STM32F7 Lockup issue after FAULTMASK is set

[Leo Cheng]

Posted on July 20, 2017 at 06:26

Hi ,

I ran into a lockup issue after  FAULTMASK is set by cpsid f. The software is running in SDRAM, and MPU is enabled, so instruction can be executed from SDRAM. At last, I found the lockup issue is gone if HFNMIENA bit is set. But I don't fully understand why from the 

STM32F7 Series Cortex�-M7 processor programming manual(PM0253):

HFNMIENA bit description:

Enables the operation of MPU during hard fault, NMI, and FAULTMASK

handlers.

  When the MPU is enabled:

  0: MPU is disabled during hard fault, NMI, and FAULTMASK handlers,

  regardless of the value of the ENABLE bit.

  1: The MPU is enabled during hard fault, NMI, and FAULTMASK handlers.

  When the MPU is disabled, if this bit is set to 1 the behavior is

  Unpredictable.

Unless HFNMIENA is set to 1, the MPU is not enabled when the processor is executing the handler for an exception with priority �1 or �2. These priorities are only possible when handling a hard fault or NMI exception, or when FAULTMASK is enabled. Setting the HFNMIENA bit to 1 enables the MPU when operating with these two priorities.

From the description, does that mean 

FAULTMASK is set will cause MPU is disabled if 

HFNMIENA bit is cleared?

#mpu #faultmask #stm32f7