+++ /dev/null
-One of the biggest challenges to getting started with embedded devices is that you
-cannot just install a copy of Linux and expect to be able to compile a firmware.
-Even if you did remember to install a compiler and every development tool offered,
-you still would not have the basic set of tools needed to produce a firmware image.
-The embedded device represents an entirely new hardware platform, which is
-most of the time incompatible with the hardware on your development machine, so in a process called
-cross compiling you need to produce a new compiler capable of generating code for
-your embedded platform, and then use it to compile a basic Linux distribution to
-run on your device.
-
-The process of creating a cross compiler can be tricky, it is not something that is
-regularly attempted and so there is a certain amount of mystery and black magic
-associated with it. In many cases when you are dealing with embedded devices you will
-be provided with a binary copy of a compiler and basic libraries rather than
-instructions for creating your own -- it is a time saving step but at the same time
-often means you will be using a rather dated set of tools. Likewise, it is also common
-to be provided with a patched copy of the Linux kernel from the board or chip vendor,
-but this is also dated and it can be difficult to spot exactly what has been
-modified to make the kernel run on the embedded platform.
-
-\subsection{Building an image}
-
-OpenWrt takes a different approach to building a firmware; downloading, patching
-and compiling everything from scratch, including the cross compiler. To put it
-in simpler terms, OpenWrt does not contain any executables or even sources, it is an
-automated system for downloading the sources, patching them to work with the given
-platform and compiling them correctly for that platform. What this means is that
-just by changing the template, you can change any step in the process.
-
-As an example, if a new kernel is released, a simple change to one of the Makefiles
-will download the latest kernel, patch it to run on the embedded platform and produce
-a new firmware image -- there is no work to be done trying to track down an unmodified
-copy of the existing kernel to see what changes had been made, the patches are
-already provided and the process ends up almost completely transparent. This does not
-just apply to the kernel, but to anything included with OpenWrt -- It is this one
-simple understated concept which is what allows OpenWrt to stay on the bleeding edge
-with the latest compilers, latest kernels and latest applications.
-
-So let's take a look at OpenWrt and see how this all works.
-
-
-\subsubsection{Download OpenWrt}
-
-OpenWrt can be downloaded via subversion using the following command:
-
-\begin{Verbatim}
-$ svn checkout svn://svn.openwrt.org/openwrt/trunk openwrt-trunk
-\end{Verbatim}
-
-Additionally, there is a trac interface on \href{https://dev.openwrt.org/}{https://dev.openwrt.org/}
-which can be used to monitor svn commits and browse the source repository.
-
-
-\subsubsection{The directory structure}
-
-There are four key directories in the base:
-
-\begin{itemize}
- \item \texttt{tools}
- \item \texttt{toolchain}
- \item \texttt{package}
- \item \texttt{target}
-\end{itemize}
-
-\texttt{tools} and \texttt{toolchain} refer to common tools which will be
-used to build the firmware image, the compiler, and the C library.
-The result of this is three new directories, \texttt{build\_dir/host}, which is a temporary
-directory for building the target independent tools, \texttt{build\_dir/toolchain-\textit{<arch>}*}
-which is used for building the toolchain for a specific architecture, and
-\texttt{staging\_dir/toolchain-\textit{<arch>}*} where the resulting toolchain is installed.
-You will not need to do anything with the toolchain directory unless you intend to
-add a new version of one of the components above.
-
-\begin{itemize}
- \item \texttt{build\_dir/host}
- \item \texttt{build\_dir/toolchain-\textit{<arch>}*}
-\end{itemize}
-
-\texttt{package} is for exactly that -- packages. In an OpenWrt firmware, almost everything
-is an \texttt{.ipk}, a software package which can be added to the firmware to provide new
-features or removed to save space. Note that packages are also maintained outside of the main
-trunk and can be obtained from subversion using the package feeds system:
-
-\begin{Verbatim}
-$ ./scripts/feeds update
-\end{Verbatim}
-
-Those packages can be used to extend the functionality of the build system and need to be
-symlinked into the main trunk. Once you do that, the packages will show up in the menu for
-configuration. You would do something like this:
-
-\begin{Verbatim}
-$ ./scripts/feeds search nmap
-Search results in feed 'packages':
-nmap Network exploration and/or security auditing utility
-
-$ ./scripts/feeds install nmap
-\end{Verbatim}
-
-To include all packages, issue the following command:
-
-\begin{Verbatim}
-$ make package/symlinks
-\end{Verbatim}
-
-\texttt{target} refers to the embedded platform, this contains items which are specific to
-a specific embedded platform. Of particular interest here is the "\texttt{target/linux}"
-directory which is broken down by platform \textit{<arch>} and contains the patches to the
-kernel, profile config, for a particular platform. There's also the "\texttt{target/image}" directory
-which describes how to package a firmware for a specific platform.
-
-Both the target and package steps will use the directory "\texttt{build\_dir/\textit{<arch>}}"
-as a temporary directory for compiling. Additionally, anything downloaded by the toolchain,
-target or package steps will be placed in the "\texttt{dl}" directory.
-
-\begin{itemize}
- \item \texttt{build\_dir/\textit{<arch>}}
- \item \texttt{dl}
-\end{itemize}
-
-\subsubsection{Building OpenWrt}
-
-While the OpenWrt build environment was intended mostly for developers, it also has to be
-simple enough that an inexperienced end user can easily build his or her own customized firmware.
-
-Running the command "\texttt{make menuconfig}" will bring up OpenWrt's configuration menu
-screen, through this menu you can select which platform you're targeting, which versions of
-the toolchain you want to use to build and what packages you want to install into the
-firmware image. Note that it will also check to make sure you have the basic dependencies for it
-to run correctly. If that fails, you will need to install some more tools in your local environment
-before you can begin.
-
-Similar to the linux kernel config, almost every option has three choices,
-\texttt{y/m/n} which are represented as follows:
-
-\begin{itemize}
- \item{\texttt{<*>} (pressing y)} \\
- This will be included in the firmware image
- \item{\texttt{<M>} (pressing m)} \\
- This will be compiled but not included (for later install)
- \item{\texttt{< >} (pressing n)} \\
- This will not be compiled
-\end{itemize}
-
-After you've finished with the menu configuration, exit and when prompted, save your
-configuration changes.
-
-If you want, you can also modify the kernel config for the selected target system.
-simply run "\texttt{make kernel\_menuconfig}" and the build system will unpack the kernel sources
-(if necessary), run menuconfig inside of the kernel tree, and then copy the kernel config
-to \texttt{target/linux/\textit{<platform>}/config} so that it is preserved over
-"\texttt{make clean}" calls.
-
-To begin compiling the firmware, type "\texttt{make}". By default
-OpenWrt will only display a high level overview of the compile process and not each individual
-command.
-
-\subsubsection{Example:}
-
-\begin{Verbatim}
-make[2] toolchain/install
-make[3] -C toolchain install
-make[2] target/compile
-make[3] -C target compile
-make[4] -C target/utils prepare
-
-[...]
-\end{Verbatim}
-
-This makes it easier to monitor which step it's actually compiling and reduces the amount
-of noise caused by the compile output. To see the full output, run the command
-"\texttt{make V=99}".
-
-During the build process, buildroot will download all sources to the "\texttt{dl}"
-directory and will start patching and compiling them in the "\texttt{build\_dir/\textit{<arch>}}"
-directory. When finished, the resulting firmware will be in the "\texttt{bin}" directory
-and packages will be in the "\texttt{bin/packages}" directory.
-
-
-\subsection{Creating packages}
-
-One of the things that we've attempted to do with OpenWrt's template system is make it
-incredibly easy to port software to OpenWrt. If you look at a typical package directory
-in OpenWrt you'll find several things:
-
-\begin{itemize}
- \item \texttt{package/\textit{<name>}/Makefile}
- \item \texttt{package/\textit{<name>}/patches}
- \item \texttt{package/\textit{<name>}/files}
-\end{itemize}
-
-The patches directory is optional and typically contains bug fixes or optimizations to
-reduce the size of the executable. The package makefile is the important item, provides
-the steps actually needed to download and compile the package.
-
-The files directory is also optional and typicall contains package specific startup scripts or default configuration files that can be used out of the box with OpenWrt.
-
-Looking at one of the package makefiles, you'd hardly recognize it as a makefile.
-Through what can only be described as blatant disregard and abuse of the traditional
-make format, the makefile has been transformed into an object oriented template which
-simplifies the entire ordeal.
-
-Here for example, is \texttt{package/bridge/Makefile}:
-
-\begin{Verbatim}[frame=single,numbers=left]
-
-include $(TOPDIR)/rules.mk
-
-PKG_NAME:=bridge
-PKG_VERSION:=1.0.6
-PKG_RELEASE:=1
-
-PKG_SOURCE:=bridge-utils-$(PKG_VERSION).tar.gz
-PKG_SOURCE_URL:=@SF/bridge
-PKG_MD5SUM:=9b7dc52656f5cbec846a7ba3299f73bd
-PKG_CAT:=zcat
-
-PKG_BUILD_DIR:=$(BUILD_DIR)/bridge-utils-$(PKG_VERSION)
-
-include $(INCLUDE_DIR)/package.mk
-
-define Package/bridge
- SECTION:=net
- CATEGORY:=Base system
- TITLE:=Ethernet bridging configuration utility
- URL:=http://bridge.sourceforge.net/
-endef
-
-define Package/bridge/description
- Manage ethernet bridging:
- a way to connect networks together to form a larger network.
-endef
-
-define Build/Configure
- $(call Build/Configure/Default, \
- --with-linux-headers="$(LINUX_DIR)" \
- )
-endef
-
-define Package/bridge/install
- $(INSTALL_DIR) $(1)/usr/sbin
- $(INSTALL_BIN) $(PKG_BUILD_DIR)/brctl/brctl $(1)/usr/sbin/
-endef
-
-$(eval $(call BuildPackage,bridge))
-\end{Verbatim}
-
-As you can see, there's not much work to be done; everything is hidden in other makefiles
-and abstracted to the point where you only need to specify a few variables.
-
-\begin{itemize}
- \item \texttt{PKG\_NAME} \\
- The name of the package, as seen via menuconfig and ipkg
- \item \texttt{PKG\_VERSION} \\
- The upstream version number that we are downloading
- \item \texttt{PKG\_RELEASE} \\
- The version of this package Makefile
- \item \texttt{PKG\_SOURCE} \\
- The filename of the original sources
- \item \texttt{PKG\_SOURCE\_URL} \\
- Where to download the sources from (no trailing slash), you can add multiple download sources by separating them with a \\ and a carriage return.
- \item \texttt{PKG\_MD5SUM} \\
- A checksum to validate the download
- \item \texttt{PKG\_CAT} \\
- How to decompress the sources (zcat, bzcat, unzip)
- \item \texttt{PKG\_BUILD\_DIR} \\
- Where to compile the package
-\end{itemize}
-
-The \texttt{PKG\_*} variables define where to download the package from;
-\texttt{@SF} is a special keyword for downloading packages from sourceforge. There is also
-another keyword of \texttt{@GNU} for grabbing GNU source releases. If any of the above mentionned download source fails, the OpenWrt mirrors will be used as source.
-
-The md5sum (if present) is used to verify the package was downloaded correctly and
-\texttt{PKG\_BUILD\_DIR} defines where to find the package after the sources are
-uncompressed into \texttt{\$(BUILD\_DIR)}.
-
-At the bottom of the file is where the real magic happens, "BuildPackage" is a macro
-set up by the earlier include statements. BuildPackage only takes one argument directly --
-the name of the package to be built, in this case "\texttt{bridge}". All other information
-is taken from the define blocks. This is a way of providing a level of verbosity, it's
-inherently clear what the contents of the \texttt{description} template in
-\texttt{Package/bridge} is, which wouldn't be the case if we passed this information
-directly as the Nth argument to \texttt{BuildPackage}.
-
-\texttt{BuildPackage} uses the following defines:
-
-\textbf{\texttt{Package/\textit{<name>}}:} \\
- \texttt{\textit{<name>}} matches the argument passed to buildroot, this describes
- the package the menuconfig and ipkg entries. Within \texttt{Package/\textit{<name>}}
- you can define the following variables:
-
- \begin{itemize}
- \item \texttt{SECTION} \\
- The section of package (currently unused)
- \item \texttt{CATEGORY} \\
- Which menu it appears in menuconfig: Network, Sound, Utilities, Multimedia ...
- \item \texttt{TITLE} \\
- A short description of the package
- \item \texttt{URL} \\
- Where to find the original software
- \item \texttt{MAINTAINER} (optional) \\
- Who to contact concerning the package
- \item \texttt{DEPENDS} (optional) \\
- Which packages must be built/installed before this package. To reference a dependency defined in the
- same Makefile, use \textit{<dependency name>}. If defined as an external package, use
- \textit{+<dependency name>}. For a kernel version dependency use: \textit{@LINUX\_2\_<minor version>}
- \item \texttt{BUILDONLY} (optional) \\
- Set this option to 1 if you do NOT want your package to appear in menuconfig.
- This is useful for packages which are only used as build dependencies.
- \end{itemize}
-
-\textbf{\texttt{Package/\textit{<name>}/conffiles} (optional):} \\
- A list of config files installed by this package, one file per line.
-
-\textbf{\texttt{Build/Prepare} (optional):} \\
- A set of commands to unpack and patch the sources. You may safely leave this
- undefined.
-
-\textbf{\texttt{Build/Configure} (optional):} \\
- You can leave this undefined if the source doesn't use configure or has a
- normal config script, otherwise you can put your own commands here or use
- "\texttt{\$(call Build/Configure/Default,\textit{<first list of arguments, second list>})}" as above to
- pass in additional arguments for a standard configure script. The first list of arguments will be passed
- to the configure script like that: \texttt{--arg 1} \texttt{--arg 2}. The second list contains arguments that should be
- defined before running the configure script such as autoconf or compiler specific variables.
-
- To make it easier to modify the configure command line, you can either extend or completely override the following variables:
- \begin{itemize}
- \item \texttt{CONFIGURE\_ARGS} \\
- Contains all command line arguments (format: \texttt{--arg 1} \texttt{--arg 2})
- \item \texttt{CONFIGURE\_VARS} \\
- Contains all environment variables that are passed to ./configure (format: \texttt{NAME="value"})
- \end{itemize}
-
-\textbf{\texttt{Build/Compile} (optional):} \\
- How to compile the source; in most cases you should leave this undefined.
-
- As with \texttt{Build/Configure} there are two variables that allow you to override
- the make command line environment variables and flags:
- \begin{itemize}
- \item \texttt{MAKE\_FLAGS} \\
- Contains all command line arguments (typically variable overrides like \texttt{NAME="value"}
- \item \texttt{MAKE\_VARS} \\
- Contains all environment variables that are passed to the make command
- \end{itemize}
-
-\textbf{\texttt{Build/InstallDev} (optional):} \\
- If your package provides a library that needs to be made available to other packages,
- you can use the \texttt{Build/InstallDev} template to copy it into the staging directory
- which is used to collect all files that other packages might depend on at build time.
- When it is called by the build system, two parameters are passed to it. \texttt{\$(1)} points to
- the regular staging dir, typically \texttt{staging\_dir/\textit{ARCH}}, while \texttt{\$(2)} points
- to \texttt{staging\_dir/host}. The host staging dir is only used for binaries, which are
- to be executed or linked against on the host and its \texttt{bin/} subdirectory is included
- in the \texttt{PATH} which is passed down to the build system processes.
- Please use \texttt{\$(1)} and \texttt{\$(2)} here instead of the build system variables
- \texttt{\$(STAGING\_DIR)} and \texttt{\$(STAGING\_DIR\_HOST)}, because the build system behavior
- when staging libraries might change in the future to include automatic uninstallation.
-
-\textbf{\texttt{Package/\textit{<name>}/install}:} \\
- A set of commands to copy files out of the compiled source and into the ipkg
- which is represented by the \texttt{\$(1)} directory. Note that there are currently
- 4 defined install macros:
- \begin{itemize}
- \item \texttt{INSTALL\_DIR} \\
- install -d -m0755
- \item \texttt{INSTALL\_BIN} \\
- install -m0755
- \item \texttt{INSTALL\_DATA} \\
- install -m0644
- \item \texttt{INSTALL\_CONF} \\
- install -m0600
- \end{itemize}
-
-The reason that some of the defines are prefixed by "\texttt{Package/\textit{<name>}}"
-and others are simply "\texttt{Build}" is because of the possibility of generating
-multiple packages from a single source. OpenWrt works under the assumption of one
-source per package Makefile, but you can split that source into as many packages as
-desired. Since you only need to compile the sources once, there's one global set of
-"\texttt{Build}" defines, but you can add as many "Package/<name>" defines as you want
-by adding extra calls to \texttt{BuildPackage} -- see the dropbear package for an example.
-
-After you have created your \texttt{package/\textit{<name>}/Makefile}, the new package
-will automatically show in the menu the next time you run "make menuconfig" and if selected
-will be built automatically the next time "\texttt{make}" is run.
-
-\subsection{Creating binary packages}
-
-You might want to create binary packages and include them in the resulting images as packages.
-To do so, you can use the following template, which basically sets to nothing the Configure and
-Compile templates.
-
-\begin{Verbatim}[frame=single,numbers=left]
-
-include $(TOPDIR)/rules.mk
-
-PKG_NAME:=binpkg
-PKG_VERSION:=1.0
-PKG_RELEASE:=1
-
-PKG_SOURCE:=binpkg-$(PKG_VERSION).tar.gz
-PKG_SOURCE_URL:=http://server
-PKG_MD5SUM:=9b7dc52656f5cbec846a7ba3299f73bd
-PKG_CAT:=zcat
-
-include $(INCLUDE_DIR)/package.mk
-
-define Package/binpkg
- SECTION:=net
- CATEGORY:=Network
- TITLE:=Binary package
-endef
-
-define Package/bridge/description
- Binary package
-endef
-
-define Build/Configure
-endef
-
-define Build/Compile
-endef
-
-define Package/bridge/install
- $(INSTALL_DIR) $(1)/usr/sbin
- $(INSTALL_BIN) $(PKG_BUILD_DIR)/* $(1)/usr/sbin/
-endef
-
-$(eval $(call BuildPackage,bridge))
-\end{Verbatim}
-
-Provided that the tarball which contains the binaries reflects the final
-directory layout (/usr, /lib ...), it becomes very easy to get your package
-look like one build from sources.
-
-Note that using the same technique, you can easily create binary pcakages
-for your proprietary kernel modules as well.
-
-\subsection{Creating kernel modules packages}
-
-The OpenWrt distribution makes the distinction between two kind of kernel modules, those coming along with the mainline kernel, and the others available as a separate project. We will see later that a common template is used for both of them.
-
-For kernel modules that are part of the mainline kernel source, the makefiles are located in \textit{package/kernel/modules/*.mk} and they appear under the section "Kernel modules"
-
-For external kernel modules, you can add them to the build system just like if they were software packages by defining a KernelPackage section in the package makefile.
-
-Here for instance the Makefile for the I2C subsytem kernel modules :
-
-\begin{Verbatim}[frame=single,numbers=left]
-
-I2CMENU:=I2C Bus
-
-define KernelPackage/i2c-core
- TITLE:=I2C support
- DESCRIPTION:=Kernel modules for i2c support
- SUBMENU:=$(I2CMENU)
- KCONFIG:=CONFIG_I2C_CORE CONFIG_I2C_DEV
- FILES:=$(MODULES_DIR)/kernel/drivers/i2c/*.$(LINUX_KMOD_SUFFIX)
- AUTOLOAD:=$(call AutoLoad,50,i2c-core i2c-dev)
-endef
-$(eval $(call KernelPackage,i2c-core))
-\end{Verbatim}
-
-To group kernel modules under a common description in menuconfig, you might want to define a \textit{<description>MENU} variable on top of the kernel modules makefile.
-
-\begin{itemize}
- \item \texttt{TITLE} \\
- The name of the module as seen via menuconfig
- \item \texttt{DESCRIPTION} \\
- The description as seen via help in menuconfig
- \item \texttt{SUBMENU} \\
- The sub menu under which this package will be seen
- \item \texttt{KCONFIG} \\
- Kernel configuration option dependency. For external modules, remove it.
- \item \texttt{FILES} \\
- Files you want to inlude to this kernel module package, separate with spaces.
- \item \texttt{AUTOLOAD} \\
- Modules that will be loaded automatically on boot, the order you write them is the order they would be loaded.
-\end{itemize}
-
-After you have created your \texttt{package/kernel/modules/\textit{<name>}.mk}, the new kernel modules package
-will automatically show in the menu under "Kernel modules" next time you run "make menuconfig" and if selected
-will be built automatically the next time "\texttt{make}" is run.
-
-\subsection{Conventions}
-
-There are a couple conventions to follow regarding packages:
-
-\begin{itemize}
- \item \texttt{files}
- \begin{enumerate}
- \item configuration files follow the convention \\
- \texttt{\textit{<name>}.conf}
- \item init files follow the convention \\
- \texttt{\textit{<name>}.init}
- \end{enumerate}
- \item \texttt{patches}
- \begin{enumerate}
- \item patches are numerically prefixed and named related to what they do
- \end{enumerate}
-\end{itemize}
-
-\subsection{Troubleshooting}
-
-If you find your package doesn't show up in menuconfig, try the following command to
-see if you get the correct description:
-
-\begin{Verbatim}
- TOPDIR=$PWD make -C package/<name> DUMP=1 V=99
-\end{Verbatim}
-
-If you're just having trouble getting your package to compile, there's a few
-shortcuts you can take. Instead of waiting for make to get to your package, you can
-run one of the following:
-
-\begin{itemize}
- \item \texttt{make package/\textit{<name>}/clean V=99}
- \item \texttt{make package/\textit{<name>}/install V=99}
-\end{itemize}
-
-Another nice trick is that if the source directory under \texttt{build\_dir/\textit{<arch>}}
-is newer than the package directory, it won't clobber it by unpacking the sources again.
-If you were working on a patch you could simply edit the sources under the
-\texttt{build\_dir/\textit{<arch>}/\textit{<source>}} directory and run the install command above,
-when satisfied, copy the patched sources elsewhere and diff them with the unpatched
-sources. A warning though - if you go modify anything under \texttt{package/\textit{<name>}}
-it will remove the old sources and unpack a fresh copy.
-
-Other useful targets include:
-
-\begin{itemize}
- \item \texttt{make package/\textit{<name>}/prepare V=99}
- \item \texttt{make package/\textit{<name>}/compile V=99}
- \item \texttt{make package/\textit{<name>}/configure V=99}
-\end{itemize}
-
-
-\subsection{Using build environments}
-OpenWrt provides a means of building images for multiple configurations
-which can use multiple targets in one single checkout. These \emph{environments}
-store a copy of the .config file generated by \texttt{make menuconfig} and the contents
-of the \texttt{./files} folder.
-The script \texttt{./scripts/env} is used to manage these environments, it uses
-\texttt{git} (which needs to be installed on your system) as backend for version control.
-
-The command
-\begin{Verbatim}
- ./scripts/env help
-\end{Verbatim}
-produces a short help text with a list of commands.
-
-To create a new environment named \texttt{current}, run the following command
-\begin{Verbatim}
- ./scripts/env new current
-\end{Verbatim}
-This will move your \texttt{.config} file and \texttt{./files} (if it exists) to
-the \texttt{env/} subdirectory and create symlinks in the base folder.
-
-After running make menuconfig or changing things in files/, your current state will
-differ from what has been saved before. To show these changes, use:
-\begin{Verbatim}
- ./scripts/env diff
-\end{Verbatim}
-
-If you want to save these changes, run:
-\begin{Verbatim}
- ./scripts/env save
-\end{Verbatim}
-If you want to revert your changes to the previously saved copy, run:
-\begin{Verbatim}
- ./scripts/env revert
-\end{Verbatim}
-
-If you want, you can now create a second environment using the \texttt{new} command.
-It will ask you whether you want to make it a clone of the current environment (e.g.
-for minor changes) or if you want to start with a clean version (e.g. for selecting
-a new target).
-
-To switch to a different environment (e.g. \texttt{test1}), use:
-\begin{Verbatim}
- ./scripts/env switch test1
-\end{Verbatim}
-
-To rename the current branch to a new name (e.g. \texttt{test2}), use:
-\begin{Verbatim}
- ./scripts/env rename test2
-\end{Verbatim}
-
-If you want to get rid of environment switching and keep everything in the base directory
-again, use:
-\begin{Verbatim}
- ./scripts/env clear
-\end{Verbatim}
projects / openwrt / staging / dedeckeh.git / blobdiff