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>The <SPAN
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>eCos</SPAN
> Component Writer's Guide</TH
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><H2
>Name</H2
>Property <SPAN
CLASS="PROPERTY"
>parent</SPAN
> -- Control the location of an option in the configuration hierarchy.</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN4881"><H2
>Synopsis</H2
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><PRE
CLASS="SYNOPSIS"
>cdl_option <name> {
parent <component or package>
…
}</PRE
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><H2
>Description</H2
><P
>Configuration options live in a hierarchy of packages and components.
By default a given option's position in the hierarchy is a simple
consequence of its position within the CDL scripts. Packages are
generally placed at the top-level of the configuration. Any components
or options that are defined at the same level as the <TT
CLASS="LITERAL"
>cdl_package</TT
>
command in a package's top-level CDL script are placed immediately
below that package in the hierarchy. Any options or components that
are defined in the body of a <TT
CLASS="LITERAL"
>cdl_package</TT
> or <TT
CLASS="LITERAL"
>cdl_component</TT
> command,
or that are read in as a result of processing a component's <SPAN
CLASS="PROPERTY"
>script</SPAN
>
property, will be placed immediately below that package or component
in the hierarchy.</P
><P
>In some circumstances it is useful to specify an alternative position
in the hierarchy for a given option. For example it is often
convenient to re-parent device driver packages below
<TT
CLASS="VARNAME"
>CYGPKG_IO</TT
> in the configuration hierarchy, thus
reducing the number of packages at the top level of the hierarchy and
making navigation easier. The <SPAN
CLASS="PROPERTY"
>parent</SPAN
> property can be used to achieve
this. </P
><P
>The <SPAN
CLASS="PROPERTY"
>parent</SPAN
> property takes a single argument, which should be the
name of a package or component. The body of a <TT
CLASS="LITERAL"
>cdl_option</TT
> or other
CDL entity can contain at most one <SPAN
CLASS="PROPERTY"
>parent</SPAN
> property.</P
><P
>Although the <SPAN
CLASS="PROPERTY"
>parent</SPAN
> property affects an option's position in the
overall hierarchy and hence whether or not that option is active, a
re-parented option still belongs to the package that defines it. By
default any <TT
CLASS="LITERAL"
>#define's</TT
> will be exported to that
package's configuration header file. Any <SPAN
CLASS="PROPERTY"
>compile</SPAN
> properties can only
reference source files present in that package, and it is not directly
possible to cause some file in another package to be built by
re-parenting. </P
><P
>As a special case, if an empty string is specified for the parent then
the option is placed at the top of the hierarchy, ahead of any
packages which are not explicitly re-parented in this way. This
facility is useful for configuration options such as global
preferences and default compiler flags.</P
><DIV
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><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>If an option is re-parented somewhere below another package and that
other package is not actually loaded, the option is an orphan and its
active/inactive state is undefined. In such cases it is a good idea
for the owning package to require the presence of the other one.
Unfortunately this technique does not work if a package as a whole is
reparented below another one that has not been loaded: the package is
orphaned so it may be automatically inactive, and hence any <SPAN
CLASS="PROPERTY"
>requires</SPAN
>
properties would have no effect.</P
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><H2
>Example</H2
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><PRE
CLASS="PROGRAMLISTING"
>cdl_package CYGPKG_HAL_I386 {
display "i386 architecture"
parent CYGPKG_HAL
hardware
include_dir cyg/hal
define_header hal_i386.h
…
}
cdl_component CYGBLD_GLOBAL_OPTIONS {
display "Global build options"
parent ""
…
}</PRE
></TD
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></A
><H2
>See Also</H2
><P
>Property <A
HREF="ref.script.html"
><SPAN
CLASS="PROPERTY"
>script</SPAN
></A
>,
commands <A
HREF="ref.cdl-component.html"
><TT
CLASS="LITERAL"
>cdl_component</TT
></A
> and
<A
HREF="ref.cdl-package.html"
><TT
CLASS="LITERAL"
>cdl_package</TT
></A
>.</P
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