Using RTC#

BeaglePlay has an onboard Real Time Clock (BQ32002). If you have installed a CR1220 battery, you can use this to keep the time even when the device has been powered off, or has no Internet access to get time using ntp servers.

Understanding multiple rtc devices#

On the BeaglePlay there’s 2 separate RTC devices. One is the inbuilt one - which by default shows up as /dev/rtc0. And the other is BQ32002 - which is it’s own discrete chip - and shows up as /dev/rtc1 by default.

You can find out the time set in both these clocks with the hwclock command.

debian@BeaglePlay:~$ sudo hwclock -r --rtc /dev/rtc0
2023-12-21 12:43:52.007564+05:30
debian@BeaglePlay:~$ sudo hwclock -r --rtc /dev/rtc1
1970-01-01 05:33:28.877722+05:30

Note that the time in rtc0 has been set after booting up using ntp servers automatically.

Get the current time, timezone, and other settings#

debian@BeaglePlay:~$ timedatectl
            Local time: Thu 2023-12-21 00:20:19 EST
            Universal time: Thu 2023-12-21 05:20:19 UTC
            RTC time: Thu 2023-12-21 05:20:20
            Time zone: America/New_York (EST, -0500)
            System clock synchronized: yes
            NTP service: active
            RTC in local TZ: no

The above command shows the time set on BeaglePlay, the universal time, the time set on the RTC, the timezone, and more. From the above we can see that the time in UTC is 5:20hrs and the time as per the timezone is 00:20hrs.

Setting the timezone#

You can see the available timezones using the following command -

debian@BeaglePlay:~$ timedatectl list-timezones

You can quit viewing the list by pressing the q character on your keyboard.

Once you have selected your timezone, you can set it as follows

debian@BeaglePlay:~$ sudo timedatectl set-timezone America/New_York

Enable ntp#

We can set the time using ntp servers. This requires us to be connected to the Internet.

debian@BeaglePlay:~$ sudo timedatectl set-ntp true

Setting the time manually#

You might want to set the time manually on your BeaglePlay. In this case you need to first disable the ntp synchronization.

debian@BeaglePlay:~$ sudo timedatectl set-ntp false
debian@BeaglePlay:~$ sudo timedatectl set-time "2023-12-21 03:00:00"

Using the above command we have set the time to 0300hrs on 21st December 2023.

Using `rtcwake` to sleep#

If you would like to put your BeaglePlay to sleep for a predetermined period of time, you can use the rtcwake command

debian@BeaglePlay:~$ sudo sudo rtcwake -m disk --seconds 120 -d /dev/rtc1 -v
Using UTC time.
     delta   = 0
     tzone   = 0
     tzname  = UTC
     systime = 1703147162, (UTC) Thu Dec 21 08:26:02 2023
     rtctime = 1703147162, (UTC) Thu Dec 21 08:26:02 2023
alarm 0, sys_time 1703147162, rtc_time 1703147162, seconds 120
rtcwake: wakeup from "disk" using /dev/rtc1 at Thu Dec 21 08:28:03 2023
suspend mode: disk; suspending system

The above command puts your BeaglePlay to sleep for 120 seconds, by writing the contents of your memory to disk. You can find what are the different modes that are supported similar to disk by running the --list-modes subcommand.

debian@BeaglePlay:~$ rtcwake --list-modes
freeze mem disk off no on disable show

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