Raspberry Pi Compute Module 4 Board RTC (pcf85063a)

Hello everyone.

I’ve got a CM4 with the onboard Wi-Fi, loaded it with the official Canonical UC20 image.
It seems that I cannot get the RTC working on boot. But when I “load” the driver (modprobe rtc-pcf85063) manually and invoking the i2c new-device add, it works, and is detected in hwclock.

I can can confirm that I can do a i2c scan, and detect the RTC on Address 0x51 on i2c-11 (snappy.i2cdetect) as per datasheet/document of the Raspberry Pi CM4 Board.
What seems to be the problem with the dtoverlay?
I’ve tried everything mentioned here: https://www.raspberrypi.org/forums/viewtopic.php?t=293632
And still hitting a brick wall.
dmesg only states that two i2c muxes is added, nothing related to the RTC itself.

Do I have to wait for a kernel/update to fix this issue that I have? I have refreshed all my snaps, all up to date.


We’re discussing it with the kernel team for the whole day already :slight_smile:

If you follow my guide you will see /dev/rtc showing up but there is a “hwclock --hctosys” call missing in the whole setup … the github issue i linked has a udev rule you can put in place as a temporary hack in /etc/udev/rules.d that will then set your clock from the rtc during boot…