Torbjorn,

thanks for the fast reply.

On 2022-10-16 10:13, Torbjorn SVENSSON wrote:

> >/  #0  0xeffffffe in ?? () />/  #1  0x0c000a9c in HardFault_Handler () />/      at />/C:/dvl/stm32l5trustzone/GPIO_IOToggle_TrustZone/Secure/Src/stm32l5xx_it.c:99 
> />/  #2  0x2002ffd8 in ?? () />/  Backtrace stopped: previous frame identical to this frame (corrupt />/stack?) />/  (gdb) />/---------------- />/The frame #1 is at correct PC taken from LR, #2 is a total nonsense. /
> I think your assumption here is wrong as 0xeffffffe is a valid value for
> Cortex-M33 with TrustZone (FNC_RETURN with S=0). See more on the comment
> below.
'B3.17 Function returns from Non-secure state' states:
The FNC_RETURN value is:
... the original is a binary value in a table, hard to convert to plain 
text ...
so if I convert correctly
0xfefffffe or 0xfeffffff depending on S bit.

Starts with 0xfe not 0xef as the lockup magic!

> Reading B3.33 (revision B.m) in the ARMv8-M documentation about lockup
> state, it's written that DHCSR.S_LOCKUP=1 AND PC=0xeffffffe. My
> interpretations that the PC value alone is not enough.

Hmm, how would we read DHCSR then?
IMO the PC value is enough.

Tomas