path: root/doc/source/introduction.rst

Introduction
============

This is a compilation and usage manual for the port of the eCos :abbr:`RTOS (real-time operating system)` for the `Toradex Colibri VF61 Freescale Vybrid Computer on Module <http://developer.toradex.com/product-selector/colibri-vf61>`_.
It gives a brief overview on how to get the port, compile it and run an example program on the module using a Linux host.

The eCos port is targeted for the Cortex-M core of the heterogeneous Vybrid CPU, to provide a robust way to drive a real-time control setup, and is best combined with Linux or similar OS running on the Colibri VF61 Cortex-A core for handling non-critical outside communication, user interfaces etc.

ECos
----

ECos is a configurable real-time operating system intended for use in embedded applications.
The documentation for eCos 3.0, which is the most recent version of the system as well as the one ported to Colibri VF61, can be found at http://ecos.sourceware.org/docs-3.0/.

Licence
-------

*(based on the* `eCos licence overview <http://ecos.sourceware.org/license-overview.html>`_\ *)*

ECos is released under a modified version of the well known `GNU General Public License (GPL) <http://www.gnu.org/copyleft/gpl.html>`_. The eCos license is officially recognised as a GPL-compatible Free Software License. An **exception clause** has been added which limits the circumstances in which the license applies to other code when used in conjunction with eCos. The exception clause is as follows:

   As a special exception, if other files instantiate templates or use macros or inline functions from this file, or you compile this file and link it with other works to produce a work based on this file, this file does not by itself cause the resulting work to be covered by the GNU General Public License. However the source code for this file must still be made available in accordance with section (3) of the GNU General Public License.

   This exception does not invalidate any other reasons why a work based on this file might be covered by the GNU General Public License.

**The license does not require users to release the source code of any** *applications* **that are developed with eCos.**

Supported features
------------------

This eCos port provides the following software packages specific for Toradex Colibri Vybrid VF61 Vybrid module:

* HAL package
* debug UART driver
* serial port driver
* Flex Timer Module
* GPIO handling

Version information
-------------------

.. csv-table::
   :header: Author,Content,Date,Version

   Peter Katarzynski,Draft version,2014-03-21,0.1.0
   Michael Gielda,Revamp,2014-03-27,0.2.0
   Michael Gielda,Prerequisites & compiling sample programs,2014-03-27,0.3.0
   Michael Gielda,Running programs,2014-03-28,0.3.1
   Michael Gielda,Further updates,2014-04-02,0.3.2

Compiling the system
====================

The compilation process was tested on the Gentoo, Debian, Ubuntu and Mint Linux distributions. The procedures described here should also work on other systems, but if you find any way to improve this manual with respect to tested platforms, please e-mail us at contact@antmicro.com.

.. _prerequisites:

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

Toolchain
~~~~~~~~~

This port of eCos was prepared using a pre-built standard eCos toolchain, which can be obtained e.g. from the `GWDG FTP server <ftp://ftp.gwdg.de/pub/misc/sources.redhat.com/ecos/gnutools/i386linux/test/>`_.

.. code-block:: bash
   
   wget ftp://ftp.gwdg.de/pub/misc/sources.redhat.com/ecos/gnutools/i386linux/test/\
   ecos-gnutools-arm-eabi-20120623.i386linux.tar.bz2
   tar xjvf ecos-gnutools-arm-eabi-20120623.i386linux.tar.bz2 
	
Alternatively it is possible to compile eCos software using self-built toolchains as described `on the eCos website <http://ecos.sourceware.org/getstart.html>`_, and proceed with the instructions given there.

To compile eCos and eCos applications, the toolchain's :file:`bin` directory has to be included in the PATH variable.
The proper availability of the toolchain can be checked by finding out if ``arm-eabi-gcc`` is available from the shell.

:program:`ecosconfig`
~~~~~~~~~~~~~~~~~~~~~

The :program:`ecosconfig` tool, available from the `eCosCentric website <http://www.ecoscentric.com/snapshots/ecosconfig-100305.bz2>`_, is used to generate the build tree from the main repository and is a mandatory requirement.
:program:`ecosconfig` requires the tcl compiler to work. 

.. topic:: Installing tcl on Debian-based distributions

   .. code-block:: bash

      sudo apt-get install tcl8.5 # use sudo emerge dev-lang/tcl for Gentoo

Now you can download and use :program:`ecosconfig`. You also need to make :program:`ecosconfig` executable after downloading and extracting it from the archive. It is also a good idea to make it available system-wide by moving it to ``/usr/local/bin``.

.. topic:: Installing ecosconfig

   .. code-block:: bash

      wget http://www.ecoscentric.com/snapshots/ecosconfig-100305.bz2
      bunzip2 ecosconfig-100305.bz2
      chmod +x ecosconfig-100305
      sudo mv ecosconfig-100305 /usr/local/bin/ecosconfig

.. warning::

   :program:`ecosconfig` is a 32bit application, thus if you are using a 64bit OS you have to provide 32bit run-time libraries for compatibility. In a Debian-based Linux distributions these could be installed using the command ``sudo apt-get install ia32-libs``.

.. note::

   The output of :program:`ecosconfig` are :abbr:`.ecc (eCos Configuration)` files which are in essence ``tcl`` scripts storing all the information on what elements will be included in the system image and how they will be configured.
   
.. note::
   
   A `handbook on ecosconfig <http://ecos.sourceware.org/docs-3.0/user-guide/using-ecosconfig-on-linux.html>`_ exists to help in the manual creation of :abbr:`.ecc` files.
   Also, if you want to create custom eCos configuration files, see :ref:`custom-config`.

Source code
-----------

The source of the port can be downloaded by using the following command:

.. topic:: Downloading the Colibri VF61 eCos source

   .. code-block:: bash

      git clone https://github.com/mgielda/ecos-colibri-vf61.git

Building eCos
=============

Preparing an :abbr:`.ecc` file
------------------------------

The actual configuration of the eCos system is maintained and modified through :program:`ecosconfig`.
The following commands will prepare a sample :abbr:`.ecc` file for a kernel with default settings.

.. topic:: Generating the kernel ecc file from scratch.

   .. code-block:: bash

	export ECOS_REPOSITORY="{path/to/ecos-vybrid/ecos}/packages"  # modify this
	# Create ecos.ecc file based on Colibri VF61 default template
	ecosconfig new col_vf61 default

You now have a ``ecos.ecc`` file that holds the default eCos configuration for Colibri VF61.
The file can be further  edited manually with a text editor and/or :program:`ecosconfig` or graphically using :program:`configtool` (see :ref:`custom-config`), but at this moment it is already enough to compile a sample eCos kernel.

.. _build-kernel:

Building the kernel
-------------------

A short shell script is proposed to make the compilation process easier:

.. topic:: Making the eCos kernel script

   .. code-block:: bash

      export ECOS_REPOSITORY="{path/to/ecos-vybrid/ecos}/packages"  # modify this
      export PATH="{path/to/toolchain}/bin:$PATH"                   # modify this

      mkdir -p ecos-kernel
      rm -rf ecos-kernel/*
      cd ecos-kernel

      ecosconfig --config={path/to}/ecos.ecc tree                   # modify this
      make

The resulting kernel files can be found in :file:`ecos-kernel/install/lib`.

Application
-----------

With a compiled kernel files in the :file:`ecos-kernel/install/lib` directory (see :ref:`build-kernel`), a user space eCos application can be compiled and linked to it.

A listing for a short sample application (taken from :file:`ecos/examples/hello.c`) is given below.

.. topic:: hello.c - sample application

   .. code-block:: c

      #include <stdio.h>

      int main(void)
      {
          printf("Hello, eCos world!\r\n");
          return 0;
      }

You can compile an eCos program with a procedure similar to the following listing (which you can save for reuse, for example as ``make.sh``):

.. topic:: Building a user space application

   .. code-block:: bash

      export PATH="{path/to/toolchain}/bin:$PATH"                   # modify this

      # Set compiler options
      OPT="-Wall -Wpointer-arith -Wstrict-prototypes -Wundef  \
           -Wno-write-strings -mthumb -g -O2 -fdata-sections  \
           -ffunction-sections -fno-exceptions -nostdlib      \
           -mcpu=cortex-m4"

      # Set path to eCos kernel
      KPATH="{path/to/kernel}"                                      # modify this

      # Do compilation and link your application with kernel
      arm-eabi-gcc -g -I./ -g -I${KPATH}/install/include hello.c \
                   -L${KPATH}/install/lib -Ttarget.ld ${OPT}

      # Use objcopy to generate a binary
      arm-eabi-objcopy -O binary a.out hello.bin

Running and usage
=================

This chapter will explain how to run the eCos application on the Vybrid Cortex-M core from the Cortex-A core in two ways: either from Linux using ``MQXBboot`` or from U-Boot using TFTP.

Vybrid has three available memory regions:

* OCRAM - 256KB - Default.
* DRAM - 10MB - Available, but needs limiting Linux RAM memory.
* TCML - 32KB - Small. Not recommended.

.. note::

   Out of the 16MB of the DRAM memory in the CPU, 6MB was reserved for enabling the passing of large data blocks between Cortex-A and Cortex-M. This setting can be changed in the ``ecos/packages/hal/cortexm/vybrid/col_vf61/current/include/pkgconf/mlt_vybrid_ext_dram.ldi`` file by modifying the ``DRAM LENGTH`` and ``hal_startup_stack`` values (currently ``0x9FFFF0``).

U-Boot over TFTP
----------------

Set up TFTP on your host machine and put the binary to be loaded (for example, ``hello.bin``) there. Make sure your host machine is connected to the network and you know its IP address.

.. _u-boot:

Configuring U-Boot
~~~~~~~~~~~~~~~~~~

.. note::

   The memory restriction is mandatory only if DRAM is used to run eCos. See :ref:`memory` for details.

Connect the module to the network with an Ethernet cable, power it on.
Enter U-Boot and then use the following command sequence:

.. code-block:: bash
  
   dhcp                         # set module IP address
   set memargs mem=240M         # restrict Linux memory space
   set serverip xxx.xxx.xxx.xxx # set TFTP server address
   save                         # save the configuration

Run the application
~~~~~~~~~~~~~~~~~~~

The application can then be run over TFTP with the ``tftp`` command.
The two other ``mw`` commands will set the entry point and turn on the clocks, respectively.
OCRAM is recommended as default, but you may refer to :ref:`memory` for information on what memory to use and how to get eCos to run from it.

.. topic:: OCRAM (default)

   .. code-block:: bash

      tftp 0x3f000400 hello.bin
      mw.l 0x4006e028 0x1f000411
      mw.l 0x4006b08c 0x00015a5a

.. topic:: DRAM

   .. code-block:: bash

      tftp 0x8f000400 hello.bin
      mw.l 0x4006e028 0x0f000411
      mw.l 0x4006b08c 0x00015a5a

.. topic:: TCML

   .. code-block:: bash
   
      tftp 0x1f800400 hello.bin
      mw.l 0x4006e028 0x1f800411
      mw.l 0x4006b08c 0x00015a5a

Linux over MQXBoot
------------------

Requirements
~~~~~~~~~~~~

The following have to be present on the Cortex-A Linux (apart from the eCos binary) to make this method possible:

* ``mcc.ko`` kernel module
* ``mqxboot`` binary

.. _running:

Running
~~~~~~~

The command to run the binary depends on the memory we want to use.
OCRAM is recommended as default, but you may refer to :ref:`memory` for information on what memory to use and how to get eCos to run from it.

.. topic:: Loading to OCRAM (default)

   .. code-block:: bash

      mqxboot hello.bin 0x3f000400 0x1f000411

.. topic:: Loading to DRAM

   .. code-block:: bash

      mqxboot hello.bin 0x8f000400 0x0f000411

.. topic:: Loading to TCML

   .. code-block:: bash

      mqxboot hello.bin 0x1f800400 0x1f800411

.. _custom-config:

Appendix A: custom eCos configuration
=====================================

ECos is called a *configurable* system for a reason: it contains a powerful infrastructure for choosing what system components and abstractions are included and how they are configured.

This Appendix will describe briefly how to deal with :abbr:`.ecc` files for the Colibri VF61.

Background
----------

The main tool used for building the eCos operating system is :program:`ecosconfig` (see :ref:`prerequisites`).
The source tree of eCos, called **eCos repository** (like for example the source code tree provided in this release) is not built directly but instead first trimmed down and configured to suit the needs of a specific user and platform using :program:`ecosconfig`.
This static pick-and-build procedure allows the user to exclude these elements of the system which are not necessary, thus reducing the memory footprint.
This mechanism also enables easy configuration of system-wide variables and driver specific features.

What exactly can be included, excluded or configured is determined by the contents of :file:`.cdl` files residing side by side with all source files in the eCos repository (usually in the :file:`cdl` directory on the same level as the :file:`src` directory of a given package, like a driver for a particular interface).

:program:`configtool`
---------------------

:program:`configtool` is a GUI front-end to :program:`ecosconfig` to facilitate the creation of eCos configuration files.
It also may be downloaded from `eCosCentric <http://www.ecoscentric.com/snapshots/configtool-100305.bz2>`_.

.. warning::

   :program:`configtool` (just like :program:`ecosconfig`) is a 32bit application, thus if you are using a 64bit OS you have to provide 32bit run-time libraries for compatibility. In a Debian-based Linux distributions these could be installed using the command ``sudo apt-get install ia32-libs``.

Templates
---------

:program:`configtool` allows the user to build the system however they want using a graphical user interface, provided constraints in :file:`.cdl` files describing the system structure are maintained.

While creating a new :abbr:`.ecc` file it is easier to also use a predefined template representing common use scenarios, such as **posix** which represents a system which has all the necessary packages to run typical POSIX programs or **redboot** which understandably is used to build a binary of RedBoot, the eCos bootloader.

In order to select a template to base upon, use :menuselection:`build --> templates`.

.. warning::

   Remember that the templates are just general scenarios, which may contain settings incompatible with the desired ones (baudrates, console mangling, debug console choice, presence of RedBoot ROM monitor). It is necessary to tweak them according to your needs.

Preparing an :abbr:`.ecc` file using :program:`configtool`
----------------------------------------------------------

Launch :program:`configtool`. 

Select :menuselection:`build --> repository` specify the path to eCos repository (the ``packages`` directory).
Select the :menuselection:`build --> template` option and choose the :guilabel:`Toradex Colibri VF61` as your hardware platform with default set of packages.
Click :guilabel:`continue` to proceed.

When the default set of packages is used for the platform, the associated :abbr:`.ecc` file can already be prepared.
Save it in a directory accessible by your build script and **remember to point to it in** :ref:`the kernel build script <build-kernel>`.

Other packages can be added from :menuselection:`build --> packages`, bear in mind that you may need to alter the chosen packages and options to satisfy some ``.cdl`` constraints.

.. _memory:

Startup memory choice
---------------------

There are three memories from which eCos software may be launched in Colibri VF61.
This is determined in the :abbr:`.ecc` file the eCos kernel was based on.

By default the software is prepared to be launched from OnChip RAM (OCRAM).
Alternatively DRAM memory may be used for booting.
In this approach however the DDR memory block assigned to Linux must be limited to prevent Linux from accessing the memory region already occupied by eCos.
This may be achieved by altering the boot arguments from U-Boot as described in the section entitled :ref:`u-boot`.

The OCRAM and DDR scenarios are recommended; alternatively you may also try to run eCos from TCML, but this method was not tested.
Besides, TCML offers a limited amount of memory which may be insufficient for many eCos applications.

To modify the startup memory scenario in the eCos kernel, :program:`configtool` can be used.
The appropriate menu option is:

:menuselection:`eCos HAL --> Cortex-M Architecture --> Freescale Vybrid Cortex-M4 Variant --> Toradex Colibri VF61 Platform --> Startup type`

The associated parameters are:

* CYG_HAL_STARTUP_PLF (ByVariant / DRAM)
* CYG_HAL_STARTUP_VAR  (OCRAM / TCML)