One of the biggest challenges to getting started with embedded devices is that you
-just can't 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,
+can't 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 wouldn't have the basic set of tools needed to produce a firmware image.
The embedded device represents an entirely new hardware platform, which is
-incompatible with the hardware on your development machine, so in a process called
+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
+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's not something that's
-regularly attempted and so the there's a certain amount of mystery and black magic
+The process of creating a cross compiler can be tricky, it's not something that's
+regularly attempted and so there's a certain amount of mystery and black magic
associated with it. In many cases when you're dealing with embedded devices you'll
-be provided with a binary copy of a compiler and basic libraries rather than
-instructions for creating your own -- it's a time saving step but at the same time
-often means you'll be using a rather dated set. Likewise, it's also common to be
-provided with a patched copy of the Linux kernel from the board or chip vendor,
+be provided with a binary copy of a compiler and basic libraries rather than
+instructions for creating your own -- it's a time saving step but at the same time
+often means you'll be using a rather dated set of tools. Likewise, it's 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
-changed to make the kernel run on the embedded platform.
+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. Or to put it
-in simpler terms, OpenWrt doesn't contain any executables or even sources, it's an
-automated system for downloading the sources, patching them to work with the given
-platform and compiling them correctly for the platform. What this means is that
+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 doesn't contain any executables or even sources, it's 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
+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's 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 doesn't
+a new firmware image -- there's 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 doesn't
just apply to the kernel, but to anything included with OpenWrt -- It's 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
+So let's take a look at OpenWrt and see how this all works.
\subsubsection{Download openwrt}
subversion using the following command:
\begin{Verbatim}
-svn co https://svn.openwrt.org/openwrt/trunk kamikaze
+$ svn co https://svn.openwrt.org/openwrt/trunk kamikaze
\end{Verbatim}
Additionally, there's a trac interface on \href{https://dev.openwrt.org/}{https://dev.openwrt.org/}
There are four key directories in the base:
\begin{itemize}
- \item tools
- \item toolchain
- \item package
- \item target
+ \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 and the compiler and c library.
+used to build the firmware image, the compiler, and the c library.
The result of this is three new directories, \texttt{tool\_build}, which is a temporary
directory for building the target independent tools, \texttt{toolchain\_build\_\textit{<arch>}}
which is used for building the toolchain for a specific architecture, and
You won't need to do anything with the toolchain directory unless you intend to
add a new version of one of the components above.
-\texttt{package} is for exactly that -- packages. In an OpenWrt firmware, almost everything
+\begin{itemize}
+ \item \texttt{tool\_build}
+ \item \texttt{toolchain\_build\_\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.
+features or removed to save space. Note that packages are also maintained outside of the main
+trunk and can be obtained from subversion at the following location:
+
+\begin{Verbatim}
+$ svn co https://svn.openwrt.org/openwrt/packages ../packages
+\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. From kamikaze you would do something like this:
+
+\begin{Verbatim}
+$ ls
+kamikaze packages
+$ ln -s packages/net/nmap kamikaze/package/nmap
+\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 and contains the kernel config and patches
+a specific embedded platform. Of particular interest here is the "\texttt{target/linux}"
+directory which is broken down by platform and contains the kernel config and patches
to the kernel for a particular platform. There's also the "\texttt{target/image}" directory
which describes how to package a firmware for a specific platform.
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\_\textit{<arch>}}
+ \item \texttt{dl}
+\end{itemize}
\subsubsection{Building OpenWrt}
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. Similar to the linux kernel config, almost every option has three choices,
+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
+ \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
+After you've finished with the menu configuration, exit and when prompted, save your
configuration changes. 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.
\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
+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}"
+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\_\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 two things:
\begin{itemize}
- \item \texttt{package/\textit{<name>}/Makefile}
- \item \texttt{package/\textit{<name>}/patches}
+ \item \texttt{package/\textit{<name>}/Makefile}
+ \item \texttt{package/\textit{<name>}/patches}
\end{itemize}
The patches directory is optional and typically contains bug fixes or optimizations to
Here for example, is \texttt{package/bridge/Makefile}:
\begin{Verbatim}[frame=single,numbers=left]
+#
+# Copyright (C) 2006 OpenWrt.org
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+# $Id: Makefile 5624 2006-11-23 00:29:07Z nbd $
+
include $(TOPDIR)/rules.mk
PKG_NAME:=bridge
PKG_VERSION:=1.0.6
PKG_RELEASE:=1
-PKG_BUILD_DIR:=$(BUILD_DIR)/bridge-utils-$(PKG_VERSION)
PKG_SOURCE:=bridge-utils-$(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:=base
- CATEGORY:=Network
- DEFAULT:=y
+ SECTION:=net
+ CATEGORY:=Base system
TITLE:=Ethernet bridging configuration utility
+ DESCRIPTION:=\
+ Manage ethernet bridging: a way to connect networks together to \\\
+ form a larger network.
URL:=http://bridge.sourceforge.net/
endef
-define Package/bridge/description
-Ethernet bridging configuration utility
- 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))
+ $(call Build/Configure/Default, \
+ --with-linux-headers="$(LINUX_DIR)" \
+ )
endef
define Package/bridge/install
- install -m0755 -d $(1)/usr/sbin
- install -m0755 $(PKG_BUILD_DIR)/brctl/brctl \
- $(1)/usr/sbin/
+ $(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're downloading
- \item \texttt{PKG\_RELEASE} \\
- The version of this package Makefile
- \item \texttt{PKG\_BUILD\_DIR} \\
- Where to compile the package
- \item \texttt{PKG\_SOURCE} \\
- The filename of the original sources
- \item \texttt{PKG\_SOURCE\_URL} \\
- Where to download the sources from
- \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\_NAME} \\
+ The name of the package, as seen via menuconfig and ipkg
+ \item \texttt{PKG\_VERSION} \\
+ The upstream version number that we're 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)
+ \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.
+\texttt{@SF} is a special keyword for downloading packages from sourceforge. There is also
+another keyword of \texttt{@GNU} for grabbing GNU source releases.
+
The md5sum 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
-setup by the earlier include statements. BuildPackage only takes one argument directly --
+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{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 type of package (currently unused)
- \item \texttt{CATEGORY} \\
- Which menu it appears in menuconfig
- \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
- \end{itemize}
+ \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 type of package (currently unused)
+ \item \texttt{CATEGORY} \\
+ Which menu it appears in menuconfig
+ \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
+ \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{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.
-
+ which is represented by the \texttt{\$(1)} directory. Note that there are currently
+ 3 defined install macros:
+ \begin{itemize}
+ \item \texttt{INSTALL\_DIR} \\
+ install -d -m0755
+ \item \texttt{INSTALL\_BIN} \\
+ install -m0755
+ \item \texttt{INSTALL\_DATA} \\
+ install -m0644
+ \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
+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've created your \texttt{package/\textit{<name>}/Makefile}, the new package
+After you've 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.
-\subsubsection{Troubleshooting}
-If you find your package doesn't show up in menuconfig, try the following command to
+\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}
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}
+ \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\_\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\_\textit{<arch>}/\textit{<source>}} directory and run the install command above,
-when satisfied, copy the patched sources elsewhere and diff them with the unpatched
+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}
+
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