• State Not Answered
  • Locked Locked
  • Replies 0 replies
  • Subscribers 350 subscribers
  • Views 523 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Can Cortex-M33 MCUs enable SAU and MPU_NS simultaneously?

kiko

Hi everyone, I was trying to run FreeRTOS-MPU at the non-secure world (MPU_NS enabled) and some trusted code at the secure world (MPU_S disabled).

When I enabled SAU but disabled both MPU_S and MPU_NS, the program ran normally.

However, if I configured MPU_NS with proper permissions, the program encountered unexplainable errors.

In the vRestoreContextOfFirstTask function, the load instruction (address 0x08041030) after the store instruction (address 0x08041026) that enabled the MPU, triggered a Secure HardFault.


And I then checked the HFSR register, its value was 0x40000000. HFSR.FORCED indicated that there was an escalated exception.

So I further checked the CFSR_NS register, its value was 0x00000082. Apparently, there was a MemMange Fault and it finally escalated to a HardFault.

And I also checked the MMFAR register, its value was 0x2002b460, where was exactly read by the load instruction at address 0x08041030.


However, MPU_NS allowed read and write access to 0x2002b460 by any privileged level. Below is the configurations of MPU_NS, region 4 allows any privilege level read and write to range 0x200274a0 and 0x2002b4bf.


So the program tried to read 4 bytes of memory and its target was permitted by MPU_NS. However, it still triggered an MemManage Fault and escalated to a HardFault eventually.

However, it seemed strange that the value of SHCSR_NS indicating that the MemMange Fault for non-secure world was enabled.

Is there anything configured wrong or something conflicted between SAU and MPU? Thanks!

0