What is the correct procedure to recover an STM32L4x that has been put in Shutdown and experiences a brown out or POR. it shows the correct flags after reset, but the same flags appear after subsequent Shutdown periods.

[dtrae.1]

This is the sequence of events:

1. Enter Shutdown with RTC Wake up timer enabled (5 seconds)
2. Brown out, remove and restore power
3. POR Reset occurs, correct PWR->CSR = 0x0C000600
4. Clear CSR flags by writing 1 to RMVF in CSR
5. Read CSR flags and confirm they are clear
6. Enter Shutdown with RTC Wake up timer enabled (5 seconds)
7. Reset occurs from Wake up timer, incorrect PWR->CSR = 0x0C000600

[waclawek.jan]

Which 'L4 exactly? Is this some "known good" hardware like Nucleo/Disco? Is there any battery/capacitor on VBAT? Is the supply removal complete (VDD shoes hard to ground)? Is the power supply voltage high enough and stable during second wake-up? Is the behaviour different without the brownout?

JW

[dtrae.1]

I'm seeing this on STM32L475VGT and STM32L475VET. I've demonstrated the issue on the B-L475E-IOT01A Discovery kit as well as my own hardware. Powered by battery or a power supply.

[waclawek.jan]

 Is the behaviour different without the brownout?

JW

[dtrae.1]

Yes, for example if you give a low going pulse on the NRST pin, you get the PINRST flag for the corresponding wake/reset. The following wake the flag is cleared as it should be.