; First MCB block is always at 00540
mcb_first:
	mov ax, 0x54
	mov ds, ax
	ret

mcb_init:
	call mcb_first
	mov dx, ds
	inc dx
	xor si, si
	int 0x12
	mov cl, 6
	shl ax, cl
	sub ax, dx
	mov byte [si+0], 'Z'
	mov word [si+1], 0
	mov word [si+3], ax
	mov dx, cs
	call mcb_find
	int 3
	ret

	; IN	dx	segment we look for
	; OUT	ds	segment where mcb starts
mcb_find:
	call mcb_first
	xor si, si
.loop:	stc
	adc ax, [si+3]
	cmp dx, ax
	jc .found
	cmp byte [si+0], 'Z'
	jz .fail
	mov ds, ax
	jmp .loop
.fail:	stc
	ret
.found:	clc
	ret