460 lines
20 KiB
XML
460 lines
20 KiB
XML
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<!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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The intent of this document is to define 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 thatspecified 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 slyers 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 being used.
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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 shipt 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, meta-bsp in this example,
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where "bsp" is a placeholder for the machine or platform name.
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Examples of some files that it could contain are:
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</para>
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<para>
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<literallayout class='monospaced'>
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meta-bsp/
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meta-bsp/binary/zImage
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meta-bsp/binary/poky-image-minimal.directdisk
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meta-bsp/conf/layer.conf
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meta-bsp/conf/machine/*.conf
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meta-bsp/conf/machine/include/tune-*.inc
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meta-bsp/packages/bootloader/bootloader_0.1.bb
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meta-bsp/packages/linux/linux-bsp-2.6.50/*.patch
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meta-bsp/packages/linux/linux-bsp-2.6.50/defconfig-bsp
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meta-bsp/packages/linux/linux-bsp_2.6.50.bb
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meta-bsp/packages/modem/modem-driver_0.1.bb
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meta-bsp/packages/modem/modem-daemon_0.1.bb
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meta-bsp/packages/image-creator/image-creator-native_0.1.bb
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meta-bsp/prebuilds/
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</literallayout>
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</para>
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<para>
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The following sections detail what these files and directories could contain.
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</para>
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</section>
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<section id="bsp-filelayout-binary">
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<title>Prebuilt User Binaries (meta-bsp/binary/*)</title>
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<para>
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This optional area contains useful prebuilt kernels and userspace filesystem
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images appropriate to the target system.
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Users could use these to get a system
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running and quickly get started on development tasks.
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The exact types of binaries
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present will be highly hardware-dependent but a README file should be present
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explaining how to use them with the target hardware.
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If prebuilt binaries are
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present, source code to meet licensing requirements must also be provided in
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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/conf/layer.conf)</title>
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<para>
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This file identifies the structure as a Poky layer by identifying the
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contents of the layer and containing information about how Poky should use
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it.
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Generally, a standard boilerplate file consisting of the following works.
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</para>
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<para>
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<literallayout class='monospaced'>
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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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</literallayout>
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</para>
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<para>
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This file simply makes bitbake aware of the recipes and conf directories and is required
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for recognition of the BSP by Poky.
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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/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/OpenEmbedded 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 what kernel package to use
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(PREFERRED_PROVIDER of virtual/kernel), what 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/conf/machine/include/tune-*.inc)</title>
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<para>
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These 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 tune-atom.inc:
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</para>
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<para>
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<literallayout class='monospaced'>
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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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</literallayout>
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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/packages/linux/*)</title>
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<para>
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These files make up the definition of a kernel to use with this
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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 but kernels can be shared between many
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machines as well.
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Following is an example:
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<literallayout class='monospaced'>
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meta-bsp/packages/linux/linux-bsp_2.6.50.bb
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</literallayout>
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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 so this could
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be a release tarball, some 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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It can reuse the main Poky kernel build class, so the definitions here can remain very simple.
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</para>
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<para>
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<literallayout class='monospaced'>
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linux-bsp-2.6.50/*.patch
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</literallayout>
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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, wherever
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they may have been obtained from.
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</para>
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<para>
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<literallayout class='monospaced'>
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meta-bsp/packages/linux/linux-bsp-2.6.50/defconfig-bsp
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</literallayout>
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</para>
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<para>
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Finally, this last example file contains configuration information to use to configure the kernel.
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</para>
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<para>
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Examples of kernel recipes are available in Poky itself.
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These files are optional since a kernel from Poky itself could be selected, although it
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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/packages/*)</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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These are examples of the kinds of things that you could encounter.
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The examples used in this section 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 reflash hardware.
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</para>
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<para>
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<literallayout class='monospaced'>
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meta-bsp/packages/bootloader/bootloader_0.1.bb
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</literallayout>
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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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<literallayout class='monospaced'>
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meta-bsp/packages/modem/modem-driver_0.1.bb
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meta-bsp/packages/modem/modem-daemon_0.1.bb
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</literallayout>
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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 reflash 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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<literallayout class='monospaced'>
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meta-bsp/packages/image-creator/image-creator-native_0.1.bb
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</literallayout>
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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, which is where
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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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It allows you to easily merge BSP-specific information with the original recipe.
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Whenever bitbake finds any <filename>.bbappend</filename> files, they will be
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included after bitbake loads the associated <filename>.bb</filename> but before any finalize
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or anonymous methods 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 ${PN} (the package name).
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</para>
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<literallayout class='monospaced'>
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FILESEXTRAPATHS := "${THISDIR}/${PN}"
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</literallayout>
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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>Prebuild Data (meta-bsp/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 precompiled
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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 is here as a description of how
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click-through licensing is expected to work, and is
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not yet not impemented.
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</para></note>
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<para>
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In some cases, a BSP may contain separately licensed IP
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(Intellectual Property) for a component, which imposes
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upon the user a requirement to accept the terms of a
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'click-through' license. Once the license is accepted
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(in whatever form that may be, see details below) 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. Some
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affected components may 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. Other components may 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 which may substituted for in the BSP recipe.
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</para>
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<para>
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For the latter cases, where it is possible to do so from
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a functionality perspective, the Poky website will make
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available a 'de-featured' BSP completely free of
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encumbered IP, which can be used directly and without
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any further licensing requirements. If present, this
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fully 'de-featured' BSP will be named meta-bsp (i.e. the
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normal default naming convention). This is the simplest
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and therefore preferred option if available, assuming
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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
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the 'free' version would provide unsuitable
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functionality or quality, an encumbered version can be
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used. Encumbered versions of a BSP are given names of
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the form meta-bsp-nonfree. There are several ways
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within the Poky build system to satisfy the licensing
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requirements for an encumbered BSP, in roughly the
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following order of preference:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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Get a license key (or keys) for the encumbered BSP
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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 web form there the name of the BSP and your e-mail address.
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</para>
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<literallayout class='monospaced'>
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[screenshot of dialog box]
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</literallayout>
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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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given and can be used by specifying BSPKEY_<keydomain>
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environment variables when building the image:
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</para>
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<literallayout class='monospaced'>
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$ BSPKEY_<keydomain>=<key> bitbake poky-image-sato
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</literallayout>
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<para>
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This will 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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local.conf 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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may be multiple licenses in effect for a give BSP; a
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given <keydomain> in such cases corresponds to
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a particular license. In order for an encumbered
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BSP encompassing multiple key domains to be built
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successfully, a <keydomain> entry for each
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applicable license must be present in local.conf or
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supplied on the command-line.
|
||
|
</para>
|
||
|
</listitem>
|
||
|
<listitem>
|
||
|
<para>
|
||
|
Do nothing - build as you normally would, and follow
|
||
|
any license prompts that originate from the
|
||
|
encumbered BSP (the build will cleanly stop at this
|
||
|
point). These usually take the form of instructions
|
||
|
needed to manually fetch the encumbered package(s)
|
||
|
and md5 sums into e.g. the poky/build/downloads
|
||
|
directory. Once the manual package fetch has been
|
||
|
completed, restarting the build will continue where
|
||
|
it left off, this time without the prompt since the
|
||
|
license requirements will have been satisfied.
|
||
|
</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 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>
|
||
|
</itemizedlist>
|
||
|
<para>
|
||
|
Note that method 3 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>
|