Raspberry Pi RTC clock configuration and systemd service

[paul-onolan]

I'm trying to get Ubuntu Core 20.04 working with a DS3132 RTC on a Raspberry Pi 3/4. Have done this without difficulty using RaspiOS in the past. I've got it detecting the hardware but systemd service is not working as expected. So far the most useful things I've found are:


https://spellfoundry.com/docs/setting-up-the-real-time-clock-on-raspbian-jessie-or-stretch/
https://www.raspberrypi.org/forums/viewtopic.php?p=1320052
https://www.willhughes.name/post/ds3231_raspi3/#an-2

First contains instructions on installing i2c-tools, which are not included in Ubuntu, and on editing /lib/udev/hwclock-set. The systemd unit in the second link doesn't work (and the hardware isn't detected). With that in the 3rd link the hardware is detected and readable but the systemd service doesn't work. Pointers / advice welcome. Thanks.

My /boot/config.sys


dtparam=i2c_arm=on
dtoverlay=i2c-rtc,ds3231


Modprobe results

ubuntu@pi4:~$ sudo modprobe rtc-ds1307
ubuntu@pi4:~$ sudo modprobe rtc-ds3231
modprobe: FATAL: Module rtc-ds3231 not found in directory /lib/modules/5.4.0-1032-rasp


Not sure how to interpret this. There's a ds3232 driver in both /lib/modules/5.4.0-1028-raspi/kernel/drivers/rtc and /lib/modules/5.4.0-1032-raspi/kernel/drivers/rtc :confused:

[ActionParsnip]

Use TAB to autocomplete the module names. Stop after 'rtc' and press TAB to see what is available

[paul-onolan]

ubuntu@ubuntu:/lib/modules/5.4.0-1032-raspi/kernel/drivers/rtc$ sudo modprobe rtc-
rtc-88pm80x rtc-cadence rtc-ds1307 rtc-ds1742 rtc-isl12022 rtc-max6900 rtc-mcp795 rtc-pcf8523 rtc-rp5c01 rtc-rx8025 rtc-tps80031
rtc-88pm860x rtc-cpcap rtc-ds1343 rtc-ds2404 rtc-isl1208 rtc-max6902 rtc-msm6242 rtc-pcf85363 rtc-rs5c348 rtc-rx8581 rtc-v3020
rtc-ab3100 rtc-cros-ec rtc-ds1347 rtc-ds3232 rtc-lp8788 rtc-max6916 rtc-mt6397 rtc-pcf8563 rtc-rs5c372 rtc-s35390a rtc-wm831x
rtc-ab-b5ze-s3 rtc-da9052 rtc-ds1374 rtc-efi rtc-m41t80 rtc-max77686 rtc-palmas rtc-pcf8583 rtc-rv3028 rtc-s5m rtc-wm8350
rtc-ab-eoz9 rtc-da9055 rtc-ds1390 rtc-em3027 rtc-m41t93 rtc-max8907 rtc-pcap rtc-pl030 rtc-rv3029c2 rtc-sd3078 rtc-x1205
rtc-abx80x rtc-da9063 rtc-ds1511 rtc-fm3130 rtc-m41t94 rtc-max8925 rtc-pcf2123 rtc-r7301 rtc-rv8803 rtc-snvs rtc-zynqmp
rtc-as3722 rtc-ds1286 rtc-ds1553 rtc-ftrtc010 rtc-m48t35 rtc-max8997 rtc-pcf2127 rtc-r9701 rtc-rx4581 rtc-stk17ta8
rtc-bq32k rtc-ds1302 rtc-ds1672 rtc-hid-sensor-time rtc-m48t59 rtc-max8998 rtc-pcf50633 rtc-rc5t583 rtc-rx6110 rtc-tps6586x
rtc-bq4802 rtc-ds1305 rtc-ds1685 rtc-hym8563 rtc-m48t86 rtc-mc13xxx rtc-pcf85063 rtc-rk808 rtc-rx8010 rtc-tps65910


I've already looked at this. Not clear what you're suggesting. That I should use rtc-ds3232? As far as I can ascertain (https://www.maximintegrated.com/en/design/technical-documents/app-notes/5/5143.html) it's "similar" to the ds3132.

[paul-onolan]

I checked a raspbian installation and found it also had a ds3232 driver, not a ds3132. Strange to find almost no references online to the ds3232 -- just this one (https://www.raspberrypi.org/forums/viewtopic.php?t=16218&start=100) from someone else having systemd issues. And this (https://www.raspberrypi.org/forums/viewtopic.php?f=131&t=285762&p=1729223&hilit=ubuntu+rtc#p1729223) from someone else unable to get things working with Ubuntu 20.04.

It doesn't seem to matter whether the device is identified in /boot/config.sys as a ds3132 or ds3232. The hwclock-start.service with
ExecStartPre=/bin/bash -c "echo ds1307 0x68 | tee /sys/class/i2c-adapter/i2c-1/new_device" seems to cause it to be recognized as a ds1307. I'm not clear whether I need to have something loaded in /etc/modules or not. Currently I don't and
sudo timedatectl status shows that the system clock is synchronized.

I'd still like to find clear and current instructions on getting things working, with explanations. For Ubuntu. With SystemD. A lot of what's findable online seems raspbian-specific and out of date. I'm not even sure I need to run hwclock-start at all (I've read that systemd-timesyncd service, which is running, will update the RTC automatically); still poking at this.