Int 67 Fn 5B  - LIM EMS 4.0 - Alternate Map Register Set                   [m]

   AH = 5Bh
   AL = subfunction
       00h get alternate map register set

       Return: BL = current active alternate map register set number
           ES:DI -> map register context save area if BL=00h
       01h set alternate map register set
       BL = new alternate map register set number
       ES:DI -> map register context save area if BL=0
       02h get alternate map save array size

       Return: DX = array size in bytes
       03h allocate alternate map register set

       Return: BL = number of map register set; 00h = not supported
       04h deallocate alternate map register set
       BL = number of alternate map register set

Return: AH = status (00h,80h,81h,84h,8Fh,9Ah-9Dh,A3h,A4h) (see below)

Note:  this function is for use by operating systems only, and can be
     enabled or disabled at any time by the operating system

Values for status:
 00h   successful
 80h   internal error
 81h   hardware malfunction
 84h   undefined function requested
 8Fh   undefined subfunction
 9Ah   specified alternate map register or DMA register set not supported
 9Bh   all alternate map register or DMA register sets currently allocated
 9Ch   alternate map register or DMA register sets not supported
 9Dh   undefined or unallocated alternate map register/DMA register set
 9Eh   dedicated DMA channels not supported
 9Fh   specified dedicated DMA channel not supported
 A3h   source array corrupted
 A4h   operating system denied access