ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Virtual Memory System Architecture (VMSA)
Accessing the NSACR
If multiple coprocessors are used to control a feature then the Non-secure access enable bits
for those coprocessors must be set to the same value, otherwise behavior is UNPREDICTABLE.
For example, when the VFP extension is implemented it is controlled by coprocessors 10
and 11, and bits [10,11] of the NSACR must be set to the same value.
For bits that correspond to coprocessors that are not implemented, it is IMPLEMENTATION
DEFINED whether the bits:
behave as RAZ/WI
can be written by Secure privileged modes.
To access the NSACR you read or write the CP15 registers with set to 0, set to c1, set to
c1, and set to 2. For example:
MRC p15,0,,c1,c1,2 ; Read CP15 Non-Secure Access Control Register
MCR p15,0,,c1,c1,2 ; Write CP15 Non-Secure Access Control Register
You can write to the NSACR only in Secure privileged modes.
You can read the register in any privileged mode.
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