MCXN947 DPD entry fails with LPACK timeout

[wima88]

Hello, 

I'm using following platform 

Board :  MCX-N9XX-EVK 

RTOS : Zephyr 4.3 

my goal is to Enter Deep Power Down (DPD) mode in Zephyr. Since Zephyr Lacks PM support in this particular chip. I attempt to port the SDK bare-metal DPD example (mcxn9xxevk_power_mode_switch_low_level) to Zephyr(without using the PM subsystem). but every DPD entry attempt fails with:

CMC SRS = 0x00000810 — LPACK timeout (bit 11) + WARM reset (bit 4)

The SDK example enters DPD successfully with the same LPTMR wakeup config.

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WHAT HAS BEEN RULED OUT
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- SysTick disabled before WFI (CTRL = 0x00000006, bit0=0 confirmed).

SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk; // clear ENABLE bit (bit 0) — stops the counter
SCB->ICSR = SCB_ICSR_PENDSTCLR_Msk; // clear any already-pending SysTick interrupt

- WUU flags cleared before entry.
- LPTMR armed correctly: WUU ME = 0x00001000 (module 6, bits[13:12]=01).
- SPC LP_CFG = 0x00021504 — identical to working SDK dump.

The LPACK fires consistently, suggesting an AHB initiator is not ACKing the
low-power request, but it is not clear which one or how to identify it.

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REGISTER DUMP — JUST BEFORE WFI (Zephyr, failing)
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SPC LP_CFG = 0x00021504 (matches SDK )
SPC EVD_CFG = 0x003F1E00 (EVDLPISO = 0x1E for LPTMR wakeup)
SPC LPREQ_CFG = 0x00000003 (EN=1, low-true polarity)
WUU ME = 0x00001000 (LPTMR module wakeup armed )
WUU PF = 0x00000000 (no stale flags)
SysTick CTRL = 0x00000006 (STOPPED)

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QUESTIONS
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Q1. Is there a way to identify WHICH AHB initiator is failing to ACK the LP
request and causing the LPACK timeout?

Q2. Are there any Zephyr-initialized subsystems (UART driver, ARM MPU, cache,
or anything else Zephyr enables at boot) that are known to hold an AHB bus
master active and block DPD entry on MCXN947?