B1.41
Architectural Feature Access Control Register
The CPACR characteristics are:
Purpose
Controls access to CP0 to CP13, and indicates which of CP0 to CP13 are implemented.
Usage constraints
This register is accessible as follows:
EL0
(NS)
EL0
(S)
EL1
(NS)
EL1
(S)
EL2 EL3
(SCR.NS = 1)
EL3
(SCR.NS = 0)
-
-
RW
RW RW RW
RW
The CPACR has no effect on instructions executed at EL2.
Configurations
CPACR is architecturally mapped to AArch64 register CPACR_EL1. See
Feature Access Control Register, EL1
There is one copy of this register that is used in both Secure and Non-secure states.
Bits in the NSACR control Non-secure access to the CPACR fields. See the field descriptions
cp10 and cp11.
Attributes
CPACR is a 32-bit register.
31
24 23 22 21 20 19
0
RES
0
cp11 cp10
RES
0
30
ASEDIS
Figure B1-5 CPACR bit assignments
ASEDIS, [31]
Disable Advanced SIMD functionality:
0
Does not cause any instructions to be
UNDEFINED
. This is the reset value.
1
All instruction encodings that are part of Advanced SIMD, but that are not floating-point
instructions, are
UNDEFINED
.
If Advanced SIMD and floating-point are not implemented, this bit is
RES0
.
[30:24]
Reserved,
RES0
.
cp11, [23:22]
Defines the access rights for CP11, that control the Advanced SIMD and floating-point features.
Possible values of the fields are:
0b00
Access denied. Any attempt to access Advanced SIMD and floating-point registers or
instructions generates an Undefined Instruction exception. This is the reset value.
0b01
Access at EL1 only. Any attempt to access Advanced SIMD and floating-point registers
or instructions from software executing at EL0 generates an Undefined Instruction
exception.
0b10
Reserved.
B1 AArch32 system registers
B1.41 Architectural Feature Access Control Register
100236_0100_00_en
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