------------------------------------------------------------------------------
--                                                                          --
--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
--                                                                          --
--                  S Y S T E M . O S _ P R I M I T I V E S                 --
--                                                                          --
--                                  S p e c                                 --
--                                                                          --
--          Copyright (C) 1998-2007, Free Software Foundation, Inc.         --
--                                                                          --
-- GNARL is free software; you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNARL; see file COPYING.  If not, write --
-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
-- Boston, MA 02110-1301, USA.                                              --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
-- this  unit  does not  by itself cause  the resulting  executable  to  be --
-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- GNARL was developed by the GNARL team at Florida State University.       --
-- Extensive contributions were provided by Ada Core Technologies, Inc.     --
--                                                                          --
------------------------------------------------------------------------------

--  This package provides low level primitives used to implement clock and
--  delays in non tasking applications.

--  The choice of the real clock/delay implementation (depending on whether
--  tasking is involved or not) is done via soft links (see s-soflin.ads)

--  NEVER add any dependency to tasking packages here

package System.OS_Primitives is
   pragma Preelaborate;

   Max_Sensible_Delay : constant Duration :=
                          Duration'Min (183 * 24 * 60 * 60.0,
                                        Duration'Last);
   --  Max of half a year delay, needed to prevent exceptions for large delay
   --  values. It seems unlikely that any test will notice this restriction,
   --  except in the case of applications setting the clock at run time (see
   --  s-tastim.adb). Also note that a larger value might cause problems (e.g
   --  overflow, or more likely OS limitation in the primitives used). In the
   --  case where half a year is too long (which occurs in high integrity mode
   --  with 32-bit words, and possibly on some specific ports of GNAT),
   --  Duration'Last is used instead.

   procedure Initialize;
   --  Initialize global settings related to this package. This procedure
   --  should be called before any other subprograms in this package. Note
   --  that this procedure can be called several times.

   function Clock return Duration;
   pragma Inline (Clock);
   --  Returns "absolute" time, represented as an offset relative to "the
   --  Epoch", which is Jan 1, 1970 00:00:00 UTC on UNIX systems. This
   --  implementation is affected by system's clock changes.

   function Monotonic_Clock return Duration;
   pragma Inline (Monotonic_Clock);
   --  Returns "absolute" time, represented as an offset relative to "the Unix
   --  Epoch", which is Jan 1, 1970 00:00:00 UTC. This clock implementation is
   --  immune to the system's clock changes.

   Relative          : constant := 0;
   Absolute_Calendar : constant := 1;
   Absolute_RT       : constant := 2;
   --  Values for Mode call below. Note that the compiler (exp_ch9.adb) relies
   --  on these values. So any change here must be reflected in corresponding
   --  changes in the compiler.

   procedure Timed_Delay (Time : Duration; Mode : Integer);
   --  Implements the semantics of the delay statement when no tasking is used
   --  in the application.
   --
   --    Mode is one of the three values above
   --
   --    Time is a relative or absolute duration value, depending on Mode.
   --
   --  Note that currently Ada.Real_Time always uses the tasking run time,
   --  so this procedure should never be called with Mode set to Absolute_RT.
   --  This may change in future or bare board implementations.

end System.OS_Primitives;
