Barebox is a bootloader that follows the tradition of Das U-Boot, while adopting modern design ideas from the Linux kernel.
A POSIX-based file API Inside barebox the usual open/close/read/write/lseek functions are used. This makes it familiar to everyone who has programmed under UNIX systems.
Usual shell commands like ls/cd/mkdir/echo/cat,...
The environment is not a variable store anymore, but a file store. It has currently some limitations, of course. The environment is not a real read/write filesystem, it is more like a tar archive, or even more like an ar archive, because it cannot handle directories. The saveenv command saves the files under a certain directory (by default /env) in persistent storage (by default /dev/env0). There is a counterpart called loadenv, too.
filesystem support The loader starts up with mounting a ramdisk on /. Then a devfs is mounted on /dev allowing the user (or shell commands) to access devices. Apart from these two filesystems there is currently one filesystem ported: cramfs. One can mount it with the usual mount command.
device/driver model Devices are no longer described by defines in the config file. Instead there are devices which can be registered in the board .c file or dynamically allocated. Drivers will match upon the devices automatically.
clocksource support Timekeeping has been simplified by the use of the Linux clocksource API. Only one function is needed for a new board, no [gs]et_timer[masked]() or reset_timer[masked]() functions.
Kconfig and Kernel build system Only targets which are really needed get recompiled. Parallel builds are no problem anymore. This also removes the need for many many ifdefs in the code.
simulation target barebox can be compiled to run under Linux. While this is rather useless in real world this is a great debugging and development aid. New features can be easily developed and tested on long train journeys and started under gdb. There is a console driver for Linux which emulates a serial device and a TAP-based Ethernet driver. Linux files can be mapped to devices under barebox to emulate storage devices.
device parameter support
Each device can have a unlimited number of parameters. They can be accessed
on the command line with
initcalls hooks in the startup process can be achieved with *_initcall() directives in each file.
getopt There is a small getopt implementation. Some commands got really complicated (both in code and in usage) due to the fact that U-Boot allowed only positional parameters.
editor Scripts can be edited with a small editor. This editor has no features except the ones really needed: moving the cursor and typing characters.
Barebox uses the Linux kernel's build system. It consists of two parts: the Makefile infrastructure (kbuild), plus a configuration system (kconfig). So building barebox is very similar to building the Linux kernel.
For the examples below, we use the User Mode barebox implementation, which is a port of barebox to the Linux userspace. This makes it possible to test drive the code without having real hardware. So for this test scenario, ARCH=sandbox is the valid architecture selection. This currently only works on ia32 hosts and partly on x86-64.
Selection of the architecture and the cross compiler can be done by using the environment variables ARCH and CROSS_COMPILE.
In order to configure the various aspects of barebox, start the barebox configuration system:
This command starts a menu box and lets you select all the different options available for your architecture. Once the configuration was finished (you can simulate this by using the standard demo config file with 'make sandbox_defconfig'), there is a .config file in the toplevel directory of the source code.
Once barebox is configured, we can start the compilation
If everything goes well, the result is a file called barebox:
-rwxr-xr-x 1 rsc ptx 114073 Jun 26 22:34 bareboxBarebox usually needs an environment for storing the configuration data. You can generate an environment using the example environment contained in board/sandbox/env:
To get some files to play with you can generate a cramfs image:
The barebox image is a normal Linux executable, so it can be started just like every other program:
barebox 2.0.0-trunk (Jun 26 2007 - 22:34:38)
loading environment from /dev/env0 barebox> /
Specifying -[ie]
If barebox finds a valid configuration sector on /dev/env0 it will load it to /env. It then executes /env/init if it exists. If you have loaded the example environment barebox will show you a menu asking for your settings.
If you have started barebox as root you will find a new tap device on your host which you can configure using ifconfig. Once you configured bareboxs network settings accordingly you can do a ping or tftpboot.
If you have mapped a cramfs image try mounting it with
Memory can be examined as usual using md/mw commands. They both understand
the -f
Most of the directory layout is based upon the Linux Kernel:
arch// -> contains architecture specific parts arch//mach-*/ -> SoC specific code
drivers/serial -> drivers drivers/net drivers/...
include/asm- -> architecture specific includes include/asm-/arch-* -> SoC specific includes
fs/ -> filesystem support and filesystem drivers
lib/ -> generic library functions (getopt, readline and the like)
common/ -> common stuff
commands/ -> many things previously in common/cmd_*, one command per file
net/ -> Networking stuff
scripts/ -> Kconfig system
Documentation/ -> Sphinx generated documentation. Call "make docs" to generate a HTML version in Documentation/html.
Barebox is developed with git. From time to time, tarball releases are branched from the repository and released on the project web site. Here are the release rules:
Releases follow a time based scheme:
barebox-xxxx.yy.z.tar.bz2 ^^^^ ^^ ^----------- Bugfix Number, starting at 0 \ ------------- Month ---------------- Year
Example: barebox-2009.12.0.tar.bz2
Releases are made around the beginning of the month. As we are aiming for monthly releases, development is considered to be a continuous process. If you find bugs in one release, you have the chance to get patches in on a very short time scale.
Usually, there are no bugfix releases, so z=0. If there is a need to make a bugfix release, z is the right place to increment.
If there may be a reason for pre releases, they are called
barebox-xxxx.yy.z-pren.tar.bz ^------ Number of prerelease, starting with 1
Example: barebox-2009.12.0-pre1.tar.bz2
We think that there is no need for pre releases, but if it's ever necessary, this is the scheme we follow.
Only the monthly releases are archived on the web site. The tarballs are located in https://www.barebox.org/download/ and this location does never change, in order to make life easier for distribution people.