How to choose an open source operating system for your embedded system, and why the choice is usually Yocto Project

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YOCTO PROJECT LINUX AS A PLATFORM
FOR EMBEDDED SYSTEM DESIGN
OR, WHAT IS THE BEST OPEN SOURCE OS CHOICE FOR MY EMBEDDED SYSTEM?
ALEX.GONZALEZ@DIGI.COM

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WHY THIS PRESENTATION?
• Digi manufactures System-On-Modules (SOMSs) and Single Board
Computers (SBCs)
• Provides free reference software (BSP and Yocto Project based
distribution)
• Why use a Yocto Project based distribution?

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Common embedded OS considerations:
• Power consumption
• User interface, possibly graphical
• Quick start up time
• Security
• Networking
• Some amount of RT determinism
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WHAT IS AN EMBEDDED SYSTEM?
Cost and time to market are directly proportional
to the complexity

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Common embedded OS considerations:
• Power consumption
• User interface, possibly graphical
• Quick start up time
• Security
• Networking
• Some amount of RT determinism
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REAL TIME CONSIDERATIONS
Cost and time to market are directly proportional
to the complexity

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MICROCONTROLLER OR MICROPROCESSOR
MCU CPU
• Flat memory model
• Extensive use of JTAG debuggers
• Open source operating systems
• FreeRTOS, mbed, Zephyr
• Hard real time
• Virtual memory (MMU)
• Limited use of JTAG debuggers
• Open source operating systems
• Embedded Linux
• Real time considerations
• Soft RT (PREEMPT_RT)
• Hard RT not really Linux
• RTLinux, RTAI, Xenomai

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EMBEDDED LINUX
DEVELOPMENT CONSIDERATIONS

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EMBEDDED LINUX DISTRIBUTION
An embedded Linux distribution provides:
• The bootloader
• The Linux kernel
• The root filesystem
• A software development kit
Sets system policies:
• Selection of supported packages
• Initialization system
• Graphical backend and environment
• System wide choices

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EMBEDDED LINUX DEVELOPMENT
• Bigger development teams
• Different development roles
• BSP developers
• System developers
• Application developers
• SDK used as an interface

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BSP DEVELOPMENT
• Bootloader development
• Similar to traditional embedded development
• Bring-up
• Intimate with hardware
• Flat memory model
• JTAG debuggers
• Linux kernel development
• Similar to PC kernel developers
• JTAG of little use
• BSP/drivers provided by OEM and community
• Mostly device tree customization and driver
debugging and development

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APPLICATION DEVELOPMENT
• Abstracted by Linux kernel
• Similar to PC desktop application development
• QT
• Web applications
• C and C++
• Also Python, Node.js and Java
• The application is a collection of services that
collaborate and communicate

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SYSTEM DEVELOPMENT
• System integration
• Build system
• Root filesystem generation
• SDK generation
• Toolchain
• Sysroot

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EMBEDDED LINUX DISTRIBUTIONS
BINARY OR BUILD FROM SOURCE

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EMBEDDED LINUX DISTRIBUTIONS
• A customized existing binary Linux distribution
• For example Debian
• A distribution built from source
• Do it yourself
• For example using crosstool-ng and
Cross LFS
• Standard tools
• Buildroot
• Yocto Project

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BINARY LINUX DISTRIBUTIONS
• Pre-built packages installed and removed using a
package manager
• On-target compilation common
• Package maintenance by the distribution provider
• Limited package configuration
• Generic, heavily patched packages
• Not focused on embedded applications
needs
• Bigger systems
• Slower to boot
• Require more resources to run
• More difficult to secure

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BINARY LINUX DISTRIBUTIONS
• Pre-defined policies and architectural choices
• Customization needed for most embedded systems lead to manual non-standard builds
• Difficult to reproduce
• High maintenance cost
• Package manager updates unsuited for embedded
• Can´t guarantee deployed system is the same as tested system
• Power loses while updating leave the system in inconsistent states

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EMBEDDED LINUX DISTRIBUTIONS
BINARY OR BUILD FROM SOURCE
BINARY SOURCE
• Lowest complexity and time to
market for supported hardware
• High maintainability
• Bigger images
• Slower to boot
• More resources to run
• More difficult to secure
• Low reproducibility
• Low portability and scalability
• Longer development cycles
• Full configuration possibilities
• Maximum flexibility, no pre-
determined choices
• Easier maintenance as long as
needed
• Smaller images
• Faster to boot
• Lower resources to run
• Easier to secure
• High portability and scalability

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EMBEDDED LINUX DISTRIBUTIONS
BUILDROOT OR YOCTO PROJECT

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BUILD FROM SOURCE LINUX DISTRIBUTIONS
BUILDROOT
• Easy to use
• Ideal for small projects and teams
• Uses kbuild as configuration tool
• All configuration in one place
• Good selection of well-maintained
packages
• External packages can be added
• Three months release cadence
• Yearly LTS release
• More image generator than distribution
builder
• Does not generate binary packages
• Does not support package managers
• Only performs full system updates
• Does not support on target compilation
• Full system rebuilds often required
• No concept of build cache

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BUILD FROM SOURCE LINUX DISTRIBUTIONS
YOCTO PROJECT
• Distribution builder
• Poky reference distribution
• Openembedded build system
• Bitbake scheduler
• Build binary packages that are installed into
root filesystem images
• Package managers on target for development
• Large number of packages structured in layers
• Software re-use
• Distributed maintenance
• Six month release cadence
• Current and previous releases are
maintained
• Configuration in several places
• Distro, machine, image and local
• Scales to multiple platforms and bigger
teams
• Steeper learning curve

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• No one-size-fits-all embedded operating system
• For CPUs, embedded Linux covers most use cases
• RT considerations apply
• Build from source distributions better suited than binary
distributions
• Small projects and teams are a good fit for Buildroot
• The Yocto Project scales better to bigger projects, teams and
multiple platforms
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SUMMARY

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EMBEDDED LINUX DEVELOPMENT USING YOCTO
PROJECT COOKBOOK DISCOUNT CODES
Discount codes valid until 26th March 2018.
• Ebook 50% discount: ELDUYPC50
• Paperback copy 15% discount: ELDUYPC15
• Limited availability!
Some free copies available at Digi´s booth
• Hall 3 booth 518

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Questions?
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Thanks for listening.
Alex González, Software Supervisor, Digi International
Alex.Gonzalez@digi.com