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How to update the trusted firmware for Juno board?

Shengye Wan

Hi experts ,

I have a Juno r1 board and I'm using it as the instruction of this page's "Building from source" section.

Now I want to update some secure related registers (e.g., SCR_EL3) for my board. These update operations require EL3 privilege.

In this case, I think I need to write the code in secure monitor layer. I hope I can update the register value while booting time so I think I should add code in the BL2 or BL31 according to the Linaro slides page8.

My workspace contains the folder arm-tf which looks like the part I should work with.

However, after running script build-arm-tf.sh, I do get the bl2.bin and bl31.bin while I don't know how to push these files into my board and use them for trusted booting. 

So my questions are:

1. To update the register with EL3 privilege, should I add code in trusted firmware layer?

2. Can I update the trusted firmware by myself for Juno r1? If I can, how?

If I misunderstand any part, please let me know. 

Thank you in advance.

Shengye

Parents Reply Children
  • 0 in reply to Mark Nicholson

    Hi Mark,

    Thank you for the reply. Your post did help me rebuild the firmware bin file.

    However, now I met a new problem.

    Currently I'm trying to write several system control registers with EL3 privilege such as SCR_EL3. 

    I put my code in the trusted firmware boot loader (BL31).

    Here is my code that I put in the bl31_main of arm-trusted-firmware-source-code:

    asm("MRS    %x[result], SCR_EL3"
    : [result] "=r" (scr)
);

asm("MSR    SCR_EL3, %x[value]"
    :
    : [value] "r"   (scr)
);

    I can read the value of the register correctly and I checked the register CurrentEL which says I did have the EL3 privilege.

    However, every time after I write new value to SCR_EL3, its value doesn't change.

    I also tried several other registers (some registers only requires EL1 privilege while I can't write anyone successfully with the instruction MSR).

    Now I cannot come up with what might cause this problem. Do you have any idea or suggestion for my problem?

    Thank you in advanced.

    Simon

  • 0 Arm Employee Badge in reply to Shengye Wan

    AT BL3-1 I don't see any immediate reason why you can't modify these registers because of privilege.

    Do you have a debugger (e.g. DS-5/DSTREAM) so you can step through this one instruction and a time and check the status of these system register updates?

    GUESSES, but...

    - Are you using the right access size for the register (check the ARM ARM)?

    - Could the update be successful, but changes are overwritten again elsewhere in the firmware? You could try putting some instrumentation/printfs in the code to see if you can learn more.