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

Autonomous Machines Jetson & Embedded Systems Jetson Nano
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#1

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

#4

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

#7

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.

#10

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?

#12

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
#13

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)

#14

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.

#16

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

#17

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?

#18

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

#19

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?

#20

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?

image
image804×377 10.4 KB

D46
D464160×3120 3.14 MB

#21

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?

#22

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

#23

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?

#26

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.