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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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<!-- and conditions set forth in the Open Publication License, v1.0  -->
<!-- or later (the latest version is presently available at          -->
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<!-- Distribution of the work or derivative of the work in any       -->
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<HTML
><HEAD
><TITLE
>CDL Commands</TITLE
><meta name="MSSmartTagsPreventParsing" content="TRUE">
<META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
"><LINK
REL="HOME"
TITLE="The eCos Component Writer's Guide"
HREF="cdl-guide.html"><LINK
REL="UP"
TITLE="The CDL Language"
HREF="language.html"><LINK
REL="PREVIOUS"
TITLE="The CDL Language"
HREF="language.html"><LINK
REL="NEXT"
TITLE="CDL Properties"
HREF="language.properties.html"></HEAD
><BODY
CLASS="SECT1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
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><TR
><TH
COLSPAN="3"
ALIGN="center"
>The <SPAN
CLASS="APPLICATION"
>eCos</SPAN
> Component Writer's Guide</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="language.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 3. The CDL Language</TD
><TD
WIDTH="10%"
ALIGN="right"
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><A
HREF="language.properties.html"
ACCESSKEY="N"
>Next</A
></TD
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></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LANGUAGE.COMMANDS">CDL Commands</H1
><P
>There are four <SPAN
CLASS="APPLICATION"
>CDL</SPAN
>-related commands which can occur at the top-level
of a <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> script: <TT
CLASS="LITERAL"
>cdl_package</TT
>, <TT
CLASS="LITERAL"
>cdl_component</TT
>, <TT
CLASS="LITERAL"
>cdl_option</TT
> and
<TT
CLASS="LITERAL"
>cdl_interface</TT
>. These correspond to the basic building blocks of the
language (CDL interfaces are described in <A
HREF="language.interface.html"
>the Section called <I
>Interfaces</I
></A
>). All of these take the same basic form:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cdl_package &lt;name&gt; {
    &#8230;
}
 
cdl_component &lt;name&gt; {
    &#8230;
}
 
cdl_option &lt;name&gt; {
    &#8230;
}
 
cdl_interface &lt;name&gt; {
    &#8230;
}</PRE
></TD
></TR
></TABLE
><P
>The command is followed by a name and by a body of properties, the
latter enclosed in braces. Packages and components can contain other
entities, so the <TT
CLASS="LITERAL"
>cdl_package</TT
> and <TT
CLASS="LITERAL"
>cdl_component</TT
> can also have
nested commands in their bodies. All names must be unique within a
given configuration. If say the C library package and a TCP/IP stack
both defined an option with the same name then it would not be
possible to load both of them into a single configuration. There is a
<A
HREF="language.naming.html"
>naming convention</A
> which should
make accidental name clashes very unlikely.</P
><P
>It is possible for two packages to use the same name if there are no
reasonable circumstances under which both packages could be loaded at
the same time. One example would be architectural HAL packages: a
given <SPAN
CLASS="APPLICATION"
>eCos</SPAN
> configuration can be used on only one processor, so the
architectural HAL packages <TT
CLASS="VARNAME"
>CYGPKG_HAL_ARM</TT
> and
<TT
CLASS="VARNAME"
>CYGPKG_HAL_I386</TT
> can re-use option names; in fact
in some cases they are expected to.</P
><P
>Each package has one top-level <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> script, which is specified in the
packages <A
HREF="language.database.html"
><SPAN
CLASS="DATABASE"
>ecos.db</SPAN
> database
entry</A
>. Typically the name of this top-level script is related to
the package, so the kernel package uses
<TT
CLASS="FILENAME"
>kernel.cdl</TT
>, but this is just a convention. The
first command in the top-level script should be <TT
CLASS="LITERAL"
>cdl_package</TT
>, and the
name used should be the same as in the <SPAN
CLASS="DATABASE"
>ecos.db</SPAN
>
database. There should be only one <TT
CLASS="LITERAL"
>cdl_package</TT
> command per package.</P
><P
>The various <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> entities live in a hierarchy. For example the kernel
package contains a scheduling component, a synchronization primitives
component, and a number of others. The synchronization component
contains various options such as whether or not mutex priority
inheritance is enabled. There is no upper bound on how far components
can be nested, but it is rarely necessary to go more than three or
four levels deeper than the package level. Since the naming convention
incorporates bits of the hierarchy, this has the added advantage of
keeping the names down to a more manageable size.</P
><P
>The hierarchy serves two purposes. It allows options to be controlled
en masse, so disabling a component automatically disables all the
options below it in the hierarchy. It also permits a much simpler
representation of the configuration in the graphical configuration
tool, facilitating navigation and modification.</P
><P
>By default a package is placed at the top-level of the hierarchy, but
it is possible to override this using a <SPAN
CLASS="PROPERTY"
>parent</SPAN
> property. For example
an architectural HAL package such as <TT
CLASS="VARNAME"
>CYGPKG_HAL_SH</TT
>
typically re-parents itself below <TT
CLASS="VARNAME"
>CYGPKG_HAL</TT
>, and a
platform HAL package would then re-parent itself below the
architectural HAL. This makes it a little bit easier for users to
navigate around the hierarchy. Components, options and interfaces can
also be re-parented, but this is less common.</P
><P
>All components, options and interfaces that are defined directly in
the top-level script will be placed below the package in the hierarchy.
Alternatively they can be nested in the body of the <TT
CLASS="LITERAL"
>cdl_package</TT
>
command. The following two script fragments are equivalent:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cdl_package CYGPKG_LIBC {
    &#8230;
}
 
cdl_component CYGPKG_LIBC_STRING {
    &#8230;
}
 
cdl_option CYGPKG_LIBC_CTYPE_INLINES {
    &#8230;
}</PRE
></TD
></TR
></TABLE
><P
>and:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cdl_package CYGPKG_LIBC {
    &#8230;
 
    cdl_component CYGPKG_LIBC_STRING {
        &#8230;
    }
 
    cdl_option CYGPKG_LIBC_CTYPE_INLINES {
        &#8230;
    }
}</PRE
></TD
></TR
></TABLE
><P
>If a script defines options both inside and outside the body of the
<TT
CLASS="LITERAL"
>cdl_package</TT
> then the ones inside will be processed first. Language
purists may argue that it would have been better if all contained
options and components had to go into the body, but in practice it is
often convenient to be able to skip this level of nesting and the
resulting behavior is still well-defined.</P
><P
>Components can also contain options and other <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> entities, in fact
that is what distinguishes them from options. These can be defined in
the body of the <TT
CLASS="LITERAL"
>cdl_component</TT
> command:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cdl_component CYGPKG_LIBC_STDIO {
 
    cdl_component CYGPKG_LIBC_STDIO_FLOATING_POINT {
        &#8230;
    }
 
    cdl_option CYGSEM_LIBC_STDIO_THREAD_SAFE_STREAMS {
        &#8230;
    }
}</PRE
></TD
></TR
></TABLE
><P
>Nesting options inside the bodies of components like this is fine for
simple packages with only a limited number of configuration options,
but it becomes unsatisfactory as the number of options increases.
Instead it is possible to split the <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> data into multiple <SPAN
CLASS="APPLICATION"
>CDL</SPAN
>
scripts, on a per-component basis. The <SPAN
CLASS="PROPERTY"
>script</SPAN
> property should be
used for this. For example, in the case of the C library all
stdio-related configuration options could be put into
<TT
CLASS="FILENAME"
>stdio.cdl</TT
>, and the top-level CDL script
<TT
CLASS="FILENAME"
>libc.cdl</TT
> would contain the following:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cdl_package CYGPKG_LIBC {
    &#8230;
 
    cdl_component CYGPKG_LIBC_STDIO {
        &#8230;
        script stdio.cdl
    }
}</PRE
></TD
></TR
></TABLE
><P
>The <TT
CLASS="VARNAME"
>CYGPKG_LIBC_STDIO_FLOATING_POINT</TT
> component and
the <TT
CLASS="VARNAME"
>CYGSEM_LIBC_STDIO_THREAD_SAFE_STREAMS</TT
> option
can then be placed at the top-level of <TT
CLASS="FILENAME"
>stdio.cdl</TT
>.
It is possible to have some options nested in the body of a
<TT
CLASS="LITERAL"
>cdl_component</TT
> command and other options in a separate file accessed
by the <SPAN
CLASS="PROPERTY"
>script</SPAN
> property. In such a case the nested options would be
processed first, and then the other script would be read in. A script
specified by a <SPAN
CLASS="PROPERTY"
>script</SPAN
> property should only define new options,
components or interfaces: it should not contain any additional
properties for the current component.</P
><P
>It is possible for a component's <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> script to have a sub-component
which also has a <SPAN
CLASS="PROPERTY"
>script</SPAN
> property, and so on. In practice excessive
nesting like this is rarely useful. It is also possible to ignore the
<SPAN
CLASS="APPLICATION"
>CDL</SPAN
> language support for constructing hierarchies automatically and
use the <SPAN
CLASS="PROPERTY"
>parent</SPAN
> property explicitly for every single option and
component. Again this is not generally useful.</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>At the time of writing interfaces cannot act as containers. This may
change in a future version of the component framework. If the change
is made then interfaces would support the <SPAN
CLASS="PROPERTY"
>script</SPAN
> property, just like
components.</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
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><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="language.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="cdl-guide.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="language.properties.html"
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>Next</A
></TD
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><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>The CDL Language</TD
><TD
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[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [cdl-guide/] [language.commands.html] - Blame information for rev 174

Line No.	Rev	Author	Line
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			`>CDL Commands</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="UP"`
22			`TITLE="The CDL Language"`
23			`HREF="language.html"><LINK`
24			`REL="PREVIOUS"`
25			`TITLE="The CDL Language"`
26			`HREF="language.html"><LINK`
27			`REL="NEXT"`
28			`TITLE="CDL Properties"`
29			`HREF="language.properties.html"></HEAD`
30			`><BODY`
31			`CLASS="SECT1"`
32			`BGCOLOR="#FFFFFF"`
33			`TEXT="#000000"`
34			`LINK="#0000FF"`
35			`VLINK="#840084"`
36			`ALINK="#0000FF"`
37			`><DIV`
38			`CLASS="NAVHEADER"`
39			`><TABLE`
40			`SUMMARY="Header navigation table"`
41			`WIDTH="100%"`
42			`BORDER="0"`
43			`CELLPADDING="0"`
44			`CELLSPACING="0"`
45			`><TR`
46			`><TH`
47			`COLSPAN="3"`
48			`ALIGN="center"`
49			`>The <SPAN`
50			`CLASS="APPLICATION"`
51			`>eCos</SPAN`
52			`> Component Writer's Guide</TH`
53			`></TR`
54			`><TR`
55			`><TD`
56			`WIDTH="10%"`
57			`ALIGN="left"`
58			`VALIGN="bottom"`
59			`><A`
60			`HREF="language.html"`
61			`ACCESSKEY="P"`
62			`>Prev</A`
63			`></TD`
64			`><TD`
65			`WIDTH="80%"`
66			`ALIGN="center"`
67			`VALIGN="bottom"`
68			`>Chapter 3. The CDL Language</TD`
69			`><TD`
70			`WIDTH="10%"`
71			`ALIGN="right"`
72			`VALIGN="bottom"`
73			`><A`
74			`HREF="language.properties.html"`
75			`ACCESSKEY="N"`
76			`>Next</A`
77			`></TD`
78			`></TR`
79			`></TABLE`
80			`><HR`
81			`ALIGN="LEFT"`
82			`WIDTH="100%"></DIV`
83			`><DIV`
84			`CLASS="SECT1"`
85			`><H1`
86			`CLASS="SECT1"`
87			`><A`
88			`NAME="LANGUAGE.COMMANDS">CDL Commands</H1`
89			`><P`
90			`>There are four <SPAN`
91			`CLASS="APPLICATION"`
92			`>CDL</SPAN`
93			`>-related commands which can occur at the top-level`
94			`of a <SPAN`
95			`CLASS="APPLICATION"`
96			`>CDL</SPAN`
97			`> script: <TT`
98			`CLASS="LITERAL"`
99			`>cdl_package</TT`
100			`>, <TT`
101			`CLASS="LITERAL"`
102			`>cdl_component</TT`
103			`>, <TT`
104			`CLASS="LITERAL"`
105			`>cdl_option</TT`
106			`> and`
107			`<TT`
108			`CLASS="LITERAL"`
109			`>cdl_interface</TT`
110			`>. These correspond to the basic building blocks of the`
111			`language (CDL interfaces are described in <A`
112			`HREF="language.interface.html"`
113			`>the Section called <I`
114			`>Interfaces</I`
115			`></A`
116			`>). All of these take the same basic form:</P`
117			`><TABLE`
118			`BORDER="5"`
119			`BGCOLOR="#E0E0F0"`
120			`WIDTH="70%"`
121			`><TR`
122			`><TD`
123			`><PRE`
124			`CLASS="PROGRAMLISTING"`
125			`>cdl_package <name> {`
126			`…`
127			`}`
128
129			`cdl_component <name> {`
130			`…`
131			`}`
132
133			`cdl_option <name> {`
134			`…`
135			`}`
136
137			`cdl_interface <name> {`
138			`…`
139			`}</PRE`
140			`></TD`
141			`></TR`
142			`></TABLE`
143			`><P`
144			`>The command is followed by a name and by a body of properties, the`
145			`latter enclosed in braces. Packages and components can contain other`
146			`entities, so the <TT`
147			`CLASS="LITERAL"`
148			`>cdl_package</TT`
149			`> and <TT`
150			`CLASS="LITERAL"`
151			`>cdl_component</TT`
152			`> can also have`
153			`nested commands in their bodies. All names must be unique within a`
154			`given configuration. If say the C library package and a TCP/IP stack`
155			`both defined an option with the same name then it would not be`
156			`possible to load both of them into a single configuration. There is a`
157			`<A`
158			`HREF="language.naming.html"`
159			`>naming convention</A`
160			`> which should`
161			`make accidental name clashes very unlikely.</P`
162			`><P`
163			`>It is possible for two packages to use the same name if there are no`
164			`reasonable circumstances under which both packages could be loaded at`
165			`the same time. One example would be architectural HAL packages: a`
166			`given <SPAN`
167			`CLASS="APPLICATION"`
168			`>eCos</SPAN`
169			`> configuration can be used on only one processor, so the`
170			`architectural HAL packages <TT`
171			`CLASS="VARNAME"`
172			`>CYGPKG_HAL_ARM</TT`
173			`> and`
174			`<TT`
175			`CLASS="VARNAME"`
176			`>CYGPKG_HAL_I386</TT`
177			`> can re-use option names; in fact`
178			`in some cases they are expected to.</P`
179			`><P`
180			`>Each package has one top-level <SPAN`
181			`CLASS="APPLICATION"`
182			`>CDL</SPAN`
183			`> script, which is specified in the`
184			`packages <A`
185			`HREF="language.database.html"`
186			`><SPAN`
187			`CLASS="DATABASE"`
188			`>ecos.db</SPAN`
189			`> database`
190			`entry</A`
191			`>. Typically the name of this top-level script is related to`
192			`the package, so the kernel package uses`
193			`<TT`
194			`CLASS="FILENAME"`
195			`>kernel.cdl</TT`
196			`>, but this is just a convention. The`
197			`first command in the top-level script should be <TT`
198			`CLASS="LITERAL"`
199			`>cdl_package</TT`
200			`>, and the`
201			`name used should be the same as in the <SPAN`
202			`CLASS="DATABASE"`
203			`>ecos.db</SPAN`
204			`>`
205			`database. There should be only one <TT`
206			`CLASS="LITERAL"`
207			`>cdl_package</TT`
208			`> command per package.</P`
209			`><P`
210			`>The various <SPAN`
211			`CLASS="APPLICATION"`
212			`>CDL</SPAN`
213			`> entities live in a hierarchy. For example the kernel`
214			`package contains a scheduling component, a synchronization primitives`
215			`component, and a number of others. The synchronization component`
216			`contains various options such as whether or not mutex priority`
217			`inheritance is enabled. There is no upper bound on how far components`
218			`can be nested, but it is rarely necessary to go more than three or`
219			`four levels deeper than the package level. Since the naming convention`
220			`incorporates bits of the hierarchy, this has the added advantage of`
221			`keeping the names down to a more manageable size.</P`
222			`><P`
223			`>The hierarchy serves two purposes. It allows options to be controlled`
224			`en masse, so disabling a component automatically disables all the`
225			`options below it in the hierarchy. It also permits a much simpler`
226			`representation of the configuration in the graphical configuration`
227			`tool, facilitating navigation and modification.</P`
228			`><P`
229			`>By default a package is placed at the top-level of the hierarchy, but`
230			`it is possible to override this using a <SPAN`
231			`CLASS="PROPERTY"`
232			`>parent</SPAN`
233			`> property. For example`
234			`an architectural HAL package such as <TT`
235			`CLASS="VARNAME"`
236			`>CYGPKG_HAL_SH</TT`
237			`>`
238			`typically re-parents itself below <TT`
239			`CLASS="VARNAME"`
240			`>CYGPKG_HAL</TT`
241			`>, and a`
242			`platform HAL package would then re-parent itself below the`
243			`architectural HAL. This makes it a little bit easier for users to`
244			`navigate around the hierarchy. Components, options and interfaces can`
245			`also be re-parented, but this is less common.</P`
246			`><P`
247			`>All components, options and interfaces that are defined directly in`
248			`the top-level script will be placed below the package in the hierarchy.`
249			`Alternatively they can be nested in the body of the <TT`
250			`CLASS="LITERAL"`
251			`>cdl_package</TT`
252			`>`
253			`command. The following two script fragments are equivalent:</P`
254			`><TABLE`
255			`BORDER="5"`
256			`BGCOLOR="#E0E0F0"`
257			`WIDTH="70%"`
258			`><TR`
259			`><TD`
260			`><PRE`
261			`CLASS="PROGRAMLISTING"`
262			`>cdl_package CYGPKG_LIBC {`
263			`…`
264			`}`
265
266			`cdl_component CYGPKG_LIBC_STRING {`
267			`…`
268			`}`
269
270			`cdl_option CYGPKG_LIBC_CTYPE_INLINES {`
271			`…`
272			`}</PRE`
273			`></TD`
274			`></TR`
275			`></TABLE`
276			`><P`
277			`>and:</P`
278			`><TABLE`
279			`BORDER="5"`
280			`BGCOLOR="#E0E0F0"`
281			`WIDTH="70%"`
282			`><TR`
283			`><TD`
284			`><PRE`
285			`CLASS="PROGRAMLISTING"`
286			`>cdl_package CYGPKG_LIBC {`
287			`…`
288
289			`cdl_component CYGPKG_LIBC_STRING {`
290			`…`
291			`}`
292
293			`cdl_option CYGPKG_LIBC_CTYPE_INLINES {`
294			`…`
295			`}`
296			`}</PRE`
297			`></TD`
298			`></TR`
299			`></TABLE`
300			`><P`
301			`>If a script defines options both inside and outside the body of the`
302			`<TT`
303			`CLASS="LITERAL"`
304			`>cdl_package</TT`
305			`> then the ones inside will be processed first. Language`
306			`purists may argue that it would have been better if all contained`
307			`options and components had to go into the body, but in practice it is`
308			`often convenient to be able to skip this level of nesting and the`
309			`resulting behavior is still well-defined.</P`
310			`><P`
311			`>Components can also contain options and other <SPAN`
312			`CLASS="APPLICATION"`
313			`>CDL</SPAN`
314			`> entities, in fact`
315			`that is what distinguishes them from options. These can be defined in`
316			`the body of the <TT`
317			`CLASS="LITERAL"`
318			`>cdl_component</TT`
319			`> command:</P`
320			`><TABLE`
321			`BORDER="5"`
322			`BGCOLOR="#E0E0F0"`
323			`WIDTH="70%"`
324			`><TR`
325			`><TD`
326			`><PRE`
327			`CLASS="PROGRAMLISTING"`
328			`>cdl_component CYGPKG_LIBC_STDIO {`
329
330			`cdl_component CYGPKG_LIBC_STDIO_FLOATING_POINT {`
331			`…`
332			`}`
333
334			`cdl_option CYGSEM_LIBC_STDIO_THREAD_SAFE_STREAMS {`
335			`…`
336			`}`
337			`}</PRE`
338			`></TD`
339			`></TR`
340			`></TABLE`
341			`><P`
342			`>Nesting options inside the bodies of components like this is fine for`
343			`simple packages with only a limited number of configuration options,`
344			`but it becomes unsatisfactory as the number of options increases.`
345			`Instead it is possible to split the <SPAN`
346			`CLASS="APPLICATION"`
347			`>CDL</SPAN`
348			`> data into multiple <SPAN`
349			`CLASS="APPLICATION"`
350			`>CDL</SPAN`
351			`>`
352			`scripts, on a per-component basis. The <SPAN`
353			`CLASS="PROPERTY"`
354			`>script</SPAN`
355			`> property should be`
356			`used for this. For example, in the case of the C library all`
357			`stdio-related configuration options could be put into`
358			`<TT`
359			`CLASS="FILENAME"`
360			`>stdio.cdl</TT`
361			`>, and the top-level CDL script`
362			`<TT`
363			`CLASS="FILENAME"`
364			`>libc.cdl</TT`
365			`> would contain the following:</P`
366			`><TABLE`
367			`BORDER="5"`
368			`BGCOLOR="#E0E0F0"`
369			`WIDTH="70%"`
370			`><TR`
371			`><TD`
372			`><PRE`
373			`CLASS="PROGRAMLISTING"`
374			`>cdl_package CYGPKG_LIBC {`
375			`…`
376
377			`cdl_component CYGPKG_LIBC_STDIO {`
378			`…`
379			`script stdio.cdl`
380			`}`
381			`}</PRE`
382			`></TD`
383			`></TR`
384			`></TABLE`
385			`><P`
386			`>The <TT`
387			`CLASS="VARNAME"`
388			`>CYGPKG_LIBC_STDIO_FLOATING_POINT</TT`
389			`> component and`
390			`the <TT`
391			`CLASS="VARNAME"`
392			`>CYGSEM_LIBC_STDIO_THREAD_SAFE_STREAMS</TT`
393			`> option`
394			`can then be placed at the top-level of <TT`
395			`CLASS="FILENAME"`
396			`>stdio.cdl</TT`
397			`>.`
398			`It is possible to have some options nested in the body of a`
399			`<TT`
400			`CLASS="LITERAL"`
401			`>cdl_component</TT`
402			`> command and other options in a separate file accessed`
403			`by the <SPAN`
404			`CLASS="PROPERTY"`
405			`>script</SPAN`
406			`> property. In such a case the nested options would be`
407			`processed first, and then the other script would be read in. A script`
408			`specified by a <SPAN`
409			`CLASS="PROPERTY"`
410			`>script</SPAN`
411			`> property should only define new options,`
412			`components or interfaces: it should not contain any additional`
413			`properties for the current component.</P`
414			`><P`
415			`>It is possible for a component's <SPAN`
416			`CLASS="APPLICATION"`
417			`>CDL</SPAN`
418			`> script to have a sub-component`
419			`which also has a <SPAN`
420			`CLASS="PROPERTY"`
421			`>script</SPAN`
422			`> property, and so on. In practice excessive`
423			`nesting like this is rarely useful. It is also possible to ignore the`
424			`<SPAN`
425			`CLASS="APPLICATION"`
426			`>CDL</SPAN`
427			`> language support for constructing hierarchies automatically and`
428			`use the <SPAN`
429			`CLASS="PROPERTY"`
430			`>parent</SPAN`
431			`> property explicitly for every single option and`
432			`component. Again this is not generally useful.</P`
433			`><DIV`
434			`CLASS="NOTE"`
435			`><BLOCKQUOTE`
436			`CLASS="NOTE"`
437			`><P`
438			`><B`
439			`>Note: </B`
440			`>At the time of writing interfaces cannot act as containers. This may`
441			`change in a future version of the component framework. If the change`
442			`is made then interfaces would support the <SPAN`
443			`CLASS="PROPERTY"`
444			`>script</SPAN`
445			`> property, just like`
446			`components.</P`
447			`></BLOCKQUOTE`
448			`></DIV`
449			`></DIV`
450			`><DIV`
451			`CLASS="NAVFOOTER"`
452			`><HR`
453			`ALIGN="LEFT"`
454			`WIDTH="100%"><TABLE`
455			`SUMMARY="Footer navigation table"`
456			`WIDTH="100%"`
457			`BORDER="0"`
458			`CELLPADDING="0"`
459			`CELLSPACING="0"`
460			`><TR`
461			`><TD`
462			`WIDTH="33%"`
463			`ALIGN="left"`
464			`VALIGN="top"`
465			`><A`
466			`HREF="language.html"`
467			`ACCESSKEY="P"`
468			`>Prev</A`
469			`></TD`
470			`><TD`
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472			`ALIGN="center"`
473			`VALIGN="top"`
474			`><A`
475			`HREF="cdl-guide.html"`
476			`ACCESSKEY="H"`
477			`>Home</A`
478			`></TD`
479			`><TD`
480			`WIDTH="33%"`
481			`ALIGN="right"`
482			`VALIGN="top"`
483			`><A`
484			`HREF="language.properties.html"`
485			`ACCESSKEY="N"`
486			`>Next</A`
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489			`><TR`
490			`><TD`
491			`WIDTH="33%"`
492			`ALIGN="left"`
493			`VALIGN="top"`
494			`>The CDL Language</TD`
495			`><TD`
496			`WIDTH="34%"`
497			`ALIGN="center"`
498			`VALIGN="top"`
499			`><A`
500			`HREF="language.html"`
501			`ACCESSKEY="U"`
502			`>Up</A`
503			`></TD`
504			`><TD`
505			`WIDTH="33%"`
506			`ALIGN="right"`
507			`VALIGN="top"`
508			`>CDL Properties</TD`
509			`></TR`
510			`></TABLE`
511			`></DIV`
512			`></BODY`
513			`></HTML`
514			`>`