OMAP-L138: How can I access PBBPR register?

Part Number:OMAP-L138

Hi Champs,

My application using SYS/BIOS can not access the DDR2/mDDR.PBBPR register.
I'm trying to access it in main() before BIOS_start(), but I can not. Is there any setting what I should do before the access?
Is the privileged mode required? Do I have to set it in the initializing procedure?

Regards,
j-breeze