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