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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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>eCos</SPAN
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> Component Writer's Guide</TH
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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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><A
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HREF="ref.doc.html"
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>Prev</A
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="REF.FLAVOR"><SPAN
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CLASS="PROPERTY"
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>flavor</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="AEN4315"
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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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>flavor</SPAN
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>&nbsp;--&nbsp;Specify the nature of a configuration option.</DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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><A
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NAME="AEN4319"><H2
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>Synopsis</H2
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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="SYNOPSIS"
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>cdl_option &lt;name&gt; {
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    flavor &lt;flavor&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="AEN4321"
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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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>The state of a <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> configuration option is a somewhat complicated
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concept. This state determines what happens when a build tree is
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generated: it controls what files get built and what
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<TT
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CLASS="LITERAL"
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>#define's</TT
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> end up in configuration header files. The
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state also controls the values used during expression evaluation. The
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key concepts are:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>An option may or may not be loaded into the current configuration.
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However it is still possible for packages to reference options which
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are not loaded in a <SPAN
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CLASS="PROPERTY"
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>requires</SPAN
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> constraint or other expression. If an
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option is not loaded then it will have no direct effect on the build
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process, and <TT
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CLASS="LITERAL"
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>0</TT
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> will be used for expression
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evaluation. </P
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></LI
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><LI
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><P
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>Even if an option is loaded it may still be inactive. Usually this is
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controlled by the option's location in the configuration hierarchy. If
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an option's parent is active and enabled then the option will normally
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be active. If the parent is either inactive or disabled then the
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option will be inactive. For example, if kernel timeslicing is diabled
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then the option <TT
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CLASS="LITERAL"
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>CYGNUM_KERNEL_SCHED_TIMESLICE_TICKS</TT
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>
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is irrelevant and must have no effect. The <SPAN
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CLASS="PROPERTY"
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>active_if</SPAN
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> property can be
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used to specify additional constraints. If an option is inactive then
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it will have no direct effect on the build process, in other words it
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will not cause any files to get built or <TT
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CLASS="LITERAL"
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>#define's</TT
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>
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to be generated. For the purposes of expression evaluation an inactive
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option has a value of <TT
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CLASS="LITERAL"
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>0</TT
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>.</P
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></LI
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><LI
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><P
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>An option may be enabled or disabled. Most options are boolean in
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nature, for example a particular function may get inlined or it may
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involve a full procedure call. If an option is disabled then it has no
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direct effect on the build process, and for the purposes of expression
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evaluation it has a value of 0.</P
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></LI
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><LI
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><P
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>An option may also have additional data associated with it, for
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example a numerical value used to control the size of an array.</P
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></LI
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></OL
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><P
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>Most options are boolean in nature and do not have any additional
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associated data. For some options only the data part makes sense and
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users should be unable to manipulate the enabled/disabled part of the
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state. For a comparatively small number of options it makes sense to
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have the ability to disable that option or to enable it and associate
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data as well. Finally, when constructing an option hierarchy it is
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occasionally useful to have entities which serve only as placeholders.
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The <SPAN
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CLASS="PROPERTY"
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>flavor</SPAN
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> property can be used to control all this. There are four
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possible values. It should be noted that the active or inactive state
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of an option takes priority over the flavor: if an option is inactive
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then no <TT
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CLASS="LITERAL"
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>#define's</TT
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> will be generated and any
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build-related properties such as <SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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> will be ignored.</P
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><P
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></P
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><DIV
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CLASS="VARIABLELIST"
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><DL
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><DT
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>flavor&nbsp;<TT
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CLASS="LITERAL"
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>none</TT
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></DT
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><DD
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><P
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>The <TT
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CLASS="LITERAL"
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>none</TT
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> is intended primarily for placeholder
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components in the hierarchy, although it can be used for other
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purposes. Options with this flavor are always enabled and do not have
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any additional data associated with them, so there is no way for users
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to modify the option. For the purposes of expression evaluation an
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option with flavor <TT
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CLASS="LITERAL"
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>none</TT
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> always has the value
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<TT
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CLASS="LITERAL"
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>1</TT
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>. Normal <TT
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CLASS="LITERAL"
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>#define</TT
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> processing
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will take place, so typically a single <TT
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CLASS="LITERAL"
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>#define</TT
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> will
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be generated using the option name and a value of
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<TT
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CLASS="LITERAL"
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>1</TT
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>. Similarly build-related properties such as
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<SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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> will take effect.</P
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></DD
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><DT
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>flavor&nbsp;<TT
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CLASS="LITERAL"
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>bool</TT
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></DT
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><DD
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><P
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>Boolean options can be either enabled or disabled, and there is no
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additional data associated with them. If a boolean option is disabled
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then no <TT
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CLASS="LITERAL"
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>#define</TT
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> will be generated and any
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build-related properties such as <SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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> will be ignored. For the
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purposes of expression evaluation a disabled option has the value
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<TT
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CLASS="LITERAL"
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>0</TT
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>. If a boolean option is enabled then normal
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<TT
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CLASS="LITERAL"
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>#define</TT
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> processing will take place, all
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build-related properties take effect, and the option's value will be
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<TT
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CLASS="LITERAL"
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>1</TT
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>.</P
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></DD
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><DT
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>flavor&nbsp;<TT
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CLASS="LITERAL"
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>data</TT
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></DT
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><DD
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><P
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>Options with this flavor are always enabled, and have some additional
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data associated with them which can be edited by the user. This data
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can be any sequence of characters, although in practice the
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<SPAN
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CLASS="PROPERTY"
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>legal_values</SPAN
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> property will often be used to impose constraints. In
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appropriate contexts such as expressions the configuration tools will
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attempt to interpret the data as integer or floating point numbers.
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Since an option with the <TT
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CLASS="LITERAL"
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>data</TT
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> flavor cannot be
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disabled, normal <TT
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CLASS="LITERAL"
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>#define</TT
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> processing takes place and
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the data will be used for the value. Similarly all build-related
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properties take effect, and the option's value for the purposes of
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expression evaluation is the data.</P
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></DD
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><DT
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>flavor&nbsp;<TT
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CLASS="LITERAL"
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>booldata</TT
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></DT
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><DD
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><P
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>This combines the <TT
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CLASS="LITERAL"
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>bool</TT
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> and <TT
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CLASS="LITERAL"
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>data</TT
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>
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flavors. The option may be enabled or disabled, and in addition the
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option has some associated data. If the option is disabled then no
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<TT
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CLASS="LITERAL"
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>#define</TT
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> will be generated, the build-related
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properties have no effect, and for the purposes of expression
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evaluation the option's value is <TT
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CLASS="LITERAL"
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>0</TT
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>. If the option
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is enabled then a <TT
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CLASS="LITERAL"
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>#define</TT
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> will be generated using
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the data as the value, all build-related properties take effect, and
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the option's value for the purposes of expression evaluation is the
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data. If <TT
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CLASS="LITERAL"
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>0</TT
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> is legal data then it is not possible to
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distinguish this case from the option being disabled or inactive.</P
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></DD
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></DL
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></DIV
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><P
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>Options and components have the <TT
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CLASS="LITERAL"
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>bool</TT
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> flavor by
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default, but this can be changed as desired. Packages always have the
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<TT
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CLASS="LITERAL"
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>booldata</TT
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> flavor, and this cannot be changed.
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Interfaces have the <TT
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CLASS="LITERAL"
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>data</TT
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> flavor by default, since
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the value of an interface is a count of the number of active and
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enabled interfaces, but they can be given the <TT
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CLASS="LITERAL"
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>bool</TT
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>
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or <TT
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CLASS="LITERAL"
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>booldata</TT
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> flavors.</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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>The expression syntax needs to be extended to allow the loaded,
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active, enabled and data aspects of an option's state to be examined
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individually. This would allow component writers to distinguish
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between a disabled <TT
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CLASS="LITERAL"
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>booldata</TT
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> option and an enabled
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one which has a value of <TT
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CLASS="LITERAL"
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>0</TT
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>. Such an enhancement to
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the expression syntax may also prove useful in other circumstances.</P
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></BLOCKQUOTE
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></DIV
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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="AEN4397"
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></A
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><H2
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>Example</H2
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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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>&#13;cdl_component CYGPKG_LIBM_COMPATIBILITY {
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    cdl_component CYGNUM_LIBM_COMPATIBILITY {
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        flavor booldata
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        &#8230;
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        cdl_option CYGNUM_LIBM_COMPAT_DEFAULT {
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            flavor data
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            &#8230;
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        }
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    }
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    &#8230;
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}
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cdl_component CYGPKG_LIBM_TRACE {
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    flavor        bool
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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="AEN4400"
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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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>Properties <A
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HREF="ref.calculated.html"
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><SPAN
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CLASS="PROPERTY"
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>calculated</SPAN
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></A
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>,
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<A
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HREF="ref.default-value.html"
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><SPAN
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CLASS="PROPERTY"
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>default_value</SPAN
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></A
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> and
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<A
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HREF="ref.legal-values.html"
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><SPAN
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CLASS="PROPERTY"
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>legal_values</SPAN
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></A
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>,</P
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>Home</A
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