B2.31
Architectural Feature Access Control Register, EL1
The CPACR_EL1 characteristics are:
Purpose
Controls access to trace functionality and access to registers associated with Advanced SIMD
and floating-point execution.
CPACR_EL1 is part of the Other system registers functional group.
Usage constraints
This register is accessible as follows:
EL0 EL1
(NS)
EL1
(S)
EL2 EL3
(SCR.NS = 1)
EL3
(SCR.NS = 0)
-
RW
RW RW RW
RW
Configurations
CPACR_EL1 is architecturally mapped to AArch32 register CPACR. See
Feature Access Control Register
.
Attributes
CPACR_EL1 is a 32-bit register.
31
0
RES
0
TTA
RES
0
FPEN
19
28 27
20
21
22
29
RES
0
Figure B2-6 CPACR_EL1 bit assignments
[31:29]
Reserved,
RES0
.
TTA, [28]
Causes access to the Trace functionality to trap to EL1 when executed from EL0 or EL1.
This bit is
RES0
.
[27:22]
Reserved,
RES0
.
FPEN, [21:20]
Traps instructions that access registers associated with Advanced SIMD and floating-point
execution to trap to EL1 when executed from EL0 or EL1. The possible values are:
0bX0
Trap any instruction in EL0 or EL1 that uses registers associated with Advanced SIMD
and floating-point execution. The reset value is
0b00
.
0b01
Trap any instruction in EL0 that uses registers associated with Advanced SIMD and
floating-point execution. Instructions in EL1 are not trapped.
0b11
No instructions are trapped.
This field is
RES0
if Advanced SIMD and floating-point are not implemented.
[19:0]
Reserved,
RES0
.
B2 AArch64 system registers
B2.31 Architectural Feature Access Control Register, EL1
100236_0100_00_en
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B2-402
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Summary of Contents for Cortex-A35
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