clock outdated after unplugged several hours

Hello,

I am working with several Tegra Jetson, some are TX1, a few TX2. I am facing the same issue in all of them.

I can set the clock fine with “date” command. The time is good some minutes after, even if I reboot the tegras. But if I leave them unplugged one day and turn them on the following day, I see all strange behaviors. For example they could stay “frozen” at the time they were turned off, or change randomly even to 2016, etc.

TX1 INFO

/etc/nv_tegra_release
1 # R24 (release), REVISION: 2.1, GCID: 7791156, BOARD: t210ref, EABI: aarch64, DATE: Thu Sep 29 00:59:21 UTC 2016

uname -a
kernel tegra-ubuntu 3.10.96 #1 SMP PREEMPT Wed Jan 3 19:07:57 UTC 2018 aarch64 aarch64 aarch64 GNU/Linux

TX2 INFO

/etc/nv_tegra_release

R28 (release), REVISION: 1.0, GCID: 9379712, BOARD: t210ref, EABI: aarch64, DATE: Thu Jul 20 07:45:59 UTC 2017

uname -a
Linux tegra-ubuntu 4.4.38-tegra #1 SMP PREEMPT Thu Jan 3 19:07:16 UTC 2019 aarch64 aarch64 aarch64 GNU/Linux

There is only a super capacitor and no battery. I doubt it was designed to last that long with power out, although some boards might actually go a day.

Normally these boards are intended to set time via network (NTP). I am guessing you don’t have a network, or the network doesn’t have access to the NTP server.

I’m not actually sure which pins are designed for custom clock battery backup on the TX1 dev board, but those were specific pins provided for on the TK1. Would anyone know if there are published examples of a battery backup for the RTC of a TX1 dev board?

Hi linuxdev,

Thanks for your answer.

Yes, we need to handle a situation where the device is unplugged and/or away from internet for (maybe) several days.

Yes, it would be of great help if someone could point out some link or resource showing guidance to develop a battery backup for the RTC of a TX1/TX2 dev board.

In case of TX2, where we need same feature, do you recommend to start a new thread on TX2 forum?

The TK1 has the correct pins exposed for adding an external battery, but I’m not sure what the TX1/TX2 dev carrier has. The J27 connector supports external charging, and perhaps use of this might help, but someone else will have to comment on whether this would do the job for the RTC. I am thinking this is for an external battery powering the whole system, and not just for the supercap on the RTC. If this system is powered off, then not much power is required to power the whole system, but it isn’t what I would think of as battery backup to the clock.

Would anyone be able to comment on ways to back up the RTC clock power instead of the supercap? Would it be necessary to actually modify the developer carrier board?