1. OpenEmbedded & BitBake
Open Source Software
Carlos Ramirez Martinez-Eiroa
Professor: Corby Schmitz

2. Index
Build Tools
Make
Ant
Maven
OpenZaurus
OpenEmbedded
BitBake

3. Evolution
Make Ant Maven
BuiltRoot BitBake

4. Build Tools
The process of building a computer program is usually managed by a build tool
Build Tool: program that coordinates and controls other programs
The build utility needs to compile and link the various files, in the correct order

5. Make
Initial release: 1977
Already seen in class

6. Ant I Similar to make, but:
Implemented using the Java language
Requires the Java platform
Is best suited to building Java projects
Ant uses XML to describe the build process and its dependencies - Make has its Makefile format

7. Ant II
Conceived by James Duncan Davidson while turning Apache Tomcat (from Sun) into open source
A proprietary version of Make was used to build it on the Solaris Operating Environment

8. Ant III
In the open source world there was no way of controlling which platform was used to build Tomcat
Ant was created as a simple, platform-independent tool to build Tomcat from directives in an XML "build file”

9. Ant IV
In a Makefile the actions required to create a target are specified as shell commands which are specific to the current platform (usually Unix)
Ant provides a large amount of built-in functionality which can guarantee will behave (nearly) identically on all platforms

10. Ant V
January 2000, Ant was moved to a separate CVS module and was promoted to a project of its own, independent of Tomcat, and became Apache Ant

11. Maven uses a construct known as a Project Object Model (POM) to describe:
The software project being built
Its dependencies on other external modules and components
The build order
A key feature of Maven is that it is network-ready - The core engine can dynamically download plug-ins from a repository

12. Towards OpenEmbedded

13. A Bit of History I 2001: Sharp introducestheSL-5000 PDA running Linux
2002: Chris Larson finds out that the SharpROM sucks and starts hacking on a build system for a customized Linux distribution called "OpenZaurus”
: The OpenZaurus build system is getting stretched (beyond belief) by adding support for many more packages and target devices
January 2003: Brainstorming towards a new distribution and device independent build system

14. A Bit of History II
February 2003: Holger Schurig creates the OpenEmbedded repository and starts hacking on the first version
May 2003: Chris Larson adds major functionality to the OpenEmbedded core and starts converting packages from the OpenZaurus build system
December 2003: Michael Lauer releases OpenZaurus3.3.5, abandons the OpenZaurus build system, and converts100s of packages to OpenEmbedded
December 2004: OpenEmbedded is split up into the BitBake build system and the OpenEmbedded metadata

15. OpenZaurus
OpenEmbedded is the successor to the great OpenZaurus project
The OpenZaurus project was created as an alternative ROM image for the Sharp Zaurus Personal Mobile Tool

16. (ROM image)
(ROM image: computer file which contains a copy of the data from a read-only memory chip
Software which is being developed for embedded computers is often written to ROM files for testing on a standard computer before it is written to a ROM chip for use in the embedded system)

17. OpenZaurus II The project had pushed buildroot to its limits
Buildroot: set of Makefiles and patches that makes it easy generate a cross-compilation toolchain and root filesystem for a target Linux system using the uClibc C library

18. OpenZaurus III
Buildroot supported the creation of ipk packages, feeds and images and had support for more than one machine
But => impossible to use different patches, files for different architectures, machines or distributions
(ipk: lightweight package management system designed specifically for use in Linux devices with limited storage)

19. OpenEmbedded OpenEmbedded was created to overcome this shortcoming
On 7 December 2004 Chris Larson split the project into two parts: BitBake, a generic task executor and OpenEmbedded, the metadata for BitBake

20. OpenEmbedded II
Software framework to create Linux distributions for embedded systems
This may include bootloader, Linux, and applications
Is a set of metadata used to cross-compile, package and install software packages
License: GPL

21. Objectives Be self-contained
Be able to use external toolchains or build them
Easily cross-compile software, build packages or create root-filesystems
Easily add new features, machines, architectures,…

22. BitBake I OpenEmbedded built tool
Controls how to build things and the build dependencies
Collects and manages an open set of largely independent build descriptions (package recipes) and builds them in proper order

23. BitBake II
Used to compile different Linux kernels for a variety of PDAs
Easier to use (in theory) than manually using tools like patch and make
Programming language: Python
License: GNU General Public License (GPL), MIT/X Consortium License

24. Process of Making Images
Binary
Packages
BitBake
Recipes
Flash Image
Task Graph

25. BitBake File and Data Types
Three different file types:
.conf: configuration data
.bbclass: (build) classes
.bb (.inc): package recipes
BitBake parses the build classes, config files, and recipes
For every task BitBake creates a shell script on-the-fly and executes it

26. Main Tasks TASK DESCRIPTION FUNCTION Fetch
Downloads data from upstream
do_fetch()
Unpack
Unpacks data
do_unpack()
Patch
Applies patches
do_patch()
Configure
Configures the source tree
do_configure()
Compile
Compiles the source tree
do_compile()
Stage
Installs to the staging area
do_stage()
Install
Installs into the packaging are
do_install()
Package
Creates packages
do_package()

27. BitBake Recipe DESCRIPTION = "Hello world program“ PR = "r0“
SRC_URI = "file://myhelloworld.c \ file://README.txt“
do_compile() {
${CC} ${CFLAGS} ${LDFLAGS} ${WORKDIR}/myhelloworld.c -o myhelloworld }
do_install() {
install -m d ${D}${bindir} ${D}${docdir}/myhelloworld
install -m 0644 ${S}/myhelloworld ${D}${bindir}
install -m 0644 ${WORKDIR}/README.txt ${D}${docdir}/myhelloworld

28. Summary I OpenEmbedded: A metadata repository containing Build classes
Machine configurations
Distribution policies
Recipes
To create complete embedded Linux distributions from scratch

29. Summary II BitBake: A simple tool to execute tasks on metadata
Parser to handle metadata
Package graph to handle package interdependencies
Task graph to handle task interdependencies
On-the-fly shell script generator

30. Why all this?
SlugOS/BE is a replacement firmware image for the Linksys NSLU2
It is produced using OpenEmbedded

31. Questions?