How to place FreeRTOS in secure memory and the user tasks in non-secure memory?

In Non-secure task stack：

The stack frame as following:

Thanks

Regarding stack frame, sorry for not clear. I meant the stack frame you created in Non-secure stack for the exception return to take place. What is in that stack frame?

Hi Joseph

1) The psp_ns set to Non-secure memory.

2) The stack frame is standard stack frame , the value of the xPSR seems to be incorrect(T bit set , IPSR=3)

3) In PendSV interrupt, the PC is pointing Secure memory, new PC value is stored in the non-secure task stack and the new PC will point Non-secure memory.

4) The value of the fault status registers are shown as following:

CFSR:0X00000000 

HFSR:0X40000000

DFSR:0X00000001

AFSR:0X00000000

SFSR:0X00000000

Can you help me analyze the cause of the HardFault?

Thanks.

Best Regards

Yang Zhang

There could be different causes for the HardFault:

- is the PSP_NS set correctly to Non-secure memory?

- what is in the stack frame? Was the stacked xPSR correct? (T bit set and IPSR=0)

- Is the PC value really pointing to Non-secure memory?

- what is showing in the fault status registers?

Hi Joseph

Thank you for your answer, but after I change the value of r14 (EXC_RETURN) from 0XFFFFFFFD to 0XFFFFFFBD in the PendSV interrupt, when the "bx r14" is executed, the program enters the hardfault state, it seems 0XFFFFFFBD is an illegal EXC_RETURN value?

Best Regards

Yang Zhang

Assumed that

- Non-secure task use PSP_NS (pointing to return stack for the Non-secure task)

- At the beginning of the Non-secure task, FPCA was 0 (no floating point context at start)

You can return from Secure handler to Non-secure thread with a EXC_RETURN code of 0xFFFFFFBD.

However, with the guidance from PSA & Trusted Firmware team, the plan for FreeRTOS port is to have the OS running in Non-secure world, and OS helper APIs in Secure world to help context switching.

regards,

Joseph