On Tuesday, 18 August 2020 14:45:23 UTC+3, Robert Heller wrote: > > At Tue, 18 Aug 2020 02:40:41 -0700 (PDT) beagl...@googlegroups.com > <javascript:> wrote: > > I am using beagle Bone Black with debian image. Could any please suggest > > how to automatically set the system time (on every reboot) by external > RTC > > module DS3231. Once internet is connected, i want to update both system > > time and DS3231 with the network time. > > > > I am controlling a relay based on system time, my application should > take > > DS3231 time and run perfectly even if internet is disconnected and not > > available for so many days. > > > > Few things i have tried, the following content has been kept in the > script > > and running @reboot script in crontab. The system time has been changed > if > > we enter this command manually after boot but not in auto start script. > > Please advice. > > > > *echo ds3231 0x68 > /sys/class/i2c-adapter/i2c-1/new_device* > > > > *hwclock -r -f /dev/rtc1* > > Well, the simple / dumb option would be to put the above two lines in > /etc/rc.local, which will restore the system clock from the RTC. > > The other option is to create a proper RTC service. A properly setup RTC > service will restore the system clock from the RTC early in the boot > process > and save the system clock late in the shutdown process. > A proper RTC service is already implemented by the systemd-timesyncd service, installed by default on the debian images: https://www.freedesktop.org/software/systemd/man/systemd-timesyncd.service.html
It does everything Niresh needs out of box. There's a caveat: systemd-timesyncd only works with */dev/rtc0* device. By default */dev/rtc0* is grabbed by the AM335x CPU-s internal RTC (which has no battery backup) and the external RTC is left with */dev/rtc1* which gets ignored. I did not find any way to configure systemd-timesyncd to use the other device. Robert pointed me to a device tree which very conveniently swapped the device nodes for those RTCs so the external one got */dev/rtc0*. I just had to load the device tree via /boot/uEnv.txt and time syncing worked beautifully. For Niresh, I suggest trying this one: https://github.com/beagleboard/bb.org-overlays/blob/master/src/arm/BB-I2C2-RTC-DS3231.dts -- Kind regards, Tarmo -- 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 beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/f0fdc385-9663-4dd4-a35b-b8844bdb92f3o%40googlegroups.com.
