INT 2F - MS WINDOWS - VIRTUAL DEVICE CALL OUT API
        AX = 1607h
        BX = virtual device ID (see INT 2F/AX=1684h)
        CX = (usually) callout subfunction
Return: (usually) AX,BX,CX,DX,ES contain results
Notes:  more of a convention than an API, this call specifies a standard
          mechanism for Windows enhanced-mode virtual devices (VxD's) to talk
          to DOS device drivers and TSRs
        see below for details on several virtual devices
SeeAlso: AX=1605h,AX=1607h/BX=000Ch,AX=1607h/BX=0014h