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1 281 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
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--                                                                          --
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--                  S Y S T E M . O S _ P R I M I T I V E S                 --
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--                                                                          --
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--                                  S p e c                                 --
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--                                                                          --
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--          Copyright (C) 1998-2009, Free Software Foundation, Inc.         --
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--                                                                          --
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-- GNARL is free software; you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
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--                                                                          --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception,   --
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-- version 3.1, as published by the Free Software Foundation.               --
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--                                                                          --
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-- You should have received a copy of the GNU General Public License and    --
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-- a copy of the GCC Runtime Library Exception along with this program;     --
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-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
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-- <http://www.gnu.org/licenses/>.                                          --
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--                                                                          --
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-- GNARL was developed by the GNARL team at Florida State University.       --
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-- Extensive contributions were provided by Ada Core Technologies, Inc.     --
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--                                                                          --
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------------------------------------------------------------------------------
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--  This package provides low level primitives used to implement clock and
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--  delays in non tasking applications.
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--  The choice of the real clock/delay implementation (depending on whether
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--  tasking is involved or not) is done via soft links (see s-soflin.ads)
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--  NEVER add any dependency to tasking packages here
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package System.OS_Primitives is
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   pragma Preelaborate;
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   Max_Sensible_Delay : constant Duration :=
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                          Duration'Min (183 * 24 * 60 * 60.0,
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                                        Duration'Last);
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   --  Max of half a year delay, needed to prevent exceptions for large delay
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   --  values. It seems unlikely that any test will notice this restriction,
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   --  except in the case of applications setting the clock at run time (see
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   --  s-tastim.adb). Also note that a larger value might cause problems (e.g
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   --  overflow, or more likely OS limitation in the primitives used). In the
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   --  case where half a year is too long (which occurs in high integrity mode
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   --  with 32-bit words, and possibly on some specific ports of GNAT),
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   --  Duration'Last is used instead.
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   procedure Initialize;
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   --  Initialize global settings related to this package. This procedure
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   --  should be called before any other subprograms in this package. Note
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   --  that this procedure can be called several times.
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   function Clock return Duration;
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   pragma Inline (Clock);
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   --  Returns "absolute" time, represented as an offset relative to "the
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   --  Epoch", which is Jan 1, 1970 00:00:00 UTC on UNIX systems. This
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   --  implementation is affected by system's clock changes.
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   function Monotonic_Clock return Duration;
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   pragma Inline (Monotonic_Clock);
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   --  Returns "absolute" time, represented as an offset relative to "the Unix
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   --  Epoch", which is Jan 1, 1970 00:00:00 UTC. This clock implementation is
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   --  immune to the system's clock changes.
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   Relative          : constant := 0;
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   Absolute_Calendar : constant := 1;
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   Absolute_RT       : constant := 2;
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   --  Values for Mode call below. Note that the compiler (exp_ch9.adb) relies
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   --  on these values. So any change here must be reflected in corresponding
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   --  changes in the compiler.
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   procedure Timed_Delay (Time : Duration; Mode : Integer);
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   --  Implements the semantics of the delay statement when no tasking is used
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   --  in the application.
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   --
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   --    Mode is one of the three values above
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   --
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   --    Time is a relative or absolute duration value, depending on Mode.
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   --
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   --  Note that currently Ada.Real_Time always uses the tasking run time,
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   --  so this procedure should never be called with Mode set to Absolute_RT.
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   --  This may change in future or bare board implementations.
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end System.OS_Primitives;

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