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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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<!-- This material may be distributed only subject to the terms      -->
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<!-- Distribution of the work or derivative of the work in any       -->
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<HTML
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><HEAD
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><TITLE
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>The CDL Language</TITLE
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><meta name="MSSmartTagsPreventParsing" content="TRUE">
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<META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
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"><LINK
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REL="HOME"
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TITLE="The eCos Component Writer's Guide"
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TITLE="Making a Package Distribution"
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TITLE="CDL Commands"
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><TR
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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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CLASS="APPLICATION"
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>eCos</SPAN
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> Component Writer's Guide</TH
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></TR
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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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VALIGN="bottom"
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><A
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HREF="package.distrib.html"
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>Prev</A
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></TD
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><TD
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ALIGN="right"
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><A
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HREF="language.commands.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="LANGUAGE">Chapter 3. The CDL Language</H1
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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><A
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HREF="language.html#LANGUAGE.OVERVIEW"
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>Language Overview</A
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></DT
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><DT
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><A
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HREF="language.commands.html"
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>CDL Commands</A
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></DT
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><DT
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><A
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HREF="language.properties.html"
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>CDL Properties</A
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></DT
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><DT
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><A
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HREF="language.naming.html"
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>Option Naming Convention</A
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></DT
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><DT
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><A
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HREF="language.tcl.html"
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>An Introduction to Tcl</A
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></DT
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><DT
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><A
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HREF="language.values.html"
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>Values and Expressions</A
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></DT
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><DT
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><A
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HREF="language.interface.html"
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>Interfaces</A
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></DT
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><DT
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><A
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HREF="language.database.html"
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>Updating the <SPAN
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CLASS="DATABASE"
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>ecos.db</SPAN
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> database</A
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></DT
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></DL
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></DIV
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><P
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>The <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> language is a key part of the <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> component framework.
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All packages must come with at least one <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> script, to describe
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that package to the framework. The information in that script includes
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details of all the configuration options and how to build the package.
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Implementing a new component or turning some existing code into an
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<SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> component always involves writing corresponding <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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>. This
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chapter provides a description of the <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> language. Detailed
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information on specific parts of the language can be found in <A
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HREF="reference.html"
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>Chapter 5</A
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>.</P
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="LANGUAGE.OVERVIEW">Language Overview</H1
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><P
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>A very simple <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> script would look like this:</P
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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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>cdl_package CYGPKG_ERROR {
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    display       "Common error code support"
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    compile       strerror.cxx
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    include_dir   cyg/error
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    description   "
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        This package contains the common list of error and
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        status codes. It is held centrally to allow
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        packages to interchange error codes and status
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        codes in a common way, rather than each package
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        having its own conventions for error/status
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        reporting. The error codes are modelled on the
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        POSIX style naming e.g. EINVAL etc. This package
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        also provides the standard strerror() function to
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        convert error codes to textual representation."
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}</PRE
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></TD
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></TR
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></TABLE
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><P
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>This describes a single package, the error code package, which does
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not have any sub-components or configuration options. The package has
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an internal name, <TT
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CLASS="VARNAME"
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>CYGPKG_ERROR</TT
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>, which can be
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referenced in other <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> scripts using e.g.
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<TT
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CLASS="LITERAL"
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>requires&nbsp;CYGPKG_ERROR</TT
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>. There will also be a
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<TT
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CLASS="LITERAL"
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>#define</TT
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> for this symbol in a configuration header
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file. In addition to the package name, this script provides a number
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of properties for the package as a whole. The <SPAN
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CLASS="PROPERTY"
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>display</SPAN
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> property
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provides a short description. The <SPAN
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CLASS="PROPERTY"
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>description</SPAN
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> property involves a
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rather longer one, for when users need a bit more information. The
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<SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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> and <SPAN
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CLASS="PROPERTY"
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>include_dir</SPAN
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> properties list the consequences of this
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package at build-time. The package appears to lack any on-line
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documentation. </P
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><P
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>Packages could be even simpler than this. If the package only provides
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an interface and there are no files to be compiled then there is no
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need for a <SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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> property. Alternatively if there are no exported
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header files, or if the exported header files should go to the
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top-level of the <TT
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CLASS="FILENAME"
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>install/include</TT
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> directory, then there is
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no need for an <SPAN
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CLASS="PROPERTY"
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>include_dir</SPAN
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> property. Strictly speaking the
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<SPAN
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CLASS="PROPERTY"
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>description</SPAN
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> and <SPAN
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CLASS="PROPERTY"
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>display</SPAN
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> properties are optional as well, although
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application developers would not appreciate the resulting lack of
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information about what the package is supposed to do.</P
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><P
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>However many packages tend to be a bit more complicated than the error
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package, containing various sub-components and configuration options.
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These are also defined in the <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> scripts and in much the same way
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as the package. For example, the following excerpt comes from the
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infrastructure package:</P
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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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>cdl_component CYGDBG_INFRA_DEBUG_TRACE_ASSERT_BUFFER {
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    display       "Buffered tracing"
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    default_value 1
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    active_if     CYGDBG_USE_TRACING
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    description   "
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        An output module which buffers output from tracing and
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        assertion events. The stored messages are output when an
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        assert fires, or CYG_TRACE_PRINT() (defined in
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        &lt;cyg/infra/cyg_trac.h&gt;) is called. Of course, there will
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        only be stored messages if tracing per se (CYGDBG_USE_TRACING)
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        is enabled above."
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    cdl_option CYGDBG_INFRA_DEBUG_TRACE_BUFFER_SIZE {
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        display       "Trace buffer size"
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        flavor        data
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        default_value 32
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        legal_values  5 to 65535
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        description   "
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            The size of the trace buffer. This counts the number of
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            trace records stored. When the buffer fills it either
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            wraps, stops recording, or generates output."
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    }
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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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><P
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>Like a <TT
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CLASS="LITERAL"
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>cdl_package</TT
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>, a <TT
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CLASS="LITERAL"
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>cdl_component</TT
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> has a name and a body. The
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body contains various properties for that component, and may also
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contain sub-components or options. Similarly a <TT
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CLASS="LITERAL"
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>cdl_option</TT
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> has a
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name and a body of properties. This example lists a number of
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new properties: <SPAN
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CLASS="PROPERTY"
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>default_value</SPAN
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>, <SPAN
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CLASS="PROPERTY"
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>active_if</SPAN
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>, <SPAN
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CLASS="PROPERTY"
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>flavor</SPAN
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> and
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<SPAN
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CLASS="PROPERTY"
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>legal_values</SPAN
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>. The meaning of most of these should be fairly obvious.
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The next sections describe the various <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> commands and properties. </P
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><P
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>There is one additional and very important point: <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> is not a
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completely new language; instead it is implemented as an extension of
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the existing <SPAN
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CLASS="APPLICATION"
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>Tcl</SPAN
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> scripting language. The syntax of a <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> script is
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<SPAN
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CLASS="APPLICATION"
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>Tcl</SPAN
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> syntax, which is described below. In addition some of the more
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advanced facilities of <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> involve embedded fragments of <SPAN
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CLASS="APPLICATION"
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>Tcl</SPAN
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> code,
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for example there is a <SPAN
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CLASS="PROPERTY"
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>define_proc</SPAN
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> property which specifies some
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code that needs to be executed when the component framework generates
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the configuration header files.</P
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></DIV
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><A
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HREF="package.distrib.html"
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ACCESSKEY="P"
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>Prev</A
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="cdl-guide.html"
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>Home</A
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></TD
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><A
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HREF="language.commands.html"
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></TD
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ALIGN="left"
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>Making a Package Distribution</TD
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><TD
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ALIGN="center"
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VALIGN="top"
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>&nbsp;</TD
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><TD
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WIDTH="33%"
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>CDL Commands</TD
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