RPi U-Boot

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Revision as of 21:44, 10 February 2014 by Stephenwarren (talk | contribs) (Updated instructions for copying U-Boot to SD card)
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Software & Distributions:

Software - an overview.

Distributions - operating systems and development environments for the Raspberry Pi.

Kernel Compilation - advice on compiling a kernel.

Performance - measures of the Raspberry Pi's performance.

Programming - programming languages that might be used on the Raspberry Pi.


Das U-Boot, often abbreviated to just U-Boot, is a bootloader commonly used on embedded systems. U-Boot can be used on the RPi to add flexibility by allowing other boot configurations to be used on top of the single specified file on the SD card. If you wish to run an upstream kernel, booting it via U-Boot is recommended.

This page explains how to get U-Boot working on the RPi, and explains how to boot images off both the SD card and over TFTP from the network.

Get the source

Various forks of U-Boot contain (different levels of) support for the Raspberry Pi.

If you don't need USB networking support in U-Boot, the mainline repository is recommended. If you do need USB networking support in U-Boot, Stephen Warren's repository is recommended.


The primary repository for U-Boot is git://git.denx.de/u-boot.git master branch. This supports the UART (serial port), SD card, and HDMI display. As of 20140110, the primary missing feature is USB support, and hence networking support.

To download this repository into a new local repository (this is what you want if you don't know better):

git clone git://git.denx.de/u-boot.git

To add this repository to an existing local repository:

git remote add u-boot git://git.denx.de/u-boot.git
git fetch u-boot

Stephen Warren's work-in-progress branch

Stephen Warren is working on getting BCM2835 USB support into the mainline repository described above. His work-in-progress repository is git://github.com/swarren/u-boot.git rpi_dev branch. Note that this branch is often rebased, and may contain work other than mainline-quality RPi-related patches.

To download this repository into a new local repository (this is what you want if you don't know better):

git clone git://github.com/swarren/u-boot.git
git checkout -b rpi_dev origin/rpi_dev

To add this repository to an existing local repository:

git remote add github_swarren_u-boot git://github.com/swarren/u-boot.git
git fetch github_swarren_u-boot
git checkout -b rpi_dev github_swarren_u-boot/rpi_dev

Oleksandr Tymoshenko's branch

Oleksandr's branch is based on an old U-Boot release, but does contain working USB support. It is available at git://github.com/gonzoua/u-boot-pi.git branch master.

To download this repository into a new local repository (this is what you want if you don't know better):

git clone git://github.com/gonzoua/u-boot-pi.git

To add this repository to an existing local repository:

git remote add github_gonzoua_u-boot-pi git://github.com/gonzoua/u-boot-pi.git
git fetch github_gonzoua_u-boot-pi

You can download a source tarball from this link.

Get an ARM compiler

If you are building U-Boot on a Raspberry Pi, or other ARM platform, you can skip this step; the native compiler already generates ARM instructions.

If you are building U-Boot on a different system, e.g. an x86 PC, you will need an ARM cross-compiler. Options available are:

Ubuntu packages

(Stephen Warren recommends this option)

Ubuntu includes an ARM cross compiler in its standard package step. You can install it as follows:

apt-get install gcc-arm-linux-gnueabi

Each time you wish to compile U-Boot, run the following first:

export CROSS_COMPILE=arm-linux-gnueabi-

Other distributions likely also provide ARM cross-compilers. Consult distro-specific documentation for details.

Raspberry Pi Foundation Tools

The Raspberry Pi Foundation provides a compiler in their tools repository. You can obtain it by:

cd $HOME
git clone git://github.com/raspberrypi/tools rpi-tools

Each time you wish to compile U-Boot, run one of the following first, depending on which particular toolchain you want to use:

export CROSS_COMPILE=$HOME/rpi-tools/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin/arm-bcm2708hardfp-linux-gnueabi-
export CROSS_COMPILE=$HOME/rpi-tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi-
export CROSS_COMPILE=$HOME/rpi-tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/arm-linux-gnueabihf/bin/

Linaro Compilers

As of 20140110, the standalone Linaro toolchains builds are known to generate a U-Boot image that doesn't work.

Compile the source

(Remember to set up CROSS_COMPILE as described above.)

Then, in the U-Boot source directory, run the following to start the build:

make -j8 -s rpi_b

You may wish to change the "8" in "-j8" to match the number of CPUs on your build system, or whatever make job limit you find works best.

The build process should take no more than a few minutes. This should generate u-boot.bin.

Copy U-Boot to your SD card

The RPi binary firmware can boot U-Boot just like it can boot a downstream kernel. As such, you can simply copy u-boot.bin to kernel.img on the SD card. You shouldn't need any options in config.txt for this to work. Something like the following should work, as root:

mount /dev/sdb1 /mnt/tmp
cp u-boot.bin /mnt/tmp/kernel.img
mv /mnt/tmp/config.txt /mnt/tmp/config.txt.pre-uboot
umount /mnt/tmp

Alternatively, you may wish not to rename the U-Boot binary. If so, the following should work, as root:

mount /dev/sdb1 /mnt/tmp
cp u-boot.bin /mnt/tmp/
mv /mnt/tmp/config.txt /mnt/tmp/config.txt.pre-uboot
echo 'kernel=uboot.img' > /mnt/tmp/config.txt
umount /mnt/tmp

In the commands above, you may need to replace "/dev/sdb1" with a different device filename, depending on where your SD card reader shows up. cat /proc/partitions should help you locate the correct device filename.

Test the image

Boot up the RPi with your new U-Boot image. You should see U-Boot load on the screen, and also on the serial port output (if you have it connected up).

Preparing a kernel image for use with U-Boot

This assumes you have the kernel source and are familiar with the kernel compilation process. As the kernel source already has the ability to build U-Boot image files, preparing a kernel image is relatively easy. First, you will need to put the U-Boot tool mkimage where it can be found by the kernel make process. This is done by copying it to the cross-compiler bin directory. From the U-Boot source directory, run the following, substituting the location and prefix of your cross compiler accordingly:

cp tools/mkimage <your_cross_compiler_path>/bin/arm-none-linux-gnueabi-mkimage

In the kernel source directory, you can now build the U-Boot image:

make uImage

The generated boot image file can be found at arch/arm/boot/uImage.

U-Boot boot options

Boot from SD card

Booting from the SD card allows multiple kernel images to be used without having to edit the config.txt file. Place your uImage file(s) on the SD card, then boot up. Press a key to drop to the command line, then enter the following:

mmc rescan
fatload mmc 0:1 ${loadaddr} <your_uImage_file>

Network boot via TFTP

You will need to have a TFTP server configured. Place your uImage file(s) in the TFTP root directory, and ensure that the file permissions are set accordingly (everyone should have read access - use chmod a+r uImage if unsure).

To boot using DHCP, ensure that the next-server and filename options are set in your DHCP server. Then, boot up the RPi, press a key to drop to the command line, then enter the following:

usb start

To boot using static IP:

usb start
setenv serverip <tftp_server_ip>
setenv ipaddr <a_spare_ip_address>
tftpboot uImage

U-Boot script files

The above instructions can be written into a text file and compiled into a U-Boot script file so that it automatically executes on boot. First, generate the script as follows (substituting your mkimage with that created earlier:

arm-none-linux-gnueabi-mkimage -A arm -O linux -T script -C none -d <your_script_text_file> boot.scr

Place the boot.scr file on the SD card and it will automatically be used when you power up the RPi.