Add script to auto-set local time on reboot/daily with timedatectl

[jezdez]

Hey, so maybe I'm doing this wrong, but I wondered how to use the RV3028 to have my Raspi auto-set the time on boot using the RTC and also handle the case in which it doesn't have network connection to an optionally configured NTP server.

Here's the script I use for this (via /etc/crontab), does that make any sense?

#!/usr/bin/env python3
"""
A script to run on reboot to automatically set the system time to
the RTC time. Will disable Automatic time synchronization while running
(if enabled) and re-enable it again. This is to ensure that setting from RTC
works without network connection.

Add to the system crontab:

$ sudo nano /etc/crontab

And then add:

@daily root python3 /path/to/timedatectl-set-time-from-rtc.py

(c) Jannis Leidel 2019
"""
import time
from subprocess import run

import rv3028

TIMEDATECTL = "/usr/bin/timedatectl"

# Create RV3028 instance
rtc = rv3028.RV3028()

# Switches RTC to backup battery if VCC goes below 2V
# Other settings: 'switchover_disabled', 'direct_switching_mode', 'standby_mode'
rtc.set_battery_switchover('level_switching_mode')

rtc_time = rtc.get_time_and_date()
iso_rtc_time = rtc_time.isoformat(" ")
print("The RTC time is: {}".format(iso_rtc_time))

# Disabling NTP now so we can set the time manually
# in case network connection isn't there right now
timedatectl_output = run([TIMEDATECTL], capture_output=True)
ntp_enabled = b"NTP service: active" in timedatectl_output.stdout
if ntp_enabled:
    run([TIMEDATECTL, "set-ntp", "false"])

time.sleep(1)

try:
    # run timedatectl set-time with the time returned from the RTC
    # The time may be specified in the format "2012-10-30 18:17:16".
    run([TIMEDATECTL, "set-time", iso_rtc_time])
finally:
    print("Successfully set local time using the RV3028.")
    # definitely re-enable NTP in case something goes wrong with setting
    # the time.
    if ntp_enabled:
        run([TIMEDATECTL, "set-ntp", "true"])

[Gadgetoid]

This seems sensible to me. Is it working for you?

It wont handle your ntp case, but you might have some luck configuring the rtc-rv3028 kernel module to handle this. I'd totally forgotten that I'd submitted an upstream patch for battery switchover support, but just noticed that the module is available on my Pi 4 with kernel 4.19.58.

See - https://github.com/raspberrypi/linux/blob/8222f38b1ceadd0642d49812fd34a3a6cb00e264/arch/arm/boot/dts/overlays/i2c-rtc-gpio-overlay.dts

Something like: dtoveray=i2c-rtc-gpio-overlay:rc3028,backup-switchover-mode=1

[jezdez]

Woah! I didn't realize there is a kernel module to do that. The script works for me so far, but I would probably accept a bit of drift in favor of a kernel module.

That would require to add rtc-rv3028 to /etc/modules right? Never done this before, any chance you could update the docs how to do that?

[Gadgetoid]

See above regarding the dtoverlay line which you should add to /boot/config.txt- this makes sure the module is configured correctly. I don't have hardware with me to double-check that it works, but it should.

IIRC there are also tools for reading the RTC - timedatectl and hwclock as mentioned here - https://developer.toradex.com/knowledge-base/how-to-use-the-real-time-clock-in-linux

I've done the whole rounds of figuring this stuff out, raising the patch for the kernel module, and forgetting it all again. Story of my life!