+++ /dev/null
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-><H1
-><A
-NAME="REF.CDL-INTERFACE"><TT
-CLASS="LITERAL"
->cdl_interface</TT
-></H1
-><DIV
-CLASS="REFNAMEDIV"
-><A
-NAME="AEN3484"
-></A
-><H2
->Name</H2
->Command <TT
-CLASS="LITERAL"
->cdl_interface</TT
-> -- Define an interface, functionality that can be provided by
-a number of different implementations.</DIV
-><DIV
-CLASS="REFSYNOPSISDIV"
-><A
-NAME="AEN3488"><H2
->Synopsis</H2
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="SYNOPSIS"
->cdl_interface <name> {
- …
-}</PRE
-></TD
-></TR
-></TABLE
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN3490"
-></A
-><H2
->Description</H2
-><P
->An interface is a special type of calculated configuration option.
-It provides an abstraction mechanism that is often useful in <SPAN
-CLASS="APPLICATION"
->CDL</SPAN
->
-expressions. As an example, suppose that some package relies on the
-presence of code that implements the standard kernel scheduling
-interface. However the requirement is no more stringent than this, so
-the constraint can be satisfied by the mlqueue scheduler, the bitmap
-scheduler, or any additional schedulers that may get implemented in
-future. A first attempt at expressing the dependency might be:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
-> requires CYGSEM_KERNEL_SCHED_MLQUEUE || CYGSEM_KERNEL_SCHED_BITMAP</PRE
-></TD
-></TR
-></TABLE
-><P
->This constraint is limited, it may need to be changed if a new
-scheduler were to be added to the system. Interfaces provide a way of
-expressing more general relationships:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
-> requires CYGINT_KERNEL_SCHEDULER</PRE
-></TD
-></TR
-></TABLE
-><P
->The interface <TT
-CLASS="LITERAL"
->CYGINT_KERNEL_SCHEDULER</TT
-> is
-<SPAN
-CLASS="emphasis"
-><I
-CLASS="EMPHASIS"
->implemented</I
-></SPAN
-> by both the mlqueue and bitmap
-schedulers, and may be implemented by future schedulers as well. The
-value of an interface is the number of implementors that are active
-and enabled, so in a typical configuration only one scheduler will be
-in use and the value of the interface will be <TT
-CLASS="LITERAL"
->1</TT
->. If
-all schedulers are disabled then the interface will have a value
-<TT
-CLASS="LITERAL"
->0</TT
-> and the <SPAN
-CLASS="PROPERTY"
->requires</SPAN
-> constraint will not be
-satisfied.</P
-><P
->Some component writers may prefer to use the first <SPAN
-CLASS="PROPERTY"
->requires</SPAN
->
-constraint on the grounds that the code will only have been tested
-with the mlqueue and bitmap schedulers and cannot be guaranteed to
-work with any new schedulers. Other component writers may take a more
-optimistic view and assume that their code will work with any
-scheduler until proven otherwise.</P
-><P
->Interfaces must be defined in CDL scripts, just like options,
-components and packages. This involves the command <TT
-CLASS="LITERAL"
->cdl_interface</TT
->
-which 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_interface</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_interface</TT
->.
-The valid properties are a subset of those for a <TT
-CLASS="LITERAL"
->cdl_option</TT
->.</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 interface.</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 interface is active.</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 interface'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 interface.</P
-></DD
-><DT
-><A
-HREF="ref.display.html"
-><SPAN
-CLASS="PROPERTY"
->display</SPAN
-></A
-></DT
-><DD
-><P
->Provide a short string describing this interface.</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 interface.</P
-></DD
-><DT
-><A
-HREF="ref.flavor.html"
-><SPAN
-CLASS="PROPERTY"
->flavor</SPAN
-></A
-></DT
-><DD
-><P
->Interfaces have the <TT
-CLASS="LITERAL"
->data</TT
-> flavor by default, but
-they can also be given the <TT
-CLASS="LITERAL"
->bool</TT
-> or
-<TT
-CLASS="LITERAL"
->booldata</TT
-> flavor when necessary. A
-<TT
-CLASS="LITERAL"
->bool</TT
-> interface is disabled if there are no active
-and enabled implementors, otherwise it is enabled. A
-<TT
-CLASS="LITERAL"
->booldata</TT
-> interface is also disabled if there are no
-active and enabled implementors, otherwise it is enabled and the data
-is a number corresponding to the number of these implementors.</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
->If this interface is active it 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
->Interfaces always have a small numerical value. The <SPAN
-CLASS="PROPERTY"
->legal_values</SPAN
-> can
-be used to apply additional constraints such as an upper limit.</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
-><P
->A number of properties are not applicable to interfaces:</P
-><P
-></P
-><DIV
-CLASS="VARIABLELIST"
-><DL
-><DT
-><A
-HREF="ref.calculated.html"
-><SPAN
-CLASS="PROPERTY"
->calculated</SPAN
-></A
-></DT
-><DD
-><P
->Interfaces are always calculated, based on the number of active and
-enabled entities that implement the interface.</P
-></DD
-><DT
-><A
-HREF="ref.default-value.html"
-><SPAN
-CLASS="PROPERTY"
->default_value</SPAN
-></A
-></DT
-><DD
-><P
->Interface values are calculated so a <SPAN
-CLASS="PROPERTY"
->default_value</SPAN
-> property would be
-meaningless.</P
-></DD
-></DL
-></DIV
-><P
->Interfaces are not containers, so they cannot hold other entities such
-as options or components.</P
-><P
->A commonly used constraint on interface values takes the form:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
-> requires CYGINT_KERNEL_SCHEDULER == 1</PRE
-></TD
-></TR
-></TABLE
-><P
->This constraint specifies that there can be only one scheduler in the
-system. In some circumstances it is possible for the configuration
-tools to detect this pattern and act accordingly, so for example
-enabling the bitmap scheduler would automatically disable the mlqueue
-scheduler.</P
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN3644"
-></A
-><H2
->Example</H2
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->cdl_interface CYGINT_KERNEL_SCHEDULER {
- display "Number of schedulers in this configuration"
- requires 1 == CYGINT_KERNEL_SCHEDULER
-}</PRE
-></TD
-></TR
-></TABLE
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN3647"
-></A
-><H2
->See Also</H2
-><P
->Property <A
-HREF="ref.implements.html"
-><SPAN
-CLASS="PROPERTY"
->implements</SPAN
-></A
->,
-command <A
-HREF="ref.cdl-option.html"
-><TT
-CLASS="LITERAL"
->cdl_option</TT
-></A
->.
-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
->.</P
-></DIV
-><DIV
-CLASS="NAVFOOTER"
-><HR
-ALIGN="LEFT"
-WIDTH="100%"><TABLE
-SUMMARY="Footer navigation table"
-WIDTH="100%"
-BORDER="0"
-CELLPADDING="0"
-CELLSPACING="0"
-><TR
-><TD
-WIDTH="33%"
-ALIGN="left"
-VALIGN="top"
-><A
-HREF="ref.cdl-package.html"
-ACCESSKEY="P"
->Prev</A
-></TD
-><TD
-WIDTH="34%"
-ALIGN="center"
-VALIGN="top"
-><A
-HREF="cdl-guide.html"
-ACCESSKEY="H"
->Home</A
-></TD
-><TD
-WIDTH="33%"
-ALIGN="right"
-VALIGN="top"
-><A
-HREF="ref.active-if.html"
-ACCESSKEY="N"
->Next</A
-></TD
-></TR
-><TR
-><TD
-WIDTH="33%"
-ALIGN="left"
-VALIGN="top"
-><TT
-CLASS="LITERAL"
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-></TD
-><TD
-WIDTH="34%"
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-VALIGN="top"
-><A
-HREF="reference.html"
-ACCESSKEY="U"
->Up</A
-></TD
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-WIDTH="33%"
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