The Correct way to add a RTC

[fruit-uk]

Mm... indeed it does say that - and I missed it completely!

That section appears to set hwclock based on the current timezone time then immediately after
sets hwclock from system time.

It does seem rather odd to my small brain!

man hwclock on this wheeezy desktop says

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--systz
[snip]
This is an alternate option to --hctosys  that does not read the hardware clock, and may be used in system startup scripts for recent 2.6 kernels where you know the System Time contains the Hardware Clock time.

So why both?

Edit:
There is an explanation of why here https://lists.debian.org/debian-kernel/ ... 00207.html though I haven't checked for other links

[Al Fernandez]

Really useful post -- it's helped me a lot setting up a hardware clock based on bq32000. This chip can use a capacitor or a standard battery as backup supply. If you choose battery backup, you can set it up as a DS1307 by following instructions posted earlier on this thread.
If, like me, you go for a capacitor backup, you'll want to use the bq32k driver which supports trickle charging. Options are passed to the driver via the device tree and it took some trial an error to get everything right. I'm posting the detailed instructions here in case someone else wants to experiment with this chip.

Step 1: Enable i2c and install i2c tools as documented earlier on this thread. Check that your rtc is detected:

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pi@raspi ~ $ i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- 18 -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- 77                         

If at this point you get UU instead of 68, there’s a driver using the rtc. Check the output of lsmod -- you don’t need to load any rtc driver via /etc/modules.

Step 2: We’ll now create an overlay with support for bq32000 and we need a device tree compiler for that:

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pi@raspi ~ $ sudo apt-get install device-tree-compiler 	

Create a .dts file from i2c-rtc-overlay.dtb in /boot/overlays. Give the output file a new name to reflect support for bq32000:

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pi@raspi ~ $ sudo dtc -I dtb -O dts -o /tmp/i2c-rtc-bq32k-overlay.dts /boot/overlays/i2c-rtc-overlay.dtb

Now it's time to edit the .dts file. Follow the existing tree structure and paste this entry:

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bq32000@68 {
        compatible = "ti,bq32000";
        trickle-resistor-ohms = <1120>;
        reg = <0x68>;
};

For syntax and more available options check out this link.
The configuration above enables trickle charging. DO NOT enable trickle charging if using battery backup!
Next, convert the .dts file to .dtb:

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pi@raspi ~ $ sudo dtc -I dts -O dtb -o /boot/overlays/i2c-rtc-bq32k-overlay.dtb /tmp/i2c-rtc-bq32k-overlay.dts

Step 3: Get rid of fake-hwclock.

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pi@raspi ~ $ sudo apt-get remove fake-hwclock
pi@raspi ~ $ sudo update-rc.d -f fake-hwclock remove
pi@raspi ~ $ sudo rm /etc/fake-hwclock.data

Unplug the network cable and reboot. The system date will go back to Jan 1st 1970 00:00:00.

Step 4: Add "dtoverlay=i2c-rtc-bq32k,bq32000” to /boot/config.txt. Reboot and check that your rtc is accessible via hwclock.

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pi@raspi ~ $ sudo hwclock -r

Your system is now ready to get its time from the hardware clock. However, the rtc gets updated in the early stages of booting so it’ll end up on Jan 1st 1970 even when the Pi is connected to the internet and can get its time via ntp. A small change in hwclock-set will fix this:

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pi@raspi ~ $ sudo nano /lib/udev/hwclock-set

Comment the following three lines near the top of the script:

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#if [ -e /run/systemd/system ] ; then
#    exit 0
#fi

Update the hwclock manually:

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pi@raspi ~ $ sudo hwclock -w

Unplug the network cable and reboot. The time should now be correct on both the Pi and hwclock.
This is it. No need to use the hwclock.sh as mentioned earlier on this thread. In fact, on my system it just doesn't run, even when enabled in rc.d. I'm using the latest release of raspbian:

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pi@raspi ~ $ uname -a
Linux raspi 4.1.12+ #825 PREEMPT Fri Nov 6 17:53:21 GMT 2015 armv6l GNU/Linux

[gregsmith_to]

Al Fernandez, that looks exactly what I was looking for - I've been trying to sort through all the old info for hours - and I have the situation you describe where the time goes to Jan 1 1970 at powerup.
But I can't comment out the lines you specify since I don't have them, my /lib/udev/hwclock-set looks like the below (and the /sys/fs/cgroup directory appears to be empty... I commented out those 3 lines anyway, it made no difference. ). I'm using 2015-05-05-raspbian-wheezy fresh from the image.

I've enabled i2c and drivers in raspi-config, and added "dtoverlay=i2c-rtc,ds1307" to config.txt, and after that hwclock seems to work; I see the i2c_bcm2708 and rtc_ds1307 drivers in lsmod.

And then I've removed fake-hwclock etc. and I can't get it to read the rtc at powerup. In fact the first 'hwclock -r' after reboot now always says the rtc is corrupt, which was not the case before I removed fake-hwclock -- which makes me wonder if hwclock was actually reading fake-hwclock before. I can 'repair' it by setting the time and doing hwclock -w, and then hwclock -r works but then it's corrupt again on reboot (even if I don't remove the power).

It would be nice to try i2cdetect on my machine, I installed it and it just points out that /dev/i2c(something) is not present. There is indeed no /dev/i2c*. I've been assuming this was using a now-obsolete dev interface - but you're the first really recent post I've seen which is using i2cdetect, so I guess that's not the case. Rather baffled.

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#!/bin/sh
# Reset the System Clock to UTC if the hardware clock from which it
# was copied by the kernel was in localtime.

dev=$1

if [ -e /sys/fs/cgroup/systemd ] ; then
    exit 0
fi

if [ -f /etc/default/rcS ] ; then
    . /etc/default/rcS
fi

# These defaults are user-overridable in /etc/default/hwclock
BADYEAR=no
HWCLOCKACCESS=yes
HWCLOCKPARS=
HCTOSYS_DEVICE=rtc0
if [ -f /etc/default/hwclock ] ; then
    . /etc/default/hwclock
fi

if [ yes = "$BADYEAR" ] ; then
    /sbin/hwclock --rtc=$dev --systz --badyear
else
    /sbin/hwclock --rtc=$dev --systz
fi

[nospam2000]

After this, in the boottime parameters and bootargs of RaspberryPi, add the following argument:
rtc.i2c=pcf8563,1,0x68

Which kernel version are you using? I can't find the code which reads the "rtc.i2c" parameter in the kernel source of version "raspberrypi 4.1.11-v7+". I think it has been replaced with the devicetree options and is no longer existent.

Michael

[dontjinxit123]

Hi,

Really useful post thanks, I've consolidated into a list of instructions to save darting about all over the net....
----------------------

Enable the Kernel modules:-

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sudo nano /etc/modules

Add the following:-

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i2c-bcm2708 
i2c-dev

Save

Remove them from the blacklist by adding #

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sudo nano /etc/modprobe.d/raspi-blacklist.conf

Make sure you see:-

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#blacklist spi-bcm2708
#blacklist i2c-bcm2708

Save & reboot

Install the i2c tools for testing:-

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sudo apt-get install i2c-tools

Run a test to see if all is well... for a rev 1 pi :

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sudo i2cdetect -y 0

or for later, rev 2 Pi's :

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sudo i2cdetect -y 1

You should see something like:-

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pi@raspberrypi ~ $ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- UU -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

load up the RTC module and test by running :

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sudo modprobe rtc-ds1307

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sudo bash

For older rev 1 pi's :

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echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-0/new_device
exit

or for newer, rev 2 pi's :

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echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device
exit

Check the clock is running and can be read:-

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sudo hwclock -r

Make sure pi is connected to internet so correct time is set....

Write the current system time to the hardware clock:-

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sudo hwclock -w

Add the clock to the Kernel modules:-

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sudo nano /etc/modules

Add:-

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rtc-ds1307

Save

Reconfigure the hwclock.sh script:-

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sudo nano /etc/init.d/hwclock.sh

After "unset TZ" at top add..

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init_rtc_device()
{
  [ -e /dev/rtc0 ] && return 0;

  # load i2c and RTC kernel modules
  modprobe i2c-dev
  modprobe rtc-ds1307

  # iterate over every i2c bus as we're supporting Raspberry Pi rev. 1 and 2
  # (different I2C busses on GPIO header!)
  for bus in $(ls -d /sys/bus/i2c/devices/i2c-*);
  do
    echo ds1307 0x68 >> $bus/new_device;
    if [ -e /dev/rtc0 ];
    then
      log_action_msg "RTC found on bus `cat $bus/name`";
      break; # RTC found, bail out of the loop
    else
      echo 0x68 >> $bus/delete_device
    fi
  done
}

Find "case "$1" in" and edit as per:-

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case "$1" in
	start)
	    # If the admin deleted the hwclock config, create a blank
	    # template with the defaults.
	    if [ -w /etc ] && [ ! -f /etc/adjtime ] && [ ! -e /etc/adjtime ]; then
	        printf "0.0 0 0.0\n0\nUTC" > /etc/adjtime
	    fi
		init_rtc_device

            # Raspberry Pi doesn't have udev detectable RTC
	    #if [ -d /run/udev ] || [ -d /dev/.udev ]; then
		#return 0
	    #fi

Save

Update the real HW Clock and remove the fake:-

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sudo update-rc.d hwclock.sh enable
sudo update-rc.d fake-hwclock remove

Now that real hardware clock is installed, remove the fake package and it’s crons:-

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sudo apt-get remove fake-hwclock
sudo rm /etc/cron.hourly/fake-hwclock
sudo rm /etc/init.d/fake-hwclock

Reboot

After addng init_rtc_device(), i get this error.

hwclock: Cannot access the Hardware Clock via any known method.
hwclock: Use the --debug option to see the details of our search for an access method.

why?

[GTR2Fan]

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hwclock -r

...won't work.

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sudo hwclock -r

...should work.

[gordon77]

I just did the following and it appears to work....

1. Edit the file /boot/config.txt and add the following:
dtoverlay=i2c-rtc,ds1307

2. Edit the file /lib/udev/hwclock-set, commenting out the three lines:
#if [ -e /run/systemd/system ] ; then
# exit 0
#fi

Then set the clock, then
Sudo hwclock -w
Sudo hwclock -r

[ingeniapp]

Hi,

Why not run the hwcloch.sh script in runlevel S?
I see that when OS (raspbian) start runlevel is unknown. I typed "runlevel" and returns "unknown". I've added some echo lines in hwclock.sh but I have clearly this script not run. Only works if I call it in rc.local script (works with "sudo /etc/init.d/hwclock.sh start" and "sudo /etc/init.d/rcS")

How it works to you to launch scripts are stored in the runlevel S?

Thanks

[shadowfxd]

I have tried everything in the OP and I keep getting this error:

hwclock: The Hardware Clock registers contain values that are either invalid (e.g. 50th day of month) or beyond the range we can handle (e.g. Year 2095).

with two different RTC. If I do "sudo hwclock -w" it resyncs the RTC, but won't do on fresh boot or reboot. Can anyone help?

[m1geo]

Hello all.

I, too, am getting the error:

george@camera:~ $ sudo hwclock -r --debug
[sudo] password for george:
hwclock from util-linux 2.25.2
Using the /dev interface to the clock.
Last drift adjustment done at 1472774297 seconds after 1969
Last calibration done at 1472774297 seconds after 1969
Hardware clock is on UTC time
Assuming hardware clock is kept in UTC time.
Waiting for clock tick...
/dev/rtc does not have interrupt functions. Waiting in loop for time from /dev/rtc to change
...got clock tick
Time read from Hardware Clock: 2066/01/01 00:00:36
Invalid values in hardware clock: 2066/01/01 00:00:36
hwclock: The Hardware Clock registers contain values that are either invalid (e.g. 50th day of month) or beyond the range we can handle (e.g. Year 2095).

What I've got:

Latest Rasbian image `Raspbian GNU/Linux 8 (jessie)`.

george@camera:~ $ uname -a
Linux camera 4.4.13-v7+ #894 SMP Mon Jun 13 13:13:27 BST 2016 armv7l GNU/Linux
george@camera:~ $

What I've done:

- DS3231 correctly fitted (I had it working once, briefly, but it stopped on reboot).
- Added "dtoverlay=i2c-rtc,ds3231" to /boot/config.txt
- Commented out the 3 udev lines from /etc/init.d/hwclock.sh
- Disabled fake-hwclock, and enable hwclock.sh (ran the exact commands from allfox's post, they all completed succesfully)
- Also deleted /etc/fake-hwclock.data
- Rebooted (several times)

What I have NOT done:

- included `init_rtc_device` into `/etc/init.d/hwclock.sh` (not used as instructions from allfox didn't say to)

Upon booting, the rtc0 device is found:

george@camera:~ $ dmesg | grep -i rtc
[ 3.010136] rtc-ds1307 1-0068: rtc core: registered ds3231 as rtc0
george@camera:~ $

When I checked the system date, I found that the Pi system time was 1 Jan 1970. The RTC was set correctly, so I used NTP to re-sync the system time, as follows.

george@camera:~ $ sudo service ntp stop
george@camera:~ $ sudo ntpd -gq -c /etc/ntp.conf
ntpd: time set +1472772209.221351s
george@camera:~ $ sudo service ntp start
george@camera:~ $ date
Fri 2 Sep 00:51:20 BST 2016
george@camera:~ $

I also added `tinker panic 0` which should stop NTP from worrying about very large (50 years) offsets in daemon mode. Setting the time with `--debug` went as follows:

george@camera:~ $ sudo hwclock -w --debug
hwclock from util-linux 2.25.2
Using the /dev interface to the clock.
Last drift adjustment done at 630 seconds after 1969
Last calibration done at 630 seconds after 1969
Hardware clock is on UTC time
Assuming hardware clock is kept in UTC time.
Waiting for clock tick...
/dev/rtc does not have interrupt functions. Waiting in loop for time from /dev/rtc to change
...got clock tick
Time read from Hardware Clock: 2066/01/01 00:25:20
Invalid values in hardware clock: 2066/01/01 00:25:20
missed it - 1472773728.725485 is too far past 1472773728.500000 (0.225485 > 0.001000)
1472773729.500000 is close enough to 1472773729.500000 (0.000000 < 0.002000)
Set RTC to 1472773729 (1472773728 + 1; refsystime = 1472773728.000000)
Setting Hardware Clock to 23:48:49 = 1472773729 seconds since 1969
ioctl(RTC_SET_TIME) was successful.
Not adjusting drift factor because the Hardware Clock previously contained garbage.
george@camera:~ $

It now reads back correctly:

george@camera:~ $ sudo hwclock -r
Fri 02 Sep 2016 00:54:47 BST -0.029005 seconds
george@camera:~ $

However, after rebooting, the system time is okay, but the hardware clock is screwed again, but writing the correct system time back to the hardware and then re-reading the hardware cures it (until another reboot).

george@camera:~ $ date
Fri 2 Sep 00:56:32 BST 2016
george@camera:~ $ sudo hwclock -r --debug
hwclock from util-linux 2.25.2
Using the /dev interface to the clock.
Last drift adjustment done at 1472773728 seconds after 1969
Last calibration done at 1472773728 seconds after 1969
Hardware clock is on UTC time
Assuming hardware clock is kept in UTC time.
Waiting for clock tick...
/dev/rtc does not have interrupt functions. Waiting in loop for time from /dev/rtc to change
...got clock tick
Time read from Hardware Clock: 2066/01/01 00:01:29
Invalid values in hardware clock: 2066/01/01 00:01:29
hwclock: The Hardware Clock registers contain values that are either invalid (e.g. 50th day of month) or beyond the range we can handle (e.g. Year 2095).
george@camera:~ $
george@camera:~ $ date
Fri 2 Sep 00:58:10 BST 2016
george@camera:~ $ sudo hwclock -w
george@camera:~ $ sudo hwclock -r
Fri 02 Sep 2016 00:58:22 BST -0.925611 seconds
george@camera:~ $

It's almost as if the hardware clock is set correctly from previous boot, then re-set when the Pi3 reboots anew, but BEFORE NTP has synced the clock, thus pushing 1970 back into the hardware clock.

Any help on this would be greatly appreciated.

George
M1GEO

[buruhazard]

After I did all of this:
"hwclock: Cannot access the Hardware Clock via any known method."

Any idea?

[mikebar]

After searching for a long while, and after a lot of experiments, I've putted togheter all the information I've collected all around the Net about how to connect a realtime clock to the Raspberry and allow the OS use it as system clock even if no connections to a NTP server.
I've used a DS3231, but the following should work even with a DS1307. Just use ds1307 where into the following instructions is used ds3231.

The following, definitively worked for me, using Raspbian Jessie. So:
edit the file using sudo nano /boot/config.txt and add or modify a line that looks like the following:

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dtoverlay=i2c-rtc,ds3231

Edit the file using sudo nano /etc/init.d/hwclock.sh and comment out the content in order to be sure that the content looks like the following:

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    #if [ -d /run/udev ] || [ -d /dev/.udev ]; then
    #    return 0
    #fi

Then disable the fake-hwclock and enable the hwclock.sh with the following group of commands:

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     sudo apt-get remove fake-hwclock
     sudo rm /etc/cron.hourly/fake-hwclock
     sudo update-rc.d -f fake-hwclock remove
     sudo rm /etc/init.d/fake-hwclock
     sudo update-rc.d hwclock.sh enable

Then modify the file using sudo nano /lib/udev/hwclock-set locate the following lines and be sure to comment it out:

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   # if [ -e /run/systemd/system ] ; then
   #    exit 0
   # fi

Now, create two system services in order to set the system's clock when the OS boot and also to write to the RTC at the shutdown. So, the first one:

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sudo nano /etc/systemd/system/hwclock-start.service

...and paste in it the following:

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 [Unit]
 Description=Set time from RTC on startup
 After=network.target
 
 [Service]
 Type=oneshot
 ExecStart=/sbin/hwclock -s
 TimeoutSec=0
 
 [Install]
 WantedBy=multi-user.target

and the second one:

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sudo nano /etc/systemd/system/hwclock-stop.service

Paste in it the following:

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 [Unit]
 Description=Synchronise Hardware Clock to System Clock
 DefaultDependencies=no
 Before=shutdown.target
 
 [Service]
 Type=oneshot
 ExecStart=/sbin/hwclock --systohc
 
 [Install]
 WantedBy=reboot.target halt.target poweroff.target

Finally, enable the services issuing once the following command:

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sudo systemctl enable hwclock-start hwclock-stop

You can also verify that the RTC module has been loaded using

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sudo lsmod

[brunosso]

Now, create two system services in order to set the system's clock when the OS boot and also to write to the RTC at the shutdown.

...

and the second one:

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sudo nano /etc/systemd/system/hwclock-stop.service

Paste in it the following:

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 [Unit]
 Description=Synchronise Hardware Clock to System Clock
 DefaultDependencies=no
 Before=shutdown.target
 
 [Service]
 Type=oneshot
 ExecStart=/sbin/hwclock --systohc
 
 [Install]
 WantedBy=reboot.target halt.target poweroff.target

The second script doesn't work. I have a raspbian strech! If i run

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pi@raspberrypi:~ $ sudo systemctl status hwclock-stop.service
● hwclock-stop.service - Synchronise Hardware Clock to System Clock
   Loaded: loaded (/etc/systemd/system/hwclock-stop.service; enabled; vendor preset: enabled)
   Active: inactive (dead)
pi@raspberrypi:~ $