How to build the RTEMS kernel
=============================

Prerequisites
-------------

RTEMS cross tools have to be installed for this.
(see :ref:`crosstools <crosstools>`).

Introduction
------------

The RTEMS kernel is not built directly but with the project "rtems-build-tool". This project not just builds the RTEMS kernel but creates a bootable image that is used at the mvme2100-cpu here at the Helmholtz-Zentrum Berlin.

For RTEMS 4.9 this image also contains "cexp" and "GeSys". Both are needed to
have an interactive shell and support for a startup-script that is executed
after the kernel is loaded.

All later RTEMS versions basically only contain the RTEMS kernel. 

How to build
------------

You first have to review or change some configuration variables in file CONFIG.COMMON.
(see :ref:`common configuration variables <common_config_variables>`).

Review RTEMS kernel directory settings
--------------------------------------

.. _rtems_kernel_config_variables:

+------------------------------+------------------------------------+------------------------------------------+
| Variable                     | default value                      | explanation                              |
+==============================+====================================+==========================================+
| RTEMS_BUILD_TOOL_SRC_DIR     | $TOP/src/kernel/$RTEMS_VERSION     | Directory where rtems-build-tool sources |
|                              |                                    | are put                                  |
+------------------------------+------------------------------------+------------------------------------------+
| RTEMS_BUILD_TOOL_INSTALL_DIR | $INSTALLTOP/rtems/$RTEMS_VERSION   | Directory where rtems-build-tool is      |
|                              |                                    | installed                                |
+------------------------------+------------------------------------+------------------------------------------+
| RTEMS_BUILD_TOOL_URL         | https://www-csr.bessy.de/          | URL where RTEMS_BUILD_TOOL_URL is        |
|                              | cgi-bin/hgweb.cgi/rtems-build-tool | downloaded from                          |
+------------------------------+------------------------------------+------------------------------------------+
| RTEMS_BUILD_TOOL_TESTS       | "no"                               | If set to "yes", RTEMS tests are built   |
|                              |                                    | too                                      |
+------------------------------+------------------------------------+------------------------------------------+

Build the cross tools
---------------------

Just enter::

  bin/build-kernel.sh CONFIGFILE

where CONFIGFILE is the file "CONFIG-RTEMS-NN" that specifies the RTEMS version.