OSThing

BITS 16

start:
    mov ax, 07C0h       ; Set up 4K stack space after this bootloader
    add ax, 288     ; (4096 + 512) / 16 bytes per paragraph
    mov ss, ax
    mov sp, 4096

    mov ax, 07C0h       ; Set data segment to where we're loaded
    mov ds, ax


    mov ah, 11h
    int 10h

    mov si, text_string ; Put string position into SI
    call print_string   ; Call our string-printing routine

    jmp $           ; Jump here - infinite loop!

text_string:
    db 020h, 0DBh, 0DBh, 0DBh, 020h, 020h, 020h, 0DBh, 0DBh, 0DBh, 020h, 1
    db 0DBh, 020h, 020h, 020h, 0DBh, 020h, 0DBh, 020h, 020h, 020h, 0DBh, 1
    db 0DBh, 020h, 020h, 020h, 0DBh, 020h, 0DBh, 020h, 020h, 020h, 020h, 1
    db 0DBh, 020h, 020h, 020h, 0DBh, 020h, 020h, 0DBh, 0DBh, 0DBh, 020h, 1
    db 0DBh, 020h, 020h, 020h, 0DBh, 020h, 020h, 020h, 020h, 020h, 0DBh, 1
    db 0DBh, 020h, 020h, 020h, 0DBh, 020h, 0DBh, 020h, 020h, 020h, 0DBh, 1
    db 020h, 0DBh, 0DBh, 0DBh, 020h, 020h, 020h, 0DBh, 0DBh, 0DBh, 020h, 1
    db "Press ENTER to start.", 0


print_string:           ; Routine: output string in SI to screen
    mov ah, 0Eh     ; int 10h 'print char' function

.repeat:
    lodsb           ; Get character from string
    cmp al, 0
    je .done        ; If char is zero, end of string
    cmp al, 1
    je .next_line
    int 10h         ; Otherwise, print it
    jmp .repeat

.done:
    ret

.next_line:
    push ax
    push bx
    push cx
    push dx
    mov ah, 03h
    int 10h
    mov dl, 00h
    add dh, 01h
    mov ah, 02h
    int 10h
    pop dx
    pop cx
    pop bx
    pop ax
    jmp .repeat

    times 510-($-$$) db 0   ; Pad remainder of boot sector with 0s
    dw 0xAA55       ; The standard PC boot signature