1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                    S Y S T E M . P A R A M E T E R S                     --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2003 Free Software Foundation, Inc.          --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
17-- for  more details.  You should have  received  a copy of the GNU General --
18-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
19-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
20-- MA 02111-1307, USA.                                                      --
21--                                                                          --
22-- As a special exception,  if other files  instantiate  generics from this --
23-- unit, or you link  this unit with other files  to produce an executable, --
24-- this  unit  does not  by itself cause  the resulting  executable  to  be --
25-- covered  by the  GNU  General  Public  License.  This exception does not --
26-- however invalidate  any other reasons why  the executable file  might be --
27-- covered by the  GNU Public License.                                      --
28--                                                                          --
29-- GNAT was originally developed  by the GNAT team at  New York University. --
30-- Extensive contributions were provided by Ada Core Technologies Inc.      --
31--                                                                          --
32------------------------------------------------------------------------------
33
34--  This is the default VxWorks AE 653 version of the package.`
35
36--  This package defines some system dependent parameters for GNAT. These
37--  are values that are referenced by the runtime library and are therefore
38--  relevant to the target machine.
39
40--  The parameters whose value is defined in the spec are not generally
41--  expected to be changed. If they are changed, it will be necessary to
42--  recompile the run-time library.
43
44--  The parameters which are defined by functions can be changed by modifying
45--  the body of System.Parameters in file s-parame.adb. A change to this body
46--  requires only rebinding and relinking of the application.
47
48--  Note: do not introduce any pragma Inline statements into this unit, since
49--  otherwise the relinking and rebinding capability would be deactivated.
50
51package System.Parameters is
52pragma Pure (Parameters);
53
54   ---------------------------------------
55   -- Task And Stack Allocation Control --
56   ---------------------------------------
57
58   type Task_Storage_Size is new Integer;
59   --  Type used in tasking units for task storage size
60
61   type Size_Type is new Task_Storage_Size;
62   --  Type used to provide task storage size to runtime
63
64   Unspecified_Size : constant Size_Type := Size_Type'First;
65   --  Value used to indicate that no size type is set
66
67   subtype Ratio is Size_Type range -1 .. 100;
68   Dynamic : constant Size_Type := -1;
69   --  The secondary stack ratio is a constant between 0 and 100 which
70   --  determines the percentage of the allocated task stack that is
71   --  used by the secondary stack (the rest being the primary stack).
72   --  The special value of minus one indicates that the secondary
73   --  stack is to be allocated from the heap instead.
74
75   Sec_Stack_Ratio : constant Ratio := 50;
76   --  This constant defines the handling of the secondary stack
77
78   Sec_Stack_Dynamic : constant Boolean := Sec_Stack_Ratio = Dynamic;
79   --  Convenient Boolean for testing for dynamic secondary stack
80
81   function Default_Stack_Size return Size_Type;
82   --  Default task stack size used if none is specified
83
84   function Minimum_Stack_Size return Size_Type;
85   --  Minimum task stack size permitted
86
87   function Adjust_Storage_Size (Size : Size_Type) return Size_Type;
88   --  Given the storage size stored in the TCB, return the Storage_Size
89   --  value required by the RM for the Storage_Size attribute. The
90   --  required adjustment is as follows:
91   --
92   --    when Size = Unspecified_Size, return Default_Stack_Size
93   --    when Size < Minimum_Stack_Size, return Minimum_Stack_Size
94   --    otherwise return given Size
95
96   Default_Env_Stack_Size : constant Size_Type := 14_336;
97   --  Assumed size of the environment task, if no other information
98   --  is available. This value is used when stack checking is
99   --  enabled and no GNAT_STACK_LIMIT environment variable is set.
100   --  This value is chosen as the VxWorks default stack size is 20kB,
101   --  and a little more than 4kB is necessary for the run time.
102
103   Stack_Grows_Down  : constant Boolean := True;
104   --  This constant indicates whether the stack grows up (False) or
105   --  down (True) in memory as functions are called. It is used for
106   --  proper implementation of the stack overflow check.
107
108   ----------------------------------------------
109   -- Characteristics of types in Interfaces.C --
110   ----------------------------------------------
111
112   long_bits : constant := Long_Integer'Size;
113   --  Number of bits in type long and unsigned_long. The normal convention
114   --  is that this is the same as type Long_Integer, but this is not true
115   --  of all targets. For example, in OpenVMS long /= Long_Integer.
116
117   ----------------------------------------------
118   -- Behavior of Pragma Finalize_Storage_Only --
119   ----------------------------------------------
120
121   --  Garbage_Collected is a Boolean constant whose value indicates the
122   --  effect of the pragma Finalize_Storage_Entry on a controlled type.
123
124   --    Garbage_Collected = False
125
126   --      The system releases all storage on program termination only,
127   --      but not other garbage collection occurs, so finalization calls
128   --      are ommitted only for outer level onjects can be omitted if
129   --      pragma Finalize_Storage_Only is used.
130
131   --    Garbage_Collected = True
132
133   --      The system provides full garbage collection, so it is never
134   --      necessary to release storage for controlled objects for which
135   --      a pragma Finalize_Storage_Only is used.
136
137   Garbage_Collected : constant Boolean := False;
138   --  The storage mode for this system (release on program exit)
139
140   ---------------------
141   -- Tasking Profile --
142   ---------------------
143
144   --  In the following sections, constant parameters are defined to
145   --  allow some optimizations and fine tuning within the tasking run time
146   --  based on restrictions on the tasking features.
147
148   ----------------------
149   -- Locking Strategy --
150   ----------------------
151
152   Single_Lock : constant Boolean := False;
153   --  Indicates whether a single lock should be used within the tasking
154   --  run-time to protect internal structures. If True, a single lock
155   --  will be used, meaning less locking/unlocking operations, but also
156   --  more global contention. In general, Single_Lock should be set to
157   --  True on single processor machines, and to False to multi-processor
158   --  systems, but this can vary from application to application and also
159   --  depends on the scheduling policy.
160
161   -------------------
162   -- Task Abortion --
163   -------------------
164
165   No_Abort : constant Boolean := False;
166   --  This constant indicates whether abort statements and asynchronous
167   --  transfer of control (ATC) are disallowed. If set to True, it is
168   --  assumed that neither construct is used, and the run time does not
169   --  need to defer/undefer abort and check for pending actions at
170   --  completion points. A value of True for No_Abort corresponds to:
171   --  pragma Restrictions (No_Abort_Statements);
172   --  pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
173
174   ----------------------
175   -- Dynamic Priority --
176   ----------------------
177
178   Dynamic_Priority_Support : constant Boolean := True;
179   --  This constant indicates whether dynamic changes of task priorities
180   --  are allowed (True means normal RM mode in which such changes are
181   --  allowed). In particular, if this is False, then we do not need to
182   --  poll for pending base priority changes at every abort completion
183   --  point. A value of False for Dynamic_Priority_Support corresponds
184   --  to pragma Restrictions (No_Dynamic_Priorities);
185
186   ---------------------
187   -- Task Attributes --
188   ---------------------
189
190   Default_Attribute_Count : constant := 4;
191   --  Number of pre-allocated Address-sized task attributes stored in the
192   --  task control block.
193
194   --------------------
195   -- Runtime Traces --
196   --------------------
197
198   Runtime_Traces : constant Boolean := False;
199   --  This constant indicates whether the runtime outputs traces to a
200   --  predefined output or not (True means that traces are output).
201   --  See System.Traces for more details.
202
203end System.Parameters;
204