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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.

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
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'
@vinnyt
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vinnyt commented Jul 26, 2021

Thank you for this. Is there another flag I would need to compile with to be able to run resize2fs so I can expand the filesystem on the pi when it is running?

@martin-niklasson
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martin-niklasson commented Jul 26, 2021

Thank you for this. Is there another flag I would need to compile with to be able to run resize2fs so I can expand the filesystem on the pi when it is running?

No. You cannot resize the partition on the running machine itself. This needs to be done by mounting the SD card or the eMMC flash on a separate Linux machine. DFRobot's wiki gives detailed instructions on how to expand the partition.

Otherwise, this should be it. You will have a running router with WAN, LAN and the web interface, so any software packages you need after this can easily be installed from the web interface.

@flipyou
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flipyou commented Aug 5, 2021

I followed this with rc3 and rc4, works great! only issue I've had is eth0 ends up dropping to 100Mbps intermittently unless you use ethtool to disable eee.

@ripplecart
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ripplecart commented Aug 16, 2021

Thanks for the write-up @martin-niklasson! Tried it out with rc4 and it worked fine. Only thing is the orange LED does not light up on the LAN (RTL8111) port but the port itself works fine (green LED works as normal).

@martin-niklasson
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martin-niklasson commented Aug 16, 2021

@ripplecart

Happy it worked for you. I noticed the missing orange LED myself, but both ethtool on the router and the switch on the other end report 1000Mbit/s full duplex, so I didn't dig deeper ;-)

@neetopia
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neetopia commented Nov 28, 2021

worth mentioning that you can expand the rootfs partition size with image builder as well, instead of expanding with fdisk afterwards.

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