MCX MicrocontrollersのトピックRe: iRTC failed to initialized using 32k osc on MCXN947

iRTC failed to initialized using 32k osc on MCXN947

jimmyli — Fri, 12 Dec 2025 08:56:27 GMT

Hi NXP,

I need to use outside 32K oscillator for iRTC in MCXN947.

When I used MCUXpresso IDE to config and initialize the iRTC peripheral, it will fail when initialize clock source for iRTC.

Hope you can check and provide a help to resolve this problem.

Thanks very much.

1>MCUXpresso IDE config for iRTC

2>initial and hang here

Re: iRTC failed to initialized using 32k osc on MCXN947

Celeste_Liu — Mon, 15 Dec 2025 08:27:56 GMT

Hello @jimmyli ,

Thanks for your post. I have reproduced your issue. The “RTC0->CTRL |= RTC_CTRL_CLK_SEL_MASK;” generated by Config Tools does have a problem. I will report it to the internal team. Please refer to the workaround below.

1. Comment out the following code in clock_config.c.

2. In hardware_init.c, call the BOARD_InitBootPeripherals(); function declared in peripherals.h. This file contains the RTC-related configurations generated by the Peripherals Config Tools.

3. Modify the main function to test:

4. Test result:

Hope it helps.

Celeste

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Re: iRTC failed to initialized using 32k osc on MCXN947

jimmyli — Mon, 15 Dec 2025 08:49:03 GMT

Hi Celeste,

Thanks very much for your replying.

But I have a comment that maybe you need to mask the code shown as below, it maybe affect the code function.

Can you help to check again ?

Thanks very much.

Re: iRTC failed to initialized using 32k osc on MCXN947

Celeste_Liu — Tue, 16 Dec 2025 02:42:33 GMT

Hello @jimmyli ,

Please refer to Marek's response on this matter. It appears that FRO16K must be enabled, and the outputs to both VBAT and MAIN domains should be enabled. We are awaiting clarification from the internal team and will address this issue accordingly.

Have a nice day.

Celeste

Re: iRTC failed to initialized using 32k osc on MCXN947

marek_neuzil — Mon, 15 Dec 2025 15:11:50 GMT

Hello,

I have been able to reproduce the error you have reported. The issue is caused by invalid configuration of the FRO16K of the VBAT. The FRO16K must be enabled and the outputs to VBAT and MAIN domain enabled. See the following screenshot:

This dependency on the FRO16K is not clearly stated in the reference manuals of the MCXN947 MCU. I will ask the responsible team for clarification of the correct initialization sequence for the the RTCCLKSEL clock selector that is a part of the RTC subsystem. The FRO16K must be enable to access the RTC subsystem register. We will also provide the fix for the MCXN947 MCU in the Clock tool to provide correct initialization code and dependencies in the Clocks model UI.

In the mean time, use the workaround specified above to use 32kHz crystal oscillator clock source as the LP_OSC clock source.

Best Regards,

Marek Neuzil

Re: iRTC failed to initialized using 32k osc on MCXN947

jimmyli — Tue, 16 Dec 2025 13:11:47 GMT

Hello Marek,

Got it.

Thanks very much.

Re: iRTC failed to initialized using 32k osc on MCXN947

jimmyli — Mon, 05 Jan 2026 04:01:59 GMT

Hello Marek,

Update a new case:

When I configure shown as below, iRTC can be initialized and work, but the second is wrong.

1>iRTC pin for external xtal32k

2>iRTC clock

3>iRTC peripheral

4>Question

when I using test code shown as below, the second is wrong.

Hope you can provide some tips to fix this problem.

Thanks very much.

--test code

--debug print

Re: iRTC failed to initialized using 32k osc on MCXN947

marek_neuzil — Mon, 05 Jan 2026 13:16:01 GMT

Hello @jimmyli,

In your last use case, you disabled the FRO16K internal reference oscillator. I am not sure whether the RTC 32kHz external oscillator and the RTCCLKSEL can work properly when the internal reference FRO16K is disabled. I have recommended to enable the FRO16K and the outputs to VBAT and MAIN domains to properly initialize the 32kHz external oscillator.

I didn't receive the response for the issue of the OSC_32K initialization yet. When the first issue is resolved and the RTC clock source works reliable we can analyze the iRTC functionality (the iRTC issue may by caused by incorrect initialization of the OSC_32K too). I will urge the answer for the first issue.

Best Regards,

Marek Neuzil

Re: iRTC failed to initialized using 32k osc on MCXN947

jimmyli — Tue, 06 Jan 2026 08:50:04 GMT

Hi Marek,

Got it.

Thanks a lot.

BTW, I found that only enable external 32k crystal, the iRTC can run but the output of second is wrong. But but, when I let the MCU run continuously, iRTC will run accurately later;.

It is queer to me.

You can check again.

Thanks again.

Re: iRTC failed to initialized using 32k osc on MCXN947

jmullen_condose — Fri, 24 Apr 2026 16:37:22 GMT

Thank you for this solution. This exact issue exists with mcuxpresso and MCXN236 MCU.