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U2Boot
------
This is u2boot, our proposal for a next generation of the famous U-Boot
bootloader. U-Boot offers an excellent choice as a bootloader for
today's embedded systems, seen from a user's point of view.
Nevertheless, there are quite some design flaws which turned out over
the last years and we think that they cannot be solved in a production
tree. So this tree tries to do several things right - without caring
about losing support for old boards. So if you aim at stability at this
time, stay with the official U-Boot releases.
Building U-Boot
---------------
U-Boot uses the Linux kernel's build system. It consists of two parts:
the makefile infrastructure (kbuild), plus a configuration system
(kconfig). So building U-Boot is very similar to building the Linux
kernel.
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For the examples below, we use the User Mode U-Boot implementation, which
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is a port of U-Boot to the Linux userspace. This makes it possible to
test drive the code without having real hardware. So for this test
scenario, ARCH=linux is the valid architecture selection.
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Selection of the architecture and the cross compiler can be done in two
ways. You can either specify it using the environment variables ARCH
and CROSS_COMPILE, or you can create the soft links cross_arch and
cross_compile pointing to your architecture and compiler. For ARCH=linux
we do not need a cross compiler so it is sufficient to specify the
architecture:
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# ln -s linux cross_arch
In order to configure the various aspects of U-Boot, start the U-Boot
configuration system:
# make menuconfig
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 linux_defconfig'), there is a .config file in the toplevel
directory of the sourcode.
Once U-Boot is configured, we can start the compilation
# make
If everything goes well, the result is a file called uboot:
# ls -l uboot
-rwxr-xr-x 1 rsc ptx 114073 Jun 26 22:34 uboot
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U-Boot usually needs an environment for storing the configuation data.
You can generate an environment using the example environment contained
in examples/environment:
# ./scripts/ubootenv -s examples/environment/ env.bin
To get some files to play with you can generate a cramfs image:
# mkcramfs somedir/ cramfs.bin
The U-Boot image is a normal Linux executable, so it can be started
just like every other program:
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# ./uboot -e env.bin -i cramfs.bin
U-Boot 2.0.0-trunk (Jun 26 2007 - 22:34:38)
loading environment from /dev/env0
uboot> /
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Specifying -[ie] <file> tells U-Boot to map the file as a device
under /dev. Files given with '-e' will appear as /dev/env[n]. Files
given with '-i' will appear as /dev/fd[n].
If U-Boot 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 U-Boot will show you a menu asking for
your settings.
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FIXME: cfi currently doesn't work with um-uboot
Commands
--------
devinfo
addpart
pwd
cd
ls
cat
tftpboot <dest> <source> FIXME: order?
tftpboot /dev/nor0.1 <source>
erase -f /dev/nor0.1
help
edit -> ctrl-c ctrl-d
md -f /dev/nor0.1
exec /env/init FIXME: doesn't work yet
saveenv (makes /env persistent) -> /dev/env0
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printenv
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mount
Shell
-----
- doesn't have switch/case yet
- only one variable space
[ ] add variable space
Drivers
-------
/dev
serial
partition
environment -> /env; /env/init
Design
------
include/driver.h
board/scb9328.c
include/param.h: each device can have parameters; can be changed on
runtime; get/set can be overwritten by implementation.
- xfunctions: do panic if error
- proposed design:
arch/
arch/arm/cpu-arm920t/
arch/arm/board-.../
board/ is obsolete
- arch/*/Makefile is central makefile