I got a Radxa ROCK 4 SE on sale for 1/3 of the price, so I couldn't resist. I don't want to use a distro, but want to build everything from scratch, cross-compile and net-boot. If you want a distro, Armbian is the best I have found (but watch up for this issue).
If you want to try for instance different kernels, it is very inconvenient to flash-and-switch the SD-card all the time. The way to go is network booting. Radxa Rock 4 is said to support network boot, but requires a serial cable and manual intervention. I don't want that! The board should do a pxe boot automatically. This repo describes how it can be done with a (very) small SD-card. A wired network is required (wifi is not supported).
Development and contributions are described below.
If you have another board than Radxa Rock 4se, please see Rebuild sd.img below.
Most things are done with the admin.sh script.
./admin.sh # help printout
./admin.sh env # current settings
./admin.sh versions # Used versions and download/clone status
Everything is built in $ROCK_WORKSPACE, which defaults to
"/tmp/tmp/$USER/ROCK". Default for options can be set as environment
variables. Example:
export __dev=enp5s0
export __local_addr=192.168.40.1/24
export __dns=192.168.10.1
Find a sd-rock-4se-rk3399.img.xz in releases, download and
decompress:
xz -d sd-rock-4se-rk3399.img.xz
Unfortunately there is a problem with the u-boot serverip variable. It
should be set by the "serverid" DHCP option (54), but I have not got
that working (see below). So for now you must set it to
the address of your tftp server manually:
./admin.sh set_serverip --sdimage=sd-rock-4se-rk3399.img <address-to-your-tftp-server>
(problems with this? Please see Development and contributions)
Now you can flash your SD-card:
dev=<device-of-your-sd-card> # THIS MUST BE RIGHT!!
sudo dd if=sd-rock-4se-rk3399.img of=$dev status=progress oflag=dsync bs=4M
WARNING: If dev points to the wrong device (like your hard-disk),
it will be destroyed!
You are done! Insert the SD-card and power-on your board, and it will boot from network.
If you want to alter your SD-card, please check SD-card layout below.
Boot sequence (simplified):
sequenceDiagram
box Radxa Rock
participant fw as FirmWare
participant u as U-boot
participant p1 as SD-card<br/>partition
participant kernel
end
participant dhcpd
participant tftpd
fw->>u : Loads from sector 64
u->>p1 : Reads "boot.scr"
u->>dhcpd : request
dhcpd->>u : offer
u->>tftpd : Request pxelinux.cfg
u->>tftpd : Load kernel
u->>tftpd : Load initrd
u->>tftpd : Load ftd
u->>kernel : Starts
On power-on the board will now obtain an address via DHCP and
request a pxelinux configuration via tftp on a number of
places. An easy way to find out where is to check the tftp server
logs (narrowed):
atftpd[175531]: Serving pxelinux.cfg/01-f6-0b-6e-84-77-ec to 192.168.40.138:3284
atftpd[175531]: Serving pxelinux.cfg/C0A8288A to 192.168.40.138:3311
atftpd[175531]: Serving pxelinux.cfg/C0A8288 to 192.168.40.138:3366
atftpd[175531]: Serving pxelinux.cfg/C0A828 to 192.168.40.138:3485
atftpd[175531]: Serving pxelinux.cfg/C0A82 to 192.168.40.138:3607
atftpd[175531]: Serving pxelinux.cfg/C0A8 to 192.168.40.138:3728
atftpd[175531]: Serving pxelinux.cfg/C0A to 192.168.40.138:3846
atftpd[175531]: Serving pxelinux.cfg/C0 to 192.168.40.138:3964
atftpd[175531]: Serving pxelinux.cfg/C to 192.168.40.138:4085
atftpd[175531]: Serving pxelinux.cfg/default-arm-rk3399-rockpi4-rk3399 to 192.168.40.138:1139
atftpd[175531]: Serving pxelinux.cfg/default-arm-rk3399 to 192.168.40.138:1260
atftpd[175531]: Serving pxelinux.cfg/default-arm to 192.168.40.138:1383
atftpd[175531]: Serving pxelinux.cfg/default to 192.168.40.138:1502
Make sure that any of these files is a pxelinux.cfg file, looking
something like:
label Linux
kernel Image
initrd initrd
append console=ttyS2,115200n8
fdt rock.dtb
U-boot will load Image, initrd and rock.dtb and start Linux with
the command line in "append". The boot files are different for
everybody, so I can't say what they should be. I describe how I do
in Kernel test below.
A wired network is assumed. I use wifi for internet, so my wired
interface, enp5s0, is free and used as an example. You may configure
your wired interface yourself, or use my script. Example:
./admin.sh interface_setup --dev=enp5s0 --local-addr=192.168.40.1/24
# (requires sudo)
Dhcp and tftp servers are needed. You may setup those in your
own way (there re plenty of instructions), or you can use my script.
I use the udhcpd applet in BusyBox.
BusyBox is included in Ubuntu, but you may have to build it locally.
#./admin.sh busybox_build --local # source archive must be downloaded
#export __busybox=/path/to/local/built/busybox
./admin.sh dhcpd --dev=enp5s0 --local-addr=192.168.40.1/24
# (requires sudo)
I did not get any pre-buit tftp server to work, so I build
atftp locally. Download the tar.gz
package from the tags page.
./admin.sh atftp_build
./admin.sh tftpd --local-addr=192.168.40.1/24 --tftproot=/tmp/tftproot
# (requires sudo)
The SD-image is 54MiB, but your SD-card is much larger. This mean that the backup GPT table is in the wrong place. Example:
sudo sfdisk -l /dev/sdb
GPT PMBR size mismatch (110591 != 15523839) will be corrected by write.
The backup GPT table is not on the end of the device.
Disk /dev/sdb: 7.4 GiB, 7948206080 bytes, 15523840 sectors
Disk model: SD Card
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 3681BD8A-F200-4B40-A742-782D81AE6147
Device Start End Sectors Size Type
/dev/sdb1 32768 102399 69632 34M EFI System
This doesn't matter if you only use the SD-card for network boot, and
it will be corrected by sfdisk if you add a partition.
echo ",,L," | sudo sfdisk --append /dev/sdb
sudo mkfs.ext4 /dev/sdb2
You may note that the EFI partition starts at sector 32768? That's
because the u-boot binary is written on sector 64 and occupies ~10M
space.
This will be necessary for other boards. You must download u-boot
the tar.gz package from it's tags page, and trusted-firmware-a
from it's tags page.
Now build u-boot for another board:
#export __board=rock-4c-plus-rk3399 # and skip --board below
./admin.sh trustedf_build
./admin.sh uboot_build --board=rock-4c-plus-rk3399 --default
./admin.sh sdimage --board=rock-4c-plus-rk3399
The available configurations can be found in the configs/ directory
in the u-boot source (unpacked in $ROCK_WORKSPACE/u-boot-*). I can build
the rock-4* configurations, but not others. You may want to alter
the configuration, at least set default baud-rate to 115200.
The config is stored in $__ubootcfg which defaults to
config/uboot-$__board.config. Do not use --default again! For
subsequent updates use:
./admin.sh uboot_build --board=rock-4c-plus-rk3399 --menuconfig
The U-boot serverip variable is needed for tftp. It should be
set automatically from the "serverid" DHCP option (54), but for me it
remains undefined after dhcp. I have made a packet capture, and the
option is included in the dhcp-offer.
I have also checked the U-boot source, and it looks like it is set. I am still trouble-shooting this...
You don't need a serial console just for network boot, but for development you basically must have it.
The Radxa documentation
is still valid (for once). I bought
"Oiyagai 2pcs Debug Cable for Raspberry Pi USB Programming" from Amazon for
120SEK (~$12). They can't do 1.5Mbps, but 115200 is totally sufficient, and
since we build u-boot we can set the default baud-rate.
Update: One of my Oiyagai Debug Cable has broken already, and the device is lost about twice a day and has to be removed/re-inserted. You might want to avoid the cheap stuff.
#sudo apt install minicom
alias minicom='minicom -w -t xterm -l -R UTF-8'
cat > ~/.minirc.rockpi4 <<EOF
pu port /dev/ttyUSB0
pu baudrate 115200
pu bits 8
pu parity N
pu stopbits 1
pu rtscts No
EOF
minicom rockpi4
#ctrl-A Z for help
#ctrl-A X to exit
Issues and PR's are welcome. Please note that the license is CC0-1.0,
meaning that everything you contribute will become public domain.
I use Ubuntu Linux, 24.04.2 LTS at the moment. Other Linux distros
should work (with some tweaks), but are not tested.
The bin/mkimage program included in the repo, used by
set_serverip, is built on my PC. It will work for most Linux
distros, but if not, you must build u-boot locally as described in
Rebuild sd.img.
You may want to set $ROCK_WORKSPACE to a non-temp directory.
Source archives must be downloaded (by you).
./admin.sh versions
linux-6.15.6 (archive missing!)
busybox-1.36.1 (/home/uablrek/archive/busybox-1.36.1.tar.bz2)
atftp-0.8.0 (/home/uablrek/Downloads/atftp-0.8.0.tar.gz)
u-boot-2025.07 (/home/uablrek/Downloads/u-boot-2025.07.tar.gz)
trusted-firmware-a-lts-v2.12.4 (/home/uablrek/Downloads/trusted-firmware-a-lts-v2.12.4.tar.gz)
If you only want to Rebuild sd.img you will not need the kernel nor busybox.
After research, and queries in forums, and many attempts, I have come to the conclusion that you can't use vanilla kernels from https://kernel.org/. The kernels must be patched to get all functionality for any Radxa Rock. The vanilla kernels do boot though, but I can't get graphics to work, and I haven't even tried USB, sound, video, wifi, etc. The serial console and (wired) ethernet works, so you can build and test (and if your use-case is some kind of network server, you are good to go).
First download the source archives:
./admin.sh versions # check
eval $(./admin.sh versions --brief) # set them in your shell
curl -L --output-dir $HOME/Downloads -O https://cdn.kernel.org/pub/linux/kernel/v6.x/$ver_kernel.tar.xz
curl -L --output-dir $HOME/Downloads -O https://busybox.net/downloads/$ver_busybox.tar.bz2
./admin.sh versions # check again
With defaults:
./admin.sh kernel_build # (will unpack to $KERNELDIR)
./admin.sh busybox_build
./admin.sh initrd_build initrd/default
#initrd/default/tar - | tar t # To see contents of initrd
./admin.sh tftp_setup # (assuming atftp is used)
# boot!
If everything goes well, you will get a shell as root on the serial
console, and you can telnet to the board (no passwd).
Usually testing kernels includes many rebuild+restart cycles, so you want them to be fast. Here are some convenient settings:
eval $(./admin.sh env | grep WS=)
export __pxe_file=<your 01-f6-0b-6e-84-77-ec> # Limit the tftp search
export __tftp_setup=yes # Auto-update tftpd on kernel-build
export INITRD_OVL="initrd/default" # Auto-update initrd on kernel-build
export KCFG_BACKUP=$WS/saved-configs # Save kernel configs
alias admin=$PWD/admin.sh
alias cdws="cd $WS"
alias lscfg="ls $KCFG_BACKUP"
Now, to test a new kernel setting, just do:
admin kernel-build --menuconfig
# Reset your board, and watch the console...
If you mess up (and you will), then restore a working config with:
lscfg # Pick some working config
admin kernel-build --menuconfig --restoreconfig=<your-pick>
Radxa Rock 4se has no hardware clock, so the initrd tries to set the
date with rdate. First it
tries the DHCP serverid, which is you PC (normally), then
time.nist.gov if that fails. You may start a time-server with:
./admin.sh busybox_build --local
./admin.sh time-server # (requires sudo. Opens port 37)
The time-zone is specified in initrd/default/root/etc/env, which you
may override with --env= to "initrd_build". The timezone database is
NOT available! Meaning settings like "Europe/Stockholm" will not
work. You must set TZ the posix way.
Example:
man 3 tzset
export TZ=CET-1CEST-2,M3.5.0,M10.5.0/3 # (the default)