RTC battery

[masip85]

@KevinFFF

modify that through kernel config to use rtc0 instead of rtc1.

I’ve changed:
/lib/udev/rules.d/50-udev-default.rules
from:

SUBSYSTEM=="rtc", ATTR{hctosys}=="1", SYMLINK+="rtc"
SUBSYSTEM=="rtc", KERNEL=="rtc0", SYMLINK+="rtc", OPTIONS+="link_priority=-100"

to this:

SUBSYSTEM=="rtc", ATTR{hctosys}=="0", SYMLINK+="rtc"
SUBSYSTEM=="rtc", KERNEL=="rtc0", SYMLINK+="rtc", OPTIONS+="link_priority=-100"

Now points to rtc0. Because rtc0 still being outdated , I’ve done sudo hwdate -w. Now it has been updated with time from systemdate,which is connected to ntp.

The use case still being for an no-internet network. So I disconnect the internet, wait for a minute and restart.

Now it points to lrwxrwxrwx 1 root root 4 Mar 15 16:04 /dev/rtc → rtc0
crw------- 1 root root 250, 0 Mar 15 16:04 /dev/rtc0
crw------- 1 root root 250, 1 Mar 15 16:04 /dev/rtc1

But now, system date is not being updated from rtc0. If I connect to internet again, system date updates,and match with rtc0. So it looks like rtc0 is tracking correctly. But system doesn’t use it.

[KevinFFF]

Have you also modify the kernel config(CONFIG_RTC_HCTOSYS_DEVICE) to use rtc0?

[WayneWWW]

It is normal behavior that system does not use it automatically. You need to hwclock sync the time by yourself. Or write a script to automatically do that.

[masip85]

ok now I see:

RTC can't hold time the after system rebooted in L4T 35.1

@matanh Modify kernel configure to modify CONFIG_RTC_HCTOSYS_DEVICE to rtc0 to build new kernel for it. Thanks

for using AGX Xavier (1500$ machine) clock I have to modify the kernel … myself? I think that is a little too much. Isn’t it? What’s the problem for nvidia to not modify that?

Normal behaviour? Maybe I am missing something, because is the first computer/machine I need to do this. I guess there is a difference, but I don’t know which one.

[WayneWWW]

It is case-by-case. This kernel not only serves AGX Xavier but maybe other platofrm.
Some platforms rtc0 may not be the PMIC RTC.

[WayneWWW]

For the sync time, also try to use “sudo timedatectl set-local-rtc 0” after you modify the rtc to rtc0.

timedatectl shall to the work automatically in each boot.

[masip85]

@WayneWWW

shall to the work automatically in each boot

Automatically if I make a crontab it?

Thank yoy for your answers.

How long this battery should last? If I add cmos battery, do I need additional changes?

Could you provide me document/forum guidance about cmos batteries addition?

[Trumany]

Hi, you can calculate the time according to this topic for Xavier: RTC Current consumption in Xavier SOM

[masip85]

It works correctly now with your instructions. I will make a new topic if I don’t get the battery to work correctly.

Thanks!