ecos-v3_0-branch: host/libcdl/doc/concepts.sgml annotate

annotate host/libcdl/doc/concepts.sgml @ 2729:74dbf4c3f2e1 after-copyright-change-20090129

Update all copyright banners to reflect FSF ownership; fix and improve licence text.

author	jlarmour
date	Thu, 29 Jan 2009 17:47:46 +0000
parents	c9cbf5dfb306
children

rev	line source
210 d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	1 <!-- {{{ Banner -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	2
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	3 <!-- =============================================================== -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	4 <!-- -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	5 <!-- concepts.sgml -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	6 <!-- -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	7 <!-- Introductory chapter. -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	8 <!-- -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	9 <!-- =============================================================== -->
2729 74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	10 <!-- ####ECOSDOCCOPYRIGHTBEGIN#### -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	11 <!-- =============================================================== -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	12 <!-- Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	13 <!-- This material may be distributed only subject to the terms -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	14 <!-- and conditions set forth in the Open Publication License, v1.0 -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	15 <!-- or later (the latest version is presently available at -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	16 <!-- http://www.opencontent.org/openpub/) -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	17 <!-- Distribution of the work or derivative of the work in any -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	18 <!-- standard (paper) book form is prohibited unless prior -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	19 <!-- permission obtained from the copyright holder -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	20 <!-- =============================================================== -->
74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	21 <!-- ####ECOSDOCCOPYRIGHTEND#### -->
210 d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	22 <!-- =============================================================== -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	23 <!-- #####DESCRIPTIONBEGIN#### -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	24 <!-- -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	25 <!-- Author(s): bartv -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	26 <!-- Contact(s): bartv -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	27 <!-- Date: 2000/02/06 -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	28 <!-- Version: 0.01 -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	29 <!-- -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	30 <!-- ####DESCRIPTIONEND#### -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	31 <!-- =============================================================== -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	32
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	33 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	34
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	35 <chapter id="overview">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	36 <title>Overview</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	37
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	38 <!-- {{{ Introit -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	39
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	40 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	41 &eCos; was designed from the very beginning as a configurable
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	42 component architecture. The core &eCos; system consists of a number of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	43 different components such as the kernel, the C library, an
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	44 infrastructure package. Each of these provides a large number of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	45 configuration options, allowing application developers to build a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	46 system that matches the requirements of their particular application.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	47 To manage the potential complexity of multiple components and lots of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	48 configuration options, &eCos; comes with a component framework: a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	49 collection of tools specifically designed to support configuring
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	50 multiple components. Furthermore this component framework is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	51 extensible, allowing additional components to be added to the system
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	52 at any time.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	53 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	54
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	55 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	56 <!-- {{{ Terminology -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	57
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	58 <sect1 id="overview.terminology">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	59 <title>Terminology</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	60 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	61 The &eCos; component architecture involves a number of key concepts.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	62 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	63
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	64 <!-- {{{ Component Framework -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	65
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	66 <sect2 id="concepts.terminology.framework">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	67 <title>Component Framework</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	68
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	69 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	70 The phrase <phrase>component framework</phrase> is used to describe
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	71 the collection of tools that allow users to configure a system and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	72 administer a component repository. This includes the <application
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	73 class="software">ecosconfig</application> command line tool, the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	74 graphical configuration tool, and the package administration tool.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	75 Both the command line and graphical tools are based on a single
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	76 underlying library, the &CDL; library.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	77 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	78
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	79 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	80
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	81 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	82 <!-- {{{ Option -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	83
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	84 <sect2 id="concepts.terminology.option">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	85 <title>Configuration Option</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	86 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	87 The option is the basic unit of configurability. Typically each option
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	88 corresponds to a single choice that a user can make. For example there
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	89 is an option to control whether or not assertions are enabled, and the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	90 kernel provides an option corresponding to the number of scheduling
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	91 priority levels in the system. Options can control very small amounts
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	92 of code such as whether or not the C library's
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	93 <function>strtok</function> gets inlined. They can also control quite
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	94 large amounts of code, for example whether or not the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	95 <function>printf</function> supports floating point conversions.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	96 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	97 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	98 Many options are straightforward, and the user only gets to choose
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	99 whether the option is enabled or disabled. Some options are more
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	100 complicated, for example the number of scheduling priority levels is a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	101 number that should be within a certain range. Options should always
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	102 start off with a sensible default setting, so that it is not necessary
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	103 for users to make hundreds of decisions before any work can start on
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	104 developing the application. Once the application is running the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	105 various configuration options can be used to tune the system for the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	106 specific needs of the application.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	107 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	108 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	109 The component framework allows for options that are not directly
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	110 user-modifiable. Consider the case of processor endianness: some
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	111 processors are always big-endian or always little-endian, while with
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	112 other processors there is a choice. Depending on the user's choice of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	113 target hardware, endianness may or may not be user-modifiable.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	114 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	115 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	116
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	117 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	118 <!-- {{{ Component -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	119
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	120 <sect2 id="concepts.terminology.component">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	121 <title>Component</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	122 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	123 A component is a unit of functionality such as a particular kernel
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	124 scheduler or a device driver for a specific device. A component is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	125 also a configuration option in that users may want to enable
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	126 or disable all the functionality in a component. For example, if a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	127 particular device on the target hardware is not going to be used by
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	128 the application, directly or indirectly, then there is no point in
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	129 having a device driver for it. Furthermore disabling the device driver
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	130 should reduce the memory requirements for both code and data.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	131 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	132 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	133 Components may contain further configuration options. In the case of a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	134 device driver, there may be options to control the exact behavior of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	135 that driver. These will of course be irrelevant if the driver as a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	136 whole is disabled. More generally options and components live in a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	137 hierarchy, where any component can contain options specific to that
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	138 component and further sub-components. It is possible to view the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	139 entire &eCos; kernel as one big component, containing sub-components
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	140 for scheduling, exception handling, synchronization primitives, and so
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	141 on. The synchronization primitives component can contain further
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	142 sub-components for mutexes, semaphores, condition variables, event
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	143 flags, and so on. The mutex component can contain configuration
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	144 options for issues like priority inversion support.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	145 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	146 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	147
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	148 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	149 <!-- {{{ Package -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	150
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	151 <sect2 id="concepts.terminology.package">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	152 <title>Package</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	153 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	154 A package is a special type of component. Specifically, a package is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	155 the unit of distribution of components. It is possible to create a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	156 distribution file for a package containing all of the source code,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	157 header files, documentation, and other relevant files. This
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	158 distribution file can then be installed using the appropriate tool.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	159 Afterwards it is possible to uninstall that package, or to install a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	160 later version. The core &eCos; distribution comes with a number of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	161 packages such as the kernel and the infrastructure. Other packages
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	162 such as network stacks can come from various different sources and can
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	163 be installed alongside the core distribution.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	164 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	165 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	166 Packages can be enabled or disabled, but the user experience is a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	167 little bit different. Generally it makes no sense for the tools to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	168 load the details of every single package that has been installed. For
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	169 example, if the target hardware uses an ARM processor then there is no
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	170 point in loading the HAL packages for other architectures and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	171 displaying choices to the user which are not relevant. Therefore
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	172 enabling a package means loading its configuration data into the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	173 appropriate tool, and disabling a package is an unload operation. In
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	174 addition, packages are not just enabled or disabled: it is also
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	175 possible to select the particular version of a package that should be
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	176 used.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	177 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	178 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	179
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	180 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	181 <!-- {{{ Configuration -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	182
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	183 <sect2 id="concepts.terminology.configuration">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	184 <title>Configuration</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	185 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	186 A configuration is a collection of user choices. The various
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	187 tools that make up the component framework deal with entire
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	188 configurations. Users can create a new configuration, output a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	189 savefile (by default <filename>ecos.ecc</filename>), manipulate a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	190 configuration, and use a configuration to generate a build tree prior
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	191 to building &eCos; and any other packages that have been selected.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	192 A configuration includes details such as which packages have been
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	193 selected, in addition to finer-grained information such as which
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	194 options in those packages have been enabled or disabled by the user.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	195 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	196 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	197
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	198 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	199 <!-- {{{ Target -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	200
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	201 <sect2 id="concepts.terminology.target">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	202 <title>Target</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	203 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	204 The target is the specific piece of hardware on which the application
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	205 is expected to run. This may be an off-the-shelf evaluation board, a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	206 piece of custom hardware intended for a specific application, or it
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	207 could be something like a simulator. One of the steps when creating a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	208 new configuration is need to specify the target. The component
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	209 framework will map this on to a set of packages that are used to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	210 populate the configuration, typically HAL and device driver packages,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	211 and in addition it may cause certain options to be changed from their
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	212 default settings to something more appropriate for the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	213 specified target.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	214 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	215 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	216
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	217 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	218 <!-- {{{ Template -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	219
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	220 <sect2 id="concepts.terminology.template">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	221 <title>Template</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	222 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	223 A template is a partial configuration, aimed at providing users with
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	224 an appropriate starting point. &eCos; is shipped with a small number
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	225 of templates, which correspond closely to common ways of using the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	226 system. There is a minimal template which provides very little
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	227 functionality, just enough to bootstrap the hardware and then jump
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	228 directly to application code. The default template adds additional
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	229 functionality, for example it causes the kernel and C library packages
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	230 to be loaded as well. The uitron template adds further functionality
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	231 in the form of a &uITRON; compatibility layer. Creating a new
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	232 configuration typically involves specifying a template as well as a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	233 target, resulting in a configuration that can be built and linked with
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	234 the application code and that will run on the actual hardware. It is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	235 then possible to fine-tune configuration options to produce something
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	236 that better matches the specific requirements of the application.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	237 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	238 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	239
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	240 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	241 <!-- {{{ Properties -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	242
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	243 <sect2 id="concepts.terminology.properties">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	244 <title>Properties</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	245 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	246 The component framework needs a certain amount of information about
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	247 each option. For example it needs to know what the legal values are,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	248 what the default should be, where to find the on-line documentation if
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	249 the user needs to consult that in order to make a decision, and so on.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	250 These are all properties of the option. Every option (including
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	251 components and packages) consists of a name and a set of properties.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	252 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	253 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	254
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	255 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	256 <!-- {{{ Consequences -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	257
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	258 <sect2 id="concepts.terminology.consequences">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	259 <title>Consequences</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	260 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	261 Choices must have consequences. For an &eCos; configuration the main
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	262 end product is a library that can be linked with application code, so
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	263 the consequences of a user choice must affect the build process. This
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	264 happens in two main ways. First, options can affect which files get
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	265 built and end up in the library. Second, details of the current option
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	266 settings get written into various configuration header files using C
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	267 preprocessor <literal>#define</literal> directives, and package source
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	268 code can <literal>#include</literal> these configuration headers and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	269 adapt accordingly. This allows options to affect a package at a very
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	270 fine grain, at the level of individual lines in a source file if
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	271 desired. There may be other consequences as well, for example there
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	272 are options to control the compiler flags that get used during the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	273 build process.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	274 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	275 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	276
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	277 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	278 <!-- {{{ Constraints -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	279
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	280 <sect2 id="concepts.terminology.constraints">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	281 <title>Constraints</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	282 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	283 Configuration choices are not independent. The C library can provide
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	284 thread-safe implementations of functions like
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	285 <function>rand</function>, but only if the kernel provides support for
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	286 per-thread data. This is a constraint: the C library option has a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	287 requirement on the kernel. A typical configuration involves a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	288 considerable number of constraints, of varying complexity: many
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	289 constraints are straightforward, option <literal>A</literal> requires
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	290 option <literal>B</literal>, or option <literal>C</literal> precludes
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	291 option <literal>D</literal>. Other constraints can be more
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	292 complicated, for example option <literal>E</literal> may require the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	293 presence of a kernel scheduler but does not care whether it is the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	294 bitmap scheduler, the mlqueue scheduler, or something else.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	295 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	296 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	297 Another type of constraint involves the values that can be used for
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	298 certain options. For example there is a kernel option related to the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	299 number of scheduling levels, and there is a legal values constraint on
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	300 this option: specifying zero or a negative number for the number of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	301 scheduling levels makes no sense.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	302 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	303 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	304
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	305 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	306 <!-- {{{ Conflicts -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	307
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	308 <sect2 id="concepts.terminology.conflicts">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	309 <title>Conflicts</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	310 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	311 As the user manipulates options it is possible to end up with an
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	312 invalid configuration, where one or more constraints are not
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	313 satisfied. For example if kernel per-thread data is disabled but the C
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	314 library's thread-safety options are left enabled then there are
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	315 unsatisfied constraints, also known as conflicts. Such conflicts will
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	316 be reported by the configuration tools. The presence of conflicts does
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	317 not prevent users from attempting to build &eCos;, but the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	318 consequences are undefined: there may be compile-time failures, there
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	319 may be link-time failures, the application may completely fail to run,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	320 or the application may run most of the time but once in a while there
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	321 will be a strange failure… Typically users will want to resolve
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	322 all conflicts before continuing.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	323 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	324 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	325 To make things easier for the user, the configuration tools contain an
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	326 inference engine. This can examine a conflict in a particular
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	327 configuration and try to figure out some way of resolving the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	328 conflict. Depending on the particular tool being used, the inference
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	329 engine may get invoked automatically at certain times or the user may
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	330 need to invoke it explicitly. Also depending on the tool, the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	331 inference engine may apply any solutions it finds automatically or it
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	332 may request user confirmation.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	333 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	334 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	335
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	336 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	337 <!-- {{{ CDL -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	338
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	339 <sect2 id="concepts.terminology.cdl">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	340 <title>CDL</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	341 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	342 The configuration tools require information about the various options
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	343 provided by each package, their consequences and constraints, and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	344 other properties such as the location of on-line documentation. This
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	345 information has to be provided in the form of &CDL; scripts. CDL
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	346 is short for Component Definition Language, and is specifically
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	347 designed as a way of describing configuration options.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	348 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	349 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	350 A typical package contains the following:
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	351 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	352 <orderedlist>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	353 <listitem><para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	354 Some number of source files which will end up in a library. The
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	355 application code will be linked with this library to produce an
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	356 executable. Some source files may serve other purposes, for example to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	357 provide a linker script.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	358 </para></listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	359 <listitem><para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	360 Exported header files which define the interface provided by the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	361 package.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	362 </para></listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	363 <listitem><para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	364 On-line documentation, for example reference pages for each exported
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	365 function.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	366 </para></listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	367 <listitem><para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	368 Some number of test cases, shipped in source format, allowing users to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	369 check that the package is working as expected on their particular
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	370 hardware and in their specific configuration.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	371 </para></listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	372 <listitem><para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	373 One or more &CDL; scripts describing the package to the configuration
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	374 system.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	375 </para></listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	376 </orderedlist>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	377 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	378 Not all packages need to contain all of these. For example some
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	379 packages such as device drivers may not provide a new interface,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	380 instead they just provide another implementation of an existing
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	381 interface. However all packages must contain a &CDL; script that
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	382 describes the package to the configuration tools.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	383 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	384 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	385
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	386 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	387 <!-- {{{ Component Repository -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	388
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	389 <sect2 id="concepts.terminology.repo">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	390 <title>Component Repository</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	391 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	392 All &eCos; installations include a component repository. This is a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	393 directory structure where all the packages get installed. The
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	394 component framework comes with an administration tool that allows new
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	395 packages or new versions of a package to be installed, old packages to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	396 be removed, and so on. The component repository includes a simple
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	397 database, maintained by the administration tool, which contains
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	398 details of the various packages.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	399 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	400 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	401 Generally application developers do not need to modify anything inside
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	402 the component repository, except by means of the administration tool.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	403 Instead their work involves separate build and install trees. This
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	404 allows the component repository to be treated as a read-only resource
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	405 that can be shared by multiple projects and multiple users. Component
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	406 writers modifying one of the packages do need to manipulate files in
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	407 the component repository.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	408 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	409 </sect2>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	410
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	411 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	412
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	413 </sect1>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	414
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	415 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	416 <!-- {{{ Why configurability ? -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	417
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	418 <sect1 id="overview.configurability">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	419 <title>Why Configurability?</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	420 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	421 The &eCos; component framework places a great deal of emphasis on
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	422 configurability. The fundamental goal is to allow large parts of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	423 embedded applications to be constructed from re-usable software
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	424 components, which does not a priori require that those components be
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	425 highly configurable. However embedded application development often
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	426 involves some serious constraints.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	427 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	428 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	429 Many embedded applications have to work with very little memory, to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	430 keep down manufacturing costs. The final application image that will
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	431 get blown into EPROM's or used to manufacture ROMs should contain only
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	432 the code that is absolutely necessary for the application to work, and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	433 nothing else. If a few tens of kilobytes are added unnecessarily to a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	434 typical desktop application then this is regrettable, but is quite
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	435 likely to go unnoticed. If an embedded application does not fit on the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	436 target hardware then the problem is much more serious. The component
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	437 framework must allow users to configure the components so that any
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	438 unnecessary functionality gets removed.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	439 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	440 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	441 Many embedded applications need deterministic behavior so that they
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	442 can meet real-time requirements. Such deterministic behavior can
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	443 often be provided, but at a cost in terms of code size, slower
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	444 algorithms, and so on. Other applications have no such real-time
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	445 requirements, or only for a small part of the overall system, and the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	446 bulk of the system should not suffer any penalties. Again the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	447 component framework must allow the users control over the timing
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	448 behavior of components.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	449 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	450 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	451 Embedded systems tend to be difficult to debug. Even when it is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	452 possible to get information out of the target hardware by means other
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	453 than flashing an LED, the more interesting debugging problems are
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	454 likely to be timing-related and hence very hard to reproduce and track
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	455 down. The re-usable components can provide debugging assistance in
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	456 various ways. They can provide functionality that can be exploited by
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	457 source level debuggers such as gdb, for example per-thread debugging
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	458 information. They can also contain various assertions so that problems
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	459 can be detected early on, tracing mechanisms to figure out what
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	460 happened before the assertion failure, and so on. Of course all of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	461 these involve overheads, especially code size, and affect the timing.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	462 Allowing users to control which debugging features are enabled for any
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	463 given application build is very desirable.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	464 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	465 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	466 However, although it is desirable for re-usable components to provide
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	467 appropriate configuration options this is not required. It is possible
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	468 to produce a package which does not provide a single configuration
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	469 option — although the user still gets to choose
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	470 whether or not to use the package. In such cases it is still necessary
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	471 to provide a minimal CDL script, but its main purpose would be to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	472 integrate the package with the component framework's build system.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	473 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	474 </sect1>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	475
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	476 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	477 <!-- {{{ Approaches -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	478
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	479 <sect1 id="overview.approaches">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	480 <title>Approaches to Configurability</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	481
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	482 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	483 The purpose of configurability is to control the behavior of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	484 components. A scheduler component may or may not support time slicing;
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	485 it may or may not support multiple priorities; it may or may not
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	486 perform error checking on arguments passed to the scheduler routines.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	487 In the context of a desktop application a button widget may contain
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	488 some text or it may contain a picture; the text may be displayed in a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	489 variety of fonts; the foreground and background color may vary. When
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	490 an application uses a component there must be some way of specifying
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	491 the desired behavior. The component writer has no way of knowing in
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	492 advance exactly how a particular component will end up being used.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	493 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	494 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	495 One way to control the behavior is at run time. The application
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	496 creates an instance of a button object, and then instructs this object
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	497 to display either text or a picture. No special effort by the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	498 application developer is required, since a button can always support
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	499 all desired behavior. There is of course a major disadvantage in
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	500 terms of the size of the final application image: the code that gets
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	501 linked with the application has to provide support for all possible
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	502 behavior, even if the application does not require it.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	503 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	504 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	505 Another approach is to control the behavior at link-time, typically
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	506 by using inheritance in an object-oriented language. The button
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	507 library provides an abstract base class <classname>Button</classname>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	508 and derived classes <classname>TextButton</classname> and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	509 <classname>PictureButton</classname>. If an application only uses text
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	510 buttons then it will only create objects of type
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	511 <classname>TextButton</classname>, and the code for the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	512 <classname>PictureButton</classname> class does not get used. In
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	513 many cases this approach works rather well and reduces the final image
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	514 size, but there are limitations. The main one is that you can only
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	515 have so many derived classes before the system gets unmanageable: a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	516 derived class
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	517 <classname>TextButtonUsingABorderWidthOfOnePlusAWhiteBackgroundAndBlackForegroundAndATwelvePointTimesFontAndNoErrorCheckingOrAssertions</classname>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	518 is not particularly sensible as far as most application developers are
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	519 concerned.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	520 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	521 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	522 The &eCos; component framework allows the behavior of components to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	523 be controlled at an even earlier time: when the component source code
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	524 gets compiled and turned into a library. The button component could
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	525 provide options, for example an option that only text buttons need to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	526 be supported. The component gets built and becomes part of a library
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	527 intended specifically for the application, and the library will
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	528 contain only the code that is required by this application and nothing
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	529 else. A different application with different requirements would need
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	530 its own version of the library, configured separately.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	531 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	532 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	533 In theory compile-time configurability should give the best possible
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	534 results in terms of code size, because it allows code to be controlled
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	535 at the individual statement level rather than at the function or
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	536 object level. Consider an example more closely related to embedded
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	537 systems, a package to support multi-threading. A standard routine
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	538 within such a package allows applications to kill threads
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	539 asynchronously: the POSIX routine for this is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	540 <function>pthread_cancel</function>; the equivalent routine in &uITRON;
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	541 is <function>ter_tsk</function>. These routines themselves tend to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	542 involve a significant amount of code, but that is not the real
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	543 problem: other parts of the system require extra code and data for the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	544 kill routine to be able to function correctly. For example if a thread
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	545 is blocked while waiting on a mutex and is killed off by another
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	546 thread then the kill operation may have to do two things: remove the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	547 thread from the mutex's queue of waiting threads; and undo the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	548 effects, if any, of priority inheritance. The implementation requires
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	549 extra fields in the thread data structure so that the kill routine
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	550 knows about the thread's current state, and extra code in the mutex
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	551 routines to fill in and clear these extra fields correctly.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	552 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	553 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	554 Most embedded applications do not require the ability to kill off a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	555 thread asynchronously, and hence the kill routine will not get linked
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	556 into the final application image. Without compile-time configurability
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	557 this would still mean that the mutex code and similar parts of the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	558 system contain code and data that serve no useful purpose in this
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	559 application. The &eCos; approach allows the user to select that the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	560 thread kill functionality is not required, and all the components can
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	561 adapt to this at compile-time. For example the code in the mutex lock
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	562 routine contains statements to support the killing of threads, but
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	563 these statements will only get compiled in if that functionality is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	564 required. The overall result is that the final application image
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	565 contains only the code and data that is really needed for the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	566 application to work, and nothing else.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	567 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	568 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	569 Of course there are complications. To return to the button example,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	570 the application code might only use text buttons directly, but it
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	571 might also use some higher-level widget such as a file selector and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	572 this file selector might require buttons with pictures. Therefore the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	573 button code must still be compiled to support pictures as well as
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	574 text. The configuration tools must be aware of the dependencies
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	575 between components and ensure that the internal constraints are met,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	576 as well as the external requirements of the application code. An area
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	577 of particular concern is conflicting requirements: a button component
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	578 might be written in such a way that it can only support either text
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	579 buttons or picture buttons, but not both in one application; this
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	580 would represent a weakness in the component itself rather than in the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	581 component framework as a whole.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	582 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	583 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	584 Compile-time configurability is not intended to replace the other
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	585 approaches but rather to complement them. There will be times when
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	586 run-time selection of behavior is desirable: for example an
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	587 application may need to be able to change the baud rate of a serial
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	588 line, and the system must then provide a way of doing this at
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	589 run-time. There will also be times when link-time selection is
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	590 desirable: for example a C library might provide two different random
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	591 number routines <function>rand</function> and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	592 <function>lrand48</function>; these do not affect other code so there
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	593 is no good reason for the C library component not to provide both of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	594 these, and allow the application code to use none, one, or both of
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	595 them as appropriate; any unused functions will just get eliminated at
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	596 link-time. Compile-time selection of behavior is another option, and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	597 it can be the most powerful one of the three and the best suited to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	598 embedded systems development.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	599 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	600
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	601 </sect1>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	602
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	603 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	604 <!-- {{{ Degrees -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	605
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	606 <sect1 id="overview.degress">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	607 <title>Degrees of Configurability</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	608
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	609 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	610 Components can support configurability in varying degrees. It is not
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	611 necessary to have any configuration options at all, and the only user
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	612 choice is whether or not to load a particular package. Alternatively
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	613 it is possible to implement highly-configurable code. As an example
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	614 consider a typical facility that is provided by many real-time
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	615 kernels, mutex locks. The possible configuration options include:
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	616 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	617
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	618 <orderedlist>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	619
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	620 <listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	621 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	622 If no part of the application and no other component requires mutexes
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	623 then there is no point in having the mutex code compiled into a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	624 library at all. This saves having to compile the code. In addition
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	625 there will never be any need for the user to configure the detailed
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	626 behavior of mutexes. Therefore the presence of mutexes is a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	627 configuration option in itself.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	628 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	629 </listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	630
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	631 <listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	632 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	633 Even if the application does make use of mutexes directly or
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	634 indirectly, this does not mean that all mutex functions have to be
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	635 included. The minimum functionality consists of lock and unlock
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	636 functions. However there are variants of the locking primitive such as
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	637 try-lock and try-with-timeout which may or may not be needed.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	638 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	639 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	640 Generally it will be harmless to compile the try-lock function even if
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	641 it is not actually required, because the function will get eliminated
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	642 at link-time. Some users might take the view that the try-lock
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	643 function should never get compiled in unless it is actually needed, to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	644 reduce compile-time and disk usage. Other users might argue that there
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	645 are very few valid uses for a try-lock function and it should not be
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	646 compiled by default to discourage incorrect uses. The presence of a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	647 try-lock function is a possible configuration option, although it may
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	648 be sensible to default it to true.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	649 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	650 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	651 The try-with-timeout variant is more complicated because it adds a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	652 dependency: the mutex code will now rely on some other component to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	653 provide a timer facility. To make things worse the presence of this
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	654 timer might impact other components, for example it may now be
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	655 necessary to guard against timer interrupts, and thus have an
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	656 insidious effect on code size. The presence of a lock-with-timeout
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	657 function is clearly a sensible configuration option, but the default
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	658 value is less obvious. If the option is enabled by default then the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	659 final application image may end up with code that is not actually
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	660 essential. If the option is disabled by default then users will have
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	661 to enable the option somehow in order to use the function, implying
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	662 more effort on the part of the user. One possible approach is to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	663 calculate the default value based on whether or not a timer component
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	664 is present anyway.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	665 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	666 </listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	667
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	668 <listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	669 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	670 The application may or may not require the ability to create and
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	671 destroy mutexes dynamically. For most embedded systems it is both less
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	672 error-prone and more efficient to create objects like mutexes
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	673 statically. Dynamic creation of mutexes can be implemented using a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	674 pre-allocated pool of mutex objects, involving some extra code to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	675 manipulate the pool and an additional configuration option to define
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	676 the size of the pool. Alternatively it can be implemented using a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	677 general-purpose memory allocator, involving quite a lot of extra code
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	678 and configuration options. However this general-purpose memory
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	679 allocator may be present anyway to support the application itself or
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	680 some other component. The ability to create and destroy mutexes
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	681 dynamically is a configuration option, and there may not be a sensible
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	682 default that is appropriate for all applications.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	683 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	684 </listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	685
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	686 <listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	687 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	688 An important issue for mutex locks is the handling of priority
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	689 inversion, where a high priority thread is prevented from running
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	690 because it needs a lock owned by a lower priority thread. This is only
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	691 an issue if there is a scheduler with multiple priorities: some
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	692 systems may need multi-threading and hence synchronization primitives,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	693 but a single priority level may suffice. If priority inversion is a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	694 theoretical possibility then the application developer may still want
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	695 to ignore it because the application has been designed such that the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	696 problem cannot arise in practice. Alternatively the developer may want
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	697 some sort of exception raised if priority inversion does occur,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	698 because it should not happen but there may still be bugs in the code.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	699 If priority inversion can occur legally then there are three main ways
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	700 of handling it: priority ceilings, priority inheritance, and ignoring
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	701 the problem. Priority ceilings require little code but extra effort on
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	702 the part of the application developer. Priority inheritance requires
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	703 more code but is automatic. Ignoring priority inversion may or may not
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	704 be acceptable, depending on the application and exactly when priority
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	705 inversion can occur. Some of these choices involve additional
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	706 configuration options, for example there are different ways of raising
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	707 an exception, and priority inheritance may or may not be applied
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	708 recursively.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	709 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	710 </listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	711
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	712 <listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	713 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	714 As a further complication some mutexes may be hidden inside a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	715 component rather than being an explicit part of the application. For
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	716 example, if the C library is configured to provide a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	717 <function>malloc</function> call then there may be an associated mutex
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	718 to make the function automatically thread-safe, with no need for
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	719 external locking. In such cases the memory allocation component of the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	720 C library can impose a constraint on the kernel, requiring that
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	721 mutexes be provided. If the user attempts to disable mutexes anyway
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	722 then the configuration tools will report a conflict.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	723 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	724 </listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	725
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	726 <listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	727 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	728 The mutex code should contain some general debugging code such as
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	729 assertions and tracing. Usually such debug support will be enabled or
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	730 disabled at a coarse level such as the entire system or everything
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	731 inside the kernel, but sometimes it will be desirable to enable the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	732 support more selectively. One reason would be memory requirements: the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	733 target may not have enough memory to hold the system if all debugging
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	734 is enabled. Another reason is if most of the system is working but
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	735 there are a few problems still to resolved; enabling debugging in the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	736 entire system might change the system's timing behavior too much, but
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	737 enabling some debug options selectively can still be useful. There
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	738 should be configuration options to allow specific types of debugging
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	739 to be enabled at a fine-grain, but with default settings inherited
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	740 from an enclosing component or from global settings.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	741 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	742 </listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	743
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	744 <listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	745 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	746 The mutex code may contain specialized code to interact
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	747 with a debugging tool running on the host. It should be
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	748 possible to enable or disable this debugging code, and there may
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	749 be additional configuration options controlling the detailed
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	750 behavior.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	751 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	752 </listitem>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	753
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	754 </orderedlist>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	755
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	756 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	757 Altogether there may be something like ten to twenty configuration
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	758 options that are specific to the mutex code. There may be a similar
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	759 number of additional options related to assertions and other debug
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	760 facilities. All of the options should have sensible default values,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	761 possibly fixed, possibly calculated depending on what is happening
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	762 elsewhere in the configuration. For example the default setting for
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	763 an assertion option should generally inherit from a kernel-wide
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	764 assertion control option, which in turn inherits from a global option.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	765 This allows users to enable or disable assertions globally or at
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	766 a more fine-grained level, as desired.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	767 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	768 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	769 Different components may be configurable to different degrees, ranging
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	770 from no options at all to the fine-grained configurability of the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	771 above mutex example (or possibly even further). It is up to component
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	772 writers to decide what options should be provided and how best to
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	773 serve the needs of application developers who want to use that
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	774 component.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	775 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	776 </sect1>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	777
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	778 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	779 <!-- {{{ Warning -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	780
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	781 <sect1 id="overview.warning">
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	782 <title>Warnings</title>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	783 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	784 Large parts of &eCos; were developed concurrently with the development
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	785 of the configuration technology, or in some cases before design work
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	786 on that technology was complete. As a consequence the various &eCos;
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	787 packages often make only limited use of the available functionality.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	788 This situation is expected to change over time. It does mean that many
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	789 of the descriptions in this guide will not correspond exactly to how
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	790 the &eCos; packages work right now, but rather to how they could work.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	791 Some of the more extreme discrepancies such as the location of on-line
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	792 documentation in the component repository will be mentioned in the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	793 appropriate places in the guide.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	794 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	795 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	796 A consequence of this is that developers of new components can look at
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	797 existing &CDL; scripts for examples, and discover discrepancies
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	798 between what is recommended in this guide and what actually happens at
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	799 present. In such cases this guide should be treated as authoritative.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	800 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	801 <para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	802 It is also worth noting that the current component framework is not
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	803 finished. Various parts of this guide will refer to possible changes
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	804 and enhancements in future versions. Examining the source code of the
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	805 configuration tools may reveal hints about other likely developments,
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	806 and there are many more possible enhancements which only exist at a
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	807 conceptual level right now.
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	808 </para>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	809
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	810 </sect1>
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	811
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	812 <!-- }}} -->
d2c90368aeef Merge from eCos master repository on 2002-05-23-21:39:14-BST jlarmour parents: diff changeset	813
2729 74dbf4c3f2e1 Update all copyright banners to reflect FSF ownership; fix and improve licence text. jlarmour parents: 334 diff changeset	814 </chapter>

Mercurial > ecos-v3_0-branch

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