Compatibility: EMS 4.0+
Expects: AH    5bH
AL    subfn: 00H=Query alternate map register set
01H=Set alternate map register set
BL = new alternate map register set number
ES:DI => buffer to receive data
02H=Query alternate map register set array size
03H=Allocate alternate map register set
04H=Deallocate alternate map register set
05H=Allocate DMA register set
06H=Enable DMA on alternate map register set
BL = DMA register set number
DL = DMA channel number
ES:DI => buffer to receive data
07H=Disable DMA on alternate map register set
BL = alternate map register set number
08H=Deallocate DMA register set
BL = DMA register set number
                                                                  
Returns: AH    EMM status (0=successful)
BL    (5b00H) current active alternate register map set
(5b03H) alternate map registers set number
(5b05H) DMA register set number
ES:DI (5b00H) map register context save area (if BL=0)
DX    (5b02H) size of array
                                                                  
Info: This is designed for use by operating systems only and may be
disabled at any time.

These fns are used by an operating system in support of low-level
functions such as tampering with DMA.

- -

INT 67H 5bxxH: Alternate Map Register Set