S32K324 results in a "power on reset" instead of "wakeup reason" on wake

[the_chuck77]

Hi,

When our S32K324 is in low power mode, we are encountering an issue with the Reset Type when wake.

If we wake the device immediately after the device enters low power mode, the Reset Type is a "Power on Reset" (0x00). However, if I wait ~5 seconds after the device enters low power mode, the Reset Type is "Wakeup_Reason" (0x1C).

What is causing this Power on Reset to occur when I am trying to wake? This is resulting the RTC counter value being reset.

I haven't been able to find anything with in the data sheet that could explain this behavior.

[Julián_AragónM]

Hi @the_chuck77,

Are you reading the reset reason with Power_Ip_GetResetReason? Also, could you please show the steps being done for "waking the device immediately"? And which wake-up source is being used as well.

Also, please check the state of PRTN1_COFB1_CLKEN. BLOCK53(FXOSC) and PRTN1_COFB1_CLKEN. BLOCK56(PLL). These two bits may impact the reset reason after the functional reset is triggered when either of the two bits are disabled and PLL is enabled.

Best regards,
Julián

[the_chuck77]

Hi @Julián_AragónM ,

Yes, I am reading the reset reason from Power_Ip_GetResetReason. I am also checking the RTC counter register value after a reset, and I can see the value being reset to 0 when the reset reason is "power on reset".

I am waking from one of the WKUP pins. Pin 102, configured as WKPU15. 

The steps I am following are:

1. Remove signal keeping device awake, and allow for it to begin its process of entering low power mode.
2. Watch current meter, wait for current to drop to low power mode current draw (just under 1 mA).
3. Once current has dropped to low power mode, send wake up signal to WKPU15. 
4. Observe the wakeup reason, and RTC counter value

Following these steps, I am able to reproduce the "power on reset" reset reason consistently if I perform step 3 within ~5 seconds of the current draw going below 1 mA. If I perform step 3 several seconds (>5+) after current draw I will consistently get "wakeup reason" as the reset reason.

PRTN1_COFB1_CLKEN Req 53 and Req56 are both 1 prior to setting the low power mode. When entering low power mode they are set to 0. 

[Julián_AragónM]

Hi @the_chuck77,

I'm not sure what is the cause of this issue. I am unable to reproduce it on the S32K344-T172 EVB. Attached is the project I used to test the case. It configures the OpenSDA UART instance and prints the reset reason (in my case, only "MCU_F_EXR_RESET" and "MCU_WAKEUP_REASON" apply):

With this, no matter the timing in the WKPU channel 42, I always get MCU_WAKEUP_REASON, unless I completely power-cycle the board (with Reset push button), in which case I will get MCU_F_EXR_RESET.

Could you compare your routine for entering and exiting standby to the project attached? And if possible, test this same project on your board. It would also be helpful to share your project/configuration.

Best regards,
Julián