Yocto - Embedded Linux Distribution Maker

Embedded Linux @ Information Technology Institute 1
Embedded Linux
Yocto
Information Technology Institute
Sherif Mousa

Agenda
●
What is Yocto?
●
Why Yocto?
●
Yocto Project Overview
●
Yocto Key Concept (recipe)
●
Yocto Workflow
●
Yocto Member Organizations
●
Working with Yocto

What is Yocto?
It's not an embedded Linux distribution -
It creates a custom one for you.
●
www.yoctoproject.org
●
The Yocto Project is an open-source collaboration project. It
provides templates, tools and methods to help you create custom
Linux-based systems for embedded products regardless of
hardware architecture.
●
Yocto Project uses a build system based on the OpenEmbedded
(OE) project, which uses the BitBake tool, to construct complete
Linux images. The BitBake and OE components are combined
together to form Poky, a reference build system.

Why Yocto?
●
Develop using one common Linux OS for different
architectures.
●
Re-use your software stack with future devices.
●
Changing hardware platforms with updating just one line
in a config file and rebuild.
●
Base your work on a validated collection of software and
libraries.
Developers spend lots of time porting or making build systems, leaves
less time and resources to develop value-adding software features.

Yocto Project Overview
●
OpenEmbedded (OE) – The overall build architecture
used by the Yocto Project.
●
BitBake – Task executor and scheduler.
●
Metadata – Task definitions.
●
Configuration (*.conf) – global definitions of variables.
●
Classes (*.bbclass) – encapsulation and inheritance of
build logic, packaging, etc.
●
Recipes (*.bb) – the logical units of software/images to
build.

Yocto Project Overview (cont'd)
●
OpenEmbedded Core (oe-core) – A core set of
metadata shared by the OpenEmbedded and the
Yocto Project.
●
meta-yocto – Reference policy/distro configuration
and reference hardware support layer.
●
Poky – A pre-prepared combination of the build
system components needed; also the name of our
reference distro in meta-yocto
Poky = Bitbake + OE-core + meta-yocto + docs

Yocto Key Concept (recipe)
●
The Yocto Project provides tools and metadata for
creating custom Linux images.
●
These images are created from a repository of 'baked'
recipes.
●
A recipe is a set of instructions for building packages:
– Where to obtain the upstream sources and which patches to
apply
– Dependencies (on libraries or other recipes)
– Configuration/compilation options
– Define which files go into what output packages

Yocto Workflow

Yocto Member Organizations

Working with Yocto

Yocto First Shot
●
Download Yocto source
– All releases: http://downloads.yoctoproject.org/releases/yocto/
– Current final release: poky-dizzy-12.0.1.tar.bz2
●
Untar the downloaded file
$ tar xvf pokydizzy12.0.1.tar.bz2
●
Go inside the project directory: $ cd pokydizzy12.0.1
●
Source the poky default environment script
$ source oeinitbuildenv
●
Configure (if you want) your conf ile: $ vim conf/local.conf
●
Start the build process (and wait ….)
bitbake coreimageminimal
●
Run Qemu emulator with output image
runqemu qemux86

Poky Directory Structure
●
bitbake: the BitBake utility itself.
●
documentation: documentation sources.
●
scripts: various support scripts (e.g, runqemu)
●
meta/conf: important configuration files,
bitbake.conf, reference distro config, machine
configs for QEMU architectures.
●
meta/classes: BitBake classes.
●
meta/recipes-* : recipes for all packages & libs

Recipe Skeleton
●
Example of a recipe
SUMMARY = “”
DISCRIPTION = “”
HOMEPAGE = “”
LICENSE = “”
SRC_URI = “”
SRC_URI[md5sum] = “”
inherit stuff
don't edit the poky default recipes, but create
your own recipes & layers

Yocto Configuration Files
●
Build directory files
●
conf/bblayers.conf
– Contains locations for all layers needed for your build process.
BBLAYERS ?= "
/home/user/yocto/poky/metayocto ............
●
conf/local.conf
– Set your build options, choose target machine, add or remove features
from your build image
BB_NUMBER_THREADS = "threads"
PARALLEL_MAKE = "j threads"
MACHINE ?= "qemuarm"
DL_DIR ?= <downloaddirpath>

Recipe build steps
●
Building recipes involves executing the following
functions, which can be overridden when needed for
customizations.
– do_fetch
– do_unpack
– do_patch
– do_configure
– do_compile
– do_install
– do_package

Layers
●
The Yocto Project build system is composed of
layers.
●
A layer is a logical collection of recipes
representing the core, a Board Support
Package (BSP), or an application stack.
●
All layers have a priority and can override policy
and config settings of the layers beneath it.

Board Support Package (BSP)
●
BSPs are layers to enable support for specific
hardware platforms.
●
Defines machine configuration for the “board”.
●
Adds machine-specific recipes and
customizations.
– Kernel config
– Graphics drivers (e.g, Xorg)
– Additional recipes to support hardware features

Yocto Layers Stacking
Developers-Specific Layer
Commercial Layer
UI - Optional Layer
Hardware Specific BSP
Yocto Layer Metadata (meta-yocto)
OpenEmbedded Core Metadata (oe-core)

Useful Links
●
Yocto Project quick start guide
– yocto-project-qs
●
Bitbake user manual
– bitbake-user-manual
●
Yocto Project development manual
– dev-manual

sherif.e.mousa@gmail.com
http://about.me/shatrix

Yocto - Embedded Linux Distribution Maker

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