408 lines
24 KiB
XML
408 lines
24 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-start'>
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<title>Getting Started with the Yocto Project</title>
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<para>
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This chapter introduces the Yocto Project and gives you an idea of what you need to get started.
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You can find enough information to set up your development host and build or use images for
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hardware supported by the Yocto Project by reading the
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<ulink url='&YOCTO_DOCS_QS_URL;'>Yocto Project Quick Start</ulink>.
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</para>
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<para>
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The remainder of this chapter summarizes what is in the Yocto Project Quick Start and provides
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some higher-level concepts you might want to consider.
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</para>
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<section id='introducing-the-yocto-project'>
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<title>Introducing the Yocto Project</title>
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<para>
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The Yocto Project is an open-source collaboration project focused on embedded Linux development.
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The project currently provides a build system that is
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referred to as the OpenEmbedded build system in the Yocto Project documentation.
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The Yocto Project provides various ancillary tools for the embedded developer
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and also features the Sato reference User Interface, which is optimized for
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stylus driven, low-resolution screens.
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</para>
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<para>
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You can use the OpenEmbedded build system, which uses
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BitBake to develop complete Linux
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images and associated user-space applications for architectures based
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on ARM, MIPS, PowerPC, x86 and x86-64.
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<note>
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By default, using the Yocto Project creates a Poky distribution.
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However, you can create your own distribution by providing key
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<link linkend='metadata'>Metadata</link>.
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See the "<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
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section for more information.
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</note>
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While the Yocto Project does not provide a strict testing framework,
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it does provide or generate for you artifacts that let you perform target-level and
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emulated testing and debugging.
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Additionally, if you are an <trademark class='trade'>Eclipse</trademark>
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IDE user, you can install an Eclipse Yocto Plug-in to allow you to
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develop within that familiar environment.
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</para>
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</section>
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<section id='getting-setup'>
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<title>Getting Set Up</title>
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<para>
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Here is what you need to get set up to use the Yocto Project:
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<itemizedlist>
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<listitem><para><emphasis>Host System:</emphasis> You should have a reasonably current
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Linux-based host system.
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You will have the best results with a recent release of Fedora,
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OpenSUSE, Debian, Ubuntu, or CentOS as these releases are frequently tested against the Yocto Project
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and officially supported.
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For a list of the distributions under validation and their status, see the
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"<ulink url='&YOCTO_DOCS_REF_URL;#detailed-supported-distros'>Supported Linux Distributions</ulink>" section
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in the Yocto Project Reference Manual and the wiki page at
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<ulink url='&YOCTO_WIKI_URL;/wiki/Distribution_Support'>Distribution Support</ulink>.</para>
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<para>
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You should also have about 100 gigabytes of free disk space for building images.
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</para></listitem>
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<listitem><para><emphasis>Packages:</emphasis> The OpenEmbedded build system
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requires certain packages exist on your development system (e.g. Python 2.6 or 2.7).
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See "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>"
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section in the Yocto Project Quick Start and the
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"<ulink url='&YOCTO_DOCS_REF_URL;#required-packages-for-the-host-development-system'>Required Packages for the Host Development System</ulink>"
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section in the Yocto Project Reference Manual for the exact
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package requirements and the installation commands to install
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them for the supported distributions.
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</para></listitem>
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<listitem id='local-yp-release'><para><emphasis>Yocto Project Release:</emphasis>
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You need a release of the Yocto Project.
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You set that up with a local <link linkend='source-directory'>Source Directory</link>
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one of two ways depending on whether you
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are going to contribute back into the Yocto Project or not.
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<note>
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Regardless of the method you use, this manual refers to the resulting local
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hierarchical set of files as the "Source Directory."
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</note>
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<itemizedlist>
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<listitem><para><emphasis>Tarball Extraction:</emphasis>
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If you are not going to contribute back into the Yocto
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Project, you can simply go to the
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<ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink>,
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select the "Downloads" tab, and choose what you want.
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Once you have the tarball, just extract it into a
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directory of your choice.</para>
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<para>For example, the following command extracts the
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Yocto Project &DISTRO; release tarball
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into the current working directory and sets up the local Source Directory
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with a top-level folder named <filename>&YOCTO_POKY;</filename>:
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<literallayout class='monospaced'>
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$ tar xfj &YOCTO_POKY_TARBALL;
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</literallayout></para>
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<para>This method does not produce a local Git repository.
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Instead, you simply end up with a snapshot of the release.</para></listitem>
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<listitem><para><emphasis>Git Repository Method:</emphasis> If you are going to be contributing
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back into the Yocto Project or you simply want to keep up
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with the latest developments, you should use Git commands to set up a local
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Git repository of the upstream <filename>poky</filename> source repository.
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Doing so creates a repository with a complete history of changes and allows
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you to easily submit your changes upstream to the project.
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Because you clone the repository, you have access to all the Yocto Project development
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branches and tag names used in the upstream repository.</para>
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<note>You can view the Yocto Project Source Repositories at
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<ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink></note>
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<para>The following transcript shows how to clone the <filename>poky</filename>
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Git repository into the current working directory.
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The command creates the local repository in a directory named <filename>poky</filename>.
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For information on Git used within the Yocto Project, see the
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"<link linkend='git'>Git</link>" section.
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<literallayout class='monospaced'>
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$ git clone git://git.yoctoproject.org/poky
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Cloning into 'poky'...
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remote: Counting objects: 203728, done.
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remote: Compressing objects: 100% (52371/52371), done.
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remote: Total 203728 (delta 147444), reused 202891 (delta 146614)
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Receiving objects: 100% (203728/203728), 95.54 MiB | 308 KiB/s, done.
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Resolving deltas: 100% (147444/147444), done.
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</literallayout></para>
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<para>For another example of how to set up your own local Git repositories, see this
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<ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP'>
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wiki page</ulink>, which describes how to create both <filename>poky</filename>
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and <filename>meta-intel</filename> Git repositories.</para></listitem>
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</itemizedlist></para></listitem>
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<listitem id='local-kernel-files'><para><emphasis>Yocto Project Kernel:</emphasis>
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If you are going to be making modifications to a supported Yocto Project kernel, you
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need to establish local copies of the source.
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You can find Git repositories of supported Yocto Project Kernels organized under
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"Yocto Linux Kernel" in the Yocto Project Source Repositories at
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<ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.</para>
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<para>This setup can involve creating a bare clone of the Yocto Project kernel and then
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copying that cloned repository.
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You can create the bare clone and the copy of the bare clone anywhere you like.
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For simplicity, it is recommended that you create these structures outside of the
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Source Directory (usually <filename>poky</filename>).</para>
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<para>As an example, the following transcript shows how to create the bare clone
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of the <filename>linux-yocto-3.10</filename> kernel and then create a copy of
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that clone.
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<note>When you have a local Yocto Project kernel Git repository, you can
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reference that repository rather than the upstream Git repository as
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part of the <filename>clone</filename> command.
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Doing so can speed up the process.</note></para>
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<para>In the following example, the bare clone is named
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<filename>linux-yocto-3.10.git</filename>, while the
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copy is named <filename>my-linux-yocto-3.10-work</filename>:
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<literallayout class='monospaced'>
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$ git clone --bare git://git.yoctoproject.org/linux-yocto-3.10 linux-yocto-3.10.git
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Cloning into bare repository 'linux-yocto-3.10.git'...
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remote: Counting objects: 3364487, done.
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remote: Compressing objects: 100% (507178/507178), done.
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remote: Total 3364487 (delta 2827715), reused 3364481 (delta 2827709)
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Receiving objects: 100% (3364487/3364487), 722.95 MiB | 423 KiB/s, done.
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Resolving deltas: 100% (2827715/2827715), done.
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</literallayout></para>
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<para>Now create a clone of the bare clone just created:
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<literallayout class='monospaced'>
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$ git clone linux-yocto-3.10.git my-linux-yocto-3.10-work
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Cloning into 'my-linux-yocto-3.10-work'...
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done.
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</literallayout></para></listitem>
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<listitem id='meta-yocto-kernel-extras-repo'><para><emphasis>
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The <filename>meta-yocto-kernel-extras</filename> Git Repository</emphasis>:
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The <filename>meta-yocto-kernel-extras</filename> Git repository contains Metadata needed
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only if you are modifying and building the kernel image.
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In particular, it contains the kernel BitBake append (<filename>.bbappend</filename>)
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files that you
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edit to point to your locally modified kernel source files and to build the kernel
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image.
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Pointing to these local files is much more efficient than requiring a download of the
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kernel's source files from upstream each time you make changes to the kernel.</para>
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<para>You can find the <filename>meta-yocto-kernel-extras</filename> Git Repository in the
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"Yocto Metadata Layers" area of the Yocto Project Source Repositories at
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<ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
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It is good practice to create this Git repository inside the Source Directory.</para>
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<para>Following is an example that creates the <filename>meta-yocto-kernel-extras</filename> Git
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repository inside the Source Directory, which is named <filename>poky</filename>
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in this case:
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<literallayout class='monospaced'>
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$ cd ~/poky
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$ git clone git://git.yoctoproject.org/meta-yocto-kernel-extras meta-yocto-kernel-extras
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Cloning into 'meta-yocto-kernel-extras'...
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remote: Counting objects: 727, done.
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remote: Compressing objects: 100% (452/452), done.
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remote: Total 727 (delta 260), reused 719 (delta 252)
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Receiving objects: 100% (727/727), 536.36 KiB | 102 KiB/s, done.
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Resolving deltas: 100% (260/260), done.
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</literallayout></para></listitem>
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<listitem><para id='supported-board-support-packages-(bsps)'><emphasis>Supported Board
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Support Packages (BSPs):</emphasis>
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The Yocto Project provides a layer called <filename>meta-intel</filename> and
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it is maintained in its own separate Git repository.
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The <filename>meta-intel</filename> layer contains many supported
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<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>.</para>
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<para>Similar considerations exist for setting up the <filename>meta-intel</filename>
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layer.
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You can get set up for BSP development one of two ways: tarball extraction or
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with a local Git repository.
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It is a good idea to use the same method that you used to set up the Source Directory.
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Regardless of the method you use, the Yocto Project uses the following BSP layer
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naming scheme:
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<literallayout class='monospaced'>
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meta-<BSP_name>
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</literallayout>
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where <filename><BSP_name></filename> is the recognized BSP name.
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Here are some examples:
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<literallayout class='monospaced'>
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meta-crownbay
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meta-emenlow
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meta-n450
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</literallayout>
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See the
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"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
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section in the Yocto Project Board Support Package (BSP) Developer's Guide for more
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information on BSP Layers.
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<itemizedlist>
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<listitem><para><emphasis>Tarball Extraction:</emphasis> You can download any released
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BSP tarball from the same "Downloads" page of the
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<ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink>
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to get the Yocto Project release.
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Once on the "Download" page, look for "BSP" under the
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"Type" heading.</para>
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<para>Once you have the tarball, just extract it into a directory of your choice.
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Again, this method just produces a snapshot of the BSP layer in the form
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of a hierarchical directory structure.</para></listitem>
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<listitem><para><emphasis>Git Repository Method:</emphasis> If you are working
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with a local Git repository for your Source Directory, you should also use this method
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to set up the <filename>meta-intel</filename> Git repository.
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You can locate the <filename>meta-intel</filename> Git repository in the
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"Yocto Metadata Layers" area of the Yocto Project Source Repositories at
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<ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.</para>
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<para>Typically, you set up the <filename>meta-intel</filename> Git repository inside
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the Source Directory.
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For example, the following transcript shows the steps to clone the
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<filename>meta-intel</filename>
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Git repository inside the local <filename>poky</filename> Git repository.
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<literallayout class='monospaced'>
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$ cd ~/poky
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$ git clone git://git.yoctoproject.org/meta-intel.git
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Cloning into 'meta-intel'...
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remote: Counting objects: 7366, done.
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remote: Compressing objects: 100% (2491/2491), done.
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remote: Total 7366 (delta 3997), reused 7299 (delta 3930)
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Receiving objects: 100% (7366/7366), 2.31 MiB | 95 KiB/s, done.
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Resolving deltas: 100% (3997/3997), done.
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</literallayout></para>
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<para>The same
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<ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP'>wiki page</ulink>
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referenced earlier covers how to
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set up the <filename>meta-intel</filename> Git repository.
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</para></listitem>
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</itemizedlist></para></listitem>
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<listitem><para><emphasis>Eclipse Yocto Plug-in:</emphasis> If you are developing
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applications using the Eclipse Integrated Development Environment (IDE),
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you will need this plug-in.
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See the
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"<link linkend='setting-up-the-eclipse-ide'>Setting up the Eclipse IDE</link>"
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section for more information.</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='building-images'>
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<title>Building Images</title>
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<para>
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The build process creates an entire Linux distribution, including the toolchain, from source.
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For more information on this topic, see the
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"<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>"
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section in the Yocto Project Quick Start.
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</para>
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<para>
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The build process is as follows:
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<orderedlist>
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<listitem><para>Make sure you have set up the Source Directory described in the
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previous section.</para></listitem>
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<listitem><para>Initialize the build environment by sourcing a build environment
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script.</para></listitem>
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<listitem><para>Optionally ensure the <filename>conf/local.conf</filename> configuration file,
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which is found in the
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<link linkend='build-directory'>Build Directory</link>,
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is set up how you want it.
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This file defines many aspects of the build environment including
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the target machine architecture through the
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<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'>MACHINE</ulink></filename> variable,
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the development machine's processor use through the
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<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BB_NUMBER_THREADS'>BB_NUMBER_THREADS</ulink></filename> and
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<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'>PARALLEL_MAKE</ulink></filename> variables, and
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a centralized tarball download directory through the
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<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'>DL_DIR</ulink></filename> variable.</para></listitem>
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<listitem><para>Build the image using the <filename>bitbake</filename> command.
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If you want information on BitBake, see the user manual included in the
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<filename>bitbake/doc/manual</filename> directory of the
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<link linkend='source-directory'>Source Directory</link>.</para></listitem>
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<listitem><para>Run the image either on the actual hardware or using the QEMU
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emulator.</para></listitem>
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</orderedlist>
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</para>
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</section>
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<section id='using-pre-built-binaries-and-qemu'>
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<title>Using Pre-Built Binaries and QEMU</title>
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<para>
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Another option you have to get started is to use pre-built binaries.
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The Yocto Project provides many types of binaries with each release.
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See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
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chapter in the Yocto Project Reference Manual
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for descriptions of the types of binaries that ship with a Yocto Project
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release.
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</para>
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<para>
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Using a pre-built binary is ideal for developing software applications to run on your
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target hardware.
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To do this, you need to be able to access the appropriate cross-toolchain tarball for
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the architecture on which you are developing.
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If you are using an SDK type image, the image ships with the complete toolchain native to
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the architecture.
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If you are not using an SDK type image, you need to separately download and
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install the stand-alone Yocto Project cross-toolchain tarball.
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</para>
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<para>
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Regardless of the type of image you are using, you need to download the pre-built kernel
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that you will boot in the QEMU emulator and then download and extract the target root
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filesystem for your target machine’s architecture.
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You can get architecture-specific binaries and file systems from
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<ulink url='&YOCTO_MACHINES_DL_URL;'>machines</ulink>.
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You can get installation scripts for stand-alone toolchains from
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<ulink url='&YOCTO_TOOLCHAIN_DL_URL;'>toolchains</ulink>.
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Once you have all your files, you set up the environment to emulate the hardware
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by sourcing an environment setup script.
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Finally, you start the QEMU emulator.
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You can find details on all these steps in the
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"<ulink url='&YOCTO_DOCS_QS_URL;#using-pre-built'>Using Pre-Built Binaries and QEMU</ulink>"
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section of the Yocto Project Quick Start.
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</para>
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<para>
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Using QEMU to emulate your hardware can result in speed issues
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depending on the target and host architecture mix.
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For example, using the <filename>qemux86</filename> image in the emulator
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on an Intel-based 32-bit (x86) host machine is fast because the target and
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host architectures match.
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On the other hand, using the <filename>qemuarm</filename> image on the same Intel-based
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host can be slower.
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But, you still achieve faithful emulation of ARM-specific issues.
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</para>
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<para>
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To speed things up, the QEMU images support using <filename>distcc</filename>
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to call a cross-compiler outside the emulated system.
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If you used <filename>runqemu</filename> to start QEMU, and the
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<filename>distccd</filename> application is present on the host system, any
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BitBake cross-compiling toolchain available from the build system is automatically
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used from within QEMU simply by calling <filename>distcc</filename>.
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You can accomplish this by defining the cross-compiler variable
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(e.g. <filename>export CC="distcc"</filename>).
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Alternatively, if you are using a suitable SDK image or the appropriate
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stand-alone toolchain is present,
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the toolchain is also automatically used.
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</para>
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<note>
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Several mechanisms exist that let you connect to the system running on the
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QEMU emulator:
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<itemizedlist>
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<listitem><para>QEMU provides a framebuffer interface that makes standard
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consoles available.</para></listitem>
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<listitem><para>Generally, headless embedded devices have a serial port.
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If so, you can configure the operating system of the running image
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to use that port to run a console.
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The connection uses standard IP networking.</para></listitem>
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<listitem><para>SSH servers exist in some QEMU images.
|
||
The <filename>core-image-sato</filename> QEMU image has a Dropbear secure
|
||
shell (SSH) server that runs with the root password disabled.
|
||
The <filename>core-image-basic</filename> and <filename>core-image-lsb</filename> QEMU images
|
||
have OpenSSH instead of Dropbear.
|
||
Including these SSH servers allow you to use standard <filename>ssh</filename> and
|
||
<filename>scp</filename> commands.
|
||
The <filename>core-image-minimal</filename> QEMU image, however, contains no SSH
|
||
server.</para></listitem>
|
||
<listitem><para>You can use a provided, user-space NFS server to boot the QEMU session
|
||
using a local copy of the root filesystem on the host.
|
||
In order to make this connection, you must extract a root filesystem tarball by using the
|
||
<filename>runqemu-extract-sdk</filename> command.
|
||
After running the command, you must then point the <filename>runqemu</filename>
|
||
script to the extracted directory instead of a root filesystem image file.</para></listitem>
|
||
</itemizedlist>
|
||
</note>
|
||
</section>
|
||
</chapter>
|
||
<!--
|
||
vim: expandtab tw=80 ts=4
|
||
-->
|