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><TR
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COLSPAN="3"
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ALIGN="center"
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>The <SPAN
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>eCos</SPAN
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> Component Writer's Guide</TH
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><H1
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NAME="REF.PARENT"><SPAN
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CLASS="PROPERTY"
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>parent</SPAN
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></H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN4877"
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></A
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><H2
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>Name</H2
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>Property <SPAN
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CLASS="PROPERTY"
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>parent</SPAN
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>&nbsp;--&nbsp;Control the location of an option in the configuration hierarchy.</DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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NAME="AEN4881"><H2
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>Synopsis</H2
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><TR
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><TD
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><PRE
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CLASS="SYNOPSIS"
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>cdl_option &lt;name&gt; {
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    parent &lt;component or package&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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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN4883"
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></A
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><H2
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>Description</H2
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><P
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>Configuration options live in a hierarchy of packages and components.
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By default a given option's position in the hierarchy is a simple
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consequence of its position within the CDL scripts. Packages are
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generally placed at the top-level of the configuration. Any components
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or options that are defined at the same level as the <TT
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CLASS="LITERAL"
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>cdl_package</TT
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>
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command in a package's top-level CDL script are placed immediately
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below that package in the hierarchy. Any options or components that
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are defined in the body of a <TT
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CLASS="LITERAL"
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>cdl_package</TT
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> or <TT
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CLASS="LITERAL"
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>cdl_component</TT
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> command,
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or that are read in as a result of processing a component's <SPAN
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CLASS="PROPERTY"
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>script</SPAN
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>
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property, will be placed immediately below that package or component
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in the hierarchy.</P
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><P
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>In some circumstances it is useful to specify an alternative position
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in the hierarchy for a given option. For example it is often
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convenient to re-parent device driver packages below
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<TT
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CLASS="VARNAME"
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>CYGPKG_IO</TT
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> in the configuration hierarchy, thus
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reducing the number of packages at the top level of the hierarchy and
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making navigation easier. The <SPAN
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CLASS="PROPERTY"
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>parent</SPAN
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> property can be used to achieve
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this. </P
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><P
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>The <SPAN
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CLASS="PROPERTY"
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>parent</SPAN
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> property takes a single argument, which should be the
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name of a package or component. The body of a <TT
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CLASS="LITERAL"
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>cdl_option</TT
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> or other
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CDL entity can contain at most one <SPAN
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CLASS="PROPERTY"
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>parent</SPAN
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> property.</P
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><P
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>Although the <SPAN
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CLASS="PROPERTY"
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>parent</SPAN
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> property affects an option's position in the
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overall hierarchy and hence whether or not that option is active, a
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re-parented option still belongs to the package that defines it. By
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default any <TT
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CLASS="LITERAL"
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>#define's</TT
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> will be exported to that
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package's configuration header file. Any <SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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> properties can only
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reference source files present in that package, and it is not directly
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possible to cause some file in another package to be built by
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re-parenting. </P
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><P
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>As a special case, if an empty string is specified for the parent then
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the option is placed at the top of the hierarchy, ahead of any
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packages which are not explicitly re-parented in this way. This
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facility is useful for configuration options such as global
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preferences and default compiler flags.</P
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><DIV
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CLASS="TIP"
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><BLOCKQUOTE
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CLASS="TIP"
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><P
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><B
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>Tip: </B
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>If an option is re-parented somewhere below another package and that
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other package is not actually loaded, the option is an orphan and its
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active/inactive state is undefined. In such cases it is a good idea
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for the owning package to require the presence of the other one.
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Unfortunately this technique does not work if a package as a whole is
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reparented below another one that has not been loaded: the package is
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orphaned so it may be automatically inactive, and hence any <SPAN
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CLASS="PROPERTY"
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>requires</SPAN
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>
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properties would have no effect.</P
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></BLOCKQUOTE
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CLASS="REFSECT1"
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NAME="AEN4905"
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>Example</H2
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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_HAL_I386 {
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    display       "i386 architecture"
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    parent        CYGPKG_HAL
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    hardware
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    include_dir   cyg/hal
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    define_header hal_i386.h
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    &#8230;
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}
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cdl_component CYGBLD_GLOBAL_OPTIONS {
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    display       "Global build options"
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    parent        ""
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    &#8230;
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}</PRE
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></TD
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CLASS="REFSECT1"
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></A
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><H2
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>See Also</H2
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><P
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>Property <A
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><SPAN
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CLASS="PROPERTY"
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>script</SPAN
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></A
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>,
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commands <A
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HREF="ref.cdl-component.html"
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><TT
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CLASS="LITERAL"
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>cdl_component</TT
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></A
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> and
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<A
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HREF="ref.cdl-package.html"
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><TT
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CLASS="LITERAL"
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>cdl_package</TT
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></A
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>.</P
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