On Tuesday, 18 August 2020 17:47:00 UTC+3, Tarmo wrote: > > On Tuesday, 18 August 2020 14:45:23 UTC+3, Robert Heller wrote: >> >> At Tue, 18 Aug 2020 02:40:41 -0700 (PDT) [email protected] >> 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 > > <https://www.google.com/url?q=https%3A%2F%2Fgithub.com%2Fbeagleboard%2Fbb.org-overlays%2Fblob%2Fmaster%2Fsrc%2Farm%2FBB-I2C2-RTC-DS3231.dts&sa=D&sntz=1&usg=AFQjCNEt87UyBS-inpep25aZNVAfhEhfXw> >
To clarify the "trying" step: you'll probably find the compiled device tree in the Beagle's file system: "/lib/firmware/BB-I2C2-RTC-DS3231.dtb". Just add this to /boot/uEnv.txt using standard method and reboot. Monitoring the boot log via dmesg should tell you which RTC device was awarded /dev/rtc0. -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/340040ae-d9d1-4f28-9518-ec4f5ab8ac1eo%40googlegroups.com.
