RTC setup wih cell coin in Jetson Nano Developer Kit 945-13450-0000-100

pmunyoz · June 30, 2020, 10:54pm

Hello,

I am trying to setup the RTC with a CR1225 battery following the instructions in the forum (just soldering the bracket and inserting the cell coin), but the RTC resets every time I power off the board.

I checked the voltage between the (+) in the battery and GND in the board and it is 3.3V, so I assume the battery holder is correctly soldered to the board and the battery should provide the necessary voltage.

After updating the clock with the Internet connection I get the following output from timedatectl:
Local time: mar 2020-06-23 15:52:55 CEST
Universal time: mar 2020-06-23 13:52:55 UTC
RTC time: mar 2020-06-23 13:52:55
Time zone: Europe/Madrid (CEST, +0200)
System clock synchronized: yes
systemd-timesyncd.service active: yes
RTC in local TZ: no

I think it is OK, but when I shutdown the system, wait for 5 minutes (current time is 15:58:00) and boot without Internet connection, I get the following output from timedatectl:
Local time: mar 2020-06-23 15:54:07 CEST
Universal time: mar 2020-06-23 13:54:07 UTC
RTC time: sáb 2000-01-01 01:01:19
Time zone: Europe/Madrid (CEST, +0200)
System clock synchronized: no
systemd-timesyncd.service active: yes
RTC in local TZ: no

As you can realize, RTC time resets to year 2000.

I think all instructions in the forum refer to Jetson Nano Developer Kit 945-13450-0000-000, but in my case I have two 945-13450-0000-100 boards. I tried both boards and the same thing happens. I don’t know if the Developer Kit version makes the difference.

What do you think? Has anyone succeed to properly setup RTC in Jetson Nano Developer Kit 945-13450-0000-100. Thanks in advance.

System description:
Jetson Nano Developer Kit 945-13450-0000-100
L4T 32.3.1. Ubuntu 18.04

Trumany · July 1, 2020, 4:01am

The coin cell should work fine per other topics like this one RTC Jetson Nano.

pmunyoz · July 1, 2020, 8:38am

Hello, thanks for your reply. I followed that topics and the tutorial posted by Ingmar-Stapel in this post:

But I am wondering if that applies to Jetson Nano Developer Kit 945-13450-0000-100, because I followed the steps (soldering the holder, placing the coin cell and configuring systemd-timesyncd.service) in the two 945-13450-0000-100 boards I have and RTC clock resets in both cases when powered off.

Trumany · July 3, 2020, 4:09am

Can you try a big capacitor to verify if the RTC time reset is because the coin cell? And per your info, the local/universal time is kept without internet connection, right?

WayneWWW · July 3, 2020, 6:33am

Hi,

Please check if below method would make RTC time work after reboot.

1. disbale NTP

# timedatectl set-ntp false

2. set time

# date -s "2019/5/26 14:11:30"
Tue May 26 14:11:30 HKT 2019
# date
Tue May 26 14:11:32 HKT 2019

3. sys time to HW clock

# hwclock -w -f /dev/rtc1
# hwclock -r
2019-05-26 14:13:50.771134+0800

4. reboot device, and check the clock

# date

Sun May 26 14:15:28 HKT 2019

pmunyoz · July 6, 2020, 7:21am

Hello, can you please tell me how should I proceed to try a big capacitor? Should I connect a capacitor between (+) and (-) in J45 connector? Which capacitance?

Yes, the local/universal time is kept without internet connection, but it gets stuck in the time it was when the board was powered off (15:54 in my previous post, instead of the current time 15:58)

pmunyoz · July 6, 2020, 7:23am

Hello, the method makes RTC time work after reboot, but not after power off.

Once I power off, RTC resets to year 2000 and local/universal time to 2018.

Trumany · July 6, 2020, 1:10pm

Did you try 80000uF super cap as reference design? It is C5 on board, one side is “+” and other side is “GND”.

pmunyoz · July 9, 2020, 10:53am

Unfortunately I can’t get such a big capacitor. But I checked continuously the voltage between the (+) in the battery and GND in the board and it is 3.3V, even when the board is powered off.

Can I check anything else on the software side? Did you successfully setup the RTC with a cell coin in Jetson Nano Developer Kit 945-13450-0000-100?

Trumany · July 9, 2020, 12:04pm

Highly suspect coin cell problem. Please try another capacitor or chargeable battery to verify.

xhdai_qqmail · July 9, 2020, 3:06pm

I have the same problem. I have tried CR1225 and CR1220 coin battery on two Jetson Nano boards, but all failed. The time in RTC module will be reset to 2000 when power on system(5V-4A adapter).

Now I have to add an external DS3231 RTC module on J41 pins. DS3231 works, but it’s ugly.

Any advise?

pmunyoz · July 9, 2020, 4:47pm

Hello, checking the schematics found in the following LINK I realized that there is a gap for a Schottky diode (D64) in the coin cell Ve line (BBAT_CONN) (see attached pictures).

Should I attach a Schottky diode in D64? Can you recommend me which one?

Trumany · July 10, 2020, 2:44am

The diode or shorting connection is necessary… It was assumed to be there, so the problem is the coin cell is not connected to RTC as no diode or shorting?

xhdai_qqmail · July 10, 2020, 4:06am

Thanks for you link of schematics.
It works! Attach a Schottky diode (SOD-12.3) in D64.

pmunyoz · July 15, 2020, 8:46am

I don’t currently have a Schottky diode, can I make a shorting connection in the meantime? What are the benefits of placing the diode instead of shorting?

edli1983 · July 30, 2020, 3:22am

Coin cell is connected to PMIC_BBAT of PMIC, PMIC_BBAT is bidirectional. It will supply power to external when nano board have DC_IN supplied.
The diode prevent current supply to Coin cell. The diode is needed on the design.

rplpozl · November 9, 2020, 3:05am

I can confirm that the coin cell on the B01 version will not work without the diode. I used one we had in stock, but I would recommend BAT54H Schottky diode or similar.