Try adding the following lines to /boot/config.txt
dtparam=i2c_arm=on
dtparam=spi=on
dtoverlay=rtc-i2c,pcf2127
And /etc/tmpfiles.d/pcf2127.conf
w /sys/class/i2c-adapter/i2c-1/new_device - - - - pcf2127 0x51
And /etc/modules
i2c-dev
rtc-pcf2127
EDIT:
As it turns out the NTP server in OSMC (RC2) doesn’t play well with RasClock RTC. I’m not sure why, perhaps it starts too early.
If no NTP server is needed it can be replaced with the lightweight systemd NTP client, which does seem to behave correctly:
osmc@osmc:~$ sudo systemctl stop ntp
osmc@osmc:~$ sudo systemctl disable ntp
osmc@osmc:~$ sudo timedatectl set-ntp true
osmc@osmc:~$ sudo timedatectl
And then as mentioned by @DBMandrake and @sam_nazarko
sudo systemctl disable fake-hwclock