Hard fault where faulting instruction address is located in static memory

[alexdr3437]

I am creating a BLE app on a nrf52833. I am running into the following fault at some point after I connect to a device (after advertising was successful). It does not occur at consistent time, but somewhere roughly 0-3 seconds after connecting.

[00:00:00.132,049] �[1;31m<err> os: ***** MPU FAULT *****�[0m
[00:00:00.132,202] �[1;31m<err> os:   Stacking error (context area might be not valid)�[0m
[00:00:00.132,263] �[1;31m<err> os:   Data Access Violation�[0m                
[00:00:00.132,324] �[1;31m<err> os:   MMFAR Address: 0x200080ec�[0m
[00:00:00.132,415] �[1;31m<err> os: r0/a1:  0x20001ea8  r1/a2:  0x20001ea8  r2/a3:  0x200080d0�[0m
[00:00:00.132,507] �[1;31m<err> os: r3/a4:  0x200080d0 r12/ip:  0x00000040 r14/lr:  0x20001ea8�[0m
[00:00:00.132,568] �[1;31m<err> os:  xpsr:  0x20001e00�[0m
[00:00:00.132,659] �[1;31m<err> os: Faulting instruction address (r15/pc): 0x20001dd0�[0m
[00:00:00.132,751] �[1;31m<err> os: >>> ZEPHYR FATAL ERROR 2: Stack overflow on CPU 0�[0m
[00:00:00.132,812] �[1;31m<err> os: Current thread: 0x20001dd0 (BT RX)�[0m
[00:00:00.307,098] �[1;31m<err> os: Halting system�[0m

The registers and faulting instruction address contain an address in static memory (except for r12)

The address 0x20001dd0 (apparently both the faulting address and the current thread?) is the bt_workq structure, with type struct k_work_q located in the file hci_core.c. Not sure if this is what is actually causing the issue.

Any idea how to fix this or what could be causing it?

[yashi]

Stacking error (context area might be not valid)

This is the key.

"AN209 – Using Cortex-M3/M4/M7 Fault Exceptions" says:

MSTKERR:
MemManage fault on stacking for exception entry:
0 = no stacking fault
1 = stacking for an exception entry has caused one or more access violations.

The SP is still adjusted but the values in the context area on the
stack might be incorrect. The processor has not written a fault
address to the MMFAR. Potential reasons:

a) Stack pointer is corrupted or not initialized
b) Stack is reaching a region not defined by the MPU as read/write memory.

Good luck!