+++ /dev/null
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-><A
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-></A
-><H2
->Name</H2
->Property <SPAN
-CLASS="PROPERTY"
->requires</SPAN
-> -- List constraints that the configuration should satisfy if
-a given option is active and enabled..</DIV
-><DIV
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-><A
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->Synopsis</H2
-><TABLE
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-><PRE
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->cdl_option <name> {
- requires <goal expression>
- …
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-><DIV
-CLASS="REFSECT1"
-><A
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-></A
-><H2
->Description</H2
-><P
->Configuration options are not independent. For example the C library
-can provide thread-safe implementations of certain functions, but only
-if the kernel is present, if the kernel provides multi-threading, and
-if the kernel options related to per-thread data are enabled. It is
-possible to express such constraints using <SPAN
-CLASS="PROPERTY"
->requires</SPAN
-> properties.</P
-><P
->The arguments to a <SPAN
-CLASS="PROPERTY"
->requires</SPAN
-> property should constitute a goal
-expression, as described in <A
-HREF="language.values.html#LANGUAGE.LIST-EXPRESSION"
->the Section called <I
->List Expressions</I
-> in Chapter 3</A
->.
-Most goal expressions are relatively simple because the constraints
-being described are simple, but complicated expressions can be used
-when necessary. The body of an option or other CDL entity can contain
-any number of <SPAN
-CLASS="PROPERTY"
->requires</SPAN
-> constraints. If the option is active and
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-CLASS="LITERAL"
->0</TT
-> will result in
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-conflicts and attempt to build the current configuration anyway, but
-there is no guarantee that anything will work. If an option is
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->requires</SPAN
-> constraints will be ignored. </P
-><P
->The configuration system contains an inference engine which can
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->A</TT
-> is enabled and requires an option
-<TT
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->B</TT
-> that is currently disabled then the inference
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-<TT
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->B</TT
->. However this will not always be possible, for
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->B</TT
-> to be disabled at present, in which case
-user intervention is required.</P
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-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->cdl_component CYGPKG_IO_SERIAL_POWERPC_COGENT_SERIAL_A {
- display "Cogent PowerPC serial port A driver"
- flavor bool
- default_value 0
- requires (CYGIMP_KERNEL_INTERRUPTS_CHAIN || \
- !CYGPKG_IO_SERIAL_POWERPC_COGENT_SERIAL_B)
- …
-}</PRE
-></TD
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-></TABLE
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-></A
-><H2
->See Also</H2
-><P
->Property <A
-HREF="ref.active-if.html"
-><SPAN
-CLASS="PROPERTY"
->active_if</SPAN
-></A
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