INT 2fH 1687H: Get Real-to-Protected Mode Switch Address

                                                    Compatibility: DPMI 0.9+ 
 Expects: AX    1687H (INT 2fH MUX ID and subfn number)
 Returns: AX    0000h = successful
                else  = no DPMI host present
          BX    flags:     bit 0: 0=32-bit programs are not supported
                                  1=32-bit programs are supported
                       bits 1-15: not used
          CL    processor type:  02H = 80286
                                 03H = 80386
                                 04H = 80486
                                 05H = Pentium
                                 >5  = reserved for future Intel CPUs
          DX    DPMI major + minor version number  (e.g., 010aH=1.10)
          SI    number of 16-byte pares needed for DPMI host private
          ES:DI entry address to call to enter Protected Mode
    Info: DPMI clients are loaded in real mode and may use this call to
          prepare for switching into protected mode.

       SI on return, this is an amount of real-mode memory, in 16-byte
          paragraphs, that you must supply when you process the switch (see
          below).  It might be 0000H, indicating no memory needed.

    ES:DI on return, this is the Entry Address you must call (via a
          FAR CALL) in order to switch to protected mode.  The calling
          parameters are:

            AX= 0000H = you'll be running as a 16-bit application
                0001H = you'll be running as a 32-bit application
            ES= the segment of the memory you're be supplying to DPMI host.
                If SI was 0 after INT 2fH 1687H, then ES is ignored.
            CF set (CY) if switch to protected mode failed
               (and AX is a DPMI Error Code)
            CS = selector for your code segment (64K limit)
            SS = selector for your stack segment (64K limit)
            DS = selector for your data segment (64K limit)
            ES = selector for your program's PSP (256-byte limit)
            FS = 0 (on 80386+ CPUs)
            GS = 0 (on 80386+ CPUs)

          Also, a selector has been prepared so that PSP:002e points to
          your copy of the DOS Environment.

    Note: To exit from protected mode, simply terminate your program via
          the standard DOS fn 4cH.

See Also: DPMI API
          INT 2fH 16xxH (Enh386 Windows Services & Notifications)
          INT 2fH: Multiplex Interrupt
          DOS Functions