Linux para Sistemas Embebidos, una fuente abierta … · Linux para Sistemas Embebidos, una fuente abierta que se adapta a tu aplicación Linux, Linux for Embedded, Linux for Multimedia,

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Confidential and Proprietary Freescale, the Freescale logo, AltiVec, C-5, CodeTEST, CodeWarrior, ColdFire,

ColdFire+, C-Ware, the Energy Efficient Solutions logo, Kinetis, mobileGT, PowerQUICC,

Processor Expert, QorIQ, Qorivva, StarCore, Symphony and VortiQa are trademarks of

Freescale Semiconductor, Inc., Reg. U.S. Pat. & Tm. Off. Airfast, BeeKit, BeeStack,

CoreNet, Flexis, MagniV, MXC, Platform in a Package, QorIQ Qonverge, QUICC Engine,

Ready Play, SafeAssure, the SafeAssure logo, SMARTMOS, TurboLink, Vybrid and

Xtrinsic are trademarks of Freescale Semiconductor, Inc. All other product or service

names are the property of their respective owners. © 2012 Freescale Semiconductor, Inc.

June 2012

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Confidential and Proprietary Freescale, the Freescale logo, AltiVec, C-5, CodeTEST, CodeWarrior, ColdFire, ColdFire+, C-Ware, the Energy Efficient Solutions logo, Kinetis,

mobileGT, PowerQUICC, Processor Expert, QorIQ, Qorivva, StarCore, Symphony and VortiQa are trademarks of Freescale Semiconductor, Inc.,

Reg. U.S. Pat. & Tm. Off. Airfast, BeeKit, BeeStack, CoreNet, Flexis, MagniV, MXC, Platform in a Package, QorIQ Qonverge, QUICC Engine,

Ready Play, SafeAssure, the SafeAssure logo, SMARTMOS, TurboLink, Vybrid and Xtrinsic are trademarks of Freescale Semiconductor, Inc. All

other product or service names are the property of their respective owners. © 2012 Freescale Semiconductor, Inc.

© Copyright 2012 Adeneo Embedded

Based on original work by Free Electrons (http://free-electrons.com) © Copyright 2012

Document sources, updates and translations: http://free-electrons.com/docs

Creative Commons BY-SA 3.0 license License text: http://creativecommons.org/licenses/by-sa/3.0/

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http://free-electrons.com/





http://free-electrons.com/docs





http://creativecommons.org/licenses/by-sa/3.0/





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• Introduction to Linux

• Development

• Compiling

• U-boot

• Linux kernel

• Building a System • LTIB/Yocto/…

• Application…

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TM 5






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• Reusability and features

• Flexibility

• Tools

• Community project

• Licensing

• Cost of ramp-up

• Support

• No real-time support out of the box

TM 7






• Board Support Package development

− Write/Adapt the machine-specific code (bootloader, kernel, drivers)

• System integration

− Integrate components: bootloader, kernel, third-party libraries and applications

• Application development

− Develop, build and debug custom applications for your device

Bootloader

Kernel

Applications

Initialization scripts

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• Usually part of the kernel space

• Can be linked statically with the kernel (built-in)

or dynamically (modules)

• Different types of drivers: Block, Character,

Specific interfaces (e.g. network, USB, ...)

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• After the kernel is done initializing itself and its drivers,

initialization scripts are typically called to:

− Start services

− Create a debug console

− Start your application

• You want to customize these scripts to:

− Remove unnecessary features

− Reduce boot times

− Implement your own scenarios (recovery, normal boot...)

TM 10






• The root file-system is where all the files contained in the file

hierarchy (including device nodes) are stored.

• Many different components:

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−Select a toolchain

−Select the packages that will run on the target

−Configure and build these packages

−Deploy them on the device

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• Portability

• Prototyping

• Leverage existing software (frameworks, libraries,

tools...)

• Tools

• Languages

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• Porting code

− Interfaces

− Components

• Hardware constraints

− resources

− Desktop is x86 centric

− Convergence between embedded and desktop

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• Linux is a high-level operating system:

− Scheduling

− Memory management: uses virtual memory

− Hardware access

− Privileges

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• Embedded Linux development must be done

using a Linux host (with a few exceptions).

→ How to choose a Linux distribution?

• Use the most mainstream distribution, i.e. Ubuntu

− LTIB tested using Ubuntu 10.04.

− Should work on more recent releases, both on 32 and 64 bit

(tested successfully on Ubuntu 11.04 for instance)

− Can use a virtual machine

TM 17






• Serial connection

Debugging: bootloader, kernel, applications

Very useful for board bring-up

• USB

USB gadgets (substitute to Ethernet and serial)

• JTAG

Board bring-up

Kernel debugging

• Ethernet

TFTP and NFS

GDB/gdbserver

TM 18






• Host: Runs TFTP and NFS servers

• Device: Bootloader downloads the kernel, kernel mounts the file system over NFS

Kernel

file system

Kernel TFTP

NFS file system (remote)

TFTP server

NFS server

Bootloader

Kernel

HOST DEVICE

TM 19






• Editors: vi, emacs (most editors can do the job)

Very efficient if you are familiar with them

• Integrated environments:

Recommended option for beginners

− Eclipse

− Commercial toolsets

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http://www.linuxfromscratch.org/



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• Manually

• Using Tools

• Build Systems

• Precompiled…

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• Open-source bootloader used in embedded devices

− Used by many different silicon vendors, widely used on Freescale platforms

− Boots Linux, Android and other operating systems

− Architectures: x86, ARM, PPC, MIPS, Coldfire

− Advanced features: scripting, networking, drivers

• http://www.denx.de/wiki/U-Boot/

• Interesting alternative (community): Barebox

− Formerly known as U-Boot-v2

− Uses the kernel coding style (and shares drivers)

http://www.denx.de/wiki/U-Boot/




TM 25






• The procedure depends on the device:

− Change a lot from device to device (and the boot medium)

− Documented in the BSP

• Several methods (typically):

− Using Linux tools on the host (e.g. to flash SD Cards)

− Using Manufacturing tools provided with the BSP

− Using JTAG

Useful for development, also skips the re-flashing part if loading to RAM

instead

TM 26






• U-Boot can be configured through environment variables:

− Similar to shell environment variables

− Used to change the behavior of other commands (e.g. set IP address)

− Used to implement scripting

• The environment can be saved to permanent storage (defined in the configuration file)

• When booting: the environment is loaded from permanent storage to RAM (otherwise, will use hardcoded defaults)

• Commands to manipulate environment variables:

− printenv, shows all variables

− printenv <variable-name>, shows the value of one variable

− setenv <variable-name> <variable- value>, changes the value of a variable (only in RAM, store using the next command)

− saveenv, saves to environment to permanent storage

TM 27






u-boot # printenv

baudrate=19200

ethaddr=00:40:95:36:35:33

netmask=255.255.255.0

ipaddr=10.0.0.11

serverip=10.0.0.1

stdin=serial

stdout=serial

stderr=serial

u-boot # printenv serverip

serverip=10.0.0.2

u-boot # setenv serverip 10.0.0.100

u-boot # saveenv

TM 28






• Using the serial port

• Using on-board hardware:

• Using JTAG

TM 29






TM 30






TM 31






• Configuring the…

Manually

LTIB

• Building the…

Manually

LTIB

• Running the…

TM 32






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• Avoid reinventing the wheel!

− A lot of third-party libraries and applications that can be leveraged

− Freely available, distributable and can and be modified according to

the needs of the project

TM 34






• Root file systems are usually entirely cross-built and packaged

on the host

• Two main directory structures during development

− Target: binaries and files actually used on the device

− Build/Staging: contains additional files (headers, documentation,

static libraries)

Build (host)

• Binaries

• Dynamic libraries

• Data

• Headers

• Documentation

• Static Librairies

Target (host → device)

• Binaries

• Dynamic libraries

• Data

TM 35






• Build systems are usually shipped with Board Support Packages.

− Based on community projects or proprietary tools

• Community projects:

− LTIB, developed mainly by Freescale

− OpenEmbedded, Yocto, Poky, more flexible but also far more complicated

− Buildroot, developed by the community

− OpenWRT

− …

• Vendor specific tools (silicon vendor or embedded Linux vendor)

http://www.bitshrine.org/

http://www.openembedded.org/

http://www.yoctoproject.org/

http://www.pokylinux.org/

http://www.buildroot.net/

http://www.openwrt.org/

TM 36






• Ubuntu GNU/Linux

• Android

• Ångström and Timesys

• Meego

http://www.android.com/







http://www.angstrom-distribution.org/





http://meego.com/

http://meego.com/

http://meego.com/

TM 37






TM 38






• On Unix systems, all files and directories are organized in a

single tree.

• File systems are mounted in a specific location in this

hierarchy of directories

− They are mounted in directories (“mount points”)

− When a file system is mounted in a directory (called mount point),

the contents of this directory reflects the contents of the storage

device.

− When the file system is unmounted, the mount point is empty again.

TM 39






• Different criteria when choosing a file system:

−What type of media will be used for storage?

MTD devices have specific requirements, e.g. wear-leveling

−Read-only or read-write?

− Is the data volatile (i.e. does it need to be saved across

reboots)?

−What are the performance requirements?

TM 40






TM 41






• LTIB = Linux Target Image Builder

• Main features:

− Support for multiple targets: PPC, ARM, Coldfire

− Runs on Linux (latest releases are tested using Ubuntu)

− Configuration based on a menu

− Builds bootloader and kernel images

− More than 200 user-space packages selectable. Automatic

management of dependencies

• License: GPL (applies to the tool itself)

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• Build framework for embedded Linux

• Highlights:

− Support for HW

− Tools for speed up the process

− Easy to customize

− Runs on any Linux distribution

− Cross-compiles 1000's of packages including GTK+, Qt, the X

Windows system, Mono, Java, and about anything else you might

ever need

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• Eclipse plug-in and user space tool suite offerings further

improve developer productivity

• Integrates Yocto ADT cross toolchain into CDT: build, deploy,

test, debug without leaving the IDE

− Intended to be used for GNU autotools projects

TM 47






LTIB OE/YoctoAngstrom

• At the moment, officially

released by Freescale

• Quick build times

• Many packages, might be

outdated

• Easier for beginners

• Easy installation

• Community project with

community support

• Very long first time build

(several hours)

• Even more packages,

usually recent

• Requires more knowledge

than LTIB

• Easy installation

TM 48






TM 49






• Portability

• Prototyping

• Leverage existing software

TM 50






Q & A

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Linux para Sistemas Embebidos, una fuente abierta … · Linux para Sistemas Embebidos, una fuente abierta que se adapta a tu aplicación Linux, Linux for Embedded, Linux for Multimedia,

Documents