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+><HR
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+><H1
+><A
+NAME="REF.CDL-OPTION"><TT
+CLASS="LITERAL"
+>cdl_option</TT
+></H1
+><DIV
+CLASS="REFNAMEDIV"
+><A
+NAME="AEN2940"
+></A
+><H2
+>Name</H2
+>Command <TT
+CLASS="LITERAL"
+>cdl_option</TT
+> -- Define a single configuration option</DIV
+><DIV
+CLASS="REFSYNOPSISDIV"
+><A
+NAME="AEN2944"><H2
+>Synopsis</H2
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SYNOPSIS"
+>cdl_option <name> {
+ …
+}</PRE
+></TD
+></TR
+></TABLE
+></DIV
+><DIV
+CLASS="REFSECT1"
+><A
+NAME="AEN2946"
+></A
+><H2
+>Description</H2
+><P
+>The option is the basic unit of configurability. Generally each option
+corresponds to a single user choice. Typically there is a certain
+amount of information associated with an option to assist the user in
+manipulating that option, for example a textual description. There
+will also be some limits on the possible values that the user can
+choose, so an option may be a simple yes-or-no choice or it may be
+something more complicated such as an array size or a device name.
+Options may have associated constraints, so if that option is enabled
+then certain conditions have to satisfied elsewhere in the
+configuration. Options usually have direct consequences such as
+preprocessor <TT
+CLASS="LITERAL"
+>#define</TT
+> symbols in a configuration
+header file.</P
+><P
+><TT
+CLASS="LITERAL"
+>cdl_option</TT
+> is implemented as a Tcl command that takes two arguments,
+a name and a body. The name must be a valid C preprocessor identifier:
+a sequence of upper or lower case letters, digits or underscores,
+starting with a non-digit character; identifiers beginning with an
+underscore should normally be avoided because they may clash with
+system packages or with identifiers reserved for use by the compiler.
+Within a single configuration, names must be unique. If a
+configuration contained two packages which defined the same entity
+<TT
+CLASS="LITERAL"
+>CYGIMP_SOME_OPTION</TT
+>, any references to that entity
+in a <SPAN
+CLASS="PROPERTY"
+>requires</SPAN
+> property or any other expression
+would be ambiguous. It is possible for a given name to be used by two
+different packages if those packages should never be loaded into a
+single configuration. For example, architectural HAL packages are
+allowed to re-use names because a single configuration cannot target
+two different architectures. For a recommended naming convention see
+<A
+HREF="package.contents.html"
+>the Section called <I
+>Package Contents and Layout</I
+> in Chapter 2</A
+>.</P
+><P
+>The second argument to <TT
+CLASS="LITERAL"
+>cdl_option</TT
+> is a body of
+properties, typically surrounded by braces so that the Tcl interpreter
+treats it as a single argument. This body will be processed by a
+recursive invocation of the Tcl interpreter, extended with additional
+commands for the various properties that are allowed inside a
+<TT
+CLASS="LITERAL"
+>cdl_option</TT
+>. The valid properties are:</P
+><P
+></P
+><DIV
+CLASS="VARIABLELIST"
+><DL
+><DT
+><A
+HREF="ref.active-if.html"
+><SPAN
+CLASS="PROPERTY"
+>active_if</SPAN
+></A
+></DT
+><DD
+><P
+>Allow additional control over the active state of this option.</P
+></DD
+><DT
+><A
+HREF="ref.calculated.html"
+><SPAN
+CLASS="PROPERTY"
+>calculated</SPAN
+></A
+></DT
+><DD
+><P
+>The option's value is not directly user-modifiable, it is calculated
+using a suitable CDL expression.</P
+></DD
+><DT
+><A
+HREF="ref.compile.html"
+><SPAN
+CLASS="PROPERTY"
+>compile</SPAN
+></A
+></DT
+><DD
+><P
+>List the source files that should be built if this option is active
+and enabled.</P
+></DD
+><DT
+><A
+HREF="ref.default-value.html"
+><SPAN
+CLASS="PROPERTY"
+>default_value</SPAN
+></A
+></DT
+><DD
+><P
+>Provide a default value for this option using a CDL expression.</P
+></DD
+><DT
+><A
+HREF="ref.define.html"
+><SPAN
+CLASS="PROPERTY"
+>define</SPAN
+></A
+></DT
+><DD
+><P
+>Specify additional <TT
+CLASS="LITERAL"
+>#define</TT
+> symbols that should go
+into the owning package's configuration header file.</P
+></DD
+><DT
+><A
+HREF="ref.define-format.html"
+><SPAN
+CLASS="PROPERTY"
+>define_format</SPAN
+></A
+></DT
+><DD
+><P
+>Control how the option's value will appear in the configuration header
+file.</P
+></DD
+><DT
+><A
+HREF="ref.define-proc.html"
+><SPAN
+CLASS="PROPERTY"
+>define_proc</SPAN
+></A
+></DT
+><DD
+><P
+>Use a fragment of Tcl code to output additional data to
+configuration header files.</P
+></DD
+><DT
+><A
+HREF="ref.description.html"
+><SPAN
+CLASS="PROPERTY"
+>description</SPAN
+></A
+></DT
+><DD
+><P
+>Provide a textual description for this option.</P
+></DD
+><DT
+><A
+HREF="ref.display.html"
+><SPAN
+CLASS="PROPERTY"
+>display</SPAN
+></A
+></DT
+><DD
+><P
+>Provide a short string describing this option.</P
+></DD
+><DT
+><A
+HREF="ref.doc.html"
+><SPAN
+CLASS="PROPERTY"
+>doc</SPAN
+></A
+></DT
+><DD
+><P
+>The location of on-line documentation for this option.</P
+></DD
+><DT
+><A
+HREF="ref.flavor.html"
+><SPAN
+CLASS="PROPERTY"
+>flavor</SPAN
+></A
+></DT
+><DD
+><P
+>Specify the nature of this option.</P
+></DD
+><DT
+><A
+HREF="ref.if-define.html"
+><SPAN
+CLASS="PROPERTY"
+>if_define</SPAN
+></A
+></DT
+><DD
+><P
+>Output a common preprocessor construct to a configuration header file. </P
+></DD
+><DT
+><A
+HREF="ref.implements.html"
+><SPAN
+CLASS="PROPERTY"
+>implements</SPAN
+></A
+></DT
+><DD
+><P
+>Enabling this option provides one instance of a more general
+interface. </P
+></DD
+><DT
+><A
+HREF="ref.legal-values.html"
+><SPAN
+CLASS="PROPERTY"
+>legal_values</SPAN
+></A
+></DT
+><DD
+><P
+>Impose constraints on the possible values for this option.</P
+></DD
+><DT
+><A
+HREF="ref.make.html"
+><SPAN
+CLASS="PROPERTY"
+>make</SPAN
+></A
+></DT
+><DD
+><P
+>An additional custom build step associated with this option, resulting
+in a target that should not go directly into a library.</P
+></DD
+><DT
+><A
+HREF="ref.make-object.html"
+><SPAN
+CLASS="PROPERTY"
+>make_object</SPAN
+></A
+></DT
+><DD
+><P
+>An additional custom build step associated with this option, resulting
+in an object file that should go into a library.</P
+></DD
+><DT
+><A
+HREF="ref.no-define.html"
+><SPAN
+CLASS="PROPERTY"
+>no_define</SPAN
+></A
+></DT
+><DD
+><P
+>Suppress the normal generation of a preprocessor
+<TT
+CLASS="LITERAL"
+>#define</TT
+> symbol in a configuration header file.</P
+></DD
+><DT
+><A
+HREF="ref.parent.html"
+><SPAN
+CLASS="PROPERTY"
+>parent</SPAN
+></A
+></DT
+><DD
+><P
+>Control the location of this option in the configuration hierarchy. </P
+></DD
+><DT
+><A
+HREF="ref.requires.html"
+><SPAN
+CLASS="PROPERTY"
+>requires</SPAN
+></A
+></DT
+><DD
+><P
+>List constraints that the configuration should satisfy if this option is
+active and enabled.</P
+></DD
+></DL
+></DIV
+></DIV
+><DIV
+CLASS="REFSECT1"
+><A
+NAME="AEN3075"
+></A
+><H2
+>Example</H2
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>cdl_option CYGDBG_INFRA_DEBUG_PRECONDITIONS {
+ display "Preconditions"
+ default_value 1
+ description "
+ This option allows individual control of preconditions.
+ A precondition is one type of assert, which it is
+ useful to control separately from more general asserts.
+ The function is CYG_PRECONDITION(condition,msg)."
+}</PRE
+></TD
+></TR
+></TABLE
+></DIV
+><DIV
+CLASS="REFSECT1"
+><A
+NAME="AEN3078"
+></A
+><H2
+>See Also</H2
+><P
+>Command <A
+HREF="ref.cdl-component.html"
+><TT
+CLASS="LITERAL"
+>cdl_component</TT
+></A
+>,
+command <A
+HREF="ref.cdl-package.html"
+><TT
+CLASS="LITERAL"
+>cdl_package</TT
+></A
+>,
+command <A
+HREF="ref.cdl-interface.html"
+><TT
+CLASS="LITERAL"
+>cdl_interface</TT
+></A
+>.</P
+></DIV
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