This discussion has been locked.

You can no longer post new replies to this discussion. If you have a question you can start a new discussion

How to enable acces to some registers in ARM cortex a9

Note: This was originally posted on 9th November 2011 at http://forums.arm.com

Hi,

I am trying to execute the following code, which hangs when it tries to execute the second instruction:
....
mrc p15, 0, r1, c15, c0, 1
mcr p15, 0, r1, c15, c0, 1
....
Could you please tell me the reason why it hangs and how it can be fixed? Is there a way how I can enable access to the registers?

Thanks

qwerty ytrewq over 12 years ago

Note: This was originally posted on 9th November 2011 at http://forums.arm.com

Hi SGS,
I could advise you to have a look at the operating modes.
Switching to Supervisor mode would allow access to special registers.
Have you had a look at the Cortex-A Programmers' Guide from ARM?
Kindly,
Alban

I have tried the following code, which I have placed in the startup function of the OS:

ldr r0, =0x13; Supervisor mode
msr cpsr_cx, r0
mrc p15, 0, r1, c15, c0, 1; This line is fine
mcr p15, 0, r1, c15, c0, 1 ; and this one hangs

No clue here...
Cancel
Vote up 0 Vote down

Cancel
qwerty ytrewq over 12 years ago

Note: This was originally posted on 9th November 2011 at http://forums.arm.com

I have tried the following code, which I have placed in the startup function of the OS:

ldr r0, =0x13; Supervisor mode
msr cpsr_cx, r0
mrc p15, 0, r1, c15, c0, 1; This line is fine
mcr p15, 0, r1, c15, c0, 1 ; and this one hangs

No clue here...

Ok, It seems that the CPU needs to be in secure state. But the problem is that OS boots in non-secure state. Is there anything that I can do to switch to secure state from non secure state. I need to write to the diagnostic register to fix some erratas. Now it seems a loot like a deadlock.
Cancel
Vote up 0 Vote down

Cancel
Jerry Fan over 12 years ago

Note: This was originally posted on 16th November 2011 at http://forums.arm.com

try smc instruction.
Cancel
Vote up 0 Vote down

Cancel
Alban Rampon over 12 years ago

Note: This was originally posted on 9th November 2011 at http://forums.arm.com

Hi SGS,
I could advise you to have a look at the operating modes.
Switching to Supervisor mode would allow access to special registers.
Have you had a look at the Cortex-A Programmers' Guide from ARM?
Kindly,
Alban
Cancel
Vote up 0 Vote down

Cancel