INT 2fH 1680H: Program Idle (Release Timeslice)

                                                         Compatibility: 3.0+ 
 Expects: AX    1680H
 Returns: AL    status: 00H = system supports Idle Calls
                        else= system does not support program suspension
    Info: DOS programs and TSRs should use this while waiting for user
          input.  It announces to the system (DOS or Windows) that the
          program is willing to give up the current timeslice.

          Before calling this the first time, you should use DOS fn 35H to
          check that the vector for INT 2FH is non-zero.

          The system does not suspend your program unless there is another
          task ready to run; most often, control will immediately return.

          You should place a call to this fn inside your idle loop,
          whenever waiting for keyboard input or polling the mouse, etc.

   Notes: This fn is also described (with the same parameters and
          functionality) as part of the DPMI specification.

See Also: INT 28H: DOS Idle
          INT 2fH 16xxH: Enh386 Windows Services & Notifications
          DPMI Services
          INT 2fH: Multiplex Interrupt
          DOS Functions