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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# 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/clock_init.sh
8. Put the contents in clock_init.sh:
#!/bin/bash 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:
[Unit] Description=PFC8563 RTC Service
[Service] Type=simple WorkingDirectory=/usr/share/rtc_pcf8563 ExecStart=/bin/bash clock_init.sh SyslogIdentifier=rtc_pcf8563
[Install] WantedBy=multi-user.target
11. Enable the service:
root@beaglebone:/home/debian# systemctl enable rtc-pcf8563.service