This is one of the reasons why OpenWrt and other firmware exists: providing a
version independent, and tools independent firmware, that can be run on various
-platforms, known to be running Linux originaly.
+platforms, known to be running Linux originally.
\subsection{Which Operating System does this device run?}
\subsubsection{Amount of flash memory}
-Linux can hardly fit in a 2MB flash device, once you have open the device and
-located the flash chip, try to find other the Internet its characteristics. If
+Linux can hardly fit in a 2MB flash device, once you have opened the device and
+located the flash chip, try to find its characteristics on the Internet. If
your flash chip is a 2MB or less device, your device is most likely to run a
proprietary OS such as WindRiver VxWorks, or a custom manufacturer OS like Zyxel ZynOS.
-OpenWrt does not currently run on devices which have equal or less than 2MB of
-flash memory. This limitation will probably not be worked around since those
-devices are most of the time micro routers, or Wireless Access Points, which are
-not the main OpenWrt target.
+OpenWrt does not currently run on devices which have 2MB or less of flash memory.
+This limitation will probably not be worked around since those devices are most
+of the time micro-routers, or Wireless Access Points, which are not the main
+OpenWrt target.
\subsubsection{Pluging a serial port}
-By using a serial port, you may reach the console that is being shown by the device
+By using a serial port and a level shifter, you may reach the console that is being shown by the device
for debugging or flashing purposes. By analysing the output of this device, you can
-easily notice if the device uses a Linux kenrel or something different.
+easily notice if the device uses a Linux kernel or something different.
\subsection{Finding and using the manufacturer SDK}
Once you are sure your device run a Linux based firmware, you will be able to start
-hacking on it. If the manufacturer respect the GPL, it will have release with the
-device, a Sample Development Kit.
+hacking on it. If the manufacturer respected the GPL, it will have released a Sample
+Development Kit with the device.
\subsubsection{GPL violations}
\item binary tools to create a valid firmware image
\end{itemize}
-Your work is now divided into the following tasks:
+Your work can be divided into the following tasks:
\begin{itemize}
\item create a clean patch of the hardware specific part of the linux kernel
-\item spot potential kernel GPL violations especially on firewall and USB stack stuff
+\item spot potential kernel GPL violations especially on netfilter and USB stack stuff
\item make the binary drivers work, until there are open source drivers
\item use standard a GNU toolchain to make working executables
\item understand and write open source tools to generate a valid firmware image
may not always be relevant, so that you have to clean up those patches to only
let the "must have" code into them.
-The fist patch will contain all the code that is needed by the board to be
+The first patch will contain all the code that is needed by the board to be
initialized at startup, as well as processor detection and other boot time
specific fixes.
-The second patch will contain all useful definitions for that board: adresses,
-kernel granularity, redifinitions, processor family and features ...
+The second patch will contain all useful definitions for that board: addresses,
+kernel granularity, redefinitions, processor family and features ...
The third patch may contain drivers for: serial console, ethernet NIC, wireless
NIC, USB NIC ... Most of the time this patch contains nothing else than "glue"
code that has been added to make the binary driver work with the Linux kernel.
-This code might not be useful if you plan on writing from scratch drivers for
+This code might not be useful if you plan on writing drivers from scratch for
this hardware.
\subsubsection{Using the device bootloader}
The bootloader is the first program that is started right after your device has
been powered on. This program, can be more or less sophisticated, some do let you
do network booting, USB mass storage booting ... The bootloader is device and
-architeture specific, some bootloaders were designed to be universal such as
+architecture specific, some bootloaders were designed to be universal such as
RedBoot or U-Boot so that you can meet those loaders on totally different
-platforms and expect to work the same way.
+platforms and expect them to behave the same way.
If your device runs a proprietary operating system, you are very likely to deal
with a proprietary boot loader as well. This may not always be a limitation,
some proprietary bootloaders can even have source code available (i.e : Broadcom CFE).
-According to the bootloader features, hacking on th device will be more or less
+According to the bootloader features, hacking on the device will be more or less
easier. It is very probable that the bootloader, even exotic and rare, has a
documentation somewhere over the Internet. In order to know what will be possible
with your bootloader and the way you are going to hack the device, look over the
\item CONFIG\_DEBUG\_KERNEL
\item CONFIG\_DETECT\_SOFTLOCKUP
\item CONFIG\_DEBUG\_KOBJECT
-\item CONFIG\_EMBEDDED
\item CONFIG\_KALLSYMS
\item CONFIG\_KALLSYMS\_ALL
\end{itemize}
of running a custom firmware on your device, because this is sometimes a blocking
part of the flashing process.
-A firmare format is most of the time composed of the following fields:
+A firmware format is most of the time composed of the following fields:
\begin{itemize}
-\item header, containing a firmare version and additional fields: Vendor, Hardware version ...
+\item header, containing a firmware version and additional fields: Vendor, Hardware version ...
\item CRC32 checksum on either the whole file or just part of it
-\item Binary or compressed kernel image
-\item Binary or compressed root filesystem image
+\item Binary and/or compressed kernel image
+\item Binary and/or compressed root filesystem image
\item potential garbage
\end{itemize}
Once you have figured out how the firmware format is partitioned, you will have
-to write your own tool that produces valid firmare binaries. One thing to be very
+to write your own tool that produces valid firmware binaries. One thing to be very
careful here is the endianness of either the machine that produces the binary
firmware and the device that will be flashed using this binary firmware.
that covers the case of the device where the bootloader can pass to the kernel its partition plan.
First of all, you need to make your flash map driver be visible in the kernel
-configuration options, this can be done by editing the file
+configuration options, this can be done by editing the file \
\textbf{linux/drivers/mtd/maps/Kconfig}:
\begin{verbatim}
return -EIO;
}
- // Initlialise the device map
+ // Initialize the device map
simple_map_init(&device_map);
/* MTD informations are closely linked to the flash map device
module_exit(device_mtd_cleanup);
-// Macros defining licence and author, parameters can be defined here too.
+// Macros defining license and author, parameters can be defined here too.
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Me, myself and I <memyselfandi@domain.tld");
\end{verbatim}
+
+\subsection{Adding your target in OpenWrt}
+
+Once you spotted the key changes that were made to the Linux kernel
+to support your target, you will want to create a target in OpenWrt
+for your hardware. This can be useful to benefit from the toolchain
+that OpenWrt builds as well as the resulting user-space and kernel
+configuration options.
+
+Provided that your target is already known to OpenWrt, it will be
+as simple as creating a \texttt{target/linux/board} directory
+where you will be creating the following directories and files.
+
+Here for example, is a \texttt{target/linux/board/Makefile}:
+
+\begin{Verbatim}[frame=single,numbers=left]
+#
+# Copyright (C) 2009 OpenWrt.org
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+include $(TOPDIR)/rules.mk
+
+ARCH:=mips
+BOARD:=board
+BOARDNAME:=Eval board
+FEATURES:=squashfs jffs2 pci usb
+
+LINUX_VERSION:=2.6.27.10
+
+include $(INCLUDE_DIR)/target.mk
+
+DEFAULT_PACKAGES += hostapd-mini
+
+define Target/Description
+ Build firmware images for Evaluation board
+endef
+
+$(eval $(call BuildTarget))
+\end{Verbatim}
+
+\begin{itemize}
+ \item \texttt{ARCH} \\
+ The name of the architecture known by Linux and uClibc
+ \item \texttt{BOARD} \\
+ The name of your board that will be used as a package and build directory identifier
+ \item \texttt{BOARDNAME} \\
+ Expanded name that will appear in menuconfig
+ \item \texttt{FEATURES} \\
+ Set of features to build filesystem images, USB, PCI, VIDEO kernel support
+ \item \texttt{LINUX\_VERSION} \\
+ Linux kernel version to use for this target
+ \item \texttt{DEFAULT\_PACKAGES} \\
+ Set of packages to be built by default
+\end{itemize}
+
+A partial kernel configuration which is either named \texttt{config-default} or which matches the kernel version \texttt{config-2.6.x} should be present in \texttt{target/linux/board/}.
+This kernel configuration will only contain the relevant symbols to support your target and can be changed using \texttt{make kernel\_menuconfig}.
+
+To patch the kernel sources with the patches required to support your hardware, you will have to drop them in \texttt{patches} or in \texttt{patches-2.6.x} if there are specific
+changes between kernel versions. Additionnaly, if you want to avoid creating a patch that will create files, you can put those files into \texttt{files} or \texttt{files-2.6.x}
+with the same directory structure that the kernel uses (e.g: drivers/mtd/maps, arch/mips ..).
+
+The build system will require you to create a \texttt{target/linux/board/image/Makefile}:
+
+\begin{Verbatim}[frame=single,numbers=left]
+#
+# Copyright (C) 2009 OpenWrt.org
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+include $(TOPDIR)/rules.mk
+include $(INCLUDE_DIR)/image.mk
+
+define Image/BuildKernel
+ cp $(KDIR)/vmlinux.elf $(BIN_DIR)/openwrt-$(BOARD)-vmlinux.elf
+ gzip -9 -c $(KDIR)/vmlinux > $(KDIR)/vmlinux.bin.gz
+ $(STAGING_DIR_HOST)/bin/lzma e $(KDIR)/vmlinux $(KDIR)/vmlinux.bin.l7
+ dd if=$(KDIR)/vmlinux.bin.l7 of=$(BIN_DIR)/openwrt-$(BOARD)-vmlinux.lzma bs=65536 conv=sync
+ dd if=$(KDIR)/vmlinux.bin.gz of=$(BIN_DIR)/openwrt-$(BOARD)-vmlinux.gz bs=65536 conv=sync
+endef
+
+define Image/Build/squashfs
+ $(call prepare_generic_squashfs,$(KDIR)/root.squashfs)
+endef
+
+define Image/Build
+ $(call Image/Build/$(1))
+ dd if=$(KDIR)/root.$(1) of=$(BIN_DIR)/openwrt-$(BOARD)-root.$(1) bs=128k conv=sync
+
+ -$(STAGING_DIR_HOST)/bin/mkfwimage \
+ -B XS2 -v XS2.ar2316.OpenWrt \
+ -k $(BIN_DIR)/openwrt-$(BOARD)-vmlinux.lzma \
+ -r $(BIN_DIR)/openwrt-$(BOARD)-root.$(1) \
+ -o $(BIN_DIR)/openwrt-$(BOARD)-ubnt2-$(1).bin
+endef
+
+$(eval $(call BuildImage))
+
+\end{Verbatim}
+
+\begin{itemize}
+ \item \texttt{Image/BuildKernel} \\
+ This template defines changes to be made to the ELF kernel file
+ \item \texttt{Image/Build} \\
+ This template defines the final changes to apply to the rootfs and kernel, either combined or separated
+ firmware creation tools can be called here as well.
+\end{itemize}
projects / openwrt.git / blobdiff