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Performed general edits to this chapter. 

many english corrections performed.

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
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Scott Rifenbark 2010-11-02 14:16:13 -07:00 committed by Richard Purdie
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documentation/poky-ref-manual/bsp.xml
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@ -1,53 +1,60 @@
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<chapter id='bsp'>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<chapter id="bsp">
<title>Board Support Packages (BSP) - Developers Guide</title>
<para>
A Board Support Package (BSP) is a collection of information which together
A Board Support Package (BSP) is a collection of information that
defines how to support a particular hardware device, set of devices, or
hardware platform. It will include information about the hardware features
hardware platform.
The BSP includes information about the hardware features
present on the device and kernel configuration information along with any
additional hardware drivers required. It will also list any additional software
additional hardware drivers required.
The BSP also lists any additional software
components required in addition to a generic Linux software stack for both
essential and optional platform features.
</para>
<para>
The intent of this document is to define a structure for these components
so that BSPs follow a commonly understood layout, allowing them to be
provided in a common form that everyone understands. It also allows end-users
to become familiar with one common format and encourages standardisation
so that BSPs follow a commonly understood layout.
Providing a common form allows end-users to understand and become familiar
with the layout.
A common form also encourages standardization
of software support of hardware.
</para>
<para>
The proposed format does have elements that are specific to the Poky and
OpenEmbedded build systems. It is intended that this information can be
used by other systems besides Poky/OpenEmbedded and that it will be simple
to extract information and convert to other formats if required. The format
described can be directly accepted as a layer by Poky using its standard
layers mechanism, but it is important to recognise that the BSP captures all
OpenEmbedded build systems.
It is intended that this information can be
used by other systems besides Poky and OpenEmbedded and thatspecified it will be simple
to extract information and convert it to other formats if required.
Poky, through its standard slyers mechanism, can directly accept The format
described as a layer.
The BSP captures all
the hardware specific details in one place in a standard format, which is
useful for any person wishing to use the hardware platform regardless of
the build system in use.
the build system being used.
</para>
<para>
The BSP specification does not include a build system or other tools -
it is concerned with the hardware specific components only. At the end
distribution point the BSP may be shipped combined with a build system
and other tools, but it is important to maintain the distinction that these
are separate components which may just be combined in certain end products.
it is concerned with the hardware-specific components only.
At the end
distribution point you can shipt the BSP combined with a build system
and other tools.
However, it is important to maintain the distinction that these
are separate components that happen to be combined in certain end products.
</para>
<section id='bsp-filelayout'>
<section id="bsp-filelayout">
<title>Example Filesystem Layout</title>
<para>
The BSP consists of a file structure inside a base directory, meta-bsp in this example, where "bsp" is a placeholder for the machine or platform name. Examples of some files that it could contain are:
The BSP consists of a file structure inside a base directory, meta-bsp in this example,
where "bsp" is a placeholder for the machine or platform name.
Examples of some files that it could contain are:
</para>
<para>
@ -76,15 +83,18 @@ meta-bsp/prebuilds/
</section>
<section id='bsp-filelayout-binary'>
<section id="bsp-filelayout-binary">
<title>Prebuilt User Binaries (meta-bsp/binary/*)</title>
<para>
This optional area contains useful prebuilt kernels and userspace filesystem
images appropriate to the target system. Users could use these to get a system
running and quickly get started on development tasks. The exact types of binaries
images appropriate to the target system.
Users could use these to get a system
running and quickly get started on development tasks.
The exact types of binaries
present will be highly hardware-dependent but a README file should be present
explaining how to use them with the target hardware. If prebuilt binaries are
explaining how to use them with the target hardware.
If prebuilt binaries are
present, source code to meet licensing requirements must also be provided in
some form.
</para>
@ -95,9 +105,10 @@ meta-bsp/prebuilds/
<title>Layer Configuration (meta-bsp/conf/layer.conf)</title>
<para>
This file identifies the structure as a Poky layer. This file identifies the
contents of the layer and contains information about how Poky should use
it. In general it will most likely be a standard boilerplate file consisting of:
This file identifies the structure as a Poky layer by identifying the
contents of the layer and containing information about how Poky should use
it.
Generally, a standard boilerplate file consisting of the following works.
</para>
<para>
@ -106,7 +117,7 @@ meta-bsp/prebuilds/
BBPATH := "${BBPATH}${LAYERDIR}"
# We have a recipes directory containing .bb and .bbappend files, add to BBFILES
BBFILES := "${BBFILES} ${LAYERDIR}/recipes/*/*.bb ${LAYERDIR}/recipes/*/*.bbappend"
BBFILES := "${BBFILES} ${LAYERDIR}/recipes/*/*.bb \ ${LAYERDIR}/recipes/*/*.bbappend"
BBFILE_COLLECTIONS += "bsp"
BBFILE_PATTERN_bsp := "^${LAYERDIR}/"
@ -115,47 +126,45 @@ BBFILE_PRIORITY_bsp = "5"
</para>
<para>
which simply makes bitbake aware of the recipes and conf directories.
</para>
<para>
This file is required for recognition of the BSP by Poky.
This file simply makes bitbake aware of the recipes and conf directories and is required
for recognition of the BSP by Poky.
</para>
</section>
<section id='bsp-filelayout-machine'>
<section id="bsp-filelayout-machine">
<title>Hardware Configuration Options (meta-bsp/conf/machine/*.conf)</title>
<para>
The machine files bind together all the information contained elsewhere
in the BSP into a format that Poky/OpenEmbedded can understand. If
the BSP supports multiple machines, multiple machine configuration files
can be present. These filenames correspond to the values users set the
MACHINE variable to.
in the BSP into a format that Poky/OpenEmbedded can understand.
If the BSP supports multiple machines, multiple machine configuration files
can be present.
These filenames correspond to the values to which users have set the MACHINE variable.
</para>
<para>
These files would define things like which kernel package to use
(PREFERRED_PROVIDER of virtual/kernel), which hardware drivers to
These files define things such as what kernel package to use
(PREFERRED_PROVIDER of virtual/kernel), what hardware drivers to
include in different types of images, any special software components
that are needed, any bootloader information, and also any special image
format requirements.
</para>
<para>
At least one machine file is required for a Poky BSP layer but more than one may be present.
At least one machine file is required for a Poky BSP layer.
However, you can supply more than one file.
</para>
</section>
<section id='bsp-filelayout-tune'>
<title>Hardware Optimisation Options (meta-bsp/conf/machine/include/tune-*.inc)</title>
<section id="bsp-filelayout-tune">
<title>Hardware Optimization Options (meta-bsp/conf/machine/include/tune-*.inc)</title>
<para>
These are shared hardware "tuning" definitions and are commonly used to
pass specific optimisation flags to the compiler. An example is
tune-atom.inc:
pass specific optimization flags to the compiler.
An example is tune-atom.inc:
</para>
<para>
<programlisting>
@ -164,40 +173,42 @@ TARGET_CC_ARCH = "-m32 -march=core2 -msse3 -mtune=generic -mfpmath=sse"
</programlisting>
</para>
<para>
which defines a new package architecture called "core2" and uses the
optimization flags specified, which are carefully chosen to give best
performance on atom cpus.
This example defines a new package architecture called "core2" and uses the
specified optimization flags, which are carefully chosen to give best
performance on atom processors.
</para>
<para>
The tune file would be included by the machine definition and can be
contained in the BSP or reference one from the standard core set of
contained in the BSP or referenced from one of the standard core set of
files included with Poky itself.
</para>
<para>
These files are optional for a Poky BSP layer.
Both the base package architecuture file and the tune file are optional for a Poky BSP layer.
</para>
</section>
<section id='bsp-filelayout-kernel'>
<title>Linux Kernel Configuration (meta-bsp/packages/linux/*)</title>
<para>
These files make up the definition of a kernel to use with this
hardware. In this case it is a complete self-contained kernel with its own
hardware.
In this case it is a complete self-contained kernel with its own
configuration and patches but kernels can be shared between many
machines as well. Taking some specific example files:
</para>
<para>
machines as well.
Following is an example:
<programlisting>
meta-bsp/packages/linux/linux-bsp_2.6.50.bb
</programlisting>
This example file is the core kernel recipe that details from where to get the kernel
source.
All standard source code locations are supported so this could
be a release tarball, some git repository, or source included in
the directory within the BSP itself.
</para>
<para>
which is the core kernel recipe which firstly details where to get the kernel
source from. All standard source code locations are supported so this could
be a release tarball, some git repository, or source included in
the directory within the BSP itself. It then contains information about which
patches to apply and how to configure and build it. It can reuse the main
Poky kernel build class, so the definitions here can remain very simple.
The file then contains information about what patches to apply and how to configure and build them.
It can reuse the main Poky kernel build class, so the definitions here can remain very simple.
</para>
<para>
<programlisting>
@ -205,7 +216,7 @@ linux-bsp-2.6.50/*.patch
</programlisting>
</para>
<para>
which are patches which may be applied against the base kernel, wherever
The above example file contains patches you can apply against the base kernel, wherever
they may have been obtained from.
</para>
<para>
@ -214,11 +225,11 @@ meta-bsp/packages/linux/linux-bsp-2.6.50/defconfig-bsp
</programlisting>
</para>
<para>
which is the configuration information to use to configure the kernel.
Finally, this last example file contains configuration information to use to configure the kernel.
</para>
<para>
Examples of kernel recipes are available in Poky itself. These files are
optional since a kernel from Poky itself could be selected, although it
Examples of kernel recipes are available in Poky itself.
These files are optional since a kernel from Poky itself could be selected, although it
would be unusual not to have a kernel configuration.
</para>
</section>
@ -227,11 +238,19 @@ meta-bsp/packages/linux/linux-bsp-2.6.50/defconfig-bsp
<title>Other Software (meta-bsp/packages/*)</title>
<para>
This area includes other pieces of software which the hardware may need for best
operation. These are just examples of the kind of things that may be
encountered. These are standard .bb file recipes in the usual Poky format,
so for examples, see standard Poky recipes. The source can be included directly,
referred to in source control systems or release tarballs of external software projects.
This section describes other pieces of software that the hardware might need for best
operation.
These are examples of the kinds of things that you could encounter.
The examples used in this section are standard <filename>.bb</filename> file recipes in the
usual Poky format.
You can include the source directly by referring to it in the source control system or
the released tarballs of external software projects.
You only need to provide these types of files if the platform requires them.
</para>
<para>
The following file is a bootloader recipe that can be used to generate a new
bootloader binary.
Sometimes these files are included in the final image format and are needed to reflash hardware.
</para>
<para>
<programlisting>
@ -239,9 +258,9 @@ meta-bsp/packages/bootloader/bootloader_0.1.bb
</programlisting>
</para>
<para>
Some kind of bootloader recipe which may be used to generate a new
bootloader binary. Sometimes these are included in the final image
format and needed to reflash hardware.
These next two files are examples of a hardware driver and a hardware daemon that might need
to be included in images to make the hardware useful.
Although the example uses "modem" there may be other components needed, such as firmware.
</para>
<para>
<programlisting>
@ -250,72 +269,62 @@ meta-bsp/packages/modem/modem-daemon_0.1.bb
</programlisting>
</para>
<para>
These are examples of a hardware driver and also a hardware daemon which
may need to be included in images to make the hardware useful. "modem"
is one example but there may be other components needed like firmware.
Sometimes the device needs an image in a very specific format so that the update
mechanism can accept and reflash it.
Recipes to build the tools needed to do this can be included with the BSP.
Following is an example.
</para>
<para>
<programlisting>
meta-bsp/packages/image-creator/image-creator-native_0.1.bb
</programlisting>
</para>
<para>
Sometimes the device will need an image in a very specific format for
its update mechanism to accept and reflash with it. Recipes to build the
tools needed to do this can be included with the BSP.
</para>
<para>
These files only need be provided if the platform requires them.
</para>
</section>
<section id='bs-filelayout-bbappend'>
<title>Append BSP specific information to existing recipes</title>
<title>Append BSP-Specific Information to Existing Recipes</title>
<para>
Say you have a recipe like pointercal which has machine-specific information in it,
and then you have your new BSP code in a layer. Before the .bbappend extension was
introduced, you'd have to copy the whole pointercal recipe and files into your layer,
and then add the single file for your machine, which is ugly.
.bbappend makes the above work much easier, to allow BSP-specific information to be merged
with the original recipe easily. When bitbake finds any X.bbappend files, they will be
included after bitbake loads X.bb but before finalise or anonymous methods run.
This allows the BSP layer to poke around and do whatever it might want to customise
the original recipe.
If your recipe needs to reference extra files it can use the FILESEXTRAPATH variable
to specify their location. The example below shows extra files contained in a folder
called ${PN} (the package name).
Suppose you have a recipe such as 'pointercal' that requires machine-specific information.
At the same time, you have your new BSP code nicely partitioned into a layer, which is where
you would also like to specify any machine-specific information associated with your new machine.
Before the <filename>.bbappend</filename> extension was introduced, you would have to copy the whole
pointercal recipe and files into your layer, and then add the single file for your machine.
</para>
<para>
With the <filename>.bbappend</filename> extension, however, your work becomes much easier.
It allows you to easily merge BSP-specific information with the original recipe.
Whenever bitbake finds any <filename>.bbappend</filename> files, they will be
included after bitbake loads the associated <filename>.bb</filename> but before any finalize
or anonymous methods run.
This allows the BSP layer to do whatever it might want to do to customize the original recipe.
</para>
<para>
If your recipe needs to reference extra files it can use the FILESEXTRAPATH variable
to specify their location.
The example below shows extra files contained in a folder called ${PN} (the package name).
</para>
<programlisting>
FILESEXTRAPATHS := "${THISDIR}/${PN}"
</programlisting>
<para>
Then the BSP could add machine-specific config files in layer directory, which will be
added by bitbake. You can look at meta-emenlow/packages/formfactor as an example.
This technique allows the BSP to add machine-specific configuration files to the layer directory,
which will be picked up by bitbake.
For an example see <filename>meta-emenlow/packages/formfactor</filename>.
</para>
</section>
<section id='bsp-filelayout-prebuilds'>
<section id="bsp-filelayout-prebuilds">
<title>Prebuild Data (meta-bsp/prebuilds/*)</title>
<para>
The location can contain a precompiled representation of the source code
contained elsewhere in the BSP layer. It can be processed and used by
Poky to provide much faster build times, assuming a compatible configuration is used.
This location can contain precompiled representations of the source code
contained elsewhere in the BSP layer.
Assuming a compatible configuration is used, Poky can process and use these optional precompiled
representations to provide much faster build times.
</para>
<para>
These files are optional.
</para>
</section>
<section id='bsp-click-through-licensing'>
<title>BSP 'Click-through' Licensing Procedure</title>
<title>BSP 'Click-Through' Licensing Procedure</title>
<note><para> This section is here as a description of how
click-through licensing is expected to work, and is
@ -367,10 +376,9 @@ FILESEXTRAPATHS := "${THISDIR}/${PN}"
<para>
Get a license key (or keys) for the encumbered BSP
by
visiting <ulink url='https://pokylinux.org/bsp-keys.html'>https://pokylinux.org/bsp-keys.html</ulink>
and give the web form there the name of the BSP
and your e-mail address.
by visiting
<ulink url='https://pokylinux.org/bsp-keys.html'>https://pokylinux.org/bsp-keys.html</ulink>
and give the web form there the name of the BSP and your e-mail address.
</para>
<programlisting>