Int 21 Fn 250E  P - Phar Lap 386/dos-extender - Call Real-mode Procedure   [E]

   AX = 250Eh
   EBX = CS:IP of real-mode procedure to call
   ECX = number of two-byte words to copy from protected-mode stack
         to real-mode stack

Return: CF clear if successful
       all segment registers unchanged
       all general registers contain values set by real-mode procedure
       all other flags set as they were left by real-mode procedure
       stack unchanged
   CF set on error
       EAX = error code
       01h not enough real-mode stack space

Note:  this function is also supported by FlashTek X-32VM; under X-32VM, the
     call will fail if ECX > 0000003Fh

See Also: AX=250Dh,AX=2510h,AH=E1h"OS/286",INT 31/AX=0301h