| 1 |
28 |
unneback |
<!-- Copyright (C) 2003 Red Hat, Inc. -->
|
| 2 |
|
|
<!-- This material may be distributed only subject to the terms -->
|
| 3 |
|
|
<!-- and conditions set forth in the Open Publication License, v1.0 -->
|
| 4 |
|
|
<!-- or later (the latest version is presently available at -->
|
| 5 |
|
|
<!-- http://www.opencontent.org/openpub/). -->
|
| 6 |
|
|
<!-- Distribution of the work or derivative of the work in any -->
|
| 7 |
|
|
<!-- standard (paper) book form is prohibited unless prior -->
|
| 8 |
|
|
<!-- permission is obtained from the copyright holder. -->
|
| 9 |
|
|
<HTML
|
| 10 |
|
|
><HEAD
|
| 11 |
|
|
><TITLE
|
| 12 |
|
|
>Overview</TITLE
|
| 13 |
|
|
><meta name="MSSmartTagsPreventParsing" content="TRUE">
|
| 14 |
|
|
<META
|
| 15 |
|
|
NAME="GENERATOR"
|
| 16 |
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
|
| 17 |
|
|
"><LINK
|
| 18 |
|
|
REL="HOME"
|
| 19 |
|
|
TITLE="The eCos Component Writer's Guide"
|
| 20 |
|
|
HREF="cdl-guide.html"><LINK
|
| 21 |
|
|
REL="PREVIOUS"
|
| 22 |
|
|
TITLE="The eCos Component Writer's Guide"
|
| 23 |
|
|
HREF="cdl-guide.html"><LINK
|
| 24 |
|
|
REL="NEXT"
|
| 25 |
|
|
TITLE="Why Configurability?"
|
| 26 |
|
|
HREF="overview.configurability.html"></HEAD
|
| 27 |
|
|
><BODY
|
| 28 |
|
|
CLASS="CHAPTER"
|
| 29 |
|
|
BGCOLOR="#FFFFFF"
|
| 30 |
|
|
TEXT="#000000"
|
| 31 |
|
|
LINK="#0000FF"
|
| 32 |
|
|
VLINK="#840084"
|
| 33 |
|
|
ALINK="#0000FF"
|
| 34 |
|
|
><DIV
|
| 35 |
|
|
CLASS="NAVHEADER"
|
| 36 |
|
|
><TABLE
|
| 37 |
|
|
SUMMARY="Header navigation table"
|
| 38 |
|
|
WIDTH="100%"
|
| 39 |
|
|
BORDER="0"
|
| 40 |
|
|
CELLPADDING="0"
|
| 41 |
|
|
CELLSPACING="0"
|
| 42 |
|
|
><TR
|
| 43 |
|
|
><TH
|
| 44 |
|
|
COLSPAN="3"
|
| 45 |
|
|
ALIGN="center"
|
| 46 |
|
|
>The <SPAN
|
| 47 |
|
|
CLASS="APPLICATION"
|
| 48 |
|
|
>eCos</SPAN
|
| 49 |
|
|
> Component Writer's Guide</TH
|
| 50 |
|
|
></TR
|
| 51 |
|
|
><TR
|
| 52 |
|
|
><TD
|
| 53 |
|
|
WIDTH="10%"
|
| 54 |
|
|
ALIGN="left"
|
| 55 |
|
|
VALIGN="bottom"
|
| 56 |
|
|
><A
|
| 57 |
|
|
HREF="cdl-guide.html"
|
| 58 |
|
|
ACCESSKEY="P"
|
| 59 |
|
|
>Prev</A
|
| 60 |
|
|
></TD
|
| 61 |
|
|
><TD
|
| 62 |
|
|
WIDTH="80%"
|
| 63 |
|
|
ALIGN="center"
|
| 64 |
|
|
VALIGN="bottom"
|
| 65 |
|
|
></TD
|
| 66 |
|
|
><TD
|
| 67 |
|
|
WIDTH="10%"
|
| 68 |
|
|
ALIGN="right"
|
| 69 |
|
|
VALIGN="bottom"
|
| 70 |
|
|
><A
|
| 71 |
|
|
HREF="overview.configurability.html"
|
| 72 |
|
|
ACCESSKEY="N"
|
| 73 |
|
|
>Next</A
|
| 74 |
|
|
></TD
|
| 75 |
|
|
></TR
|
| 76 |
|
|
></TABLE
|
| 77 |
|
|
><HR
|
| 78 |
|
|
ALIGN="LEFT"
|
| 79 |
|
|
WIDTH="100%"></DIV
|
| 80 |
|
|
><DIV
|
| 81 |
|
|
CLASS="CHAPTER"
|
| 82 |
|
|
><H1
|
| 83 |
|
|
><A
|
| 84 |
|
|
NAME="OVERVIEW">Chapter 1. Overview</H1
|
| 85 |
|
|
><DIV
|
| 86 |
|
|
CLASS="TOC"
|
| 87 |
|
|
><DL
|
| 88 |
|
|
><DT
|
| 89 |
|
|
><B
|
| 90 |
|
|
>Table of Contents</B
|
| 91 |
|
|
></DT
|
| 92 |
|
|
><DT
|
| 93 |
|
|
><A
|
| 94 |
|
|
HREF="overview.html#OVERVIEW.TERMINOLOGY"
|
| 95 |
|
|
>Terminology</A
|
| 96 |
|
|
></DT
|
| 97 |
|
|
><DT
|
| 98 |
|
|
><A
|
| 99 |
|
|
HREF="overview.configurability.html"
|
| 100 |
|
|
>Why Configurability?</A
|
| 101 |
|
|
></DT
|
| 102 |
|
|
><DT
|
| 103 |
|
|
><A
|
| 104 |
|
|
HREF="overview.approaches.html"
|
| 105 |
|
|
>Approaches to Configurability</A
|
| 106 |
|
|
></DT
|
| 107 |
|
|
><DT
|
| 108 |
|
|
><A
|
| 109 |
|
|
HREF="overview.degress.html"
|
| 110 |
|
|
>Degrees of Configurability</A
|
| 111 |
|
|
></DT
|
| 112 |
|
|
><DT
|
| 113 |
|
|
><A
|
| 114 |
|
|
HREF="overview.warning.html"
|
| 115 |
|
|
>Warnings</A
|
| 116 |
|
|
></DT
|
| 117 |
|
|
></DL
|
| 118 |
|
|
></DIV
|
| 119 |
|
|
><P
|
| 120 |
|
|
><SPAN
|
| 121 |
|
|
CLASS="APPLICATION"
|
| 122 |
|
|
>eCos</SPAN
|
| 123 |
|
|
> was designed from the very beginning as a configurable
|
| 124 |
|
|
component architecture. The core <SPAN
|
| 125 |
|
|
CLASS="APPLICATION"
|
| 126 |
|
|
>eCos</SPAN
|
| 127 |
|
|
> system consists of a number of
|
| 128 |
|
|
different components such as the kernel, the C library, an
|
| 129 |
|
|
infrastructure package. Each of these provides a large number of
|
| 130 |
|
|
configuration options, allowing application developers to build a
|
| 131 |
|
|
system that matches the requirements of their particular application.
|
| 132 |
|
|
To manage the potential complexity of multiple components and lots of
|
| 133 |
|
|
configuration options, <SPAN
|
| 134 |
|
|
CLASS="APPLICATION"
|
| 135 |
|
|
>eCos</SPAN
|
| 136 |
|
|
> comes with a component framework: a
|
| 137 |
|
|
collection of tools specifically designed to support configuring
|
| 138 |
|
|
multiple components. Furthermore this component framework is
|
| 139 |
|
|
extensible, allowing additional components to be added to the system
|
| 140 |
|
|
at any time.</P
|
| 141 |
|
|
><DIV
|
| 142 |
|
|
CLASS="SECT1"
|
| 143 |
|
|
><H1
|
| 144 |
|
|
CLASS="SECT1"
|
| 145 |
|
|
><A
|
| 146 |
|
|
NAME="OVERVIEW.TERMINOLOGY">Terminology</H1
|
| 147 |
|
|
><P
|
| 148 |
|
|
>The <SPAN
|
| 149 |
|
|
CLASS="APPLICATION"
|
| 150 |
|
|
>eCos</SPAN
|
| 151 |
|
|
> component architecture involves a number of key concepts.</P
|
| 152 |
|
|
><DIV
|
| 153 |
|
|
CLASS="SECT2"
|
| 154 |
|
|
><H2
|
| 155 |
|
|
CLASS="SECT2"
|
| 156 |
|
|
><A
|
| 157 |
|
|
NAME="CONCEPTS.TERMINOLOGY.FRAMEWORK">Component Framework</H2
|
| 158 |
|
|
><P
|
| 159 |
|
|
>The phrase <SPAN
|
| 160 |
|
|
CLASS="phrase"
|
| 161 |
|
|
><SPAN
|
| 162 |
|
|
CLASS="PHRASE"
|
| 163 |
|
|
>component framework</SPAN
|
| 164 |
|
|
></SPAN
|
| 165 |
|
|
> is used to describe
|
| 166 |
|
|
the collection of tools that allow users to configure a system and
|
| 167 |
|
|
administer a component repository. This includes the <SPAN
|
| 168 |
|
|
CLASS="APPLICATION"
|
| 169 |
|
|
>ecosconfig</SPAN
|
| 170 |
|
|
> command line tool, the
|
| 171 |
|
|
graphical configuration tool, and the package administration tool.
|
| 172 |
|
|
Both the command line and graphical tools are based on a single
|
| 173 |
|
|
underlying library, the <SPAN
|
| 174 |
|
|
CLASS="APPLICATION"
|
| 175 |
|
|
>CDL</SPAN
|
| 176 |
|
|
> library.</P
|
| 177 |
|
|
></DIV
|
| 178 |
|
|
><DIV
|
| 179 |
|
|
CLASS="SECT2"
|
| 180 |
|
|
><H2
|
| 181 |
|
|
CLASS="SECT2"
|
| 182 |
|
|
><A
|
| 183 |
|
|
NAME="CONCEPTS.TERMINOLOGY.OPTION">Configuration Option</H2
|
| 184 |
|
|
><P
|
| 185 |
|
|
>The option is the basic unit of configurability. Typically each option
|
| 186 |
|
|
corresponds to a single choice that a user can make. For example there
|
| 187 |
|
|
is an option to control whether or not assertions are enabled, and the
|
| 188 |
|
|
kernel provides an option corresponding to the number of scheduling
|
| 189 |
|
|
priority levels in the system. Options can control very small amounts
|
| 190 |
|
|
of code such as whether or not the C library's
|
| 191 |
|
|
<TT
|
| 192 |
|
|
CLASS="FUNCTION"
|
| 193 |
|
|
>strtok</TT
|
| 194 |
|
|
> gets inlined. They can also control quite
|
| 195 |
|
|
large amounts of code, for example whether or not the
|
| 196 |
|
|
<TT
|
| 197 |
|
|
CLASS="FUNCTION"
|
| 198 |
|
|
>printf</TT
|
| 199 |
|
|
> supports floating point conversions.</P
|
| 200 |
|
|
><P
|
| 201 |
|
|
>Many options are straightforward, and the user only gets to choose
|
| 202 |
|
|
whether the option is enabled or disabled. Some options are more
|
| 203 |
|
|
complicated, for example the number of scheduling priority levels is a
|
| 204 |
|
|
number that should be within a certain range. Options should always
|
| 205 |
|
|
start off with a sensible default setting, so that it is not necessary
|
| 206 |
|
|
for users to make hundreds of decisions before any work can start on
|
| 207 |
|
|
developing the application. Once the application is running the
|
| 208 |
|
|
various configuration options can be used to tune the system for the
|
| 209 |
|
|
specific needs of the application.</P
|
| 210 |
|
|
><P
|
| 211 |
|
|
>The component framework allows for options that are not directly
|
| 212 |
|
|
user-modifiable. Consider the case of processor endianness: some
|
| 213 |
|
|
processors are always big-endian or always little-endian, while with
|
| 214 |
|
|
other processors there is a choice. Depending on the user's choice of
|
| 215 |
|
|
target hardware, endianness may or may not be user-modifiable.</P
|
| 216 |
|
|
></DIV
|
| 217 |
|
|
><DIV
|
| 218 |
|
|
CLASS="SECT2"
|
| 219 |
|
|
><H2
|
| 220 |
|
|
CLASS="SECT2"
|
| 221 |
|
|
><A
|
| 222 |
|
|
NAME="CONCEPTS.TERMINOLOGY.COMPONENT">Component</H2
|
| 223 |
|
|
><P
|
| 224 |
|
|
>A component is a unit of functionality such as a particular kernel
|
| 225 |
|
|
scheduler or a device driver for a specific device. A component is
|
| 226 |
|
|
also a configuration option in that users may want to enable
|
| 227 |
|
|
or disable all the functionality in a component. For example, if a
|
| 228 |
|
|
particular device on the target hardware is not going to be used by
|
| 229 |
|
|
the application, directly or indirectly, then there is no point in
|
| 230 |
|
|
having a device driver for it. Furthermore disabling the device driver
|
| 231 |
|
|
should reduce the memory requirements for both code and data.</P
|
| 232 |
|
|
><P
|
| 233 |
|
|
>Components may contain further configuration options. In the case of a
|
| 234 |
|
|
device driver, there may be options to control the exact behavior of
|
| 235 |
|
|
that driver. These will of course be irrelevant if the driver as a
|
| 236 |
|
|
whole is disabled. More generally options and components live in a
|
| 237 |
|
|
hierarchy, where any component can contain options specific to that
|
| 238 |
|
|
component and further sub-components. It is possible to view the
|
| 239 |
|
|
entire <SPAN
|
| 240 |
|
|
CLASS="APPLICATION"
|
| 241 |
|
|
>eCos</SPAN
|
| 242 |
|
|
> kernel as one big component, containing sub-components
|
| 243 |
|
|
for scheduling, exception handling, synchronization primitives, and so
|
| 244 |
|
|
on. The synchronization primitives component can contain further
|
| 245 |
|
|
sub-components for mutexes, semaphores, condition variables, event
|
| 246 |
|
|
flags, and so on. The mutex component can contain configuration
|
| 247 |
|
|
options for issues like priority inversion support.</P
|
| 248 |
|
|
></DIV
|
| 249 |
|
|
><DIV
|
| 250 |
|
|
CLASS="SECT2"
|
| 251 |
|
|
><H2
|
| 252 |
|
|
CLASS="SECT2"
|
| 253 |
|
|
><A
|
| 254 |
|
|
NAME="CONCEPTS.TERMINOLOGY.PACKAGE">Package</H2
|
| 255 |
|
|
><P
|
| 256 |
|
|
>A package is a special type of component. Specifically, a package is
|
| 257 |
|
|
the unit of distribution of components. It is possible to create a
|
| 258 |
|
|
distribution file for a package containing all of the source code,
|
| 259 |
|
|
header files, documentation, and other relevant files. This
|
| 260 |
|
|
distribution file can then be installed using the appropriate tool.
|
| 261 |
|
|
Afterwards it is possible to uninstall that package, or to install a
|
| 262 |
|
|
later version. The core <SPAN
|
| 263 |
|
|
CLASS="APPLICATION"
|
| 264 |
|
|
>eCos</SPAN
|
| 265 |
|
|
> distribution comes with a number of
|
| 266 |
|
|
packages such as the kernel and the infrastructure. Other packages
|
| 267 |
|
|
such as network stacks can come from various different sources and can
|
| 268 |
|
|
be installed alongside the core distribution.</P
|
| 269 |
|
|
><P
|
| 270 |
|
|
>Packages can be enabled or disabled, but the user experience is a
|
| 271 |
|
|
little bit different. Generally it makes no sense for the tools to
|
| 272 |
|
|
load the details of every single package that has been installed. For
|
| 273 |
|
|
example, if the target hardware uses an ARM processor then there is no
|
| 274 |
|
|
point in loading the HAL packages for other architectures and
|
| 275 |
|
|
displaying choices to the user which are not relevant. Therefore
|
| 276 |
|
|
enabling a package means loading its configuration data into the
|
| 277 |
|
|
appropriate tool, and disabling a package is an unload operation. In
|
| 278 |
|
|
addition, packages are not just enabled or disabled: it is also
|
| 279 |
|
|
possible to select the particular version of a package that should be
|
| 280 |
|
|
used.</P
|
| 281 |
|
|
></DIV
|
| 282 |
|
|
><DIV
|
| 283 |
|
|
CLASS="SECT2"
|
| 284 |
|
|
><H2
|
| 285 |
|
|
CLASS="SECT2"
|
| 286 |
|
|
><A
|
| 287 |
|
|
NAME="CONCEPTS.TERMINOLOGY.CONFIGURATION">Configuration</H2
|
| 288 |
|
|
><P
|
| 289 |
|
|
>A configuration is a collection of user choices. The various
|
| 290 |
|
|
tools that make up the component framework deal with entire
|
| 291 |
|
|
configurations. Users can create a new configuration, output a
|
| 292 |
|
|
savefile (by default <TT
|
| 293 |
|
|
CLASS="FILENAME"
|
| 294 |
|
|
>ecos.ecc</TT
|
| 295 |
|
|
>), manipulate a
|
| 296 |
|
|
configuration, and use a configuration to generate a build tree prior
|
| 297 |
|
|
to building <SPAN
|
| 298 |
|
|
CLASS="APPLICATION"
|
| 299 |
|
|
>eCos</SPAN
|
| 300 |
|
|
> and any other packages that have been selected.
|
| 301 |
|
|
A configuration includes details such as which packages have been
|
| 302 |
|
|
selected, in addition to finer-grained information such as which
|
| 303 |
|
|
options in those packages have been enabled or disabled by the user. </P
|
| 304 |
|
|
></DIV
|
| 305 |
|
|
><DIV
|
| 306 |
|
|
CLASS="SECT2"
|
| 307 |
|
|
><H2
|
| 308 |
|
|
CLASS="SECT2"
|
| 309 |
|
|
><A
|
| 310 |
|
|
NAME="CONCEPTS.TERMINOLOGY.TARGET">Target</H2
|
| 311 |
|
|
><P
|
| 312 |
|
|
>The target is the specific piece of hardware on which the application
|
| 313 |
|
|
is expected to run. This may be an off-the-shelf evaluation board, a
|
| 314 |
|
|
piece of custom hardware intended for a specific application, or it
|
| 315 |
|
|
could be something like a simulator. One of the steps when creating a
|
| 316 |
|
|
new configuration is need to specify the target. The component
|
| 317 |
|
|
framework will map this on to a set of packages that are used to
|
| 318 |
|
|
populate the configuration, typically HAL and device driver packages,
|
| 319 |
|
|
and in addition it may cause certain options to be changed from their
|
| 320 |
|
|
default settings to something more appropriate for the
|
| 321 |
|
|
specified target.</P
|
| 322 |
|
|
></DIV
|
| 323 |
|
|
><DIV
|
| 324 |
|
|
CLASS="SECT2"
|
| 325 |
|
|
><H2
|
| 326 |
|
|
CLASS="SECT2"
|
| 327 |
|
|
><A
|
| 328 |
|
|
NAME="CONCEPTS.TERMINOLOGY.TEMPLATE">Template</H2
|
| 329 |
|
|
><P
|
| 330 |
|
|
>A template is a partial configuration, aimed at providing users with
|
| 331 |
|
|
an appropriate starting point. <SPAN
|
| 332 |
|
|
CLASS="APPLICATION"
|
| 333 |
|
|
>eCos</SPAN
|
| 334 |
|
|
> is shipped with a small number
|
| 335 |
|
|
of templates, which correspond closely to common ways of using the
|
| 336 |
|
|
system. There is a minimal template which provides very little
|
| 337 |
|
|
functionality, just enough to bootstrap the hardware and then jump
|
| 338 |
|
|
directly to application code. The default template adds additional
|
| 339 |
|
|
functionality, for example it causes the kernel and C library packages
|
| 340 |
|
|
to be loaded as well. The uitron template adds further functionality
|
| 341 |
|
|
in the form of a µITRON compatibility layer. Creating a new
|
| 342 |
|
|
configuration typically involves specifying a template as well as a
|
| 343 |
|
|
target, resulting in a configuration that can be built and linked with
|
| 344 |
|
|
the application code and that will run on the actual hardware. It is
|
| 345 |
|
|
then possible to fine-tune configuration options to produce something
|
| 346 |
|
|
that better matches the specific requirements of the application.</P
|
| 347 |
|
|
></DIV
|
| 348 |
|
|
><DIV
|
| 349 |
|
|
CLASS="SECT2"
|
| 350 |
|
|
><H2
|
| 351 |
|
|
CLASS="SECT2"
|
| 352 |
|
|
><A
|
| 353 |
|
|
NAME="CONCEPTS.TERMINOLOGY.PROPERTIES">Properties</H2
|
| 354 |
|
|
><P
|
| 355 |
|
|
>The component framework needs a certain amount of information about
|
| 356 |
|
|
each option. For example it needs to know what the legal values are,
|
| 357 |
|
|
what the default should be, where to find the on-line documentation if
|
| 358 |
|
|
the user needs to consult that in order to make a decision, and so on.
|
| 359 |
|
|
These are all properties of the option. Every option (including
|
| 360 |
|
|
components and packages) consists of a name and a set of properties.</P
|
| 361 |
|
|
></DIV
|
| 362 |
|
|
><DIV
|
| 363 |
|
|
CLASS="SECT2"
|
| 364 |
|
|
><H2
|
| 365 |
|
|
CLASS="SECT2"
|
| 366 |
|
|
><A
|
| 367 |
|
|
NAME="CONCEPTS.TERMINOLOGY.CONSEQUENCES">Consequences</H2
|
| 368 |
|
|
><P
|
| 369 |
|
|
>Choices must have consequences. For an <SPAN
|
| 370 |
|
|
CLASS="APPLICATION"
|
| 371 |
|
|
>eCos</SPAN
|
| 372 |
|
|
> configuration the main
|
| 373 |
|
|
end product is a library that can be linked with application code, so
|
| 374 |
|
|
the consequences of a user choice must affect the build process. This
|
| 375 |
|
|
happens in two main ways. First, options can affect which files get
|
| 376 |
|
|
built and end up in the library. Second, details of the current option
|
| 377 |
|
|
settings get written into various configuration header files using C
|
| 378 |
|
|
preprocessor <TT
|
| 379 |
|
|
CLASS="LITERAL"
|
| 380 |
|
|
>#define</TT
|
| 381 |
|
|
> directives, and package source
|
| 382 |
|
|
code can <TT
|
| 383 |
|
|
CLASS="LITERAL"
|
| 384 |
|
|
>#include</TT
|
| 385 |
|
|
> these configuration headers and
|
| 386 |
|
|
adapt accordingly. This allows options to affect a package at a very
|
| 387 |
|
|
fine grain, at the level of individual lines in a source file if
|
| 388 |
|
|
desired. There may be other consequences as well, for example there
|
| 389 |
|
|
are options to control the compiler flags that get used during the
|
| 390 |
|
|
build process.</P
|
| 391 |
|
|
></DIV
|
| 392 |
|
|
><DIV
|
| 393 |
|
|
CLASS="SECT2"
|
| 394 |
|
|
><H2
|
| 395 |
|
|
CLASS="SECT2"
|
| 396 |
|
|
><A
|
| 397 |
|
|
NAME="CONCEPTS.TERMINOLOGY.CONSTRAINTS">Constraints</H2
|
| 398 |
|
|
><P
|
| 399 |
|
|
>Configuration choices are not independent. The C library can provide
|
| 400 |
|
|
thread-safe implementations of functions like
|
| 401 |
|
|
<TT
|
| 402 |
|
|
CLASS="FUNCTION"
|
| 403 |
|
|
>rand</TT
|
| 404 |
|
|
>, but only if the kernel provides support for
|
| 405 |
|
|
per-thread data. This is a constraint: the C library option has a
|
| 406 |
|
|
requirement on the kernel. A typical configuration involves a
|
| 407 |
|
|
considerable number of constraints, of varying complexity: many
|
| 408 |
|
|
constraints are straightforward, option <TT
|
| 409 |
|
|
CLASS="LITERAL"
|
| 410 |
|
|
>A</TT
|
| 411 |
|
|
> requires
|
| 412 |
|
|
option <TT
|
| 413 |
|
|
CLASS="LITERAL"
|
| 414 |
|
|
>B</TT
|
| 415 |
|
|
>, or option <TT
|
| 416 |
|
|
CLASS="LITERAL"
|
| 417 |
|
|
>C</TT
|
| 418 |
|
|
> precludes
|
| 419 |
|
|
option <TT
|
| 420 |
|
|
CLASS="LITERAL"
|
| 421 |
|
|
>D</TT
|
| 422 |
|
|
>. Other constraints can be more
|
| 423 |
|
|
complicated, for example option <TT
|
| 424 |
|
|
CLASS="LITERAL"
|
| 425 |
|
|
>E</TT
|
| 426 |
|
|
> may require the
|
| 427 |
|
|
presence of a kernel scheduler but does not care whether it is the
|
| 428 |
|
|
bitmap scheduler, the mlqueue scheduler, or something else.</P
|
| 429 |
|
|
><P
|
| 430 |
|
|
>Another type of constraint involves the values that can be used for
|
| 431 |
|
|
certain options. For example there is a kernel option related to the
|
| 432 |
|
|
number of scheduling levels, and there is a legal values constraint on
|
| 433 |
|
|
this option: specifying zero or a negative number for the number of
|
| 434 |
|
|
scheduling levels makes no sense.</P
|
| 435 |
|
|
></DIV
|
| 436 |
|
|
><DIV
|
| 437 |
|
|
CLASS="SECT2"
|
| 438 |
|
|
><H2
|
| 439 |
|
|
CLASS="SECT2"
|
| 440 |
|
|
><A
|
| 441 |
|
|
NAME="CONCEPTS.TERMINOLOGY.CONFLICTS">Conflicts</H2
|
| 442 |
|
|
><P
|
| 443 |
|
|
>As the user manipulates options it is possible to end up with an
|
| 444 |
|
|
invalid configuration, where one or more constraints are not
|
| 445 |
|
|
satisfied. For example if kernel per-thread data is disabled but the C
|
| 446 |
|
|
library's thread-safety options are left enabled then there are
|
| 447 |
|
|
unsatisfied constraints, also known as conflicts. Such conflicts will
|
| 448 |
|
|
be reported by the configuration tools. The presence of conflicts does
|
| 449 |
|
|
not prevent users from attempting to build <SPAN
|
| 450 |
|
|
CLASS="APPLICATION"
|
| 451 |
|
|
>eCos</SPAN
|
| 452 |
|
|
>, but the
|
| 453 |
|
|
consequences are undefined: there may be compile-time failures, there
|
| 454 |
|
|
may be link-time failures, the application may completely fail to run,
|
| 455 |
|
|
or the application may run most of the time but once in a while there
|
| 456 |
|
|
will be a strange failure… Typically users will want to resolve
|
| 457 |
|
|
all conflicts before continuing.</P
|
| 458 |
|
|
><P
|
| 459 |
|
|
>To make things easier for the user, the configuration tools contain an
|
| 460 |
|
|
inference engine. This can examine a conflict in a particular
|
| 461 |
|
|
configuration and try to figure out some way of resolving the
|
| 462 |
|
|
conflict. Depending on the particular tool being used, the inference
|
| 463 |
|
|
engine may get invoked automatically at certain times or the user may
|
| 464 |
|
|
need to invoke it explicitly. Also depending on the tool, the
|
| 465 |
|
|
inference engine may apply any solutions it finds automatically or it
|
| 466 |
|
|
may request user confirmation.</P
|
| 467 |
|
|
></DIV
|
| 468 |
|
|
><DIV
|
| 469 |
|
|
CLASS="SECT2"
|
| 470 |
|
|
><H2
|
| 471 |
|
|
CLASS="SECT2"
|
| 472 |
|
|
><A
|
| 473 |
|
|
NAME="CONCEPTS.TERMINOLOGY.CDL">CDL</H2
|
| 474 |
|
|
><P
|
| 475 |
|
|
>The configuration tools require information about the various options
|
| 476 |
|
|
provided by each package, their consequences and constraints, and
|
| 477 |
|
|
other properties such as the location of on-line documentation. This
|
| 478 |
|
|
information has to be provided in the form of <SPAN
|
| 479 |
|
|
CLASS="APPLICATION"
|
| 480 |
|
|
>CDL</SPAN
|
| 481 |
|
|
> scripts. CDL
|
| 482 |
|
|
is short for Component Definition Language, and is specifically
|
| 483 |
|
|
designed as a way of describing configuration options.</P
|
| 484 |
|
|
><P
|
| 485 |
|
|
>A typical package contains the following:</P
|
| 486 |
|
|
><P
|
| 487 |
|
|
></P
|
| 488 |
|
|
><OL
|
| 489 |
|
|
TYPE="1"
|
| 490 |
|
|
><LI
|
| 491 |
|
|
><P
|
| 492 |
|
|
>Some number of source files which will end up in a library. The
|
| 493 |
|
|
application code will be linked with this library to produce an
|
| 494 |
|
|
executable. Some source files may serve other purposes, for example to
|
| 495 |
|
|
provide a linker script.</P
|
| 496 |
|
|
></LI
|
| 497 |
|
|
><LI
|
| 498 |
|
|
><P
|
| 499 |
|
|
>Exported header files which define the interface provided by the
|
| 500 |
|
|
package. </P
|
| 501 |
|
|
></LI
|
| 502 |
|
|
><LI
|
| 503 |
|
|
><P
|
| 504 |
|
|
>On-line documentation, for example reference pages for each exported
|
| 505 |
|
|
function. </P
|
| 506 |
|
|
></LI
|
| 507 |
|
|
><LI
|
| 508 |
|
|
><P
|
| 509 |
|
|
>Some number of test cases, shipped in source format, allowing users to
|
| 510 |
|
|
check that the package is working as expected on their particular
|
| 511 |
|
|
hardware and in their specific configuration.</P
|
| 512 |
|
|
></LI
|
| 513 |
|
|
><LI
|
| 514 |
|
|
><P
|
| 515 |
|
|
>One or more <SPAN
|
| 516 |
|
|
CLASS="APPLICATION"
|
| 517 |
|
|
>CDL</SPAN
|
| 518 |
|
|
> scripts describing the package to the configuration
|
| 519 |
|
|
system.</P
|
| 520 |
|
|
></LI
|
| 521 |
|
|
></OL
|
| 522 |
|
|
><P
|
| 523 |
|
|
>Not all packages need to contain all of these. For example some
|
| 524 |
|
|
packages such as device drivers may not provide a new interface,
|
| 525 |
|
|
instead they just provide another implementation of an existing
|
| 526 |
|
|
interface. However all packages must contain a <SPAN
|
| 527 |
|
|
CLASS="APPLICATION"
|
| 528 |
|
|
>CDL</SPAN
|
| 529 |
|
|
> script that
|
| 530 |
|
|
describes the package to the configuration tools.</P
|
| 531 |
|
|
></DIV
|
| 532 |
|
|
><DIV
|
| 533 |
|
|
CLASS="SECT2"
|
| 534 |
|
|
><H2
|
| 535 |
|
|
CLASS="SECT2"
|
| 536 |
|
|
><A
|
| 537 |
|
|
NAME="CONCEPTS.TERMINOLOGY.REPO">Component Repository</H2
|
| 538 |
|
|
><P
|
| 539 |
|
|
>All <SPAN
|
| 540 |
|
|
CLASS="APPLICATION"
|
| 541 |
|
|
>eCos</SPAN
|
| 542 |
|
|
> installations include a component repository. This is a
|
| 543 |
|
|
directory structure where all the packages get installed. The
|
| 544 |
|
|
component framework comes with an administration tool that allows new
|
| 545 |
|
|
packages or new versions of a package to be installed, old packages to
|
| 546 |
|
|
be removed, and so on. The component repository includes a simple
|
| 547 |
|
|
database, maintained by the administration tool, which contains
|
| 548 |
|
|
details of the various packages.</P
|
| 549 |
|
|
><P
|
| 550 |
|
|
>Generally application developers do not need to modify anything inside
|
| 551 |
|
|
the component repository, except by means of the administration tool.
|
| 552 |
|
|
Instead their work involves separate build and install trees. This
|
| 553 |
|
|
allows the component repository to be treated as a read-only resource
|
| 554 |
|
|
that can be shared by multiple projects and multiple users. Component
|
| 555 |
|
|
writers modifying one of the packages do need to manipulate files in
|
| 556 |
|
|
the component repository.</P
|
| 557 |
|
|
></DIV
|
| 558 |
|
|
></DIV
|
| 559 |
|
|
></DIV
|
| 560 |
|
|
><DIV
|
| 561 |
|
|
CLASS="NAVFOOTER"
|
| 562 |
|
|
><HR
|
| 563 |
|
|
ALIGN="LEFT"
|
| 564 |
|
|
WIDTH="100%"><TABLE
|
| 565 |
|
|
SUMMARY="Footer navigation table"
|
| 566 |
|
|
WIDTH="100%"
|
| 567 |
|
|
BORDER="0"
|
| 568 |
|
|
CELLPADDING="0"
|
| 569 |
|
|
CELLSPACING="0"
|
| 570 |
|
|
><TR
|
| 571 |
|
|
><TD
|
| 572 |
|
|
WIDTH="33%"
|
| 573 |
|
|
ALIGN="left"
|
| 574 |
|
|
VALIGN="top"
|
| 575 |
|
|
><A
|
| 576 |
|
|
HREF="cdl-guide.html"
|
| 577 |
|
|
ACCESSKEY="P"
|
| 578 |
|
|
>Prev</A
|
| 579 |
|
|
></TD
|
| 580 |
|
|
><TD
|
| 581 |
|
|
WIDTH="34%"
|
| 582 |
|
|
ALIGN="center"
|
| 583 |
|
|
VALIGN="top"
|
| 584 |
|
|
><A
|
| 585 |
|
|
HREF="cdl-guide.html"
|
| 586 |
|
|
ACCESSKEY="H"
|
| 587 |
|
|
>Home</A
|
| 588 |
|
|
></TD
|
| 589 |
|
|
><TD
|
| 590 |
|
|
WIDTH="33%"
|
| 591 |
|
|
ALIGN="right"
|
| 592 |
|
|
VALIGN="top"
|
| 593 |
|
|
><A
|
| 594 |
|
|
HREF="overview.configurability.html"
|
| 595 |
|
|
ACCESSKEY="N"
|
| 596 |
|
|
>Next</A
|
| 597 |
|
|
></TD
|
| 598 |
|
|
></TR
|
| 599 |
|
|
><TR
|
| 600 |
|
|
><TD
|
| 601 |
|
|
WIDTH="33%"
|
| 602 |
|
|
ALIGN="left"
|
| 603 |
|
|
VALIGN="top"
|
| 604 |
|
|
>The <SPAN
|
| 605 |
|
|
CLASS="APPLICATION"
|
| 606 |
|
|
>eCos</SPAN
|
| 607 |
|
|
> Component Writer's Guide</TD
|
| 608 |
|
|
><TD
|
| 609 |
|
|
WIDTH="34%"
|
| 610 |
|
|
ALIGN="center"
|
| 611 |
|
|
VALIGN="top"
|
| 612 |
|
|
> </TD
|
| 613 |
|
|
><TD
|
| 614 |
|
|
WIDTH="33%"
|
| 615 |
|
|
ALIGN="right"
|
| 616 |
|
|
VALIGN="top"
|
| 617 |
|
|
>Why Configurability?</TD
|
| 618 |
|
|
></TR
|
| 619 |
|
|
></TABLE
|
| 620 |
|
|
></DIV
|
| 621 |
|
|
></BODY
|
| 622 |
|
|
></HTML
|
| 623 |
|
|
>
|
