Compatibility: DPMI 0.9+
Expects: AX    0306H
Returns: CF    NC (this fn always succeeds)
BX:CX real-mode address of routine to switch to protected mode
SI:DI (or SI:EDI) prot mode addr of routine to switch to real mode
Info: This is used by applications which perform low-level mode
switching.  It obtains the addresses of the DPMI routine which
switches into or out of real mode.

See INT 31H 0305H for a way to save and restore the state of a
task when you perform raw mode-switching.

BX:CX this address can be called by real-mode applications to switch to
protected mode.

SI:(E)DI this address can be called by protected-mode applications to
switch to real mode.

Both of these routines are accessed via FAR JMP and expect:

AX = new DS
CX = new ES
DX = new SS
(E)BX = new (E)SP
SI = new CS
(E)DI = new (E)IP

The host switches modes, and sets DS, ES, SS, and (E)SP, and
jumps to SI:(E)DI.

Notes:   It is your responsibility to save and restore the CPU state
(see INT 31H 0305H) when switching modes.

  You will find it easier to use fns such as INT 31H 0300H to
force mode switching, since they handle the overhead.

See Also: DPMI API
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INT 31H 0306H: Query Raw Mode-Switch Address