1123 lines
70 KiB
XML
1123 lines
70 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='dev-manual-model'>
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<title>Common Development Models</title>
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<para>
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Many development models exist for which you can use the Yocto Project.
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This chapter overviews the following methods:
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<itemizedlist>
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<listitem><para><emphasis>System Development:</emphasis>
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System Development covers Board Support Package (BSP) development and kernel
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modification or configuration.
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If you want to examine specific examples of the system development models,
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see the "<link linkend='dev-manual-bsp-appendix'>BSP Development Example</link>"
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appendix and the
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"<link linkend='dev-manual-kernel-appendix'>Kernel Modification Example</link>" appendix.
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</para></listitem>
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||
<listitem><para><emphasis>User Application Development:</emphasis>
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User Application Development covers development of applications that you intend
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to run on some target hardware.
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For a user-space application development example that uses the
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<trademark class='trade'>Eclipse</trademark> IDE,
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see the
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<ulink url='&YOCTO_DOCS_ADT_URL;'>
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The Yocto Project Application Development Toolkit (ADT) User's Guide</ulink>.
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</para></listitem>
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<listitem><para><emphasis>Temporary Source Code Modification:</emphasis>
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Direct modification of temporary source code is a convenient development model
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to quickly iterate and develop towards a solution.
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Once the solution has been implemented, you should of course take steps to
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get the changes upstream and applied in the affected recipes.</para></listitem>
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<listitem><para><emphasis>Image Development using Hob:</emphasis>
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You can use the <ulink url='&YOCTO_HOME_URL;/projects/hob'>Hob</ulink> to build
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custom operating system images within the build environment.
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Hob provides an efficient interface to the OpenEmbedded build system.</para></listitem>
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<listitem><para><emphasis>Using a Development Shell:</emphasis>
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You can use a <filename>devshell</filename> to efficiently debug commands or simply
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edit packages.
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Working inside a development shell is a quick way to set up the OpenEmbedded build
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environment to work on parts of a project.</para></listitem>
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</itemizedlist>
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</para>
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<section id='system-development-model'>
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<title>System Development Workflow</title>
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<para>
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System development involves modification or creation of an image that you want to run on
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a specific hardware target.
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Usually, when you want to create an image that runs on embedded hardware, the image does
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not require the same number of features that a full-fledged Linux distribution provides.
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Thus, you can create a much smaller image that is designed to use only the hardware
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features for your particular hardware.
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</para>
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<para>
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To help you understand how system development works in the Yocto Project, this section
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covers two types of image development: BSP creation and kernel modification or
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configuration.
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</para>
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<section id='developing-a-board-support-package-bsp'>
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<title>Developing a Board Support Package (BSP)</title>
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<para>
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A BSP is a packageof recipes that, when applied, during a build results in
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an image that you can run on a particular board.
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Thus, the package, when compiled into the new image, supports the operation of the board.
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</para>
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<note>
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For a brief list of terms used when describing the development process in the Yocto Project,
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see the "<link linkend='yocto-project-terms'>Yocto Project Terms</link>" section.
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</note>
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<para>
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The remainder of this section presents the basic steps used to create a BSP
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based on an existing BSP that ships with the Yocto Project.
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You can reference the "<link linkend='dev-manual-bsp-appendix'>BSP Development Example</link>"
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appendix for a detailed example that uses the Crown Bay BSP as a base BSP from which to start.
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</para>
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<para>
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The following illustration and list summarize the BSP creation general workflow.
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</para>
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<para>
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<imagedata fileref="figures/bsp-dev-flow.png" width="6in" depth="7in" align="center" scalefit="1" />
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</para>
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<para>
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<orderedlist>
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<listitem><para><emphasis>Set up your host development system to support
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development using the Yocto Project</emphasis>: See the
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"<ulink url='&YOCTO_DOCS_QS_URL;#the-linux-distro'>The Linux Distributions</ulink>"
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and the
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"<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" sections both
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in the Yocto Project Quick Start for requirements.</para></listitem>
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<listitem><para><emphasis>Establish a local copy of the project files on your
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system</emphasis>: You need this <link linkend='source-directory'>source
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directory</link> available on your host system.
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Having these files on your system gives you access to the build
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process and to the tools you need.
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For information on how to set up the source directory, see the
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"<link linkend='getting-setup'>Getting Setup</link>" section.</para></listitem>
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<listitem><para><emphasis>Establish a local copy of the base BSP files</emphasis>: Having
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the BSP files on your system gives you access to the build
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process and to the tools you need for creating a BSP.
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For information on how to get these files, see the
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"<link linkend='getting-setup'>Getting Setup</link>" section.</para></listitem>
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<listitem><para><emphasis>Choose a BSP that is supported by the Yocto Project
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as your base BSP</emphasis>:
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The Yocto Project ships with several BSPs that support various hardware.
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It is best to base your new BSP on an existing BSP rather than create all the
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recipes and configuration files from scratch.
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While it is possible to create everything from scratch, basing your new BSP
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on something that is close is much easier.
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Or, at a minimum, leveraging off an existing BSP
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gives you some structure with which to start.</para>
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<para>At this point you need to understand your target hardware well enough to determine which
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existing BSP it most closely matches.
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Things to consider are your hardware’s on-board features, such as CPU type and graphics support.
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You should look at the README files for supported BSPs to get an idea of which one
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you could use.
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A generic <trademark class='registered'>Intel</trademark>
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<trademark class='trade'>Atom</trademark>-based BSP to consider is the
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Crown Bay that does not support the <trademark class='registered'>Intel</trademark>
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Embedded Media Graphics Driver (EMGD).
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The remainder of this example uses that base BSP.</para>
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<para>To see the supported BSPs, go to the
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<ulink url='&YOCTO_HOME_URL;/download'>Download</ulink> page on the Yocto Project
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website and click on “BSP Downloads.”</para></listitem>
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<listitem><para><emphasis>Create your own BSP layer</emphasis>: Layers are ideal for
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isolating and storing work for a given piece of hardware.
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A layer is really just a location or area in which you place the recipes for your BSP.
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In fact, a BSP is, in itself, a special type of layer.
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</para>
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<para>
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Another example that illustrates a layer is an application.
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Suppose you are creating an application that has library or other dependencies in
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order for it to compile and run.
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The layer, in this case, would be where all the recipes that define those dependencies
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are kept.
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The key point for a layer is that it is an isolated area that contains
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all the relevant information for the project that the OpenEmbedded build
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system knows about.
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For more information on layers, see the
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||
"<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>"
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||
section.
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For more information on BSP layers, see the
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"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>" section in the
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Yocto Project Board Support Package (BSP) Developer's Guide.</para>
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<note>Four BSPs exist that are part of the
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Yocto Project release: <filename>atom-pc</filename>, <filename>beagleboard</filename>,
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<filename>mpc8315e</filename>, and <filename>routerstationpro</filename>.
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The recipes and configurations for these four BSPs are located and dispersed
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within the <link linkend='source-directory'>source directory</link>.
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On the other hand, BSP layers for Crown Bay, Emenlow, Jasper Forest,
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N450, Cedar Trail, Fish River, Fish River Island II, Romley, sys940x, tlk,
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and Sugar Bay exist in their own separate layers within the larger
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<filename>meta-intel</filename> layer.</note>
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<para>When you set up a layer for a new BSP, you should follow a standard layout.
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This layout is described in the section
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"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout'>Example Filesystem Layout</ulink>"
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section of the Board Support Package (BSP) Development Guide.
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In the standard layout, you will notice a suggested structure for recipes and
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configuration information.
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You can see the standard layout for the Crown Bay BSP in this example by examining the
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directory structure of the <filename>meta-crownbay</filename> layer inside the
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source directory.</para></listitem>
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<listitem><para><emphasis>Make configuration changes to your new BSP
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layer</emphasis>: The standard BSP layer structure organizes the files you need
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to edit in <filename>conf</filename> and several <filename>recipes-*</filename>
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directories within the BSP layer.
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Configuration changes identify where your new layer is on the local system
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and identify which kernel you are going to use.
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</para></listitem>
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||
<listitem><para><emphasis>Make recipe changes to your new BSP layer</emphasis>: Recipe
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changes include altering recipes (<filename>.bb</filename> files), removing
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recipes you don't use, and adding new recipes that you need to support your hardware.
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||
</para></listitem>
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<listitem><para><emphasis>Prepare for the build</emphasis>: Once you have made all the
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changes to your BSP layer, there remains a few things
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you need to do for the OpenEmbedded build system in order for it to create your image.
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||
You need to get the build environment ready by sourcing an environment setup script
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||
and you need to be sure two key configuration files are configured appropriately.</para>
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<para>The entire process for building an image is overviewed in the section
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"<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" section
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||
of the Yocto Project Quick Start.
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You might want to reference this information.</para></listitem>
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||
<listitem><para><emphasis>Build the image</emphasis>: The OpenEmbedded build system
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||
uses the BitBake tool to build images based on the type of image you want to create.
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||
You can find more information on BitBake
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||
<ulink url='&BITBAKE_DOCS_URL;'>here</ulink>.</para>
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||
<para>The build process supports several types of images to satisfy different needs.
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||
See the
|
||
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter
|
||
in the Yocto Project Reference Manual for information on
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supported images.</para></listitem>
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||
</orderedlist>
|
||
</para>
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<para>
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You can view a video presentation on "Building Custom Embedded Images with Yocto"
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at <ulink url='http://free-electrons.com/blog/elc-2011-videos'>Free Electrons</ulink>.
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||
You can also find supplemental information in
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||
<ulink url='&YOCTO_DOCS_BSP_URL;'>
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||
The Board Support Package (BSP) Development Guide</ulink>.
|
||
Finally, there is wiki page write up of the example also located
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<ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_creating_one_generic_Atom_BSP_from_another'>
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||
here</ulink> that you might find helpful.
|
||
</para>
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</section>
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<section id='modifying-the-kernel'>
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<title><anchor id='kernel-spot' />Modifying the Kernel</title>
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||
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||
<para>
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||
Kernel modification involves changing the Yocto Project kernel, which could involve changing
|
||
configuration options as well as adding new kernel recipes.
|
||
Configuration changes can be added in the form of configuration fragments, while recipe
|
||
modification comes through the kernel's <filename>recipes-kernel</filename> area
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||
in a kernel layer you create.
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||
</para>
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||
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<para>
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||
The remainder of this section presents a high-level overview of the Yocto Project
|
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kernel architecture and the steps to modify the kernel.
|
||
For a complete discussion of the kernel, see
|
||
<ulink url='&YOCTO_DOCS_KERNEL_URL;'>
|
||
The Yocto Project Kernel Architecture and Use Manual</ulink>.
|
||
You can reference the appendix
|
||
"<link linkend='dev-manual-kernel-appendix'>Kernel Modification Example</link>"
|
||
for a detailed example that changes the configuration of a kernel.
|
||
</para>
|
||
|
||
<section id='kernel-overview'>
|
||
<title>Kernel Overview</title>
|
||
|
||
<para>
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||
Traditionally, when one thinks of a patched kernel, they think of a base kernel
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||
source tree and a fixed structure that contains kernel patches.
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||
The Yocto Project, however, employs mechanisms, that in a sense, result in a kernel source
|
||
generator.
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||
By the end of this section, this analogy will become clearer.
|
||
</para>
|
||
|
||
<para>
|
||
You can find a web interface to the Yocto Project kernel source repositories at
|
||
<ulink url='&YOCTO_GIT_URL;'></ulink>.
|
||
If you look at the interface, you will see to the left a grouping of
|
||
Git repositories titled "Yocto Linux Kernel."
|
||
Within this group, you will find several kernels supported by
|
||
the Yocto Project:
|
||
<itemizedlist>
|
||
<listitem><para><emphasis><filename>linux-yocto-2.6.34</filename></emphasis> - The
|
||
stable Yocto Project kernel that is based on the Linux 2.6.34 released kernel.</para></listitem>
|
||
<listitem><para><emphasis><filename>linux-yocto-2.6.37</filename></emphasis> - The
|
||
stable Yocto Project kernel that is based on the Linux 2.6.37 released kernel.</para></listitem>
|
||
<listitem><para><emphasis><filename>linux-yocto-3.0</filename></emphasis> - The stable
|
||
Yocto Project kernel that is based on the Linux 3.0 released kernel.</para></listitem>
|
||
<listitem><para><emphasis><filename>linux-yocto-3.0-1.1.x</filename></emphasis> - The
|
||
stable Yocto Project kernel to use with the Yocto Project Release 1.1.x. This kernel
|
||
is based on the Linux 3.0 released kernel.</para></listitem>
|
||
<listitem><para><emphasis><filename>linux-yocto-3.2</filename></emphasis> - The
|
||
stable Yocto Project kernel to use with the Yocto Project Release 1.2. This kernel
|
||
is based on the Linux 3.2 released kernel.</para></listitem>
|
||
<listitem><para><emphasis><filename>linux-yocto-dev</filename></emphasis> - A development
|
||
kernel based on the latest upstream release candidate available.</para></listitem>
|
||
</itemizedlist>
|
||
</para>
|
||
|
||
<para>
|
||
The kernels are maintained using the Git revision control system
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||
that structures them using the familiar "tree", "branch", and "leaf" scheme.
|
||
Branches represent diversions from general code to more specific code, while leaves
|
||
represent the end-points for a complete and unique kernel whose source files
|
||
when gathered from the root of the tree to the leaf accumulate to create the files
|
||
necessary for a specific piece of hardware and its features.
|
||
The following figure displays this concept:
|
||
<para>
|
||
<imagedata fileref="figures/kernel-overview-1.png"
|
||
width="6in" depth="6in" align="center" scale="100" />
|
||
</para>
|
||
|
||
<para>
|
||
Within the figure, the "Kernel.org Branch Point" represents the point in the tree
|
||
where a supported base kernel is modified from the Linux kernel.
|
||
For example, this could be the branch point for the <filename>linux-yocto-3.0</filename>
|
||
kernel.
|
||
Thus, everything further to the right in the structure is based on the
|
||
<filename>linux-yocto-3.0</filename> kernel.
|
||
Branch points to right in the figure represent where the
|
||
<filename>linux-yocto-3.0</filename> kernel is modified for specific hardware
|
||
or types of kernels, such as real-time kernels.
|
||
Each leaf thus represents the end-point for a kernel designed to run on a specific
|
||
targeted device.
|
||
</para>
|
||
|
||
<para>
|
||
The overall result is a Git-maintained repository from which all the supported
|
||
kernel types can be derived for all the supported devices.
|
||
A big advantage to this scheme is the sharing of common features by keeping them in
|
||
"larger" branches within the tree.
|
||
This practice eliminates redundant storage of similar features shared among kernels.
|
||
</para>
|
||
|
||
<note>
|
||
Keep in mind the figure does not take into account all the supported Yocto
|
||
Project kernel types, but rather shows a single generic kernel just for conceptual purposes.
|
||
Also keep in mind that this structure represents the Yocto Project source repositories
|
||
that are either pulled from during the build or established on the host development system
|
||
prior to the build by either cloning a particular kernel's Git repository or by
|
||
downloading and unpacking a tarball.
|
||
</note>
|
||
|
||
<para>
|
||
Storage of all the available kernel source code is one thing, while representing the
|
||
code on your host development system is another.
|
||
Conceptually, you can think of the kernel source repositories as all the
|
||
source files necessary for all the supported kernels.
|
||
As a developer, you are just interested in the source files for the kernel on
|
||
on which you are working.
|
||
And, furthermore, you need them available on your host system.
|
||
</para>
|
||
|
||
<para>
|
||
You make kernel source code available on your host development system by using
|
||
Git to create a bare clone of the Yocto Project kernel Git repository
|
||
in which you are interested.
|
||
Then, you use Git again to clone a copy of that bare clone.
|
||
This copy represents the directory structure on your host system that is particular
|
||
to the kernel you want.
|
||
These are the files you actually modify to change the kernel.
|
||
See the <link linkend='local-kernel-files'>Yocto Project Kernel</link> item earlier
|
||
in this manual for an example of how to set up the kernel source directory
|
||
structure on your host system.
|
||
</para>
|
||
|
||
<para>
|
||
This next figure illustrates how the kernel source files might be arranged on
|
||
your host system.
|
||
</para>
|
||
|
||
<para>
|
||
<imagedata fileref="figures/kernel-overview-3-denzil.png"
|
||
width="6in" depth="4in" align="center" scale="100" />
|
||
</para>
|
||
|
||
<para>
|
||
In the previous figure, the file structure on the left represents the bare clone
|
||
set up to track the Yocto Project kernel Git repository.
|
||
The structure on the right represents the copy of the bare clone.
|
||
When you make modifcations to the kernel source code, this is the area in which
|
||
you work.
|
||
Once you make corrections, you must use Git to push the committed changes to the
|
||
bare clone.
|
||
The example in <xref linkend='modifying-the-kernel-source-code'>
|
||
Modifying the Kernel Source Code</xref> provides a detailed example.
|
||
</para>
|
||
|
||
<para>
|
||
What happens during the build?
|
||
When you build the kernel on your development system all files needed for the build
|
||
are taken from the source repositories pointed to by the
|
||
<filename>SRC_URI</filename> variable and gathered in a temporary work area
|
||
where they are subsequently used to create the unique kernel.
|
||
Thus, in a sense, the process constructs a local source tree specific to your
|
||
kernel to generate the new kernel image - a source generator if you will.
|
||
</para>
|
||
The following figure shows the temporary file structure
|
||
created on your host system when the build occurs.
|
||
This build directory contains all the source files used during the build.
|
||
</para>
|
||
|
||
<para>
|
||
<imagedata fileref="figures/kernel-overview-2.png"
|
||
width="6in" depth="5in" align="center" scale="100" />
|
||
</para>
|
||
|
||
<para>
|
||
Again, for a complete discussion of the Yocto Project kernel's architecture and its
|
||
branching strategy,
|
||
see <ulink url='&YOCTO_DOCS_KERNEL_URL;'>
|
||
The Yocto Project Kernel Architecture and Use Manual</ulink>.
|
||
You can also reference the
|
||
"<link linkend='modifying-the-kernel-source-code'>Modifying the Kernel Source Code</link>"
|
||
section for a detailed example that modifies the kernel.
|
||
</para>
|
||
</section>
|
||
|
||
<section id='kernel-modification-workflow'>
|
||
<title>Kernel Modification Workflow</title>
|
||
|
||
<para>
|
||
This illustration and the following list summarizes the kernel modification general workflow.
|
||
</para>
|
||
|
||
<para>
|
||
<imagedata fileref="figures/kernel-dev-flow.png"
|
||
width="6in" depth="7.5in" align="center" scalefit="1" />
|
||
</para>
|
||
|
||
<para>
|
||
<orderedlist>
|
||
<listitem><para><emphasis>Set up your host development system to support
|
||
development using the Yocto Project</emphasis>: See
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#the-linux-distro'>The Linux Distributions</ulink>" and
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" sections both
|
||
in the Yocto Project Quick Start for requirements.</para></listitem>
|
||
<listitem><para><emphasis>Establish a local copy of project files on your
|
||
system</emphasis>: Having the <link linkend='source-directory'>source
|
||
directory</link> on your system gives you access to the build process and tools
|
||
you need.
|
||
For information on how to get these files, see the bulleted item
|
||
"<link linkend='local-yp-release'>Yocto Project Release</link>" earlier in this manual.
|
||
</para></listitem>
|
||
<listitem><para><emphasis>Set up a local copy of the <filename>poky-extras</filename> Git
|
||
repository</emphasis>: This local repository is the area for your configuration
|
||
fragments, new kernel recipes, and the kernel <filename>.bbappend</filename>
|
||
file used during the build.
|
||
It is good practice to set this repository up inside your local
|
||
source directory.
|
||
For information on how to get these files, see the bulleted item
|
||
"<link linkend='poky-extras-repo'>The <filename>poky-extras</filename> Git Repository</link>"
|
||
earlier in this manual.
|
||
<note>While it is certainly possible to modify the kernel without involving
|
||
a local Git repository, the suggested workflow for kernel modification
|
||
using the Yocto Project does use a Git repository.</note></para></listitem>
|
||
<listitem><para><emphasis>Establish a local copy of the Yocto Project kernel files on your
|
||
system</emphasis>: In order to make modifications to the kernel you need two things:
|
||
a bare clone of the Yocto Project kernel you are modifying and
|
||
a copy of that bare clone.
|
||
The bare clone is required by the build process and is the area to which you
|
||
push your kernel source changes (pulling does not work with bare clones).
|
||
The copy of the bare clone is a local Git repository that contains all the kernel's
|
||
source files.
|
||
You make your changes to the files in this copy of the bare clone.
|
||
For information on how to set these two items up, see the bulleted item
|
||
"<link linkend='local-kernel-files'>Yocto Project Kernel</link>"
|
||
earlier in this manual.</para></listitem>
|
||
<listitem><para><emphasis>Make changes to the kernel source code if
|
||
applicable</emphasis>: Modifying the kernel does not always mean directly
|
||
changing source files.
|
||
However, if you have to do this, you make the changes in the local
|
||
Git repository you set up to hold the source files (i.e. the copy of the
|
||
bare clone).
|
||
Once the changes are made, you need to use Git commands to commit the changes
|
||
and then push them to the bare clone.</para></listitem>
|
||
<listitem><para><emphasis>Make kernel configuration changes
|
||
if applicable</emphasis>:
|
||
If your situation calls for changing the kernel's configuration, you can
|
||
use <filename>menuconfig</filename>
|
||
to enable and disable kernel configurations.
|
||
Using <filename>menuconfig</filename> allows you to interactively develop and test the
|
||
configuration changes you are making to the kernel.
|
||
When saved, changes using <filename>menuconfig</filename> update the kernel's
|
||
<filename>.config</filename>.
|
||
Try to resist the temptation of directly editing the <filename>.config</filename>
|
||
file found in the
|
||
<link linkend='build-directory'>build directory</link> at
|
||
<filename>tmp/sysroots/<machine-name>/kernel</filename>.
|
||
Doing so, can produce unexpected results when the OpenEmbedded build system
|
||
regenerates the configuration file.</para>
|
||
<para>Once you are satisfied with the configuration changes made using
|
||
<filename>menuconfig</filename>, you can directly examine the
|
||
<filename>.config</filename> file against a saved original and gather those
|
||
changes into a config fragment to be referenced from within the kernel's
|
||
<filename>.bbappend</filename> file.</para></listitem>
|
||
<listitem><para><emphasis>Add or extend kernel recipes if applicable</emphasis>:
|
||
The standard
|
||
layer structure organizes recipe files inside the
|
||
<filename>meta-kernel-dev</filename> layer that is within the local
|
||
<filename>poky-extras</filename> Git repository.
|
||
If you need to add new kernel recipes, you add them within this layer.
|
||
Also within this area, you will find the <filename>.bbappend</filename>
|
||
file that appends information to the kernel's recipe file used during the
|
||
build.
|
||
</para></listitem>
|
||
<listitem><para><emphasis>Prepare for the build</emphasis>: Once you have made all the
|
||
changes to your kernel (configurations, source code changes, recipe additions,
|
||
or recipe changes), there remains a few things
|
||
you need to do in order for the build system to create your image.
|
||
If you have not done so, you need to get the build environment ready by sourcing
|
||
the environment setup script described earlier.
|
||
You also need to be sure two key configuration files
|
||
(<filename>local.conf</filename> and <filename>bblayers.conf</filename>)
|
||
are configured appropriately.</para>
|
||
<para>The entire process for building an image is overviewed in the
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>"
|
||
section of the Yocto Project Quick Start.
|
||
You might want to reference this information.
|
||
Also, you should look at the detailed examples found in the appendices at
|
||
at the end of this manual.</para></listitem>
|
||
<listitem><para><emphasis>Build the image</emphasis>: The OpenEmbedded
|
||
build system uses the BitBake
|
||
tool to build images based on the type of image you want to create.
|
||
You can find more information on BitBake
|
||
<ulink url='&BITBAKE_DOCS_URL;'>here</ulink>.</para>
|
||
<para>The build process supports several types of images to satisfy different needs.
|
||
See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter in
|
||
the Yocto Project Reference Manual for information on supported images.</para></listitem>
|
||
<listitem><para><emphasis>Make your configuration changes available
|
||
in the kernel layer</emphasis>: Up to this point, all the configuration changes to the
|
||
kernel have been done and tested iteratively.
|
||
Once they are tested and ready to go, you can move them into the kernel layer,
|
||
which allows you to distribute the layer.</para></listitem>
|
||
<listitem><para><emphasis>If applicable, share your in-tree changes</emphasis>:
|
||
If the changes you made
|
||
are suited for all Yocto Project kernel users, you might want to send them on
|
||
for inclusion into the upstream kernel's Git repository.
|
||
If the changes are accepted, the Yocto Project Maintainer pulls them into
|
||
the master branch of the kernel tree.
|
||
Doing so makes them available to everyone using the kernel.</para></listitem>
|
||
</orderedlist>
|
||
</para>
|
||
</section>
|
||
</section>
|
||
</section>
|
||
|
||
<section id='application-development-workflow'>
|
||
<title>Application Development Workflow</title>
|
||
|
||
<para>
|
||
Application development involves creation of an application that you want to be able
|
||
to run on your target hardware, which is running a Yocto Project kernel image.
|
||
The Yocto Project provides an Application Development Toolkit (ADT) that
|
||
facilitates quick development and integration of your application into its run-time environment.
|
||
Using the ADT you can employ cross-development toolchains designed for your target hardware
|
||
to compile and link your application.
|
||
You can then deploy your application to the actual hardware or to the QEMU emulator for testing.
|
||
If you are familiar with the popular Eclipse IDE, you can use an Eclipse Yocto Plug-in to
|
||
allow you to develop, deploy, and test your application all from within Eclipse.
|
||
</para>
|
||
|
||
<para>
|
||
While we strongly suggest using the ADT to develop your application, you might
|
||
not want to.
|
||
If this is the case, you can still use pieces of the Yocto Project for your development process.
|
||
However, because the process can vary greatly, this manual does not provide detail on the process.
|
||
</para>
|
||
|
||
<section id='workflow-using-the-adt-and-eclipse'>
|
||
<title>Workflow Using the ADT and <trademark class='trade'>Eclipse</trademark></title>
|
||
|
||
<para>
|
||
To help you understand how application development works using the ADT, this section
|
||
provides an overview of the general development process.
|
||
If you want to see a detailed example of the process as it is used from within the Eclipse
|
||
IDE, see
|
||
<ulink url='&YOCTO_DOCS_ADT_URL;'>
|
||
The Application Development Toolkit (ADT) User's Manual</ulink>.
|
||
</para>
|
||
|
||
<para>
|
||
The following illustration and list summarize the application development general workflow.
|
||
</para>
|
||
|
||
<para>
|
||
<imagedata fileref="figures/app-dev-flow.png"
|
||
width="7in" depth="8in" align="center" scale="100" />
|
||
</para>
|
||
|
||
<para>
|
||
<orderedlist>
|
||
<listitem><para><emphasis>Prepare the Host System for the Yocto Project</emphasis>:
|
||
See
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#the-linux-distro'>The Linux Distributions</ulink>" and
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" sections both
|
||
in the Yocto Project Quick Start for requirements.</para></listitem>
|
||
<listitem><para><emphasis>Secure the Yocto Project Kernel Target Image</emphasis>:
|
||
You must have a target kernel image that has been built using the OpenEmbeded
|
||
build system.</para>
|
||
<para>Depending on whether the Yocto Project has a pre-built image that matches your target
|
||
architecture and where you are going to run the image while you develop your application
|
||
(QEMU or real hardware), the area from which you get the image differs.
|
||
<itemizedlist>
|
||
<listitem><para>Download the image from
|
||
<ulink url='&YOCTO_MACHINES_DL_URL;'>
|
||
<filename>machines</filename></ulink> if your target architecture is supported
|
||
and you are going to develop and test your application on actual hardware.
|
||
</para></listitem>
|
||
<listitem><para>Download the image from the
|
||
<ulink url='&YOCTO_QEMU_DL_URL;'>
|
||
<filename>machines/qemu</filename></ulink> if your target architecture is supported
|
||
and you are going to develop and test your application using the QEMU
|
||
emulator.</para></listitem>
|
||
<listitem><para>Build your image if you cannot find a pre-built image that matches
|
||
your target architecture.
|
||
If your target architecture is similar to a supported architecture, you can
|
||
modify the kernel image before you build it.
|
||
See the
|
||
"<link linkend='kernel-modification-workflow'>Kernel Modification Workflow</link>"
|
||
section earlier in this manual for information on how to create a modified
|
||
Yocto Project kernel.</para></listitem>
|
||
</itemizedlist></para>
|
||
<para>For information on pre-built kernel image naming schemes for images
|
||
that can run on the QEMU emulator, see the
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#using-pre-built'>Using Pre-Built Binaries and QEMU</ulink>"
|
||
section in the Yocto Project Quick Start.</para></listitem>
|
||
<listitem><para><emphasis>Install the ADT</emphasis>:
|
||
The ADT provides a target-specific cross-development toolchain, the root filesystem,
|
||
the QEMU emulator, and other tools that can help you develop your application.
|
||
While it is possible to get these pieces separately, the ADT Installer provides an
|
||
easy method.
|
||
You can get these pieces by running an ADT installer script, which is configurable.
|
||
For information on how to install the ADT, see the
|
||
"<ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Using the ADT Installer</ulink>"
|
||
section
|
||
in the Yocto Project Application Development (ADT) User's Manual.</para></listitem>
|
||
<listitem><para><emphasis>If Applicable, Secure the Target Root Filesystem</emphasis>:
|
||
If you choose not to install the ADT using the ADT Installer,
|
||
you need to find and download the
|
||
appropriate root filesystems.
|
||
You can find these tarballs in the same areas used for the kernel images.
|
||
Depending on the type of image you are running, the root filesystem you need differs.
|
||
For example, if you are developing an application that runs on an image that
|
||
supports Sato, you need to get root filesystem that supports Sato.
|
||
</para></listitem>
|
||
<listitem><para><emphasis>Create and Build your Application</emphasis>:
|
||
At this point, you need to have source files for your application.
|
||
Once you have the files, you can use the Eclipse IDE to import them and build the
|
||
project.
|
||
If you are not using Eclipse, you need to use the cross-development tools you have
|
||
installed to create the image.</para></listitem>
|
||
<listitem><para><emphasis>Deploy the Image with the Application</emphasis>:
|
||
If you are using the Eclipse IDE, you can deploy your image to the hardware or to
|
||
QEMU through the project's preferences.
|
||
If you are not using the Eclipse IDE, then you need to deploy the application using
|
||
other methods to the hardware.
|
||
Or, if you are using QEMU, you need to use that tool and load your image in for testing.
|
||
</para></listitem>
|
||
<listitem><para><emphasis>Test and Debug the Application</emphasis>:
|
||
Once your application is deployed, you need to test it.
|
||
Within the Eclipse IDE, you can use the debubbing environment along with the
|
||
set of user-space tools installed along with the ADT to debug your application.
|
||
Of course, the same user-space tools are available separately to use if you choose
|
||
not to use the Eclipse IDE.</para></listitem>
|
||
</orderedlist>
|
||
</para>
|
||
</section>
|
||
|
||
<section id='workflow-without-adt'>
|
||
<title>Workflow Without ADT</title>
|
||
|
||
<para>
|
||
If you want to develop an application outside of the Yocto Project ADT environment, you
|
||
can still employ the cross-development toolchain, the QEMU emulator, and a number of supported
|
||
target image files.
|
||
You just need to follow these general steps:
|
||
<orderedlist>
|
||
<listitem><para><emphasis>Install the cross-development toolchain for your target hardware:</emphasis>
|
||
For information on how to install the toolchain, see the
|
||
"<ulink url='&YOCTO_DOCS_ADT_URL;#using-an-existing-toolchain-tarball'>Using a Cross-Toolchain Tarball</ulink>"
|
||
section
|
||
in the Yocto Project Application Development (ADT) User's Manual.</para></listitem>
|
||
<listitem><para><emphasis>Download the Target Image:</emphasis> The Yocto Project supports
|
||
several target architectures and has many pre-built kernel images and root filesystem
|
||
images.</para>
|
||
<para>If you are going to develop your application on hardware, go to the
|
||
<ulink url='&YOCTO_MACHINES_DL_URL;'>
|
||
<filename>machines</filename></ulink> download area and choose a target machine area
|
||
from which to download the kernel image and root filesystem.
|
||
This download area could have several files in it that support development using
|
||
actual hardware.
|
||
For example, the area might contain <filename>.hddimg</filename> files that combine the
|
||
kernel image with the filesystem, boot loaders, etc.
|
||
Be sure to get the files you need for your particular development process.</para>
|
||
<para>If you are going to develop your application and then run and test it using the QEMU
|
||
emulator, go to the
|
||
<ulink url='&YOCTO_QEMU_DL_URL;'>
|
||
<filename>machines/qemu</filename></ulink> download area.
|
||
From this area, go down into the directory for your target architecture
|
||
(e.g. <filename>qemux86_64</filename> for an
|
||
<trademark class='registered'>Intel</trademark>-based 64-bit architecture).
|
||
Download kernel, root filesystem, and any other files you need for your process.
|
||
<note>In order to use the root filesystem in QEMU, you need to extract it.
|
||
See the
|
||
"<ulink url='&YOCTO_DOCS_ADT_URL;#extracting-the-root-filesystem'>Extracting the Root Filesystem</ulink>" section for information on how to extract the
|
||
root filesystem.</note></para></listitem>
|
||
<listitem><para><emphasis>Develop and Test your Application:</emphasis> At this point,
|
||
you have the tools to develop your application.
|
||
If you need to separately install and use the QEMU emulator, you can go to
|
||
<ulink url='http://www.qemu.org'>QEMU Home Page</ulink> to download and learn about the
|
||
emulator.</para></listitem>
|
||
</orderedlist>
|
||
</para>
|
||
</section>
|
||
</section>
|
||
|
||
<section id="modifying-temporary-source-code">
|
||
<title>Modifying Temporary Source Code</title>
|
||
|
||
<para>
|
||
You might
|
||
find it helpful during development to modify the temporary source code used by recipes
|
||
to build packages.
|
||
For example, suppose you are developing a patch and you need to experiment a bit
|
||
to figure out your solution.
|
||
After you have initially built the package, you can iteratively tweak the
|
||
source code, which is located in the
|
||
<link linkend='build-directory'>build directory</link>, and then
|
||
you can force a re-compile and quickly test your altered code.
|
||
Once you settle on a solution, you can then preserve your changes in the form of
|
||
patches.
|
||
You can accomplish these steps all within either a
|
||
<ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink> or
|
||
<link linkend='git'>Git</link> workflow.
|
||
</para>
|
||
|
||
<section id='finding-the-temporary-source-code'>
|
||
<title>Finding the Temporary Source Code</title>
|
||
|
||
<para>
|
||
During a build, the unpacked temporary source code used by recipes
|
||
to build packages is available in the build directory as
|
||
defined by the
|
||
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> variable.
|
||
Below is the default value for the <filename>S</filename> variable as defined in the
|
||
<filename>meta/conf/bitbake.conf</filename> configuration file in the
|
||
<link linkend='source-directory'>source directory</link>:
|
||
<literallayout class='monospaced'>
|
||
S = ${WORKDIR}/${BP}
|
||
</literallayout>
|
||
You should be aware that many recipes override the <filename>S</filename> variable.
|
||
For example, recipes that fetch their source from Git usually set
|
||
<filename>S</filename> to <filename>${WORKDIR}/git</filename>.
|
||
<note>
|
||
<filename>BP</filename> represents the "Base Package", which is the base package
|
||
name and the package version:
|
||
<literallayout class='monospaced'>
|
||
BP = ${BPN}-${PV}
|
||
</literallayout>
|
||
</note>
|
||
</para>
|
||
|
||
<para>
|
||
The path to the work directory for the recipe
|
||
(<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>) depends
|
||
on the package name and the architecture of the target device.
|
||
For example, here is the work directory for packages whose targets are not device-dependent:
|
||
<literallayout class='monospaced'>
|
||
${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
|
||
</literallayout>
|
||
Let's look at an example without variables.
|
||
Assuming a top-level source directory named <filename>poky</filename>
|
||
and a default build directory of <filename>poky/build</filename>,
|
||
the following is the work directory for the <filename>acl</filename> package:
|
||
<literallayout class='monospaced'>
|
||
~/poky/build/tmp/work/i586-poky-linux/acl-2.2.51-r3
|
||
</literallayout>
|
||
</para>
|
||
|
||
<para>
|
||
If your package is dependent on the target device, the work directory varies slightly:
|
||
<literallayout class='monospaced'>
|
||
${TMPDIR}/work/${MACHINE}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
|
||
</literallayout>
|
||
Again, assuming top-level source directory named <filename>poky</filename>
|
||
and a default build directory of <filename>poky/build</filename>, the
|
||
following is the work directory for the <filename>acl</filename> package that is being
|
||
built for a MIPS-based device:
|
||
<literallayout class='monospaced'>
|
||
~/poky/build/tmp/work/mips-poky-linux/acl-2.2.51-r2
|
||
</literallayout>
|
||
</para>
|
||
|
||
<note>
|
||
To better understand how the OpenEmbedded build system resolves directories during the
|
||
build process, see the glossary entries for the
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>,
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>,
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink>,
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>,
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_OS'><filename>TARGET_OS</filename></ulink>,
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>,
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>,
|
||
and
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
|
||
variables in the Yocto Project Reference Manual.
|
||
</note>
|
||
|
||
<para>
|
||
Now that you know where to locate the directory that has the temporary source code, you can use a
|
||
Quilt or Git workflow to make your edits, test the changes, and preserve the
|
||
changes in the form of patches.
|
||
</para>
|
||
</section>
|
||
|
||
<section id="using-a-quilt-workflow">
|
||
<title>Using a Quilt Workflow</title>
|
||
|
||
<para>
|
||
<ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink>
|
||
is a powerful tool that allows you to capture source code changes without having
|
||
a clean source tree.
|
||
This section outlines the typical workflow you can use to modify temporary source code,
|
||
test changes, and then preserve the changes in the form of a patch all using Quilt.
|
||
</para>
|
||
|
||
<para>
|
||
Follow these general steps:
|
||
<orderedlist>
|
||
<listitem><para><emphasis>Find the Source Code:</emphasis>
|
||
The temporary source code used by the OpenEmbedded build system is kept in the
|
||
build directory.
|
||
See the
|
||
"<link linkend='finding-the-temporary-source-code'>Finding the Temporary Source Code</link>"
|
||
section to learn how to locate the directory that has the temporary source code for a
|
||
particular package.</para></listitem>
|
||
<listitem><para><emphasis>Change Your Working Directory:</emphasis>
|
||
You need to be in the directory that has the temporary source code.
|
||
That directory is defined by the
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink>
|
||
variable.</para></listitem>
|
||
<listitem><para><emphasis>Create a New Patch:</emphasis>
|
||
Before modifying source code, you need to create a new patch.
|
||
To create a new patch file, use <filename>quilt new</filename> as below:
|
||
<literallayout class='monospaced'>
|
||
$ quilt new my_changes.patch
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Notify Quilt and Add Files:</emphasis>
|
||
After creating the patch, you need to notify Quilt about the files you will
|
||
be changing.
|
||
Add the files you will be modifying into the patch you just created:
|
||
<literallayout class='monospaced'>
|
||
$ quilt add file1.c file2.c file3.c
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Edit the Files:</emphasis>
|
||
Make the changes to the temporary source code.</para></listitem>
|
||
<listitem><para><emphasis>Test Your Changes:</emphasis>
|
||
Once you have modified the source code, the easiest way to test your changes
|
||
is by calling the <filename>compile</filename> task as shown in the following example:
|
||
<literallayout class='monospaced'>
|
||
$ bitbake -c compile -f <name_of_package>
|
||
</literallayout>
|
||
The <filename>-f</filename> or <filename>--force</filename>
|
||
option forces re-execution of the specified task.
|
||
If you find problems with your code, you can just keep editing and
|
||
re-testing iteratively until things work as expected.
|
||
<note>All the modifications you make to the temporary source code
|
||
disappear once you <filename>-c clean</filename> or
|
||
<filename>-c cleanall</filename> with BitBake for the package.
|
||
Modifications will also disappear if you use the <filename>rm_work</filename>
|
||
feature as described in the
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>"
|
||
section of the Yocto Project Quick Start.
|
||
</note></para></listitem>
|
||
<listitem><para><emphasis>Generate the Patch:</emphasis>
|
||
Once your changes work as expected, you need to use Quilt to generate the final patch that
|
||
contains all your modifications.
|
||
<literallayout class='monospaced'>
|
||
$ quilt refresh
|
||
</literallayout>
|
||
At this point the <filename>my_changes.patch</filename> file has all your edits made
|
||
to the <filename>file1.c</filename>, <filename>file2.c</filename>, and
|
||
<filename>file3.c</filename> files.</para>
|
||
<para>You can find the resulting patch file in the <filename>patches/</filename>
|
||
subdirectory of the source (<filename>S</filename>) directory.</para></listitem>
|
||
<listitem><para><emphasis>Copy the Patch File:</emphasis>
|
||
For simplicity, copy the patch file into a directory named <filename>files</filename>,
|
||
which you can create in the same directory as the recipe.
|
||
Placing the patch here guarantees that the OpenEmbedded build system will find
|
||
the patch.
|
||
Next, add the patch into the
|
||
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
|
||
of the recipe.
|
||
Here is an example:
|
||
<literallayout class='monospaced'>
|
||
SRC_URI += "file://my_changes.patch"
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Increment the Package Revision Number:</emphasis>
|
||
Finally, don't forget to 'bump' the
|
||
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename>
|
||
value in the same recipe since the resulting packages have changed.</para></listitem>
|
||
</orderedlist>
|
||
</para> </section>
|
||
|
||
<section id='using-a-git-workflow'>
|
||
<title>Using a Git Workflow</title>
|
||
<para>
|
||
Git is an even more powerful tool that allows you to capture source code changes without having
|
||
a clean source tree.
|
||
This section outlines the typical workflow you can use to modify temporary source code,
|
||
test changes, and then preserve the changes in the form of a patch all using Git.
|
||
For general information on Git as it is used in the Yocto Project, see the
|
||
"<link linkend='git'>Git</link>" section.
|
||
</para>
|
||
|
||
<note>
|
||
This workflow uses Git only for its ability to manage local changes to the source code
|
||
and produce patches independent of any version control system used with the Yocto Project.
|
||
</note>
|
||
|
||
<para>
|
||
Follow these general steps:
|
||
<orderedlist>
|
||
<listitem><para><emphasis>Find the Source Code:</emphasis>
|
||
The temporary source code used by the OpenEmbedded build system is kept in the
|
||
build directory.
|
||
See the
|
||
"<link linkend='finding-the-temporary-source-code'>Finding the Temporary Source Code</link>"
|
||
section to learn how to locate the directory that has the temporary source code for a
|
||
particular package.</para></listitem>
|
||
<listitem><para><emphasis>Change Your Working Directory:</emphasis>
|
||
You need to be in the directory that has the temporary source code.
|
||
That directory is defined by the
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink>
|
||
variable.</para></listitem>
|
||
<listitem><para><emphasis>Initialize a Git Repository:</emphasis>
|
||
Use the <filename>git init</filename> command to initialize a new local repository
|
||
that is based on the work directory:
|
||
<literallayout class='monospaced'>
|
||
$ git init
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Stage all the files:</emphasis>
|
||
Use the <filename>git add *</filename> command to stage all the files in the source
|
||
code directory so that they can be committed:
|
||
<literallayout class='monospaced'>
|
||
$ git add *
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Commit the Source Files:</emphasis>
|
||
Use the <filename>git commit</filename> command to initially commit all the files in
|
||
the work directory:
|
||
<literallayout class='monospaced'>
|
||
$ git commit
|
||
</literallayout>
|
||
At this point, your Git repository is aware of all the source code files.
|
||
Any edits you now make to files will be tracked by Git.</para></listitem>
|
||
<listitem><para><emphasis>Edit the Files:</emphasis>
|
||
Make the changes to the temporary source code.</para></listitem>
|
||
<listitem><para><emphasis>Test Your Changes:</emphasis>
|
||
Once you have modified the source code, the easiest way to test your changes
|
||
is by calling the <filename>compile</filename> task as shown in the following example:
|
||
<literallayout class='monospaced'>
|
||
$ bitbake -c compile -f <name_of_package>
|
||
</literallayout>
|
||
The <filename>-f</filename> or <filename>--force</filename>
|
||
option forces re-execution of the specified task.
|
||
If you find problems with your code, you can just keep editing and
|
||
re-testing iteratively until things work as expected.
|
||
<note>All the modifications you make to the temporary source code
|
||
disappear once you <filename>-c clean</filename> or
|
||
<filename>-c cleanall</filename> with BitBake for the package.
|
||
Modifications will also disappear if you use the <filename>rm_work</filename>
|
||
feature as described in the
|
||
"<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>"
|
||
section of the Yocto Project Quick Start.
|
||
</note></para></listitem>
|
||
<listitem><para><emphasis>See the List of Files You Changed:</emphasis>
|
||
Use the <filename>git status</filename> command to see what files you have actually edited.
|
||
The ability to have Git track the files you have changed is an advantage that this
|
||
workflow has over the Quilt workflow.
|
||
Here is the Git command to list your changed files:
|
||
<literallayout class='monospaced'>
|
||
$ git status
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Stage the Modified Files:</emphasis>
|
||
Use the <filename>git add</filename> command to stage the changed files so they
|
||
can be committed as follows:
|
||
<literallayout class='monospaced'>
|
||
$ git add file1.c file2.c file3.c
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Commit the Staged Files and View Your Changes:</emphasis>
|
||
Use the <filename>git commit</filename> command to commit the changes to the
|
||
local repository.
|
||
Once you have committed the files, you can use the <filename>git log</filename>
|
||
command to see your changes:
|
||
<literallayout class='monospaced'>
|
||
$ git commit
|
||
$ git log
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Generate the Patch:</emphasis>
|
||
Once the changes are committed, use the <filename>git format-patch</filename>
|
||
command to generate a patch file:
|
||
<literallayout class='monospaced'>
|
||
$ git format-patch HEAD~1
|
||
</literallayout>
|
||
The <filename>HEAD~1</filename> part of the command causes Git to generate the
|
||
patch file for the most recent commit.</para>
|
||
<para>At this point, the patch file has all your edits made
|
||
to the <filename>file1.c</filename>, <filename>file2.c</filename>, and
|
||
<filename>file3.c</filename> files.
|
||
You can find the resulting patch file in the current directory.
|
||
The patch file ends with <filename>.patch</filename>.</para></listitem>
|
||
<listitem><para><emphasis>Copy the Patch File:</emphasis>
|
||
For simplicity, copy the patch file into a directory named <filename>files</filename>,
|
||
which you can create in the same directory as the recipe.
|
||
Placing the patch here guarantees that the OpenEmbedded build system will find
|
||
the patch.
|
||
Next, add the patch into the
|
||
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
|
||
of the recipe.
|
||
Here is an example:
|
||
<literallayout class='monospaced'>
|
||
SRC_URI += "file://my_changes.patch"
|
||
</literallayout></para></listitem>
|
||
<listitem><para><emphasis>Increment the Package Revision Number:</emphasis>
|
||
Finally, don't forget to 'bump' the
|
||
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename>
|
||
value in the same recipe since the resulting packages have changed.</para></listitem>
|
||
</orderedlist>
|
||
</para>
|
||
</section>
|
||
</section>
|
||
|
||
<section id='image-development-using-hob'>
|
||
<title>Image Development Using Hob</title>
|
||
|
||
<para>
|
||
The <ulink url='&YOCTO_HOME_URL;/projects/hob'>Hob</ulink> is a graphical user interface for the
|
||
OpenEmbedded build system, which is based on BitBake.
|
||
You can use the Hob to build custom operating system images within the Yocto Project build environment.
|
||
Hob simply provides a friendly interface over the build system used during system development.
|
||
In other words, building images with the Hob lets you take care of common build tasks more easily.
|
||
</para>
|
||
|
||
<para>
|
||
For a better understanding of Hob, see the project page at
|
||
<ulink url='&YOCTO_HOME_URL;/projects/hob'></ulink> on the Yocto Project website.
|
||
The page has a short introductory training video on Hob.
|
||
The following lists some features of Hob:
|
||
<itemizedlist>
|
||
<listitem><para>You can setup and run Hob using these commands:
|
||
<literallayout class='monospaced'>
|
||
$ source oe-init-build-env
|
||
$ hob
|
||
</literallayout></para></listitem>
|
||
<listitem><para>You can set the
|
||
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
|
||
for which you are building the image.</para></listitem>
|
||
<listitem><para>You can modify various policy settings such as the package format used to build with,
|
||
the parrallelism BitBake uses, whether or not to build an external toolchain, and which host
|
||
to build against.</para></listitem>
|
||
<listitem><para>You can manage
|
||
<link linkend='understanding-and-creating-layers'>layers</link>.</para></listitem>
|
||
<listitem><para>You can select a base image and then add extra packages for your custom build.
|
||
</para></listitem>
|
||
<listitem><para>You can launch and monitor the build from within Hob.</para></listitem>
|
||
</itemizedlist>
|
||
</para>
|
||
</section>
|
||
|
||
<section id="platdev-appdev-devshell">
|
||
<title>Using a Development Shell</title>
|
||
|
||
<para>
|
||
When debugging certain commands or even when just editing packages,
|
||
<filename>devshell</filename> can be a useful tool.
|
||
When you invoke <filename>devshell</filename>, source files are
|
||
extracted into your working directory and patches are applied.
|
||
Then, a new terminal is opened and you are placed in the working directory.
|
||
In the new terminal, all the OpenEmbedded build-related environment variables are
|
||
still defined so you can use commands such as <filename>configure</filename> and
|
||
<filename>make</filename>.
|
||
The commands execute just as if the OpenEmbedded build system were executing them.
|
||
Consequently, working this way can be helpful when debugging a build or preparing
|
||
software to be used with the OpenEmbedded build system.
|
||
</para>
|
||
|
||
<para>
|
||
Following is an example that uses <filename>devshell</filename> on a target named
|
||
<filename>matchbox-desktop</filename>:
|
||
<literallayout class='monospaced'>
|
||
$ bitbake matchbox-desktop -c devshell
|
||
</literallayout>
|
||
</para>
|
||
|
||
<para>
|
||
This command opens a terminal with a shell prompt within the OpenEmbedded build environment.
|
||
The default shell is xterm.
|
||
The following occurs:
|
||
<itemizedlist>
|
||
<listitem><para>The <filename>PATH</filename> variable includes the
|
||
cross-toolchain.</para></listitem>
|
||
<listitem><para>The <filename>pkgconfig</filename> variables find the correct
|
||
<filename>.pc</filename> files.</para></listitem>
|
||
<listitem><para>The <filename>configure</filename> command finds the
|
||
Yocto Project site files as well as any other necessary files.</para></listitem>
|
||
</itemizedlist>
|
||
Within this environment, you can run <filename>configure</filename>
|
||
or <filename>compile</filename> commands as if they were being run by
|
||
the OpenEmbedded build system itself.
|
||
As noted earlier, the working directory also automatically changes to the
|
||
source directory (<ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>).
|
||
</para>
|
||
|
||
<para>
|
||
When you are finished, you just exit the shell or close the terminal window.
|
||
</para>
|
||
|
||
<para>
|
||
Because an external shell is launched rather than opening directly into the
|
||
original terminal window, it allows easier interaction with BitBake's multiple
|
||
threads as well as accomodates a future client/server split.
|
||
</para>
|
||
|
||
<note>
|
||
<para>
|
||
It is worth remembering that when using <filename>devshell</filename>
|
||
you need to use the full compiler name such as <filename>arm-poky-linux-gnueabi-gcc</filename>
|
||
instead of just using <filename>gcc</filename>.
|
||
The same applies to other applications such as <filename>binutils</filename>,
|
||
<filename>libtool</filename> and so forth.
|
||
BitBake sets up environment variables such as <filename>CC</filename>
|
||
to assist applications, such as <filename>make</filename> to find the correct tools.
|
||
</para>
|
||
|
||
<para>
|
||
It is also worth noting that <filename>devshell</filename> still works over
|
||
X11 forwarding and similar situations
|
||
</para>
|
||
</note>
|
||
</section>
|
||
|
||
</chapter>
|
||
<!--
|
||
vim: expandtab tw=80 ts=4
|
||
-->
|