Thank you for a comprehensive answer. I will look into external clocks. On Sun, Apr 18, 2021 at 5:05 PM Dennis Lee Bieber <[email protected]> wrote:
> On Sat, 17 Apr 2021 14:14:03 -0700 (PDT), in > gmane.comp.hardware.beagleboard.user Mykolas Juraitis > <[email protected]> wrote: > > >Hello, > > > >I am experimenting with rtcwake on BeagleBone Blue. Running command: > > > > Note that there is no REAL RTC on most BeagleBone variants (I don't > know if the Blue has an add-on RTC). cf: > > https://learn.adafruit.com/adding-a-real-time-clock-to-beaglebone-black/overview > > > >I tried to check time before and after standby by running: > > > >sudo hwclock && date && sudo rtcwake -d /dev/rtc0 -m standby -s 20 && > date > >&& sudo hwclock > >2021-04-17 21:42:40.123908+00:00 > >Sat 17 Apr 2021 09:42:40 PM UTC > >rtcwake: wakeup from "standby" using /dev/rtc0 at Sat Apr 17 21:43:02 2021 > >Sat 17 Apr 2021 09:43:06 PM UTC > >2021-04-17 21:43:07.802256+00:00 > > > >Last 2 time lines are printed after manual wake up by pressing power > >button. They seem to be showing that only twenty some seconds passed but > >actually much more time passed until I pressed power button. Which is > weird > >because if RTC doesn't work then I would expect time to be reset. If it > >does work it should be correct time. > > > > Beaglebones periodically save the system clock value, and use that > to > reload the system clock on startup. The value you are seeing is likely that > of the last time this fake hwclock was written... cf: > https://manpages.debian.org/jessie/fake-hwclock/fake-hwclock.8.en.html > > Also... > > https://unix.stackexchange.com/questions/187261/automatically-update-hwclock-at-boot > https://groups.google.com/g/beagleboard/c/n1noGnM30sQ > > > > -- > Dennis L Bieber > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to a topic in the > Google Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/qPoSZk2XStA/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/a3mo7gls3hp901pi4r91rfvkkq7q7g2nti%404ax.com > . > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAKVuKxgb%3DQM4ek_D_zwqRzBugNAD3JhS7KYLBO_w5YmvADPhwg%40mail.gmail.com.
