Int 31 Fn 0301  P - DPMI 0.9+ - Call Real Mode Procedure With Far Return   [E]

   AX = 0301h
   BH = flags
       bit 0: reset the interrupt controller and A20 line (DPMI 0.9)
          reserved, must be 0 (DPMI 1.0+)
       others must be 0
   CX = number of words to copy from protected mode to real mode stack
   ES:(E)DI = selector:offset of real mode call structure
         (see INT 31/AX=0300h)

Return: CF clear if successful
       real mode call structure modified (all fields except SS:SP, CS:IP
         filled with return values from real mode interrupt)
   CF set on error
       AX = error code (DPMI 1.0+) (8012h,8013h,8014h,8021h)(see AX=0000h)
   protected mode stack unchanged

Notes: 16-bit programs use ES:DI as pointer, 32-bit programs use ES:EDI
   the real mode procedure must exit with a FAR return
   DPMI will provide a small (30 words) real mode stack if SS:SP is zero
   the real mode handler must return with the stack in the same state as
     it was on being called

See Also: AX=0300h,AX=0302h,INT 21/AX=250Eh,INT 21/AH=E1h"OS/286"

See Also: INT 2C/AX=0025h