This page provides information for developers who need to investigate a problem with a development kit and want to diagnose it. It contains some useful starting points for investigation and instructions for performing tasks that may be needed to help with testing.

Installing the SOM

If the SOM is not installed or has been removed, follow these instructions to install it.

  1. Power board without SOM via USB-C.
  2. Check the voltages.
The voltage points to measure

The voltage points to measure (click to enlarge)

Point Voltage
5VSOM 5.0V
3V3 3.3V
3V3P ~0(without SOM)

Each voltage is measured against ground (green circle in above image).

  1. Plug in the SOM.

Attaching a USB to Serial Adapter

  1. Solder in the UART debug plug
  2. Attach USB to Serial Adapter
UART pinout (click to enlarge)

UART pinout

PIN Color
1 black
2 n/c
3 n/c
4 green
5 white
6 n/c

PIN 1 is the one closest to the volume button while PIN 6 is the one closest to the power button.

Booting via nfsroot

The SOM comes with a pre-flashed u-boot so you can connect the USB-to-UART-Debug cable and boot the device. Breaking into uboot you can boot using a nfsroot filesystem via

setenv nfsrootboot "setenv bootargs ${args_common} debug root=/dev/nfs ip=:::::eth0:dhcp nfsrootdebug nfsroot=<nfsserverip>:<nfsrootpath>,v3,tcp; dhcp ${loadaddr} Image-librem5-devkit; dhcp ${fdt_addr} librem5-devkit.dtb; booti ${loadaddr} - ${fdt_addr}"
setenv bootcmd run nfsrootboot

You need to fill in nfsrootpath and nfsserverip above. At nfsrootpath there needs to be a armhf or arm64 root filesystem which you can e.g. create via Debian’s deboostrap.

For that to work the BOOT MODE switch needs to be set to eMMC (instead of USB).

Installing a Minimal Linux on the eMMC

You can use dd to copy a pre-built image onto the eMMC or you can just use debootstrap to create one from scratch. This can be useful if you don’t want that many services starting up by default:

e2fsck /dev/mmcblk0p2
mount /dev/mmcblk0p2 /mnt
debootstrap --arch=arm64 buster /mnt

Back in u-boot we can switch to using the rootfs on the eMMC then (we’re still pulling kernel and device tree via tftp though:

setenv emmcboot "setenv bootargs ${args_common} debug root=/dev/mmcblk0p2; dhcp ${loadaddr} Image-librem5-devkit; dhcp ${fdt_addr} librem5-devkit.dtb; booti ${loadaddr} - ${fdt_addr}"

Flashing u-boot

From u-boot using tftp

You must have a tftp server setup for this:

setenv ipaddr <tftp server ip>
setenv serverip <target ip addr>
tftp 0x43000000 u-boot-devkit-recovery.imx
mmc write 0x43000000 0x42 0x800

From the kernel command line

Download the u-boot binary u-boot-devkit-recovery.imx:

dd if=u-boot-devkit-recovery.imx of=/dev/mmcblk0 bs=1024 seek=33

Reflashing the RS9116

By default no rsi* modules get loaded. The modules without firmware are in “/lib/modules/<kernel:sub:ver>/drivers/net/wireless/rsi” . The createinitramfs script above adds the rsi firmware and reflash modules in “/usr/src”.

There is a convenience script “” that will perform the necessary steps. What the script does is it backs up the rsi modules in /lib/modules, copies the firmware into lib firmware and the modprobes the rsi flashing modules. It replaces the original modules when it’s done.

Run the script on the target to reflash.:


Creating a Test initramfs

Download the latest image and kernel

Download the latest kernel and RS9116 out of tree modules.:

./scripts/ -k

Extract the kernel

The kernel needs to be extracted from the deb for the SDP boot.:


Build the test filesystem tarball

This will create a minimal debian rootfs tarball to be used to create an initramfs. If you need additional packages you can add them to the packages variable in the script.:


Create the initramfs

This will take the tarball created above and customize it to be able to flash the RS9116 module and also adds some test scripts.:

./scripts/ -t build/test_rootfs.tgz -o files/test_initramfs.img

You can include a locally generated kernel, modules and devicetree as well.:

./scripts/ -t build/test_rootfs.tgz -o files/test_initramfs.img -i <path to kernel>

Boot the initramfs

The initramfs can be booted on a board with an empty eMMC for testing and RS9116 flashing. Ensure the boot mode switch is switched to USB boot. Run the command below and then plug in the USB C port of the devkit.:

sudo uuu uuu_scripts/test_librem5.lst

RS9116 normal operation

To use the RS9116 without flashing just load the modules by hand.:

root@pureos-test:~# modprobe rsi_sdio