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>The <SPAN
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> Component Writer's Guide</TH
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><H1
><A
NAME="REF.FLAVOR"><SPAN
CLASS="PROPERTY"
>flavor</SPAN
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN4315"
></A
><H2
>Name</H2
>Property <SPAN
CLASS="PROPERTY"
>flavor</SPAN
> -- Specify the nature of a configuration option.</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN4319"><H2
>Synopsis</H2
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SYNOPSIS"
>cdl_option <name> {
flavor <flavor>
…
}</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN4321"
></A
><H2
>Description</H2
><P
>The state of a <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> configuration option is a somewhat complicated
concept. This state determines what happens when a build tree is
generated: it controls what files get built and what
<TT
CLASS="LITERAL"
>#define's</TT
> end up in configuration header files. The
state also controls the values used during expression evaluation. The
key concepts are:</P
><P
></P
><OL
TYPE="1"
><LI
><P
>An option may or may not be loaded into the current configuration.
However it is still possible for packages to reference options which
are not loaded in a <SPAN
CLASS="PROPERTY"
>requires</SPAN
> constraint or other expression. If an
option is not loaded then it will have no direct effect on the build
process, and <TT
CLASS="LITERAL"
>0</TT
> will be used for expression
evaluation. </P
></LI
><LI
><P
>Even if an option is loaded it may still be inactive. Usually this is
controlled by the option's location in the configuration hierarchy. If
an option's parent is active and enabled then the option will normally
be active. If the parent is either inactive or disabled then the
option will be inactive. For example, if kernel timeslicing is diabled
then the option <TT
CLASS="LITERAL"
>CYGNUM_KERNEL_SCHED_TIMESLICE_TICKS</TT
>
is irrelevant and must have no effect. The <SPAN
CLASS="PROPERTY"
>active_if</SPAN
> property can be
used to specify additional constraints. If an option is inactive then
it will have no direct effect on the build process, in other words it
will not cause any files to get built or <TT
CLASS="LITERAL"
>#define's</TT
>
to be generated. For the purposes of expression evaluation an inactive
option has a value of <TT
CLASS="LITERAL"
>0</TT
>.</P
></LI
><LI
><P
>An option may be enabled or disabled. Most options are boolean in
nature, for example a particular function may get inlined or it may
involve a full procedure call. If an option is disabled then it has no
direct effect on the build process, and for the purposes of expression
evaluation it has a value of 0.</P
></LI
><LI
><P
>An option may also have additional data associated with it, for
example a numerical value used to control the size of an array.</P
></LI
></OL
><P
>Most options are boolean in nature and do not have any additional
associated data. For some options only the data part makes sense and
users should be unable to manipulate the enabled/disabled part of the
state. For a comparatively small number of options it makes sense to
have the ability to disable that option or to enable it and associate
data as well. Finally, when constructing an option hierarchy it is
occasionally useful to have entities which serve only as placeholders.
The <SPAN
CLASS="PROPERTY"
>flavor</SPAN
> property can be used to control all this. There are four
possible values. It should be noted that the active or inactive state
of an option takes priority over the flavor: if an option is inactive
then no <TT
CLASS="LITERAL"
>#define's</TT
> will be generated and any
build-related properties such as <SPAN
CLASS="PROPERTY"
>compile</SPAN
> will be ignored.</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>flavor <TT
CLASS="LITERAL"
>none</TT
></DT
><DD
><P
>The <TT
CLASS="LITERAL"
>none</TT
> is intended primarily for placeholder
components in the hierarchy, although it can be used for other
purposes. Options with this flavor are always enabled and do not have
any additional data associated with them, so there is no way for users
to modify the option. For the purposes of expression evaluation an
option with flavor <TT
CLASS="LITERAL"
>none</TT
> always has the value
<TT
CLASS="LITERAL"
>1</TT
>. Normal <TT
CLASS="LITERAL"
>#define</TT
> processing
will take place, so typically a single <TT
CLASS="LITERAL"
>#define</TT
> will
be generated using the option name and a value of
<TT
CLASS="LITERAL"
>1</TT
>. Similarly build-related properties such as
<SPAN
CLASS="PROPERTY"
>compile</SPAN
> will take effect.</P
></DD
><DT
>flavor <TT
CLASS="LITERAL"
>bool</TT
></DT
><DD
><P
>Boolean options can be either enabled or disabled, and there is no
additional data associated with them. If a boolean option is disabled
then no <TT
CLASS="LITERAL"
>#define</TT
> will be generated and any
build-related properties such as <SPAN
CLASS="PROPERTY"
>compile</SPAN
> will be ignored. For the
purposes of expression evaluation a disabled option has the value
<TT
CLASS="LITERAL"
>0</TT
>. If a boolean option is enabled then normal
<TT
CLASS="LITERAL"
>#define</TT
> processing will take place, all
build-related properties take effect, and the option's value will be
<TT
CLASS="LITERAL"
>1</TT
>.</P
></DD
><DT
>flavor <TT
CLASS="LITERAL"
>data</TT
></DT
><DD
><P
>Options with this flavor are always enabled, and have some additional
data associated with them which can be edited by the user. This data
can be any sequence of characters, although in practice the
<SPAN
CLASS="PROPERTY"
>legal_values</SPAN
> property will often be used to impose constraints. In
appropriate contexts such as expressions the configuration tools will
attempt to interpret the data as integer or floating point numbers.
Since an option with the <TT
CLASS="LITERAL"
>data</TT
> flavor cannot be
disabled, normal <TT
CLASS="LITERAL"
>#define</TT
> processing takes place and
the data will be used for the value. Similarly all build-related
properties take effect, and the option's value for the purposes of
expression evaluation is the data.</P
></DD
><DT
>flavor <TT
CLASS="LITERAL"
>booldata</TT
></DT
><DD
><P
>This combines the <TT
CLASS="LITERAL"
>bool</TT
> and <TT
CLASS="LITERAL"
>data</TT
>
flavors. The option may be enabled or disabled, and in addition the
option has some associated data. If the option is disabled then no
<TT
CLASS="LITERAL"
>#define</TT
> will be generated, the build-related
properties have no effect, and for the purposes of expression
evaluation the option's value is <TT
CLASS="LITERAL"
>0</TT
>. If the option
is enabled then a <TT
CLASS="LITERAL"
>#define</TT
> will be generated using
the data as the value, all build-related properties take effect, and
the option's value for the purposes of expression evaluation is the
data. If <TT
CLASS="LITERAL"
>0</TT
> is legal data then it is not possible to
distinguish this case from the option being disabled or inactive.</P
></DD
></DL
></DIV
><P
>Options and components have the <TT
CLASS="LITERAL"
>bool</TT
> flavor by
default, but this can be changed as desired. Packages always have the
<TT
CLASS="LITERAL"
>booldata</TT
> flavor, and this cannot be changed.
Interfaces have the <TT
CLASS="LITERAL"
>data</TT
> flavor by default, since
the value of an interface is a count of the number of active and
enabled interfaces, but they can be given the <TT
CLASS="LITERAL"
>bool</TT
>
or <TT
CLASS="LITERAL"
>booldata</TT
> flavors.</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>The expression syntax needs to be extended to allow the loaded,
active, enabled and data aspects of an option's state to be examined
individually. This would allow component writers to distinguish
between a disabled <TT
CLASS="LITERAL"
>booldata</TT
> option and an enabled
one which has a value of <TT
CLASS="LITERAL"
>0</TT
>. Such an enhancement to
the expression syntax may also prove useful in other circumstances.</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN4397"
></A
><H2
>Example</H2
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> cdl_component CYGPKG_LIBM_COMPATIBILITY {
cdl_component CYGNUM_LIBM_COMPATIBILITY {
flavor booldata
…
cdl_option CYGNUM_LIBM_COMPAT_DEFAULT {
flavor data
…
}
}
…
}
cdl_component CYGPKG_LIBM_TRACE {
flavor bool
…
}</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN4400"
></A
><H2
>See Also</H2
><P
>Properties <A
HREF="ref.calculated.html"
><SPAN
CLASS="PROPERTY"
>calculated</SPAN
></A
>,
<A
HREF="ref.default-value.html"
><SPAN
CLASS="PROPERTY"
>default_value</SPAN
></A
> and
<A
HREF="ref.legal-values.html"
><SPAN
CLASS="PROPERTY"
>legal_values</SPAN
></A
>,</P
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