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authorChris Johns <chrisj@rtems.org>2016-11-03 16:58:08 +1100
committerChris Johns <chrisj@rtems.org>2016-11-03 16:58:08 +1100
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+.. comment SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+.. COMMENT: All rights reserved.
+
+.. _Makefiles:
+
+Makefiles
+#########
+
+This chapter discusses the Makefiles associated with a BSP. It does not
+describe the process of configuring, building, and installing RTEMS. This
+chapter will not provide detailed information about this process. Nonetheless,
+it is important to remember that the general process consists of four phases as
+shown here:
+
+- ``bootstrap``
+
+- ``configure``
+
+- ``build``
+
+- ``install``
+
+During the bootstrap phase, you are using the ``configure.ac`` and
+``Makefile.am`` files as input to GNU autoconf and automake to generate a
+variety of files. This is done by running the ``bootstrap`` script found at
+the top of the RTEMS source tree.
+
+During the configure phase, a number of files are generated. These generated
+files are tailored for the specific host/target combination by the configure
+script. This set of files includes the Makefiles used to actually compile and
+install RTEMS.
+
+During the build phase, the source files are compiled into object files and
+libraries are built.
+
+During the install phase, the libraries, header files, and other support files
+are copied to the BSP specific installation point. After installation is
+successfully completed, the files generated by the configure and build phases
+may be removed.
+
+Makefiles Used During The BSP Building Process
+==============================================
+
+RTEMS uses the *GNU automake* and *GNU autoconf* automatic configuration
+package. Consequently, there are a number of automatically generated files in
+each directory in the RTEMS source tree. The ``bootstrap`` script found in the
+top level directory of the RTEMS source tree is executed to produce the
+automatically generated files. That script must be run from a directory with a
+``configure.ac`` file in it. The ``bootstrap`` command is usually invoked in
+one of the following manners:
+
+- ``bootstrap`` to regenerate all files that are generated by autoconf and
+ automake.
+
+- ``bootstrap -c`` to remove all files generated by autoconf and automake.
+
+- ``bootstrap -p`` to regenerate ``preinstall.am`` files.
+
+There is a file named ``Makefile.am`` in each directory of a BSP. This file is
+used by *automake* to produce the file named ``Makefile.in`` which is also
+found in each directory of a BSP. When modifying a ``Makefile.am``, you can
+probably find examples of anything you need to do in one of the BSPs.
+
+The configure process specializes the ``Makefile.in`` files at the time that
+RTEMS is configured for a specific development host and target. Makefiles are
+automatically generated from the ``Makefile.in`` files. It is necessary for
+the BSP developer to provide the ``Makefile.am`` files and generate the
+``Makefile.in`` files. Most of the time, it is possible to copy the
+``Makefile.am`` from another similar directory and edit it.
+
+The ``Makefile`` files generated are processed when configuring and building
+RTEMS for a given BSP.
+
+The BSP developer is responsible for generating ``Makefile.am`` files which
+properly build all the files associated with their BSP. Most BSPs will only
+have a single ``Makefile.am`` which details the set of source files to build to
+compose the BSP support library along with the set of include files that are to
+be installed.
+
+This single ``Makefile.am`` at the top of the BSP tree specifies the set of
+header files to install. This fragment from the SPARC/ERC32 BSP results in
+four header files being installed.
+
+.. code-block:: makefile
+
+ include_HEADERS = include/bsp.h
+ include_HEADERS += include/tm27.h
+ include_HEADERS += include/erc32.h
+ include_HEADERS += include/coverhd.h
+
+When adding new include files, you will be adding to the set of
+``include_HEADERS``. When you finish editing the ``Makefile.am`` file, do not
+forget to run ``bootstrap -p`` to regenerate the ``preinstall.am``.
+
+The ``Makefile.am`` also specifies which source files to build. By convention,
+logical components within the BSP each assign their source files to a unique
+variable. These variables which define the source files are collected into a
+single variable which instructs the GNU autotools that we are building
+``libbsp.a``. This fragment from the SPARC/ERC32 BSP shows how the startup
+related, miscellaneous support code, and the console device driver source is
+managed in the ``Makefile.am``.
+
+.. code-block:: makefile
+
+ startup_SOURCES = ../../sparc/shared/bspclean.c ../../shared/bsplibc.c \
+ ../../shared/bsppredriverhook.c \
+ ../../shared/bsppost.c ../../sparc/shared/bspstart.c \
+ ../../shared/bootcard.c ../../shared/sbrk.c startup/setvec.c \
+ startup/spurious.c startup/erc32mec.c startup/boardinit.S
+ clock_SOURCES = clock/ckinit.c
+ ...
+ noinst_LIBRARIES = libbsp.a
+ libbsp_a_SOURCES = $(startup_SOURCES) $(console_SOURCES) ...
+
+When adding new files to an existing directory, do not forget to add the new
+files to the list of files to be built in the corresponding ``XXX_SOURCES``
+variable in the ``Makefile.am`` and run``bootstrap``.
+
+Some BSPs use code that is built in ``libcpu``. If you BSP does this, then you
+will need to make sure the objects are pulled into your BSP library. The
+following from the SPARC/ERC32 BSP pulls in the cache, register window
+management and system call support code from the directory corresponding to its
+``RTEMS_CPU`` model.
+
+.. code-block:: makefile
+
+ libbsp_a_LIBADD = ../../../libcpu/@RTEMS_CPU@/cache.rel \
+ ../../../libcpu/@RTEMS_CPU@/reg_win.rel \
+ ../../../libcpu/@RTEMS_CPU@/syscall.rel
+
+.. note:
+
+The ``Makefile.am`` files are ONLY processed by ``bootstrap`` and the resulting
+``Makefile.in`` files are only processed during the configure process of a
+RTEMS build. Therefore, when developing a BSP and adding a new file to a
+``Makefile.am``, the already generated ``Makefile`` will not automatically
+include the new references unless you configured RTEMS with the
+``--enable-maintainer-mode`` option. Otherwise, the new file will not being be
+taken into account!
+
+Creating a New BSP Make Customization File
+==========================================
+
+When building a BSP or an application using that BSP, it is necessary to tailor
+the compilation arguments to account for compiler flags, use custom linker
+scripts, include the RTEMS libraries, etc.. The BSP must be built using this
+information. Later, once the BSP is installed with the toolset, this same
+information must be used when building the application. So a BSP must include
+a build configuration file. The configuration file is ``make/custom/BSP.cfg``.
+
+The configuration file is taken into account when building one's application
+using the RTEMS template Makefiles (``make/templates``). These application
+template Makefiles have been included with the RTEMS source distribution since
+the early 1990's. However there is a desire in the RTEMS user community to
+move all provided examples to GNU autoconf. They are included in the 4.9
+release series and used for all examples provided with RTEMS. There is no
+definite time table for obsoleting them. You are free to use these but be
+warned they have fallen out of favor with many in the RTEMS community and may
+disappear in the future.
+
+The following is a slightly shortened version of the make customization file
+for the gen68340 BSP. The original source for this file can be found in the
+``make/custom`` directory.
+
+.. code-block:: makefile
+
+ # The RTEMS CPU Family and Model
+ RTEMS_CPU=m68k
+ RTEMS_CPU_MODEL=m68340
+ include $(RTEMS_ROOT)/make/custom/default.cfg
+ # This is the actual bsp directory used during the build process.
+ RTEMS_BSP_FAMILY=gen68340
+ # This contains the compiler options necessary to select the CPU model
+ # and (hopefully) optimize for it.
+ CPU_CFLAGS = -mcpu=cpu32
+ # optimize flag: typically -O2
+ CFLAGS_OPTIMIZE_V = -O2 -g -fomit-frame-pointer
+
+The make customization files have generally grown simpler and simpler with each
+RTEMS release. Beginning in the 4.9 release series, the rules for linking an
+RTEMS application are shared by all BSPs. Only BSPs which need to perform a
+transformation from linked ELF file to a downloadable format have any
+additional actions for program link time. In 4.8 and older, every BSP specified
+the "make executable" or ``make-exe`` rule and duplicated the same actions.
+
+It is generally easier to copy a ``make/custom`` file from a BSP similar to the
+one being developed.