The NX's RTC can not work much time

Robotics & Edge Computing Jetson & Embedded Systems Jetson Xavier NX
1

Hi, everyone
Now i used my custom board for the NX module
JetPack version is 5.1.1,
nv_tegra_realease is R35.3.1.

I found the NX used device rtc1(tegra_rtc c2a0000.rtc: registered as rtc1) default.
Although setting rtc time by hwlock, it will reset when power is off every time(1970-1-1).

According to some posts in forums, i modified CONFIG_RTC_HCTOSYS_DEVICE="rtc0" in defconfig, and it seems work normally. But when i used a supercapacitor (80mF), i can only work about two hours.

So what should i do to resolve it?

Thank you.
Best regards,
Ultwcz1997

3

Hi,

have you tried a battery but not just super capacitor?

4

Hi @DaveYYY
Thanks for your reply.

No, i think the coin battery is too large.

Your mean this is because of supercapacitor?

5

Yes, please try a coin battery.
I think it’s expected that you got only 2 hours with a super capacitor.

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6

But it can work one day at TX2, so I don’t know what happened at the NX.
BTW,

This is correct?

7

I’m not sure about the design of your carrier board so I cannot comment much here,
but we still recommend using a coin battery for your purpose.

Yes, because rtc1 is inside the Tegra SoC, and is not connected to any external power supply.
Only rtc0 on the carrier board can save the time after power off.

8

Ok, I understand it.
thank you.

BTW, i suggest NVIDIA could modify the default rtc1to rtc0 because the device rtc1 seems not make sense.

9

We use rtc1 as the default rtc device because it has higher accuracy, and it’s totally fine if users want to switch to rtc0.

10

OK, If i want to use rtc1 now, how do i provide power for it? i can not find the relevant pin on the datasheet

11

I don’t think you can do that.
Please just use rtc0 if you need to preserve time across boot.

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12

Ok. Thank you. ^_^

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14

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