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,
+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 the 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. 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.
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
+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
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.
There are four key directories in the base:
\begin{itemize}
- \item tools
- \item toolchain
- \item package
- \item target
+ \item tools
+ \item toolchain
+ \item package
+ \item 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 and the compiler and 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
+\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.
\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.
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. 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.
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
endef
define Package/bridge/install
- install -m0755 -d $(1)/usr/sbin
- install -m0755 $(PKG_BUILD_DIR)/brctl/brctl \
- $(1)/usr/sbin/
+ install -m0755 -d $(1)/usr/sbin
+ install -m0755 $(PKG_BUILD_DIR)/brctl/brctl \
+ $(1)/usr/sbin/
endef
$(eval $(call BuildPackage,bridge))
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\_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)
\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.
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 --
+setup 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.
-
+
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
+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
+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
+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.
projects / openwrt.git / blobdiff