; Register a interrupt handler
; in:	AL	interrupt number
;	ES:DI	far ptr to routine/data
intr_register:
  ; backup original values
  push ax
  push es
  push di

  ; pop as ax later
  push es
  push di

  ; DI = AL * 4
  mov ah, 4
  mul ah
  mov di, ax

  ; ES = 0
  xor ax, ax
  mov es, ax

  ; store offset
  pop ax
  stosw

  ; store segment
  pop ax
  stosw

  pop di
  pop es
  pop ax
  ret