, [BP]
; Calculator String Length
Xor cx, CX
Strlop: mov ax, [BX]
CMP ax, 0x0
JZ calend
INC CX
INC BX
JMP strlop
Calend:
Push CX

MoV ah, 0x03
Xor bh, BH
Int 0x10
 
Pop CX
MoV BX, 0x0007
Push BP
MoV bp, [BP]
MoV ax, 0x1301
Int 0x10
Pop BP

; Restore registor
Pop BP
Pop DX
Pop CX
Pop BX
Pop ax
RET
Msg1: dB 13, 10
DB 'Hello world'
DB 13, 10, 13, 10

Times 510-($-$) db 0
DW 0aa55h