MCX MicrocontrollersのトピックRe: MCXN236VNLT custom board - RTC0 Peripheral hanging code when clock enabled

MCXN236VNLT custom board - RTC0 Peripheral hanging code when clock enabled

jmullen_condose — Thu, 23 Apr 2026 21:03:31 GMT

I have an MCXN236VNLT custom board being developed. When I enable the RTC0 Peripheral the MCU hangs and my Cyclone loses connection when I enable the clock then access any registers on the RTC0. clock_config.c does the following:

CLOCK_SetPLL0Freq(&pll0Setup); /*!< Configure PLL0 to the desired values */

CLOCK_SetPll0MonitorMode(kSCG_Pll0MonitorDisable); /* Pll0 Monitor is disabled */

CLOCK_SetupOsc32KClocking(kCLOCK_Osc32kToVbat); /* OSC_32 kHz output clock to Vbat enabled */

vbat_osc_config_t g_vbatOscConfig_BOARD_BootClockPLL150M = {

.coarseAdjustment = kVBAT_OscCoarseAdjustment05,

.enableInternalCapBank = true,

.enableCrystalOscillatorBypass = true,

.xtalCap = kVBAT_OscXtal12pFCap,

.extalCap = kVBAT_OscExtal12pFCap,

};

VBAT_SetOscConfig(VBAT0, &g_vbatOscConfig_BOARD_BootClockPLL150M);

SYSCON->CLOCK_CTRL |= SYSCON_CLOCK_CTRL_FRO1MHZ_CLK_ENA_MASK; /*!< Enable FRO_1M is on */

CLOCK_EnableClock(kCLOCK_Rtc0);
RTC0->CTRL |= RTC_CTRL_CLK_SEL_MASK; (HANGS HERE!)

If I skip that line in the debugger, MCU startup continues until any other code tries to access any register on the RTC0.
I have tried everything I can think of so far. Systick and MRT are also running, with higher priority Interrupts, but even when disabled, it just seems to be a clock issue with RTC0.

Strangely, when MCUxpresso stops connecting, it opens a tab for "ADC0_IRQHandler() at 0x0" and displays "No source available for "ADC0_IRQHandler() at 0x0" "

I am using an external 32768 crystal, if I change the clock to the internal 16k one, the code runs a bit further, to:

status_t IRTC_Init(RTC_Type *base, const irtc_config_t *config)

{

assert(NULL != config);

and fails at the "assert". "config" = the configuration, not NULL, so what's up with that? Ugh!

Any fresh eyes or ideas, much appreciated!

Re: MCXN236VNLT custom board - RTC0 Peripheral hanging code when clock enabled

Celeste_Liu — Mon, 27 Apr 2026 07:42:19 GMT

Hello @jmullen_condose ,

Thank you for your post. As you mentioned in iRTC failed to initialized using 32k osc on MCXN947, this issue is caused by the requirement to provide a clock source before RTC initialization and access to the RTC registers.

By default, the RTC CTRL[CLK_SEL] bitfield selects the FRO16K clock source. Therefore, the FRO16K clock must remain enabled until the RTC CTRL[CLK_SEL] is switched to the OSC32K clock source. This is the only correct way to properly initialize the RTCCLKSEL clock selector.

In addition, I will also create an internal ticket for MCXN236. Before a permanent fix is available, please refer to the workaround described in that post.

Hope it helps.

Celeste

Re: MCXN236VNLT custom board - RTC0 Peripheral hanging code when clock enabled

marek_neuzil — Wed, 13 May 2026 10:44:09 GMT

Hello @jmullen_condose,

The issue has been already reported for the MCXN947 as it was mentioned by @Celeste_Liu. The issue has been also fixed for the MCXN236 MCU in the latest release of the Config Tools version 26.03. See the following code that is provided when the FRO16K is disabled and RTC0->CTRL register is accessed:

Use the latest version 26.03 of the Config Tools that provides the correct initialization code for this use case.

Best Regards,

Marek Neuzil