HARDKERNEL RTC Shield User manual

2023/06/21 15:35 1/5 RTC Wake-up
ODROID Wiki - https://wiki.odroid.com/
RTC Wake-up
You can wake your Odroid-C4 up with our RTC Shield.
Setup system to use RTC Shield
First of all, to enable your RTC shield on your Odroid-C4, please follow the dedicated guide.
https://wiki.odroid.com/internal/common/accessory/add-on_boards/rtc_shield
Configure
Setup the system time
Set the system time up to your local time by following the commands below.
target
sudo dpkg-reconfigure tzdata
Then the final outputs will be looking like that.
target
odroid@odroid:~$ sudo dpkg-reconfigure tzdata
Current default time zone: 'Asia/Seoul'
Local time is now: Wed Apr 8 12:07:55 KST 2020.

Last update:
2020/04/08 18:38 odroid-c4:application_note:rtc_wakeup https://wiki.odroid.com/odroid-c4/application_note/rtc_wakeup?rev=1586338738
https://wiki.odroid.com/ Printed on 2023/06/21 15:35
Universal Time is now: Wed Apr 8 03:07:55 UTC 2020.
Or you can use the local NTP server that gathers the accurate DateTime by using
GPS. Please refer to the below guide.
https://wiki.odroid.com/internal/odroid-c4/application_note/gpspps_ntp_serve
r
If you have another one, you can use that server to set your system time up.
Please take care of your firewall to not to be blocking the NTP server
working.
Write the current system time to your RTC shield.
target
sudo hwclock -w -f /dev/rtc1
In Odroid-C4, the RTC shield will appear as /dev/rtc1 on your system. So you
should add -f option to choose a specify device file when you are using hwclock
command.
We assume that the RTC shield is /dev/rtc1 on the system.
Save the time when the board wakes-up
Then put the DateTime that the time you willing to wake-up your Odroid to
/sys/class/rtc/rtc1/wakealarm file.
Here's an example to enable the wakealarm feature and let the Odroid up in 4 minutes.
target
echo 0 | sudo tee /sys/class/rtc/rtc1/wakealarm
echo $(date '+%s' -d '+ 4 minutes') | sudo tee
/sys/class/rtc/rtc1/wakealarm
Read the RTC status.
target
cat /proc/driver/rtc
To check if the wakealarm feature enabled or not, see the alarm_IRQ property. It should be yes.

2023/06/21 15:35 3/5 RTC Wake-up
ODROID Wiki - https://wiki.odroid.com/
rtc_time : 09:16:35
rtc_date : 2020-04-08
alrm_time : 09:18:24
alrm_date : 2020-04-08
alarm_IRQ : yes
alrm_pending : no
update IRQ enabled : no
periodic IRQ enabled : no
periodic IRQ frequency : 1
max user IRQ frequency : 64
24hr : yes
Shutdown your Odroid and watch that to check if it wakes up automatically or not. If all went well,
your Odroid board wakes up in 4 minutes.
target
sudo poweroff
Troubleshooting
System messages
Here is the troubleshooting list that occurs on dmesg or standard output on the console with an error.
hwclock: ioctl(RTC_RD_TIME) to /dev/rtc to read the time failed: Invalid argument
RTC backup battery is not connected or RTC is not configured to be accessed.
cannot access '/dev/rtc1': No such file or directory
If the H/W clock is not configured yet, the RTC device node won't be created.
Please see the RTC shield wiki page to check if all the settings are correct.
To check further, you can use i2cdetect tool to check if the RTC shield works via I2C communication.
target
sudo apt update && sudo apt install i2c-tools
sudo i2cdetect -y 2
Then the results should be like the following contents.

Last update:
2020/04/08 18:38 odroid-c4:application_note:rtc_wakeup https://wiki.odroid.com/odroid-c4/application_note/rtc_wakeup?rev=1586338738
https://wiki.odroid.com/ Printed on 2023/06/21 15:35
odroid@odroid:~$ sudo i2cdetect -y 2
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- UU -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
rtc-pcf8563 3-0051: low voltage detected, date/time is not reliable
This error could be inaccurate but you should check the real voltages by yourself. It should close to
3V.
Using questions
RTC time isn't synced at startup
Kernel hctosys works before RTC hardware initialized because the i2c/RTC drivers are modules.
You can edit /etc/rc.local to synchronize the HW RTC time with the system time at boot time.
Refer to the following codes.
if [ -f /aafirstboot ]; then /aafirstboot start ; fi
hwclock -s -f /dev/rtc1
exit 0
In order to apply the change, reboot your Odroid.
target
sudo reboot
From:
https://wiki.odroid.com/ - ODROID Wiki
Permanent link:
https://wiki.odroid.com/odroid-c4/application_note/rtc_wakeup?rev=1586338738
Last update: 2020/04/08 18:38

2023/06/21 15:35 5/5 RTC Wake-up
ODROID Wiki - https://wiki.odroid.com/