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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
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4 -- --
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5 -- S Y S T E M . O S _ P R I M I T I V E S --
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6 -- --
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7 -- S p e c --
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8 -- --
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9 -- Copyright (C) 1998-2018, Free Software Foundation, Inc. --
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10 -- --
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11 -- GNARL is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNARL was developed by the GNARL team at Florida State University. --
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28 -- Extensive contributions were provided by Ada Core Technologies, Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package provides low level primitives used to implement clock and
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33 -- delays in non tasking applications.
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34
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35 -- The choice of the real clock/delay implementation (depending on whether
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36 -- tasking is involved or not) is done via soft links (see s-soflin.ads)
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37
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38 -- NEVER add any dependency to tasking packages here
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39
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40 package System.OS_Primitives is
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41 pragma Preelaborate;
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42
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43 Max_Sensible_Delay : constant Duration :=
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44 Duration'Min (183 * 24 * 60 * 60.0,
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45 Duration'Last);
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46 -- Max of half a year delay, needed to prevent exceptions for large delay
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47 -- values. It seems unlikely that any test will notice this restriction,
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48 -- except in the case of applications setting the clock at run time (see
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49 -- s-tastim.adb). Also note that a larger value might cause problems (e.g
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50 -- overflow, or more likely OS limitation in the primitives used). In the
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51 -- case where half a year is too long (which occurs in high integrity mode
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52 -- with 32-bit words, and possibly on some specific ports of GNAT),
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53 -- Duration'Last is used instead.
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54
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55 Max_System_Delay : constant Duration := Max_Sensible_Delay;
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56 -- If the Max_System_Delay is larger it doesn't matter. Setting it equal
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57 -- allows optimization of code in some targets delay functions.
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58
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59 procedure Initialize;
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60 -- Initialize global settings related to this package. This procedure
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61 -- should be called before any other subprograms in this package. Note
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62 -- that this procedure can be called several times.
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63
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64 function Clock return Duration;
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65 pragma Inline (Clock);
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66 -- Returns "absolute" time, represented as an offset relative to "the
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67 -- Epoch", which is Jan 1, 1970 00:00:00 UTC on UNIX systems. This
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68 -- implementation is affected by system's clock changes.
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69
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70 Relative : constant := 0;
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71 Absolute_Calendar : constant := 1;
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72 Absolute_RT : constant := 2;
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73 -- Values for Mode call below. Note that the compiler (exp_ch9.adb) relies
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74 -- on these values. So any change here must be reflected in corresponding
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75 -- changes in the compiler.
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76
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77 procedure Timed_Delay (Time : Duration; Mode : Integer);
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78 -- Implements the semantics of the delay statement when no tasking is used
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79 -- in the application.
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80 --
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81 -- Mode is one of the three values above
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82 --
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83 -- Time is a relative or absolute duration value, depending on Mode.
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84 --
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85 -- Note that currently Ada.Real_Time always uses the tasking run time,
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86 -- so this procedure should never be called with Mode set to Absolute_RT.
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87 -- This may change in future or bare board implementations.
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88
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89 end System.OS_Primitives;
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