SPI Communication and Wi-Fi Module Issues on Axon with ESP32-S3 (Master-Slave Setup)

General
1

Hello Vicharak Team,

I’ve been trying to establish an SPI-based master-slave communication between the Axon board (Master) and an ESP32-S3 (Slave). While doing so, I’ve faced the following issues that I’d appreciate some help with.

1. SPI Interface Setup (spidev issues)

I was following the standard procedure to enable spidev on Axon (running the custom Linux image). I made the necessary changes including:

  • Overlays for SPI (spidev2.dtbo)

  • Updating U-Boot using:

    sudo u-boot-update -k Image-6.1.75-axon -r initrd.img-6.1.75-axon -d rk3588-axon-linux-6.1.75-axon.dtb -o spidev2.dtbo

Despite that, the SPI device /dev/spidev* was not appearing. I attempted to manually load the device:

echo spidev | sudo tee /sys/class/spi_master/spi2/device/modalias

But received:

tee: /sys/class/spi_master/spi2/device/modalias: Permission denied

Also, modprobe spidev didn’t help even though the spidev.ko module was available. This suggests a permission or overlay-related issue. I also confirmed configfs is already mounted:

sudo mount -t configfs none /sys/kernel/config
mount: /sys/kernel/config: none already mounted or mount point busy.

2. Post-reboot Wi-Fi Module Disappearance

After making the SPI-related changes and executing:

sudo reboot

The Wi-Fi module stopped working. On reboot, the system could no longer detect any wireless interfaces. lshw was not available initially, and installing it failed due to permission errors:

E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)

Attempting to reinstall or check firmware also didn’t help:

sudo apt download firmware-misc-nonfree

But it resulted in:

E: Unable to locate package firmware-misc-nonfree

No wireless interfaces listed

Running:

iwconfig

gave:

lo        no wireless extensions.
eth0      no wireless extensions.

Log Snippets for Reference

SPI Overlay Attempt:

P: Checking for EXTLINUX directory... found.
P: Writing config for Image-6.1.75-axon...
P: Updating /boot

After sudo reboot — Wi-Fi Gone:

No Wi-Fi module/interface visible via `iwconfig` or `ip a`

Failed lshw install:

bash: lshw: command not found
sudo apt install lshw
E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)

My Environment:

  • Axon board with Linux kernel 6.1.75-axon
  • ESP32-S3 connected via SPI (slave)
  • Working on SPI Master-Slave protocol for stepper motor control
  • SSH and serial access available
  • Wi-Fi previously functional before SPI config and reboot

What I Need Help With:

  1. Why isn’t spidev getting properly registered even after overlay updates?
  2. What could cause the Wi-Fi module to disappear after SPI overlay changes and reboot?
  3. How can I safely restore wireless connectivity without reflashing the whole image?
  4. Any suggestion for debugging or resetting the network interface?

Let me know if you need any more logs or output. I really appreciate your time and help.

Thanks,
Himani Netha.

2

Here, below Answer will solve your issues.

  1. Overlay is not enabled properly, as it was not the correct way to enable and disable for vicharak-board.

  2. We also need to look into it, what does it affect to disappearance of the Wi-Fi firmware. Could you send spio.dtbo overlays with source as well.

  3. By installing kernel and firmware, all is set to be done again.

     sudo apt update
 sudo apt install linux-image-6.1.75-axon
 sudo apt install vicharak-firmware

  4. For Debugging WiFi,

  • You can see Kernel Log

    dmesg | grep -i wlan

  • Check existence of Firmware

    ls -l /lib/firmware/rtlbt/rtl8852*

    Solution :

    sudo apt install vicharak-firmware