segment code
        align 16
        call start
start:  pop bx
        mov ax, cs
        shr bx, 4
        add ax, bx
        mov ds, ax
        mov es, ax

;        mov si, hello
;        call prins

findvesa:
        mov ax, 4F00h
        mov di, data
        int 10h
        cmp ax, 004Fh
        je  .good
        mov si, bad
        call prins
        jmp .done
.good:  mov si, data
        mov cx, 4
        call prinsn
        lds si, [data+6]
        mov cx, 100
        call prinsn
        mov ax, es
        mov ds, ax
.done:  

finish:
        mov si, done
        call prins
        mov ax, 4C00h  ; exit(0) line 1
        int 21h        ; exit line 2


prins:                 ; address of string in si
.loop:  mov al, [si]
        cmp al, 0
        je  .end
        inc si
        mov ah, 0Eh    ; putch line 1
        mov bx, 0007h  ; video page then attribute
        int 10h
        jmp .loop
.end:   ret

prinsn:                ; address of string in si, len in cx
.loop:  cmp cx, 0
        je  .end
        dec cx
        mov al, [si]
        inc si
        mov ah, 0Eh    ; putch line 1
        mov bx, 0007h  ; video page then attribute
        int 10h
        jmp .loop
.end:   ret

phex:   pusha
        push ax
        mov si, ax
        and si, 00F0h
        shr si, 4
        add si, hex
        mov al, [si]
        mov ah, 0Eh
        mov bx, 0007h
        int 10h
        pop si
        and si, 000Fh
        add si, hex
        mov al, [si]
        mov ah, 0Eh
        mov bx, 0007h
        int 10h
        mov ax, 0E20h
        mov bx, 0007h
        int 10h
        popa
        ret

        segment data
hex:    db "0123456789ABCDEF"
hello:  db "hello!", 13, 10, 0
done:   db "all over.", 13, 10, 0
bad:    db "no vesa detected", 13, 10, 0
data:   dd 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        dd 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        dd 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        dd 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0