INT 67H 5bxxH: Alternate Map Register Set

                                                     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.

See Also: INT 67H: EMM Services
          Extended Memory Specification (XMS)
          Interrupts and BIOS Services
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