Release Current Virtual Machine's Time Slice

Called by a client program to indicate that the program is
idle (for example, waiting for keyboard input).  This allows
the DPMI host to pass the CPU to other clients, or take
power-conserving measures on laptop and notebook computers.

Call With:

   AX     = 1680H

Returns::

   if function supported by host
   AL     = 0

   if function not supported by host
   AL     = unchanged (80H)

Notes:

o  This function is not specific to DPMI hosts.  Some
   operating systems will recognize this call for programs
   running in real mode.  Programmers are encouraged to use
   this call in all DOS and DPMI-client programs.  All DPMI
   hosts will hook Int 2FH and so a DPMI client can use this
   API without any other precautions.  Non-DPMI programs
   that can run on DOS 2.xx or earlier should make sure that
   the Int 2FH vector is non-zero before executing the Int
   2FH.

o  When an application calls this function it will regain
   control at intervals, so it should continue to re-issue
   this function call so long as it has nothing to do.

o  DPMI client and application vendors are encouraged to use
   this function.  It can significantly improve the
   performance of a DOS-based multitasking host.