Yocto is an Embedded Linux distribution maker. This presentation is a quick start guide for Yocto buildsystem to get familiar with the tool and how to start building your own custom Linux system for a specific hardware target.

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

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

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What is Yocto?
It's not an embedded Linux distribution -
It creates a custom one for you.
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www.yoctoproject.org
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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.

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Why Yocto?
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Develop using one common Linux OS for different
architectures.
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Re-use your software stack with future devices.
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Changing hardware platforms with updating just one line
in a config file and rebuild.
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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.

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

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Yocto Project Overview (cont'd)
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OpenEmbedded Core (oe-core) – A core set of
metadata shared by the OpenEmbedded and the
Yocto Project.
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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

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Yocto Key Concept (recipe)
●
The Yocto Project provides tools and metadata for
creating custom Linux images.
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These images are created from a repository of 'baked'
recipes.
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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

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Yocto Workflow

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Yocto Member Organizations

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Working with Yocto

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

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

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Recipe Skeleton
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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

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Yocto Configuration Files
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Build directory files
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conf/bblayers.conf
– Contains locations for all layers needed for your build process.
BBLAYERS ?= "
/home/user/yocto/poky/meta­yocto ............
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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>

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Recipe build steps
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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

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

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

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

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

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