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How to make an up-to-date OpenWRT image for loading onto a Raspberry Pi Compute Module 4 with a DFRobot Router Carrier Board.
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How-To.md

The background is that the default OpenWRT image for Raspberry Pi lacks drivers for the LAN port (RTL8111) on the DFRobot board. DFRobot provide an image, but that one is made from a quite old daily snapshot of OpenWRT which is not entirely stable. Also, it is better to know how to fish than be given a fish.

DFRobot's page about the router board:
https://wiki.dfrobot.com/Compute_Module_4_IoT_Router_Board_Mini_SKU_DFR0767

OpenWRT main page:
https://openwrt.org/

You are expected to have some general knowledge on Linux and OpenWRT. The instructions for flashing the resulting firmware image are presented on DFRobot's page.

We will use the OpenWRT image builder. This is a quite nifty tool that can generate a firmware image with some additional packages not present in the default image. It is not a cross-compiler, but rather takes already compiled OpenWRT packages and creates a new firmware image.

Download the latest image builder for Raspberry Pi from OpenWRT. At the time of writing, this is RC3. It is under target bcm27xx/bcm2711
https://downloads.openwrt.org/releases/21.02.0-rc3/targets/bcm27xx/bcm2711/

I built it on a Debian VirtualBox machine, but pretty much any Linux system would do. You first need to install some Linux tools. These are the tools for Debian/Ubuntu:

root@debian:~# apt install build-essential libncurses5-dev libncursesw5-dev zlib1g-dev gawk git gettext libssl-dev xsltproc rsync wget unzip python

For other Linux distros, see the Prerequisites section here:
https://openwrt.org/docs/guide-user/additional-software/imagebuilder

Unpack your image builder:

martin@debian:~# tar Jxf openwrt-imagebuilder-21.02.0-rc3-bcm27xx-bcm2711.Linux-x86_64.tar.xz
martin@debian:~# cd openwrt-imagebuilder-21.02.0-rc3-bcm27xx-bcm2711.Linux-x86_64/

For some reason, you will need a /etc/config/network file in your image, or your LAN network will not come up.
https://openwrt.org/docs/guide-user/additional-software/imagebuilder#files_variable

martin@debian:~# mkdir -p files/etc/config

Put below file in files/etc/config/network

We need to build the image with 3 extra modules:

Go!

martin@debian:~# make image PROFILE="rpi-4" PACKAGES="luci kmod-r8169 kmod-usb-dwc2" FILES=files/

The built image(s) will end up at:
bin/targets/bcm27xx/bcm2711/

The “default” one to use would be:
openwrt-21.02.0-rc3-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

After you gunzip that file, you can follow the instructions from DFRobot for installation. Or you can use “dd” directly on Linux, instead of Rufus:

martin@debian:~# dd if=/home/martin/openwrt/openwrt-21.02.0-rc3-bcm27xx-bcm2711-rpi-4-ext4-factory.img of=/dev/sdb
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network
config interface 'loopback'
option proto 'static'
option ipaddr '127.0.0.1'
option netmask '255.0.0.0'
option device 'lo'
config globals 'globals'
option ula_prefix 'fdff:ac50:10da::/48'
config interface 'wan'
option proto 'dhcp'
option device 'eth0'
config interface 'lan'
option proto 'static'
option ipaddr '192.168.1.1'
option netmask '255.255.255.0'
option device 'eth1'
@ddschmitz
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ddschmitz commented Aug 30, 2025

Has anyone managed to get a recent OpenWRT image to build and run using this guide? Following the guide listed here as well as this one, I haven't been able to get anything to run on the DFRobot board.

The only thing I have managed to get to run is the image posted on their websites wiki but only after following the directions on this forum post. It seems as though they was a revision with the CM4 or an update in some firmware, and you need to just place the new files in the boot directory. Doing this I was able to get the board to boot and work. But I can't figure out how to get it to work with a newer build of OpenWRT.

@rudelm
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rudelm commented Aug 31, 2025

hey @ddschmitz I've found a workaround after my last comment and totally forgot this gist. For 23.05.0 onwords you have to only select kmod-usb-dwc2. To quote from my blog:

Everything else was either part of the package list or part of the Raspberry Pi base image (looking at bcm27xx-userland).

Maybe that helps. I've sold mine a few months ago and switched to a Unifi gateway instead, since the upgrade procedure was annoying. I suggest you try to create the bootimage like I've described and select only the kmod-usb-dwc2 package. Once the image is flashed, put the mentioned .dat and .elf firmware files into the /boot partition like it's recommended in the dfroboto forum. Hope that helps!

@ddschmitz
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ddschmitz commented Aug 31, 2025

@rudelm I appreciate the response on this really old gist haha!

While I don't think I followed your exact steps, it did lead me to try out the online firmware selector which I have heard about in the past but never tried. I gave this a shot following the steps mentioned in your blog and I was finally able to get a 24.X version written to the SD card that let me login to the web ui. Thank you! With the comfort of knowing I got an updated version working, I might see how my manual build compares to this online one and see if I can figure out what I'm doing wrong.

@rudelm
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rudelm commented Aug 31, 2025

Cool glad it worked out for you. I never got the local builds really working except for version 22 of OpenWRT. But even then the online firmware builder was working way better in my experience.

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