OpenCores
URL https://opencores.org/ocsvn/openrisc_2011-10-31/openrisc_2011-10-31/trunk

Subversion Repositories openrisc_2011-10-31

[/] [openrisc/] [trunk/] [rtos/] [rtems/] [README] - Blame information for rev 496

Go to most recent revision | Details | Compare with Previous | View Log

Line No. Rev Author Line
1 30 unneback
#
2
#  $Id: README,v 1.2 2001-09-27 11:59:04 chris Exp $
3
#
4
 
5
Building RTEMS
6
==============
7
See the file README.configure.
8
 
9
Directory Overview
10
==================
11
 
12
This is the top level of the RTEMS directory structure.  The following
13
is a description of the files and directories in this directory:
14
 
15
  INSTALL
16
    Rudimentary installation instructions.  For more detailed
17
    information please see the Release Notes.  The Postscript
18
    version of this manual can be found in the file
19
    c_or_ada/doc/relnotes.tgz.
20
 
21
  LICENSE
22
    Required legalese.
23
 
24
  README
25
    This file.
26
 
27
  c
28
    This directory contains the source code for the C
29
    implementation of RTEMS as well as the test suites, sample
30
    applications, Board Support Packages, Device Drivers, and
31
    support libraries.
32
 
33
  doc
34
    This directory contains the PDL for the RTEMS executive.
35
 
36
Ada versus C
37
============
38
 
39
There are two implementations of RTEMS in this source tree --
40
in Ada and in C.  These two implementations are functionally
41
and structurally equivalent.  The C implementation follows
42
the packaging conventions and hiearchical nature of the Ada
43
implementation.  In addition, a style has been followed which
44
allows one to easily find the corresponding Ada and C
45
implementations.
46
 
47
File names in C and code placement was carefully designed to insure
48
a close mapping to the Ada implementation.  The following file name
49
extensions are used:
50
 
51
   .adb - Ada body
52
   .ads - Ada specification
53
   .adp - Ada body requiring preprocessing
54
   .inc - include file for .adp files
55
 
56
   .c   - C body (non-inlined routines)
57
   .inl - C body (inlined routines)
58
   .h   - C specification
59
 
60
In the executive source, XYZ.c and XYZ.inl correspond directly to a
61
single XYZ.adb or XYZ.adp file.  A .h file corresponds directly to
62
the .ads file.  There are only a handful of .inc files in the
63
Ada source and these are used to insure that the desired simple
64
inline textual expansion is performed.  This avoids scoping and
65
calling convention side-effects in carefully constructed tests
66
which usually test context switch behavior.
67
 
68
In addition, in Ada code and data name references are always fully
69
qualified as PACKAGE.NAME.  In C, this convention is followed
70
by having the package name as part of the name itself and using a
71
capital letter to indicate the presence of a "." level.  So we have
72
PACKAGE.NAME in Ada and _Package_Name in C.  The leading "_" in C
73
is used to avoid naming conflicts between RTEMS and user variables.
74
By using these conventions, one can easily compare the C and Ada
75
implementations.
76
 
77
The most noticeable difference between the C and Ada83 code is
78
the inability to easily obtain a "typed pointer" in Ada83.
79
Using the "&" operator in C yields a pointer with a specific type.
80
The 'Address attribute is the closest feature in Ada83.  This
81
returns a System.Address and this must be coerced via Unchecked_Conversion
82
into an access type of the desired type.  It is easy to view
83
System.Address as similar to a "void *" in C, but this is not the case.
84
A "void *" can be assigned to any other pointer type without an
85
explicit conversion.
86
 
87
The solution adopted to this problem was to provide two routines for
88
each access type in the Ada implementation -- one to convert from
89
System.Address to the access type and another to go the opposite
90
direction.  This results in code which accomplishes the same thing
91
as the corresponding C but it is easier to get lost in the clutter
92
of the apparent subprogram invocations than the "less bulky"
93
C equivalent.
94
 
95
A related difference is the types which are only in Ada which are used
96
for pointers to arrays.  These types do not exist and are not needed
97
in the C implementation.

powered by: WebSVN 2.1.0

© copyright 1999-2024 OpenCores.org, equivalent to Oliscience, all rights reserved. OpenCores®, registered trademark.