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

scribnote5

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,

Parents
  • +1 in reply to scribnote5

    AFAIK runs Linux in normal world (non-secure). The bootloader (U-Boot or even the first stage boot-loader) will switch to non-secure.

    If you want to change NSACR you have to run at least a secure monitor.
    But if you have software running in privileged mode, you can check the SCR.NS (MRC p15, 0, <Rt>, c1, c1, 0 ; Read SCR into Rt).

Reply
  • +1 in reply to scribnote5

    AFAIK runs Linux in normal world (non-secure). The bootloader (U-Boot or even the first stage boot-loader) will switch to non-secure.

    If you want to change NSACR you have to run at least a secure monitor.
    But if you have software running in privileged mode, you can check the SCR.NS (MRC p15, 0, <Rt>, c1, c1, 0 ; Read SCR into Rt).

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