programming-concepts-techniques.sgml

eCos操作系统源码

	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>
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<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>