Int 2F Fn 1685  - Ms Windows - Switch Vms And Callback                     [W]

   AX = 1685h
   BX = VM ID of virtual machine to switch to
   CX = flags (see #2404)
   DX:SI = priority boost (refer to VMM.INC)
   ES:DI -> FAR procedure to callback

Return: CF set on error
       AX = error code
       01h invalid VM ID
       02h invalid priority boost
       03h invalid flags
   CF clear if successful
       event will be or has been called

Notes: some DOS devices, such as networks, need to call functions in a
     specific VM. This call forces the appropriate VM to be installed.
   the callback procedure must preserve all registers and return with IRET

See Also: AX=1683h,INT 15/AX=1117h,AX=DB06h"WINGO"

Bitfields for VM switching flags:
Bit(s) Description (Table 2404)
 0 wait until interrupts enabled
 1 wait until critical section unowned
 2-15  reserved (zero)