Configure Hardware

This section configures the I2C bus and real-time clock (RTC) on the device. The RTC steps below differ between the two variants — pick the tab that matches your device when you reach them:

FIBER (CM4)

Adds an RTC overlay for the external PCF85063A real-time clock chip.

FIBER Lite (Pi 5)

Skips the RTC overlay entirely — the Raspberry Pi 5 has a built-in RTC, so this step and its verification look different.

1. Install the I2C tools package for I2C bus diagnostics:

   sudo apt install -y i2c-tools

2. Configure the i2c-dev kernel module to load automatically at boot:

   echo 'i2c-dev' | sudo tee -a /etc/modules-load.d/i2c.conf > /dev/null

3. Add hardware configuration to the boot configuration file:

   FIBER (CM4)

   cat << EOF | sudo tee -a /boot/firmware/config.txt > /dev/null
   dtparam=i2c_arm=on
   dtparam=i2c_vc=on
   disable_poe_fan=1
   force_eeprom_read=0
   camera_auto_detect=0
   dtoverlay=i2c-rtc,pcf85063a,i2c_csi_dsi
   EOF

   tip

   This enables I2C interfaces, disables the PoE fan control, and configures the RTC overlay for the external PCF85063A RTC chip.

   FIBER Lite (Pi 5)

   cat << EOF | sudo tee -a /boot/firmware/config.txt > /dev/null
   dtparam=i2c_arm=on
   dtparam=i2c_vc=on
   disable_poe_fan=1
   force_eeprom_read=0
   camera_auto_detect=0
   EOF

   danger

   Do not add an external RTC overlay. FIBER (CM4) adds dtoverlay=i2c-rtc,pcf85063a,i2c_csi_dsi for an external PCF85063A real-time clock chip. Do not add this on FIBER Lite. The Raspberry Pi 5 has a native built-in RTC that registers automatically as rtc0 — the external overlay has no chip to talk to and only produces a harmless-but-noisy error -EREMOTEIO in the kernel log (see Troubleshooting in the sidebar if you hit this).

4. Reboot the system to apply the hardware configuration:

   sudo reboot

5. FIBER (CM4)

   Verify the I2C bus is accessible by scanning for devices:

   sudo i2cdetect -y 10

   tip

   You should see the RTC device listed on the I2C bus.

   FIBER Lite (Pi 5)

   There's no external RTC to scan for — the Pi 5's built-in RTC needs no verification step here.

6. Install additional utilities for hardware clock access:

   sudo apt install util-linux-extra

7. Verify the hardware clock is accessible:

   sudo hwclock -v