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<PART id="ecos-programming-concepts-and-techniques">
<TITLE><productname>eCos</productname> Programming Concepts and Techniques</TITLE>
<PARTINTRO id="programming-partintro">
<PARA>Programming with <productname>eCos</productname> is somewhat different from programming
      in more traditional environments. <productname>eCos</productname> is a configurable open
      source system, and you are able to configure and build a system
      specifically to meet the needs of your application. </PARA>
<PARA>Various different directory hierarchies are involved in
      configuring and building the system: the <EMPHASIS>component
	repository</EMPHASIS>, the <EMPHASIS>build tree</EMPHASIS>,
      and the <EMPHASIS>install tree</EMPHASIS>. These directories
      exist in addition to the ones used to develop
      applications.</PARA>
</PARTINTRO>
<CHAPTER id="cdl-concepts">
<TITLE>CDL Concepts</TITLE>
<SECT1 id="cdl-concepts-about">
<TITLE>About this chapter</TITLE>
<PARA>This chapter serves as a brief introduction to the
	concepts involved in <productname>eCos</productname> (Embedded Configurable Operating
	System).  It describes the configuration architecture and the
	underlying technology to a level required for the embedded
	systems developer to configure <productname>eCos</productname>.  It does not describe in
	detail aspects such as how to write reusable components for
	<productname>eCos</productname>: this information is given in the <citetitle>Component
	  Writer&rsquo;s Guide</citetitle>.</PARA>
<SECT2>
<TITLE>Background</TITLE>
<PARA>Software solutions for the embedded space place
	  particularly stringent demands on the developer, typically
	  represented as requirements for small memory footprint, high
	  performance and robustness.  These demands are addressed in
	  <productname>eCos</productname> by providing the ability to perform compile-time
	  specialization: the developer can tailor the operating
	  system to suit the needs of the application.  In order to
	  make this process manageable, <productname>eCos</productname> is built in the context
	  of a Configuration Infrastructure: a set of tools including
	  a <application>Configuration Tool</application> and a formal
	  description of the process of configuration by means of a
	  <EMPHASIS>Component Definition Language</EMPHASIS>.</PARA>
</SECT2>
<SECT2>
<TITLE>Configurations</TITLE>
<PARA><productname>eCos</productname> is tailored at source level (that is, before
	    compilation or assembly) in order to create an <productname>eCos</productname>
	    <EMPHASIS>configuration</EMPHASIS>. In concrete terms, an
	    <productname>eCos</productname> configuration takes the form of a configuration save
	    file (with extension .ecc) and set of files used to build
	    user applications (including, when built, a library file
	    against which the application is linked). </PARA>
</SECT2>
</SECT1>
<SECT1 id="cdl-component-repository">
<TITLE>Component Repository</TITLE>
<PARA><productname>eCos</productname> is shipped in source in the form of a
	  <EMPHASIS>component repository</EMPHASIS> - a directory
	  hierarchy that contains the sources and other files which
	  are used to build a configuration. The component repository
	  can be added to by, for example, downloading from the
	  net.</PARA>
</SECT1>
<SECT1 id="cdl-component-definition-language">
<TITLE>Component Definition Language</TITLE>
<PARA>Part of the component repository is a set of files
	  containing a definition of its structure.  The form used for
	  this purpose is the <EMPHASIS>Component Definition
	    Language</EMPHASIS> (CDL).  CDL defines the relationships
	  between components and other information used by tools such
	  as the <productname>eCos</productname><APPLICATION>Configuration Tool</APPLICATION>.
	  CDL is generally formulated by the writers of components: it
	  is not necessary to write or understand CDL in order for the
	  embedded systems developer to construct an <productname>eCos</productname>
	  configuration. </PARA>
</SECT1>
<SECT1 id="cdl-packages">
<TITLE>Packages</TITLE>
<PARA>The building blocks of an <productname>eCos</productname> configuration are called
	  <EMPHASIS>packages</EMPHASIS>. Packages are the units of
	  software distribution.  A set of core packages (such as
	  kernel, C library and math library) is provided by Red Hat:
	  additional third-party packages will be available in
	  future.</PARA>
<PARA>A package may exist in one of a number of <EMPHASIS>versions</EMPHASIS>.
 The default version is the <EMPHASIS>current</EMPHASIS> version.
 Only one version of a given package may be present in the component
repository at any given time.</PARA>
<PARA>Packages are organized in a tree hierarchy.  Each package
is either at the top-level or is the child of another package.</PARA>
<PARA>The <productname>eCos</productname> <application> Package Administration Tool</application> can be used to add or remove
packages from the component repository.  The <productname>eCos</productname> <APPLICATION>Configuration Tool</APPLICATION> can be used to include or exclude packages from the configuration
being built.</PARA>
</SECT1>
<SECT1 id="cdl-configuration-items">
<TITLE>Configuration Items</TITLE>
<PARA><EMPHASIS>Configuration items</EMPHASIS> are the
	  individual entities that form a configuration.  Each item
	  corresponds to the setting of a C pre-processor macro (for
	  example,
	  <literal>CYGHWR_HAL_ARM_PID_GDB_BAUD</literal>). 
	  The code of <productname>eCos</productname> itself is written to test such pre-processor
	  macros so as to tailor the code.  User code can do
	  likewise.</PARA>
<PARA>Configuration items come in the following flavors:</PARA>
<ITEMIZEDLIST>
<LISTITEM>
<PARA><EMPHASIS>None</EMPHASIS>: such entities serve only as
place holders in the hierarchy, allowing other entities to be grouped
more easily.</PARA>
</LISTITEM>
<LISTITEM>
<PARA><EMPHASIS>Boolean</EMPHASIS> entities are the most common
flavor; they correspond to units of functionality that can be either
enabled or disabled.  If the entity is enabled then there will be
a #define; code will check the setting using, for example, #ifdef</PARA>
</LISTITEM>
<LISTITEM>
<PARA><EMPHASIS>Data</EMPHASIS> entities encapsulate some arbitrary
data. Other properties such as a set or range of legal values can
be used to constrain the actual values, for example to an integer
or floating point value within a certain range.</PARA>
</LISTITEM>
<LISTITEM>
<PARA><EMPHASIS>Booldata</EMPHASIS> entities combine the attributes
of <EMPHASIS>Boolean</EMPHASIS> and <EMPHASIS>Data</EMPHASIS>: they
can be enabled or disabled and, if enabled, will hold a data value.</PARA>
</LISTITEM>
</ITEMIZEDLIST>
<PARA>Like packages, configuration items exist in a tree-based hierarchy:
each configuration item has a parent which may be another configuration
item or a package.  Under some conditions (such as when packages
are added or removed from a configuration), items may be &ldquo;re-parented&rdquo; such
that their position in the tree changes. </PARA>
<SECT2>
<TITLE>Expressions</TITLE>
<PARA>Expressions are relationships between CDL items.  There are
three types of expression in CDL:</PARA>
	<table id="cdl-expressions">
	  <title>CDL Expressions</title>
	<tgroup cols="3">
	  <thead>
	  <row>
	      <entry>Expression Type</entry>
	      <entry>Result</entry>
	      <entry>Common Use (see <xref linkend="table-configuration-properties">)</entry></row>
	  </thead>
	  <tbody>
	    <row>
	      <entry>Ordinary</entry>
	      <entry>A single value</entry>
	      <entry>legal_values property</entry>
	    </row>
	    <row>
	      <entry>List</entry><entry>A range of
		values (for example &ldquo;1 to 10&rdquo;)</entry>
	      <entry>legal_values property </entry></row>
	    <row>
	      <entry>Goal</entry><entry>True or False</entry>
	      <entry>requires and active_if properties</entry></row>
	    </tbody>
	  </tgroup>
	</table>
      </SECT2>
      <SECT2>
	<TITLE>Properties</TITLE>
<PARA>Each configuration item has a set of properties.  The following
table describes the most commonly used:</PARA>
	<table id="table-configuration-properties">
	  <title>Configuration properties</title>
	  <tgroup cols="2">
	    <thead><row>
		<entry><emphasis>Property</emphasis></entry>
<entry><emphasis>Use </emphasis></entry></row>
	    </thead>
	    <tbody>
	      <row>
		<entry>Flavor</entry>
		<entry>The &ldquo;type&rdquo; of the item, as
		  described above </entry></row>
	      <row>
		<entry>Enabled</entry><entry>Whether
		  the item is enabled </entry></row>
	      <row>
		<entry>Current_value</entry>
<entry>The current value of the item </entry></row>
	      <row>
		<entry>Default_value</entry>
<entry>An ordinary expression defining the default value of the
		    item</entry></row>
	      <row>
		<entry>Legal_values</entry><entry>A
		  list expression defining the values the item may hold (for example,
		  1 to10) </entry></row>
	      <row>
		<entry>Active_if</entry><entry>A
		  goal expression denoting the requirement for this item to be active
(see below: <emphasis>Inactive Items</emphasis>) </entry></row>
<row>
<entry>Requires</entry><entry>A goal
expression denoting requirements this item places on others (see
below: <emphasis>Conflicts</emphasis>) </entry></row>
<row>
<entry>Calculated</entry><entry>Whether
the item as non-modifiable </entry></row>
<row>
<entry>Macro</entry><entry>The corresponding
C pre-processor macro </entry></row>
<row>
<entry>File</entry><entry>The C header
file in which the macro is defined </entry></row>
<row>
<entry>URL</entry><entry>The URL of
a documentation page describing the item </entry></row>
<row>
<entry>Hardware</entry><entry>Indicates
that a particular package is related to specific hardware</entry></row>
	    </tbody>
	  </tgroup>
	</table>

<PARA>A complete description of properties is contained in the <citetitle>Component
Writer&rsquo;s Guide</citetitle>.</PARA>
</SECT2>
<SECT2>
<TITLE>Inactive Items</TITLE>
<PARA>Descendants of an item that is disabled are inactive: their
values may not be changed.  Items may also become <EMPHASIS>inactive</EMPHASIS> if
an active_if expression is used to make the item dependent
on an expression involving other items. </PARA>
</SECT2>
</SECT1>
<SECT1 id="cdl-conflicts">
<TITLE>Conflicts</TITLE>
<PARA>Not all settings of configuration items will lead to a
	  coherent configuration; for example, the use of a timeout
	  facility might require the existence of timer support, so if
	  the one is required the other cannot be removed.  Coherence
	  is policed by means of consistency rules (in particular, the
	  goal expressions that appear as CDL items
	  <EMPHASIS>requires</EMPHASIS> and
	  <EMPHASIS>active_if</EMPHASIS> attributes [see
	  above]).  A violation of consistency rules creates a
	  <EMPHASIS>conflict</EMPHASIS>, which must be resolved in
	  order to ensure a consistent configuration. Conflict
	  resolution can be performed manually or with the assistance
	  of the <productname>eCos</productname> tools.  Conflicts come in the following
	  flavors:</PARA>
<ITEMIZEDLIST>
<LISTITEM>
<PARA>An <EMPHASIS>unresolved</EMPHASIS> conflict means that
there is a reference to an entity that is not yet in the current
configuration </PARA>
</LISTITEM>
<LISTITEM>
<PARA>An <EMPHASIS>illegal value</EMPHASIS> conflict is caused
when a configuration item is set to a value that is not permitted
(that is, a <EMPHASIS>legal_values</EMPHASIS> goal expression
is failing) </PARA>
</LISTITEM>
<LISTITEM>
<PARA>An <EMPHASIS>evaluation exception</EMPHASIS> conflict
is caused when the evaluation of an expression would fail (for example,
because of a division by zero) </PARA>
</LISTITEM>
<LISTITEM>
<PARA>An <EMPHASIS>unsatisfied goal</EMPHASIS> conflict is caused
by a failing <EMPHASIS>requires</EMPHASIS> goal expression </PARA>
</LISTITEM>
<LISTITEM>
<PARA>A <EMPHASIS>bad data</EMPHASIS> conflict arises only rarely,
and corresponds to badly constructed CDL.  Such a conflict can only
be resolved by reference to the CDL writer.</PARA>
</LISTITEM>
</ITEMIZEDLIST>
</SECT1>
<SECT1 id="cdl-templates">
<TITLE>Templates</TITLE>
<PARA>A <EMPHASIS>template</EMPHASIS> is a saved configuration
	  - that is, a set of packages and configuration item
	  settings.  Templates are provided with <productname>eCos</productname> to allow you to
	  get started quickly by instantiating (copying) a saved
	  configuration corresponding to one of a number of common
	  scenarios; for example, a basic <productname>eCos</productname> configuration template
	  is supplied that contains the infrastructure, kernel, C and
	  math libraries, plus their support packages.</PARA>
</SECT1>
</CHAPTER>
<CHAPTER id="component-repo-and-working-dirs">
<TITLE>The Component Repository and Working Directories</TITLE>
<PARA>Each of the file trees involved in <productname>eCos</productname> development has a
	different role. </PARA>
<SECT1 id="component-repo">
<TITLE>Component Repository</TITLE>
<PARA>The <productname>eCos</productname> <FIRSTTERM>component repository</FIRSTTERM>
	  contains directories for all the packages that are shipped
	  with <productname>eCos</productname> or provided by third parties.</PARA>
<PARA>The component repository should not be modified as part of
application development. </PARA>
<!--
<para>
XXXXX We may want to change this picture XXXXX
</para>
-->
<FIGURE>
<TITLE>Component repository</TITLE>
<GRAPHIC ENTITYREF="graphic30"></GRAPHIC>
</FIGURE>
<SECT2>
<TITLE>Purpose</TITLE>
<PARA>The component repository is the master copy of source code
for all system and third party components. It also contains some
files needed to administer and build the system, such as <command>ecosadmin.tcl</command>.</PARA>
</SECT2>
<SECT2>
<TITLE>How is it modified?</TITLE>
<PARA>You modify it by importing new versions of packages from a
distribution or removing existing packages. These activities are
undertaken using the <productname>eCos</productname> <application>Package Administration Tool</application>.</PARA>
</SECT2>
<SECT2>
<TITLE>When is it edited manually?</TITLE>
<PARA>Files in the component repository should only be edited manually
as determined by the component maintainer.</PARA>
</SECT2>
<SECT2>
<TITLE>User Applications</TITLE>
<PARA>User application source code should <EMPHASIS>not</EMPHASIS> go
into the component repository.</PARA>
</SECT2>
<SECT2>
<TITLE>Examples of files in this hierarchy:</TITLE>
<VARIABLELIST>
<VARLISTENTRY>
<TERM><FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/doc/ref/ecos-ref.html</FILENAME></TERM>
<LISTITEM>
<PARA>The top level HTML file for the
		  <citetitle><PRODUCTNAME>eCos</PRODUCTNAME> Reference
		    Manual</citetitle>. </PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/prebuilt/pid/tests/kernel/<replaceable>&Version;</replaceable>/tests/thread_gdb.exe</FILENAME></TERM>
<LISTITEM>
<PARA></PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/prebuilt/linux/tests/kernel/<replaceable>&Version;</replaceable>/tests/thread_gdb.exe</FILENAME></TERM>
<LISTITEM>
<PARA>Pre-built tests for the supported platforms, and
		  the synthetic Linux target.</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/examples/twothreads.c</FILENAME></TERM>
<LISTITEM>
<PARA>One of the example programs.</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/ecosadmin.tcl</FILENAME></TERM>
<LISTITEM>
<para>The Tcl program which is used to  import new versions of packages
from a distribution or remove existing packages.</para>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/packages/language/c/libm/<replaceable>&Version;</replaceable>/src/double/portable-api/s_tanh.c</FILENAME></TERM>
<LISTITEM>
<para>Implementation of the hyperbolic tangent function in the standard
math library.</para>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/pkgconf/rules.mak</FILENAME></TERM>
<LISTITEM>
<para>A file with <command>make</command> rules, used
by the <FILENAME>makefile</FILENAME>.</para>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</SECT2>
</SECT1>
<SECT1 id="build-tree">
<TITLE>Build Tree</TITLE>
<PARA>The <FIRSTTERM>build tree</FIRSTTERM> is the directory
	  hierarchy in which all <EMPHASIS>generated</EMPHASIS> files
	  are placed. Generated files consist of the
	  <FILENAME>makefile</FILENAME>, the compiled object files,
	  and a dependency file (with a <FILENAME>.d</FILENAME>
	  extension) for each source file.</PARA>
<SECT2><!--<conditionaltext>-->
<TITLE>Purpose</TITLE>
<PARA>The build tree is where all intermediate object files are
	    placed. </PARA>
</SECT2>
<SECT2>
<TITLE>How is it modified?</TITLE>
<PARA>Recompiling can modify the object files.</PARA>
</SECT2>
<SECT2>
<TITLE>User applications</TITLE>
<PARA>User application source or binary code should
	    <EMPHASIS>not</EMPHASIS> go in the build tree. </PARA>
</SECT2>
<SECT2>
<TITLE>Examples of files in this hierarchy</TITLE>
<VARIABLELIST>
<VARLISTENTRY>
<TERM><FILENAME>ecos-work/language/c/libc/<replaceable>&Version;</replaceable>/src</FILENAME></TERM>
<LISTITEM>
<PARA>The directory in which object files for
		  the C library are built.</PARA>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</SECT2>
</SECT1>
<SECT1 id="install-tree">
<TITLE>Install Tree</TITLE>
<PARA>The <FIRSTTERM>install tree</FIRSTTERM> is the location
	  for all files needed for application development. The
	  <filename>libtarget.a</filename> library, which contains the
	    custom-built <productname>eCos</productname> kernel and other components, is placed
	    in the install tree, along with all packages&rsquo; public
	    header files. If you build the tests, the test executable
	    programs will also be placed in the install
	    tree. </PARA>
<PARA>By default, the install tree is created by
	  <COMMAND>ecosconfig</COMMAND> in a subdirectory of the build
	  tree called <FILENAME>install</FILENAME>. This can be
	  modified with the <OPTION>--prefix</OPTION> option (see
	  <xref linkend="manual-configuration">).
	</PARA>
<SECT2><!--<conditionaltext>-->
<TITLE>Purpose</TITLE>
<PARA>The install tree is where the custom-built
	    <FILENAME>libtarget.a</FILENAME> library, which contains
	    the <productname>eCos</productname> kernel and other components, is located. The
	    install tree is also the location for all the header files
	    that are part of a published interface for their
	    component. </PARA>
</SECT2>
<SECT2>
<TITLE>How is it modified?</TITLE>
<PARA>Recompiling can replace
	    <FILENAME>libtarget.a</FILENAME> and the test
	    executables. </PARA>
</SECT2>
<SECT2>
<TITLE>When is it edited manually?</TITLE>
<PARA>Where a memory layout requires modification without
	    use of the <productname>eCos</productname> <application>Configuration Tool</application>, the memory layout
	    files must be edited directly in the install tree. These
	    files are located at
	    <FILENAME>install/include/pkgconf/mlt_*.*</FILENAME>. 
	    Note that subsequent modification of the install tree
	    using the Configuration Tool will result in such manual
	    edits being lost.</PARA>
</SECT2>
<SECT2>
<TITLE>User applications</TITLE>
<PARA>User application source or binary code should
	    <EMPHASIS>not</EMPHASIS> go in the install tree. </PARA>
</SECT2>
<SECT2>
<TITLE>Examples of files in this hierarchy</TITLE>
<VARIABLELIST>
<VARLISTENTRY>
<TERM><FILENAME>install/lib/libtarget.a</FILENAME></TERM>
<LISTITEM>
<PARA>The library containing the kernel and other components.</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME>install/include/cyg/kernel/kapi.h</FILENAME></TERM>
<LISTITEM>
<PARA>The header file for the kernel C language API.</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME>install/include/pkgconf/mlt_arm_pid_ram.ldi</FILENAME></TERM>
<LISTITEM>
<PARA>The linker script fragment describing the memory
		  layout for linking applications intended for
		  execution on an ARM PID development board using RAM
		  startup.</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM><FILENAME>install/include/stdio.h</FILENAME></TERM>
<LISTITEM>
<PARA>The C library header file for standard I/O. </PARA>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</SECT2>
</SECT1>
<SECT1 id="repository-app-build-tree">
<TITLE>Application Build Tree</TITLE>
<PARA>This tree is not part of <productname>eCos</productname> itself: it is the
	  directory in which <productname>eCos</productname> end users write their own
	  applications.</PARA>
<PARA>Example applications and their
	  <FILENAME>Makefile</FILENAME> are located in the component
	  repository, in the directory
	  <FILENAME>BASE_DIR</FILENAME><FILENAME>/examples</FILENAME>. 
	  
	</PARA>
<PARA>There is no imposed format on this directory, but there
	  are certain compiler and linker flags that must be used to
	  compile an <productname>eCos</productname> application. The basic set of flags is shown
	  in the example <FILENAME>Makefile</FILENAME>, and additional
	  details can be found in <xref linkend="compiler-and-linker-options">. </PARA>
</SECT1>
</CHAPTER>
<CHAPTER id="compiler-and-linker-options">
<TITLE>Compiler and Linker Options</TITLE>

    <PARA><productname>eCos</productname> is built using
      the GNU C and C++ compilers. <productname>eCos</productname> relies on certain features of these
      tools such as constructor priority ordering and selective linking
      which are not part of other toolchains.
    </PARA>
    
<PARA>Some <application>GCC</application> options are required for <productname>eCos</productname>,
and others can be useful. This chapter gives a brief description
of the required options as well as some recommended <productname>eCos</productname>-specific options.
All other <application>GCC</application> options (described in the <application>GCC</application> manuals)
are available. </PARA>
<SECT1 id="compiling-c-app">
<TITLE>Compiling a C Application</TITLE>
<PARA>The following command lines demonstrate the
	  <EMPHASIS>minimum</EMPHASIS> set of options required to
	  compile and link an <productname>eCos</productname> program written in C. </PARA>
<NOTE>
<PARA>Remember that when this manual shows
	    <COMMAND><replaceable>TARGET-</replaceable>gcc</COMMAND>
	    you should use the full name of the cross compiler,
	    e.g. <COMMAND>i386-elf-gcc</COMMAND>,
	    <COMMAND>arm-elf-gcc</COMMAND>, or
	    <COMMAND>sh-elf-gcc</COMMAND>. When compiling for the
	    synthetic Linux target, use the native
	    <command>gcc</command> which must have the features
	    required by <productname>eCos</productname>.</PARA>
</NOTE>
<SCREEN>
$ <replaceable>TARGET-</replaceable>gcc -c  -I<EMPHASIS>INSTALL_DIR</EMPHASIS>/include file.c
$ <replaceable>TARGET-</replaceable>gcc -o program file.o -L<EMPHASIS>INSTALL_DIR</EMPHASIS>/lib -Ttarget.ld -nostdlib
</SCREEN>
<NOTE>
<PARA>Certain targets may require extra options, for example
	    the SPARClite architectures require the option
	    <OPTION>-mcpu=sparclite</OPTION>. Examine the
	    <FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/examples/Makefile</FILENAME> 
	    or the &ldquo;Global compiler flags&rdquo; option
	    (CYGBLD_GLOBAL_CFLAGS) in your generated
	    <productname>eCos</productname> configuration) to see if any extra options are
	    required, and if so, what they are. </PARA>
<PARA>The following command lines use some other options
	    which are recommended because they use the
	<!-- <index></index> -->selective linking feature:</PARA>
<SCREEN>$ <replaceable>TARGET-</replaceable>gcc -c  -I<REPLACEABLE>INSTALL_DIR</REPLACEABLE>/include -I. -ffunction-sections -fdata-sections -g -O2 file.c
$ <replaceable>TARGET-</replaceable>gcc -o program file.o -ffunction-sections -fdata-sections -Wl,--gc-sections -g -O2 \
          -L<REPLACEABLE>INSTALL_DIR</REPLACEABLE>/lib -Ttarget.ld -nostdlib
</SCREEN>
        
</NOTE>
</SECT1>
<SECT1 id="compiling-cpp-app">
<TITLE>Compiling a C++ Application</TITLE>
<PARA>The following command lines demonstrate the
	  <EMPHASIS>minimum</EMPHASIS> set of options required to
	  compile and link an <productname>eCos</productname> program written in C++.
	</PARA>
<NOTE>
<PARA>Remember that when this manual shows
	    <COMMAND><replaceable>TARGET-</replaceable>g++</COMMAND>
	    you should use the full name of the cross compiler,
	    e.g. <COMMAND>i386-elf-g++</COMMAND>,
	    <COMMAND>arm-elf-g++</COMMAND>, or
	    <COMMAND>sh-elf-g++</COMMAND>. When compiling for the
	    synthetic Linux target, use the native
	    <command>g++</command> which must have the features
	    required by <productname>eCos</productname>.</PARA>
</NOTE>
<SCREEN>$ <replaceable>TARGET-</replaceable>g++ -c  -I<REPLACEABLE>INSTALL_DIR</REPLACEABLE>/include -fno-rtti -fno-exceptions file.cxx
$ <replaceable>TARGET-</replaceable>g++ -o program file.o -L<REPLACEABLE>INSTALL_DIR</REPLACEABLE>/lib -Ttarget.ld -nostdlib
</SCREEN>

<NOTE>
<PARA>Certain targets may require extra options,
	    for example the SPARClite architectures require the option 
	    <OPTION>-mcpu=sparclite</OPTION>. Examine the
	    <FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/packages/targets</FILENAME>
	    file or <FILENAME><REPLACEABLE>BASE_DIR</REPLACEABLE>/examples/Makefile</FILENAME>
	    or the &ldquo;Global compiler flags&rdquo; option
	    (CYGBLD_GLOBAL_CFLAGS) in your generated
	    <productname>eCos</productname> configuration) to see if any extra options are
	    required, and if so, what they are.</PARA>
<PARA>The following command lines use some other options
	    which are recommended because they use the
	    <FIRSTTERM>selective linking</FIRSTTERM> feature:</PARA>
<SCREEN>
$ <replaceable>TARGET-</replaceable>g++ -c -I<REPLACEABLE>INSTALL_DIR</REPLACEABLE>/include -I. -ffunction-sections -fdata-sections -fno-rtti \
          -fno-exceptions -finit-priority -g -O2 file.cxx
$ <replaceable>TARGET-</replaceable>g++ -o program file.o -W1,--gc-sections -g -O2 -L<REPLACEABLE>INSTALL_DIR</REPLACEABLE>/lib -Ttarget.ld  -nostdlib</SCREEN>
</NOTE>
</SECT1>
</CHAPTER>
  
<CHAPTER id="debugging-techniques">
<TITLE>Debugging Techniques</TITLE>
<PARA><productname>eCos</productname> applications and components can be debugged in
	traditional ways, with printing statements and debugger
	single-stepping, but there are situations in which these
	techniques cannot be used. One example of this is when a
	program is getting data at a high rate from a real-time
	source, and cannot be slowed down or interrupted.</PARA>
<PARA><productname>eCos</productname>&rsquo;s infrastructure module provides a
	<EMPHASIS>tracing</EMPHASIS> formalism, allowing the
	kernel&rsquo;s tracing macros to be configured in many useful
	ways. <productname>eCos</productname>&rsquo;s kernel provides <FIRSTTERM>instrumentation
	  buffers</FIRSTTERM> which also collect specific
	(configurable) data about the system&rsquo;s history and
	performance.</PARA>
<SECT1 id="tracing">
<TITLE>Tracing</TITLE>
<PARA>To use <productname>eCos</productname>&rsquo;s tracing facilities you must first
	  configure your system to use <FIRSTTERM>tracing</FIRSTTERM>.
	  You should enable the Asserts and Tracing component
	  (<OPTION>CYGPKG_INFRA_DEBUG</OPTION>) and the
	  <OPTION>Use tracing</OPTION> component within it
	  (<OPTION>CYGDBG_USE_TRACING</OPTION>). These
	  options can be enabled with the <APPLICATION>Configuration
	    Tool</APPLICATION> or by editing the file
	  <FILENAME><REPLACEABLE>BUILD_DIR</REPLACEABLE>/pkgconf/infra.h 
	  </FILENAME> manually.</PARA>
<PARA>You should then examine all the tracing-related options in
the <citetitle>Package: Infrastructure</citetitle> chapter of the <citetitle><PRODUCTNAME>eCos</PRODUCTNAME> Reference
Manual</citetitle>. One useful set of configuration options are: <literal>CYGDBG_INFRA_DEBUG_FUNCTION_REPORTS</literal> and <literal>CYGDBG_INFRA_DEBUG_TRACE_MESSAGE</literal>,
which are both enabled by default when tracing is enabled.</PARA>
<PARA>The following &ldquo;Hello world with tracing&rdquo; shows
the output from running the hello world program (from <xref linkend="ecos-hello-world">) that was
built with tracing enabled: </PARA>
<EXAMPLE>
<TITLE>Hello world with tracing</TITLE>
<SCREEN>$ mips-tx39-elf-run --board=jmr3904  hello
Hello, eCos world!
ASSERT FAIL: &lt;2&gt;cyg_trac.h          [ 623] Cyg_TraceFunction_Report_::set_exitvoid()                                                            exitvoid used in typed function
TRACE: &lt;1&gt;mlqueue.cxx         [ 395] Cyg_ThreadQueue_Implementation::enqueue()                                                            {{enter
TRACE: &lt;1&gt;mlqueue.cxx         [ 395] Cyg_ThreadQueue_Implementation::enqueue()                                                            }}RETURNING UNSET!
TRACE: &lt;1&gt;mlqueue.cxx         [ 126] Cyg_Scheduler_Implementation::add_thread()                                                           }}RETURNING UNSET!
TRACE: &lt;1&gt;thread.cxx          [ 654] Cyg_Thread::resume()                                                                                 }}return void
TRACE: &lt;1&gt;cstartup.cxx        [ 160] cyg_iso_c_start()                                                                                    }}return void
TRACE: &lt;1&gt;startup.cxx         [ 142] cyg_package_start()                                                                                  }}return void
TRACE: &lt;1&gt;startup.cxx         [ 150] cyg_user_start()                                                                                     {{enter
TRACE: &lt;1&gt;startup.cxx         [ 150] cyg_user_start()                                                                                     (((void)))
TRACE: &lt;1&gt;startup.cxx         [ 153] cyg_user_start()                                                                                     'This is the system default cyg_user_start()'
TRACE: &lt;1&gt;startup.cxx         [ 157] cyg_user_start()                                                                                     }}return void
TRACE: &lt;1&gt;sched.cxx           [ 212] Cyg_Scheduler::start()                                                                               {{enter
TRACE: &lt;1&gt;mlqueue.cxx         [ 102] Cyg_Scheduler_Implementation::schedule()                                                             {{enter
TRACE: &lt;1&gt;mlqueue.cxx         [ 437] Cyg_ThreadQueue_Implementation::highpri()                                                            {{enter
TRACE: &lt;1&gt;mlqueue.cxx         [ 437] Cyg_ThreadQueue_Implementation::highpri()                                                            }}RETURNING UNSET!
TRACE: &lt;1&gt;mlqueue.cxx         [ 102] Cyg_Scheduler_Implementation::schedule()                                                             }}RETURNING UNSET!
TRACE: &lt;2&gt;intr.cxx            [ 450] Cyg_Interrupt::enable_interrupts()                                                                   {{enter
TRACE: &lt;2&gt;intr.cxx            [ 450] Cyg_Interrupt::enable_interrupts()                                                                   }}RETURNING UNSET!
TRACE: &lt;2&gt;thread.cxx          [  69] Cyg_HardwareThread::thread_entry()                                                                   {{enter
TRACE: &lt;2&gt;cstartup.cxx        [ 127] invoke_main()                                                                                        {{enter
TRACE: &lt;2&gt;cstartup.cxx        [ 127] invoke_main()                                                                                        ((argument is ignored))
TRACE: &lt;2&gt;dummyxxmain.cxx     [  60] __main()                                                                                             {{enter
TRACE: &lt;2&gt;dummyxxmain.cxx     [  60] __main()                                                                                             (((void)))
TRACE: &lt;2&gt;dummyxxmain.cxx     [  63] __main()                                                                                             'This is the system default __main()'
TRACE: &lt;2&gt;dummyxxmain.cxx     [  67] __main()                                                                                             }}return void
TRACE: &lt;2&gt;memcpy.c            [ 112] _memcpy()                                                                                            {{enter
TRACE: &lt;2&gt;memcpy.c            [ 112] _memcpy()                                                                                            ((dst=80002804, src=BFC14E58, n=19))
TRACE: &lt;2&gt;memcpy.c            [ 164] _memcpy()                                                                                            }}returning 80002804
TRACE: &lt;2&gt;cstartup.cxx        [ 137] invoke_main()                                                                                        'main() has returned with code 0. Calling exit()'
TRACE: &lt;2&gt;exit.cxx            [  71] __libc_exit()                                                                                        {{enter
TRACE: &lt;2&gt;exit.cxx            [  71] __libc_exit()                                                                                        ((status=0 ))
TRACE: &lt;2&gt;atexit.cxx          [  84] cyg_libc_invoke_atexit_handlers()                                                                    {{enter
TRACE: &lt;2&gt;atexit.cxx          [  84] cyg_libc_invoke_atexit_handlers()                                                                      (((void)))

Scheduler:

Lock:                0
Current Thread:      &lt;null&gt;

Threads:

Idle Thread          pri =  31 state = R      id =   1
                     stack base = 800021F0 ptr = 80002510 size = 00000400
                     sleep reason NONE     wake reason NONE    
                     queue = 80000C54      wait info = 00000000

&lt;null&gt;               pri =   0 state = R      id =   2
                     stack base = 80002A48 ptr = 8000A968 size = 00008000
                     sleep reason NONE     wake reason NONE    
                     queue = 80000BD8      wait info = 00000000
	  </SCREEN>
</EXAMPLE>
</SECT1>
<SECT1 id="kernel-instrumentation">
<TITLE>Kernel Instrumentation</TITLE>
<PARA><FIRSTTERM>Instrument buffers</FIRSTTERM> can be used to
	  find out how many events of a given type happened in the
	  kernel during execution of a program.</PARA>
<PARA>You can monitor a class of several types of events, or
	  you can just look at individual events. </PARA>
<PARA>Examples of <FIRSTTERM>events</FIRSTTERM> that can be
	  monitored are:
	</PARA>
<ITEMIZEDLIST>
<LISTITEM>
<PARA>scheduler events </PARA>
</LISTITEM>
<LISTITEM>
<PARA>thread operations</PARA>
</LISTITEM>
<LISTITEM>
<PARA>interrupts </PARA>
</LISTITEM>
<LISTITEM>
<PARA>mutex operations </PARA>
</LISTITEM>
<LISTITEM>
<PARA>binary semaphore operations </PARA>
</LISTITEM>
<LISTITEM>
<PARA>counting semaphore operations </PARA>
</LISTITEM>
<LISTITEM>
<PARA>clock ticks and interrupts </PARA>
</LISTITEM>
</ITEMIZEDLIST>
<PARA>Examples of fine-grained scheduler event types are: </PARA>
<ITEMIZEDLIST>
<LISTITEM>
<PARA>scheduler lock</PARA>
</LISTITEM>
<LISTITEM>
<PARA>scheduler unlock</PARA>
</LISTITEM>
<LISTITEM>
<PARA>rescheduling</PARA>
</LISTITEM>
<LISTITEM>
<PARA>time slicing </PARA>
</LISTITEM>
</ITEMIZEDLIST>
<PARA>Information about the events is stored in an
	  <FIRSTTERM>event record</FIRSTTERM>. The structure that
	  defines this record has type <type>struct
	  Instrument_Record</type>:
</PARA>
<PARA>The list of records is stored in an array called <TYPE>instrument_buffer</TYPE>
which you can let the kernel provide or you can provide yourself
by setting the configuration option <literal>CYGVAR_KERNEL_INSTRUMENT_EXTERNAL_BUFFER</literal>. </PARA>
<PARA>To write a program that examines the instrumentation
	  buffers: </PARA>
<ORDEREDLIST>
<LISTITEM>
<PARA>Enable instrumentation buffers in the <productname>eCos</productname> kernel configuration.
The component macro is <literal>CYGPKG_KERNEL_INSTRUMENT</literal>.</PARA>
</LISTITEM>
<LISTITEM>
<PARA>To allocate the buffers yourself, enable the configuration
option <literal>CYGVAR_KERNEL_INSTRUMENT_EXTERNAL_BUFFER</literal>. </PARA>
</LISTITEM>
<LISTITEM>
<PARA>Include the header file 
<FILENAME>cyg/kernel/instrmnt.h</FILENAME>
. 
<PROGRAMLISTING>#include &lt;cyg/kernel/instrmnt.h&gt;</PROGRAMLISTING></PARA>
</LISTITEM>
<LISTITEM>
<PARA>The <STRUCTNAME>Instrumentation_Record</STRUCTNAME> structure
is not published in the kernel header file. In the future there
will be a cleaner mechanism to access it, but for now you should
paste into your code in the following lines: 
	    </para>
<PROGRAMLISTING>struct Instrument_Record
{
 CYG_WORD16 type; // record type
 CYG_WORD16 thread; // current thread id
 CYG_WORD timestamp; // 32 bit timestamp
 CYG_WORD arg1; // first arg
 CYG_WORD arg2; // second arg
};</PROGRAMLISTING>
</LISTITEM>
<LISTITEM>
<PARA>Enable the events you want to record using 
<FUNCTION>cyg_instrument_enable()</FUNCTION>
, and disable them later. Look at 
<filename>cyg/kernel/instrmnt.h</filename>
 and the examples below to see what events can be enabled. </PARA>
</LISTITEM>
<LISTITEM>
<PARA>Place the code you want to debug between the matching
functions  
<FUNCTION>cyg_instrument_enable()</FUNCTION>
 and 
<FUNCTION>cyg_instrument_disable()</FUNCTION>
. </PARA>
</LISTITEM>
<LISTITEM>
<PARA>Examine the buffer. For now you need to look at the data
in there (the example program below shows how to do that), and future
versions of <productname>eCos</productname> will include a host-side tool to help you understand
the data. </PARA>
</LISTITEM>
</ORDEREDLIST>
<EXAMPLE>
<TITLE>Using instrument buffers</TITLE>
<PARA>This program is also provided in the
	    <FILENAME>examples</FILENAME> directory.
	  </PARA>
<PROGRAMLISTING>
/* this is a program which uses <productname>eCos</productname> instrumentation buffers; it needs
 to be linked with a kernel which was compiled with support for
 instrumentation */

#include &lt;stdio.h&gt;
#include &lt;pkgconf/kernel.h&gt;
#include &lt;cyg/kernel/instrmnt.h&gt;
#include &lt;cyg/kernel/kapi.h&gt;

#ifndef CYGVAR_KERNEL_INSTRUMENT_EXTERNAL_BUFFER
# error You must configure eCos with CYGVAR_KERNEL_INSTRUMENT_EXTERNAL_BUFFER
#endif

struct Instrument_Record
{
 CYG_WORD16 type; // record type
 CYG_WORD16 thread; // current thread id
 CYG_WORD timestamp; // 32 bit timestamp
 CYG_WORD arg1; // first arg
 CYG_WORD arg2; // second arg
};

struct Instrument_Record instrument_buffer[20];
cyg_uint32 instrument_buffer_size = 20;

int main(void)
{
 int i;

 cyg_instrument_enable(CYG_INSTRUMENT_CLASS_CLOCK, 0);
 cyg_instrument_enable(CYG_INSTRUMENT_CLASS_THREAD, 0);
 cyg_instrument_enable(CYG_INSTRUMENT_CLASS_ALARM, 0);

 printf("Program to play with instrumentation buffer\n");

 cyg_thread_delay(2);

 cyg_instrument_disable(CYG_INSTRUMENT_CLASS_CLOCK, 0);
 cyg_instrument_disable(CYG_INSTRUMENT_CLASS_THREAD, 0);
 cyg_instrument_disable(CYG_INSTRUMENT_CLASS_ALARM, 0);

 for (i = 0; i &lt; instrument_buffer_size; ++i) {
 printf("Record %02d: type 0x%04x, thread %d, ",
	i, instrument_buffer[i].type, instrument_buffer[i].thread);
 printf("time %5d, arg1 0x%08x, arg2 0x%08x\n",
	instrument_buffer[i].timestamp, instrument_buffer[i].arg1,
	instrument_buffer[i].arg2);
 }
 return 0;
}</PROGRAMLISTING>
</EXAMPLE>
<PARA>Here is how you could compile and run this program in the <filename>examples</filename> directory,
using (for example) the MN10300 simulator target: </PARA>
<SCREEN>
$ make XCC=mn10300-elf-gcc PKG_INSTALL_DIR=/tmp/ecos-work-mn10300/install instrument-test
mn10300-elf-gcc -c -o instrument-test.o -g -Wall -I/tmp/ecos-work-mn10300/install/include \
        -ffunction-sections -fdata-sections instrument-test.c
mn10300-elf-gcc -nostartfiles -L/tmp/ecos-work-mn10300/install/lib -W1,--gc-sections -o \
        instrument-test instrument-test.o -Ttarget.ld -nostdlib
$ mn10300-elf-run --board=stdeval1 instrument-test
</SCREEN>
<EXAMPLE>
<TITLE>Instrument buffer output</TITLE>
<PARA>Here is the output of the
	    <COMMAND>instrument-test</COMMAND> program. Notice that in
	    little over 2 seconds, and with very little activity, and
	    with few event types enabled, it gathered 17 records. In
	    larger programs it will be necessary to select very few
	    event types for debugging. </PARA>
<PROGRAMLISTING>Program to play with instrumentation buffer
Record 00: type 0x0207, thread 2, time  6057, arg1 0x48001cd8, arg2 0x00000002
Record 01: type 0x0202, thread 2, time  6153, arg1 0x48001cd8, arg2 0x00000000
Record 02: type 0x0904, thread 2, time  6358, arg1 0x48001d24, arg2 0x00000000
Record 03: type 0x0905, thread 2, time  6424, arg1 0x00000002, arg2 0x00000000
Record 04: type 0x0906, thread 2, time  6490, arg1 0x00000000, arg2 0x00000000
Record 05: type 0x0901, thread 2, time  6608, arg1 0x48009d74, arg2 0x48001d24
Record 06: type 0x0201, thread 2, time  6804, arg1 0x48001cd8, arg2 0x480013e0
Record 07: type 0x0803, thread 1, time    94, arg1 0x00000000, arg2 0x00000000
Record 08: type 0x0801, thread 1, time   361, arg1 0x00000000, arg2 0x00000000
Record 09: type 0x0802, thread 1, time   548, arg1 0x00000001, arg2 0x00000000
Record 10: type 0x0803, thread 1, time    94, arg1 0x00000000, arg2 0x00000000
Record 11: type 0x0801, thread 1, time   361, arg1 0x00000001, arg2 0x00000000
Record 12: type 0x0903, thread 1, time   513, arg1 0x48009d74, arg2 0x48001d24
Record 13: type 0x0208, thread 1, time   588, arg1 0x00000000, arg2 0x00000000
Record 14: type 0x0203, thread 1, time   697, arg1 0x48001cd8, arg2 0x480013e0
Record 15: type 0x0802, thread 1, time   946, arg1 0x00000002, arg2 0x00000000
Record 16: type 0x0201, thread 1, time  1083, arg1 0x480013e0, arg2 0x48001cd8
Record 17: type 0x0000, thread 0, time     0, arg1 0x00000000, arg2 0x00000000
Record 18: type 0x0000, thread 0, time     0, arg1 0x00000000, arg2 0x00000000
Record 19: type 0x0000, thread 0, time     0, arg1 0x00000000, arg2 0x00000000</PROGRAMLISTING>
</EXAMPLE>
</SECT1>
</CHAPTER>
</PART>
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