532 lines
24 KiB
XML
532 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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<chapter id='bsp'>
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<title>Board Support Packages (BSP) - Developers Guide</title>
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<para>
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A Board Support Package (BSP) is a collection of information that
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defines how to support a particular hardware device, set of devices, or
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hardware platform.
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The BSP includes information about the hardware features
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present on the device and kernel configuration information along with any
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additional hardware drivers required.
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The BSP also lists any additional software
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components required in addition to a generic Linux software stack for both
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essential and optional platform features.
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</para>
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<para>
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This section (or document if you are reading the BSP Developer's Guide) defines
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a structure for these components
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so that BSPs follow a commonly understood layout.
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Providing a common form allows end-users to understand and become familiar
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with the layout.
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A common form also encourages standardization
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of software support of hardware.
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</para>
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<para>
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The proposed format does have elements that are specific to the Poky and
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OpenEmbedded build systems.
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It is intended that this information can be
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used by other systems besides Poky and OpenEmbedded and that it will be simple
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to extract information and convert it to other formats if required.
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Poky, through its standard layers mechanism, can directly accept the format
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described as a layer.
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The BSP captures all
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the hardware-specific details in one place in a standard format, which is
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useful for any person wishing to use the hardware platform regardless of
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the build system they are using.
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</para>
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<para>
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The BSP specification does not include a build system or other tools -
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it is concerned with the hardware-specific components only.
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At the end
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distribution point you can ship the BSP combined with a build system
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and other tools.
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However, it is important to maintain the distinction that these
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are separate components that happen to be combined in certain end products.
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</para>
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<section id="bsp-filelayout">
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<title>Example Filesystem Layout</title>
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<para>
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The BSP consists of a file structure inside a base directory, which uses the following
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naming convention:
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<literallayout class='monospaced'>
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meta-<bsp_name>
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</literallayout>
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"bsp_name" is a placeholder for the machine or platform name.
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Here are some example base directory names:
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<literallayout class='monospaced'>
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meta-emenlow
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meta-intel_n450
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meta-beagleboard
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</literallayout>
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</para>
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<para>
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Below is the common form for the file structure inside a base directory.
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While you can use this basic form for the standard, realize that the actual structures
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for specific BSPs could differ.
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<programlisting>
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meta-<bsp_name>/
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meta-<bsp_name>/<bsp_license_file>
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meta-<bsp_name>/README
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meta-<bsp_name>/binary/<bootable_images>
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meta-<bsp_name>/conf/layer.conf
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meta-<bsp_name>/conf/machine/*.conf
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meta-<bsp_name>/recipes-bsp/*
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meta-<bsp_name>/recipes-bsp/formfactor/formfactor/<bsp_name>/*
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meta-<bsp_name>/recipes-graphics/*
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meta-<bsp_name>/recipes-kernel/linux/linux-wrs_git.bbappend
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</programlisting>
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</para>
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<para>
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Below is an example of the crownbay BSP:
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<programlisting>
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meta-crownbay/COPYING.MIT
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meta-crownbay/README
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meta-crownbay/binary/.gitignore
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meta-crownbay/conf/layer.conf
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meta-crownbay/conf/machine/crownbay.conf
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meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig
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meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xcorg.conf
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd-bin/.gitignore
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd-bin_1.7.99.2.bb
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/crosscompile.patch
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/fix_open_max_preprocessor_error.patch
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/macro_tweak.patch
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/nodolt.patch
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meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd_1.7.99.2.bb
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meta-crownbay/recipes-kernel/linux/linux-wrs_git.bbappend
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</programlisting>
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</para>
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<para>
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The following sections describe each part of the proposed BSP format.
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</para>
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</section>
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<section id="bsp-filelayout-license">
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<title>License Files</title>
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<programlisting>
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meta-<bsp_name>/<bsp_license_file>
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</programlisting>
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<para>
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These optional files satisfy licensing requirements for the BSP.
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The type or types of files here can vary depending on the licensing requirements.
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For example, in the crownbay BSP all licensing requirements are handled with the
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<filename>COPYING.MIT</filename> file.
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</para>
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<para>
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Licensing files can be MIT, BSD, GPLv*, and so forth.
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These files are recommended for the BSP but are optional and totally up to the BSP developer.
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</para>
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</section>
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<section id="bsp-filelayout-readme">
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<title>README File</title>
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<programlisting>
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meta-<bsp_name>/README
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</programlisting>
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<para>
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This file provides information on how to boot the live images that are optionally
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included in the <filename>/binary</filename> directory.
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The <filename>README</filename> file also provides special information needed for
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building the image.
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</para>
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<para>
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Technically speaking a <filename>README</filename> is optional but it is highly
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recommended that every BSP has one.
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</para>
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</section>
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<section id="bsp-filelayout-binary">
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<title>Pre-built User Binaries (meta-<bsp_name>/binary/*)</title>
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<para>
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This optional area contains useful pre-built kernels and userspace filesystem
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images appropriate to the target system.
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This directory contains the Application Development Toolkit (ADT) and minimal
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live images when the BSP is has been "tar-balled" and placed on the Yocto Project website.
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You can use these kernels and images to get a system running and quickly get started
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on development tasks.
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The exact types of binaries present are highly hardware-dependent.
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However, a README file should be present that explains how to use the kernels and
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images with the target hardware.
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If pre-built binaries are present, source code to meet licensing requirements must also
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be provided in some form.
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</para>
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</section>
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<section id='bsp-filelayout-layer'>
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<title>Layer Configuration (meta-<bsp_name>/conf/layer.conf)</title>
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<para>
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This file identifies the structure as a Poky layer, identifies the
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contents of the layer, and contains information about how Poky should use
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it.
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Generally, a standard boilerplate file such as the following works:
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</para>
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<para>
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<programlisting>
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# We have a conf directory, add to BBPATH
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BBPATH := "${BBPATH}:${LAYERDIR}"
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# We have a recipes directory containing .bb and .bbappend files, add to BBFILES
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BBFILES := "${BBFILES} ${LAYERDIR}/recipes/*/*.bb \ ${LAYERDIR}/recipes/*/*.bbappend"
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BBFILE_COLLECTIONS += "bsp"
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BBFILE_PATTERN_bsp := "^${LAYERDIR}/"
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BBFILE_PRIORITY_bsp = "5"
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</programlisting>
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</para>
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<para>
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This file simply makes BitBake aware of the recipes and configuration directories.
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This file must exist so that Poky can recognize the BSP.
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</para>
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</section>
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<section id="bsp-filelayout-machine">
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<title>Hardware Configuration Options (meta-<bsp_name>/conf/machine/*.conf)</title>
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<para>
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The machine files bind together all the information contained elsewhere
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in the BSP into a format that Poky can understand.
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If the BSP supports multiple machines, multiple machine configuration files
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can be present.
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These filenames correspond to the values to which users have set the MACHINE variable.
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</para>
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<para>
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These files define things such as the kernel package to use
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(PREFERRED_PROVIDER of virtual/kernel), the hardware drivers to
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include in different types of images, any special software components
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that are needed, any bootloader information, and also any special image
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format requirements.
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</para>
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<para>
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At least one machine file is required for a Poky BSP layer.
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However, you can supply more than one file.
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</para>
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</section>
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<section id="bsp-filelayout-tune">
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<title>Hardware Optimization Options (meta-<bsp_name>/conf/machine/include/tune-*.inc)</title>
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<para>
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These files are shared hardware "tuning" definitions and are commonly used to
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pass specific optimization flags to the compiler.
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An example is <filename>tune-atom.inc</filename>:
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</para>
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<para>
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<programlisting>
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BASE_PACKAGE_ARCH = "core2"
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TARGET_CC_ARCH = "-m32 -march=core2 -msse3 -mtune=generic -mfpmath=sse"
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</programlisting>
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</para>
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<para>
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This example defines a new package architecture called "core2" and uses the
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specified optimization flags, which are carefully chosen to give best
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performance on atom processors.
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</para>
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<para>
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The tune file would be included by the machine definition and can be
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contained in the BSP or referenced from one of the standard core set of
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files included with Poky itself.
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</para>
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<para>
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Both the base package architecuture file and the tune file are optional for a Poky BSP layer.
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</para>
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</section>
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<section id='bsp-filelayout-kernel'>
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<title>Linux Kernel Configuration (meta-<bsp_name>/recipes-kernel/linux/*)</title>
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<para>
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These files make up the definition of a kernel to use with this hardware.
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In this case, it is a complete self-contained kernel with its own
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configuration and patches.
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However, kernels can be shared between many machines as well.
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Following is an example:
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<programlisting>
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meta-Emenlow/recipes-kernel/linux/linux-bsp_2.6.50.bb
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</programlisting>
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This example file is the core kernel recipe that details from where to get the kernel
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source.
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All standard source code locations are supported.
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Consequently, the source could be a release tarball, a git repository, or source included in
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the directory within the BSP itself.
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</para>
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<para>
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The file then contains information about what patches to apply and how to configure and build them.
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Because the file can reuse the main Poky kernel build class, the definitions here can
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remain very simple.
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</para>
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<para>
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<programlisting>
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linux-bsp-2.6.50/*.patch
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</programlisting>
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</para>
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<para>
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The above example file contains patches you can apply against the base kernel, from wherever
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they may have been obtained.
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</para>
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<para>
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<programlisting>
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meta-Emenlow/recipes-kernel/linux/linux-bsp-2.6.50/defconfig-bsp
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</programlisting>
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</para>
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<para>
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Finally, this last example file contains kernel configuration information.
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</para>
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<para>
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Examples of kernel recipes are available in Poky itself, and thus, make these files optional.
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However, it would be unusual not to have a kernel configuration.
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</para>
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</section>
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<section id='bsp-filelayout-packages'>
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<title>Other Software (meta-<bsp_name>/recipes-kernel/*)</title>
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<para>
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This section describes other pieces of software that the hardware might need for best
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operation.
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Examples show some of the things you could encounter.
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The examples are standard <filename>.bb</filename> file recipes in the
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usual Poky format.
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You can include the source directly by referring to it in the source control system or
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the released tarballs of external software projects.
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You only need to provide these types of files if the platform requires them.
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</para>
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<para>
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The following file is a bootloader recipe that can be used to generate a new
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bootloader binary.
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Sometimes these files are included in the final image format and are needed to re-flash hardware.
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</para>
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<para>
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<programlisting>
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meta-Emenlow/recipes-kernel/bootloader/bootloader_0.1.bb
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</programlisting>
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</para>
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<para>
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These next two files are examples of a hardware driver and a hardware daemon that might need
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to be included in images to make the hardware useful.
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Although the example uses "modem" there may be other components needed, such as firmware.
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</para>
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<para>
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<programlisting>
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meta-Emenlow/recipes-Emenlow/modem/modem-driver_0.1.bb
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meta-Emenlow/recipes-Emenlow/modem/modem-daemon_0.1.bb
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</programlisting>
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</para>
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<para>
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Sometimes the device needs an image in a very specific format so that the update
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mechanism can accept and re-flash it.
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Recipes to build the tools needed to do this can be included with the BSP.
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Following is an example.
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</para>
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<para>
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<programlisting>
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meta-Emenlow/recipes-Emenlow/image-creator/image-creator-native_0.1.bb
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</programlisting>
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</para>
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</section>
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<section id='bs-filelayout-bbappend'>
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<title>Append BSP-Specific Information to Existing Recipes</title>
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<para>
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Suppose you have a recipe such as "pointercal" that requires machine-specific information.
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At the same time, you have your new BSP code nicely partitioned into a layer through which
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you would also like to specify any machine-specific information associated with your new machine.
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Before the <filename>.bbappend</filename> extension was introduced, you would have to copy the whole
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pointercal recipe and files into your layer and then add the single file for your machine.
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</para>
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<para>
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With the <filename>.bbappend</filename> extension, however, your work becomes much easier.
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This extension allows you to easily merge BSP-specific information with the original recipe.
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Whenever BitBake finds any <filename>.bbappend</filename> files BitBake will include them after
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it loads the associated <filename>.bb</filename> file but before any finalize
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or anonymous methods are run.
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This allows the BSP layer to do whatever it might want to do to customize the original recipe.
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</para>
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<para>
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If your recipe needs to reference extra files it can use the FILESEXTRAPATH variable
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to specify their location.
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The example below shows extra files contained in a folder called ${PN} (the package name).
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</para>
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<programlisting>
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FILESEXTRAPATHS := "${THISDIR}/${PN}"
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</programlisting>
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<para>
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This technique allows the BSP to add machine-specific configuration files to the layer directory,
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which will be picked up by BitBake.
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For an example see <filename>meta-emenlow/packages/formfactor</filename>.
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</para>
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</section>
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<section id="bsp-filelayout-prebuilds">
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<title>Pre-build Data (meta-<bsp_name>/prebuilds/*)</title>
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<para>
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This location can contain precompiled representations of the source code
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contained elsewhere in the BSP layer.
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Assuming a compatible configuration is used, Poky can process and use these optional pre-compiled
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representations to provide much faster build times.
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</para>
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</section>
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<section id='bsp-click-through-licensing'>
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<title>BSP 'Click-Through' Licensing Procedure</title>
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<note><para> This section describes how
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click-through licensing is expected to work.
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Currently, this functionality is not yet implemented.
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</para></note>
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<para>
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In some cases, a BSP contains separately licensed IP
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(Intellectual Property) for a component that imposes
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upon the user a requirement to accept the terms of a
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'click-through' license.
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Once the license is accepted the
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Poky build system can then build and include the
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corresponding component in the final BSP image.
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Some affected components might be essential to the normal
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functioning of the system and have no 'free' replacement
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(i.e. the resulting system would be non-functional
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without them).
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On the other hand, other components might be simply
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'good-to-have' or purely elective, or if essential
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nonetheless have a 'free' (possibly less-capable)
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version that could be used as a in the BSP recipe.
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</para>
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<para>
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For cases where you can substitute something and still maintain functionality, the Poky website will make
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available a 'de-featured' BSP completely free of the encumbered IP.
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In that case you can use the substitution directly and without any further licensing requirements.
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If present, this fully 'de-featured' BSP will be named meta-<bsp_name> (i.e. the
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normal default naming convention).
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If available, this is the simplest the most preferred option.
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This, of course, assumes the resulting functionality meets requirements.
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</para>
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<para>
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If however, a non-encumbered version is unavailable or the 'free' version would provide unsuitable
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functionality or quality, an encumbered version can be used.
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Encumbered versions of a BSP are given names of the form meta-<bsp_name>-nonfree.
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</para>
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<para>
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Several methods exist within the Poky build system to satisfy the licensing
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requirements for an encumbered BSP.
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The following list describes them in preferential order:
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</para>
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<orderedlist>
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<listitem>
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<para>
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Get a license key (or keys) for the encumbered BSP by visiting
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<ulink url='https://pokylinux.org/bsp-keys.html'>https://pokylinux.org/bsp-keys.html</ulink>
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and give the name of the BSP and your e-mail address in the web form.
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</para>
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<programlisting>
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[screenshot of dialog box]
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</programlisting>
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<para>
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After agreeing to any applicable license terms, the
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BSP key(s) will be immediately sent to the address
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you gave and you can use them by specifying BSPKEY_<keydomain>
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environment variables when building the image:
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</para>
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<programlisting>
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$ BSPKEY_<keydomain>=<key> bitbake poky-image-sato
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</programlisting>
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<para>
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These steps allow the encumbered image to be built
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with no change at all to the normal build process.
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</para>
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<para>
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Equivalently and probably more conveniently, a line
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for each key can instead be put into the user's
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<filename>local.conf</filename> file.
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</para>
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<para>
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The <keydomain> component of the
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BSPKEY_<keydomain> is required because there
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might be multiple licenses in effect for a given BSP.
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In such cases, a given <keydomain> corresponds to
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a particular license. In order for an encumbered
|
|
BSP that encompasses multiple key domains to be built
|
|
successfully, a <keydomain> entry for each
|
|
applicable license must be present in <filename>local.conf</filename> or
|
|
supplied on the command-line.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Do nothing - build as you normally would.
|
|
When a license is needed the build will stop and prompt you with instructions.
|
|
Follow the license prompts that originate from the
|
|
encumbered BSP.
|
|
These prompts usually take the form of instructions
|
|
needed to manually fetch the encumbered package(s)
|
|
and md5 sums into the required directory (e.g. the poky/build/downloads)
|
|
Once the manual package fetch has been
|
|
completed, restart the build to continue where
|
|
it left off.
|
|
During the build the prompt will not appear again since you have satisfied the
|
|
requirement.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Get a full-featured BSP recipe rather than a key, by
|
|
visiting
|
|
<ulink url='https://pokylinux.org/bsps.html'>https://pokylinux.org/bsps.html</ulink>.
|
|
Accepting the license agreement(s) presented will
|
|
subsequently allow you to download a tarball
|
|
containing a full-featured BSP that is legally cleared for
|
|
your use by the just-given license agreement(s).
|
|
This method will also allow the encumbered image to
|
|
be built with no change at all to the normal build
|
|
process.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<para>
|
|
Note that the third method is also the only option available
|
|
when downloading pre-compiled images generated from
|
|
non-free BSPs.
|
|
Those images are likewise available at
|
|
<ulink url='https://pokylinux.org/bsps.html'>https://pokylinux.org/bsps.html</ulink>.
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|