🛠 Activer I2C, SPI et UART sur le BPI-CM4 : env.txt ou armbianEnv.txt

Objectives

On the BPI-CM4, not all buses on the 26-pin header are active by default, and the mechanism depends on the image: vendor images (BSP 4.9) use /boot/env.txt with an overlays="..." line and .dtbo files in /boot/overlays/, while Armbian (mainline kernel ≥ 6.4) uses /boot/armbianEnv.txt and armbian-config. You will enable I2C1 (GPIOX_17/18), SPI_A (GPIOX_8 to 11), and UART_B (GPIOX_6/7), then verify each bus. Note: the vendor's WiringPi/RPi.GPIO fork only works on the BSP; on mainline, you work with i2c-tools, spidev, and libgpiod.

Hardware

• BPI-CM4 + BPI-CM4IO carrier board
• Vendor image Debian 10 / Ubuntu 20.04 or Armbian bananapicm4io
• Optional: level shifter — the VDDIO_C rail of the GPIOX banks is configured for 1.8 V or 3.3 V depending on the setup; the wiki never guarantees 5 V

Complete Code

# --- Image vendor BSP (noyau 4.9) ---
sudo sed -i 's/^overlays=.*/overlays="i2c2 spi0 uart1 wifi_bt_rtl8822cs"/' /boot/env.txt
ls /boot/overlays/          # vérifier les noms de .dtbo disponibles
sudo reboot

# --- Armbian (mainline) ---
grep -E '^(overlay_prefix|overlays)' /boot/armbianEnv.txt
sudo armbian-config         # System > Hardware > cocher i2c / spi / uart
sudo reboot

# --- Vérification des trois bus ---
sudo apt install -y i2c-tools gpiod
i2cdetect -l                          # lister les contrôleurs
ls -l /sys/class/i2c-dev/ | cat       # mapper /dev/i2c-N -> nom du contrôleur
ls /dev/spidev* 2>/dev/null
gpioinfo | grep -i -e spi -e uart     # broches revendiquées par un pilote

Expected Verification

After reboot: one additional /dev/i2c-N corresponding to the header controller (on mainline, the &i2c2 controller for pins GPIOX_17/18 has no alias — its number depends on enumeration, hence reading /sys/class/i2c-dev/), a /dev/spidevX.Y for SPI_A, and UART_B available on a ttyAMLx/ttySx. The pins used by a bus appear as "used" in gpioinfo.

Common Errors

• Modifying /boot/config.txt as on a Raspberry Pi: it does not exist here; it is env.txt (vendor) or armbianEnv.txt (Armbian).
• Relying on Dangku's WiringPi under Armbian: it requires the 4.9 BSP kernel and fails on mainline.
• Hardcoding the /dev/i2c-2 number in a script: on mainline, the header bus is not aliased, so the number may change — always resolve it via /sys/class/i2c-dev/.
• Confusing it with the carrier's internal buses: the i2c0 alias points to the camera controller, i2c1 to the DSI touch bus — not to the header.
• Connecting a 5 V module without checking the actual level of the GPIOX bank (VDDIO_C rail 1.8/3.3 V).