Hi Gaurav !
I found the next. That Fault is visible in case when privileged task call NSC API and this API really execute SVC call on secure side. ( This call set new MCU clock and have typical BOARD_BootClockPLL150M() context.)
Setting new clock require atomic execution of one API and better ta have it as SVC call.
If nonprivileged task call this NSC API - no problem.
It means privileged secure context cause problems with SVC call on secure side for privileged tasks. Is this have sense ?
I have tried other sequence and from privilege task on non-secure side arise SVC and it call NSC function ( without SVC on secure side) what set new clock. It works, but next simple NSC call from nonprivileged task cause other type of fault :
Entering HardFault interrupt!
SAU->SFSR:INVEP fault: Invalid entry point to secure world.
Another secure bus error.
What I can’t say for sure today if both type of SVC calls are legal.
But I think there are.
nonsecure/nonprivileged task side can call NSC and it arise SVC call asap for have privilege/atomic execution of something.
nonsecure side can arise own SVC and it call regular NSC API.
May be nonsecure SVC call can’t arise NSC what arise SVC on secure side.
It means privileged secure context have some effect for secure side.