BeagleBone® Enhanced Developer Tutorial

How to initialise and set up a service to use the Real Time Clock (RTC) 

A simple step-by-step guide applicable to all SanCloud BeagleBone® Enhanced SBCs in which the optional RTC board is installed 

You will need to add some additional script to periodically synchronise the RTC module when you have a valid network connection.


1. Enable the RTC

echo pcf8563 0x51 > /sys/class/i2c-adapter/i2c-0/new_device


2. Check the rtc1 has been created:

root@beaglebone:/home/debian# ls -l /dev/rtc*
lrwxrwxrwx 1 root root      4 Nov 24 22:21 /dev/rtc -> rtc0
crw------- 1 root root 252, 0 Nov 24 22:21 /dev/rtc0
crw------- 1 root root 252, 1 Nov 24 22:35 /dev/rtc1

3. Read the time back in the RTC will fail the first time because it has never been set up:

root@beaglebone:/home/debian# hwclock -r -f /dev/rtc1
[ 912.096315] rtc-pcf8563 0-0051: low voltage detected, date/time is not reliable.
hwclock: ioctl(RTC_RD_TIME) to /dev/rtc1 to read the time failed: Invalid argument


4. Check you have the current system time set correctly:

root@beaglebone:/home/debian# date
Tue 19 Jan 2021 11:22:50 AM UTC
root@beaglebone:/home/debian# timedatectl
               Local time: Tue 2021-01-19 11:23:10 UTC
           Universal time: Tue 2021-01-19 11:23:10 UTC
                 RTC time: Tue 2021-01-19 11:23:10
                Time zone: Etc/UTC (UTC, +0000)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

5. Update the RTC time:

root@beaglebone:/home/debian# hwclock -w -f /dev/rtc1


6. Check the time in the RTC:

root@beaglebone:/home/debian# hwclock -r -f /dev/rtc1
2021-01-19 11:23:32.810635+00:00

7. To create a startup script to enable RTC every time:

mkdir /usr/share/rtc_pcf8563
nano /usr/share/rtc_pcf8563/

8. Put the contents in

sleep 15
echo pcf8563 0x51 > /sys/class/i2c-adapter/i2c-0/new_device
hwclock -s -f /dev/rtc1
hwclock -w

9. Next create the service that will get started on boot:

root@beaglebone:/home/debian# nano /lib/systemd/system/rtc-pcf8563.service

10. Put the following contents in rtc-pcf8563.service:

Description=PFC8563 RTC Service

11. Enable the service:

root@beaglebone:/home/debian# systemctl enable rtc-pcf8563.service