223 lines
8.3 KiB
Plaintext
223 lines
8.3 KiB
Plaintext
/** @mainpage Universal Bootloader
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@section barebox_intro Introduction
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@a Barebox is a bootloader which follows the tradition of U-Boot. U-Boot
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offers an excellent choice as a bootloader for today's embedded systems,
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seen from a user's point of view. Nevertheless, there are quite some
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design flaws which turned out over the last years and we think that they
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cannot be solved in a production tree. So this tree tries to do several
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things right - without caring about losing support for old boards.
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@par General features include:
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- A posix based file API
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- inside @a barebox the usual open/close/read/write/lseek functions are used.
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This makes it familiar to everyone who has programmed under unix systems.
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- usual shell commands like ls/cd/mkdir/echo/cat,...
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- The environment is not a variable store anymore, but a file store. It has
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currently some limitations, of course. The environment is not a real
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read/write filesystem, it is more like a tar archive, or even more like
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an ar archive, because it cannot handle directories. The saveenv command
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saves the files under a certain directory (by default /env) in persistent
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storage (by default /dev/env0). There is a counterpart called loadenv, too.
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- Real filesystem support
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- The loader starts up with mounting a ramdisk on /. Then a devfs is mounted
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on /dev allowing the user (or shell commands) to access devices. Apart from
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these two filesystems there is currently one filesystem ported: cramfs. One
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can mount it with the usual mount command.
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- device/driver model
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- Devices are no longer described by defines in the config file. Instead
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there are devices which can be registered in the board .c file or
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dynamically allocated. Drivers will match upon the devices automatically.
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- clocksource support
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- Timekeeping has been simplified by the use of the Linux clocksource API.
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Only one function is needed for a new board, no [gs]et_timer[masked]() or
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reset_timer[masked]() functions.
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- Kconfig and Kernel build system
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- Only targets which are really needed get recompiled. Parallel builds are
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no problem anymore. This also removes the need for many many ifdefs in
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the code.
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- simulation target
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- @a barebox can be compiled to run under Linux. While this is rather useless
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in real world this is a great debugging and development aid. New features
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can be easily developed and tested on long train journeys and started
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under gdb. There is a console driver for linux which emulates a serial
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device and a tap based ethernet driver. Linux files can be mapped to
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devices under @a barebox to emulate storage devices.
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- device parameter support
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- Each device can have a unlimited number of parameters. They can be accessed
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on the command line with \<devid\>.\<param\>="...", for example
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'eth0.ip=192.168.0.7' or 'echo $eth0.ip'
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- initcalls
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- hooks in the startup process can be achieved with *_initcall() directives
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in each file.
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- getopt
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- There is a small getopt implementation. Some commands got really
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complicated (both in code and in usage) due to the fact that @a U-Boot only
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allowed positional parameters.
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- editor
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- Scripts can be edited with a small editor. This editor has no features
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except the ones really needed: moving the cursor and typing characters.
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@par Building barebox
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@a Barebox uses the Linux kernel's build system. It consists of two parts:
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the makefile infrastructure (kbuild), plus a configuration system
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(kconfig). So building @a barebox is very similar to building the Linux
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kernel.
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For the examples below, we use the User Mode @a barebox implementation, which
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is a port of @a barebox to the Linux userspace. This makes it possible to
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test drive the code without having real hardware. So for this test
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scenario, @p ARCH=sandbox is the valid architecture selection. This currently
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only works on ia32 hosts and partly on x86-64.
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Selection of the architecture and the cross compiler can be done in two
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ways. You can either specify it using the environment variables @p ARCH
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and @p CROSS_COMPILE, or you can create the soft links cross_arch and
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cross_compile pointing to your architecture and compiler. For @p ARCH=sandbox
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we do not need a cross compiler so it is sufficient to specify the
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architecture:
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@code # ln -s arch/sandbox cross_arch @endcode
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In order to configure the various aspects of @a barebox, start the @a barebox
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configuration system:
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@code # make menuconfig @endcode
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This command starts a menu box and lets you select all the different
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options available for your architecture. Once the configuration was
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finished (you can simulate this by using the standard demo config file
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with 'make sandbox_defconfig'), there is a .config file in the toplevel
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directory of the sourcecode.
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Once @a barebox is configured, we can start the compilation
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@code # make @endcode
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If everything goes well, the result is a file called @p barebox:
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@code
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# ls -l barebox
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-rwxr-xr-x 1 rsc ptx 114073 Jun 26 22:34 barebox
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@endcode
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@a barebox usually needs an environment for storing the configuration data.
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You can generate an environment using the example environment contained
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in arch/sanbox/board/env:
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@code # ./scripts/bareboxenv -s -p 0x10000 arch/sanbox/board/env/ env.bin @endcode
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To get some files to play with you can generate a cramfs image:
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@code # mkcramfs somedir/ cramfs.bin @endcode
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The @a barebox image is a normal Linux executable, so it can be started
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just like every other program:
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@code
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# ./barebox -e env.bin -i cramfs.bin
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barebox 2.0.0-trunk (Jun 26 2007 - 22:34:38)
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loading environment from /dev/env0
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barebox\> /
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@endcode
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Specifying -[ie] \<file\> tells @a barebox to map the file as a device
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under @p /dev. Files given with '-e' will appear as @p /dev/env[n]. Files
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given with '-i' will appear as @p /dev/fd[n].
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If @a barebox finds a valid configuration sector on @p /dev/env0 it will
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load it to @p /env. It then executes @p /env/init if it exists. If you have
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loaded the example environment @a barebox will show you a menu asking for
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your settings.
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If you have started @a barebox as root you will find a new tap device on your
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host which you can configure using ifconfig. Once you configured the
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network settings accordingly you can do a ping or tftpboot.
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If you have mapped a cramfs image try mounting it with
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@code
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# mkdir /cram
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# mount /dev/fd0 cramfs /cram
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@endcode
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Memory can be examined as usual using @p md/mw commands. They both understand
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the -f \<file\> option to tell the commands that they should work on the
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specified files instead of @p /dev/mem which holds the complete address space.
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Note that if you call 'md /dev/fd0' (without -f) @a barebox will segfault on
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the host, because it will interpret @p /dev/fd0 as a number.
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@par Directory layout
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Most of the directory layout is based upon the Linux Kernel:
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@verbatim
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arch / * / -> contains architecture specific parts
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arch / * / mach-* / -> SoC specific code
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drivers / serial -> drivers
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drivers / net
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drivers / ...
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include / asm-* -> architecture specific includes
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include / asm-* / arch-* -> SoC specific includes
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fs / -> filesystem support and filesystem drivers
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lib / -> generic library functions (getopt, readline and the
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like)
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common / -> common stuff
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commands / -> many things previously in common/cmd_*, one command
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per file
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net / -> Networking stuff
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scripts / -> Kconfig system
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Documentation / -> Parts of the documentation, also doxygen
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@endverbatim
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@section license barebox's License
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@verbatim
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of
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the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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MA 02111-1307 USA
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@endverbatim
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@subpage users_manual
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@subpage developers_manual
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@subpage supported_boards
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*/
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