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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}
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