Why NSCAR(Non-secure Access Control Register) changes often?

Hello, experts:

My platform has a Cortex-A9 MPCore CPU, It supports trustzone tech.

I tried to change NSACR.TL bit, but It needs to change in the secure state.

I checked NSACR value in non-secure state and NSACR value that I changed is changed aperiodically.

For example print value;


nsacr : 0x00000000
nsacr : 0x00000000
nsacr : 0x00000000

....
nsacr : 0x00200000
nsacr : 0x00200000
nsacr : 0x00200000
....

nsacr : 0x00000000
nsacr : 0x00000000
nsacr : 0x00000000


Is NSACR.TL changed correctly?

Why NSACR value changed aperiodcially?


Best wishes,