u-boot-aarch64-none-elf

My howto to build a working u-boot

Preamble

Yes, you might ask yourself why you fall again on another build of u-boot. Well, in my case i want the most custom framework possible to make and run bare metal application or OS for different boards. I followed a lot of tutorials only to realized they don't work for my case.

So, here is my reminder for myself and everyone finding it.

For this repo, you will need the help of the cross-compiler of my other repository.

My article will cover a build for a Raspberry Pi 3B+ and an Orange Pi R1 Plus LTS.

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U-boot for Raspberry Pi 3 B+

Building u-boot

To build u-boot, you will need to get the source first : wget https://github.com/u-boot/u-boot/archive/refs/tags/v2025.01.tar.gz
Once done, extract the tar ball and change directory to the root of the sources files (u-boot-2025-01).
You will need to generate a makefile for the board. Thanks to the u-boot team, we already have a definition file pour this board.
So run : make rpi_3_b_plus_defconfig
Once done, start the build process with : make CROSS_COMPILE=aarch64-none-elf-
When the build process is complete, we will use u-boot.bin for our project.

Setting the microsd card

We will need to partition and format our microsd card for the board to recognize it.
Plug in your card and run : sudo fdisk -l to list all the /dev/sdX available and locate your card. Mine was /dev/sdb.
I start by wiping all the card with zeros : sudo dd if=/dev/zero of=/dev/sdb bs=10M status=progress conv=fdatasync
Once complete, we will create the partition : sudo fdisk /dev/sdb
here is all the choice for a bootable fat32 partition :

n (create a new partition)
p (for a primary partition)
1 (for the partition number)
<enter> (accept the default start sector)
<enter> (accept the default end sector, so all the card will be partition)
t (to change the type of the partition)
c ( for a type : W95 FAT32 (LBA))
a (set the boot flag on)
w (write the partition)

Now the partition made, lets put a filesystem on it : sudo mkfs.vfat -F 32 /dev/sdb1

Firmware and u-boot

We will need to get the official firmware : wget https://github.com/raspberrypi/firmware/releases/download/1.20250326/raspi-firmware_1.20250326.orig.tar.xz
Extract the tar ball. The files we want are : bootcode.bin, fixup.dat, start.elf.
We will also need the device tree blob of the board : wget https://github.com/raspberrypi/firmware/raw/refs/heads/master/boot/bcm2710-rpi-3-b-plus.dtb
You will also need to create a text file called config.txt
Inside the config.txt file, you will need to add these instruction :

enable_uart=1
kernel=u-boot.bin
arm_64bit=1
core_freq=250
device_tree=bcm2710-rpi-3-b-plus.dtb

Now, put all the necessary files on your microsd card. Here is the list : bootcode.bin, fixup.dat, start.elf, u-boot.bin, config.txt, bcm2710-rpi-3-b-plus.dtb

From now on, just put the microsd card in the board and start it. u-boot will output through the uart port. You can use putty with an adapter usb-to-uart. That's it, congrat!

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U-boot for Orange Pi R1 Plus LTS

work in progress.

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Ending

And now, what should we do? An OS, a bare metal app? Stay tune. ;)