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4.3.79. CPU Extended Control Register, EL1

The CPUECTLR_EL1 characteristics are:

Purpose

Provides additional implementation defined configuration and control options for the processor.

Usage constraints

This register is accessible as follows:

EL0

EL1

(NS)

EL1

(S)

EL2

EL3

(SCR.NS = 1)

EL3

(SCR.NS = 0)

-RWRWRWRWRW

The CPUECTLR_EL1 can be written dynamically.

The CPUECTLR_EL1 is write accessible in EL1 if ACTLR_EL3.CPUECTLR is 1 and ACTLR_EL2.CPUECTLR is 1, or ACTLR_EL3.CPUECTLR is 1 and SCR.NS is 0.

The CPUECTLR_EL1 is write accessible in EL2 if ACTLR_EL3.CPUECTLR is 1.

Configurations

The CPUECTLR_EL1 is:

Attributes

CPUECTLR_EL1 is a 64-bit register.

Figure 4.72 shows the CPUECTLR_EL1 bit assignments.

Figure 4.72. CPUECTLR_EL1 bit assignments

Figure 4.72. CPUECTLR_EL1 bit assignments

Table 4.125 shows the CPUECTLR_EL1 bit assignments.

Table 4.125. CPUECTLR_EL1 bit assignments
BitsNameFunction
[63:7]-

Reserved, res0.

[6]

SMPEN

Enable hardware management of data coherency with other cores in the cluster. The possible values are:

0

Disables data coherency with other cores in the cluster. This is the reset value.

1

Enables data coherency with other cores in the cluster.

Note

Set the SMPEN bit before enabling the caches, even if there is only one core in the system.

[5:3]-

Advanced SIMD and Floating-point retention control. The possible values are:

0b000

Disable the retention circuit. This is the reset value.

0b001

2 Architectural Timer ticks are required before retention entry.

0b010

8 Architectural Timer ticks are required before retention entry.

0b011

32 Architectural Timer ticks are required before retention entry.

0b100

64 Architectural Timer ticks are required before retention entry.

0b101

128 Architectural Timer ticks are required before retention entry.

0b110

256 Architectural Timer ticks are required before retention entry.

0b111

512 Architectural Timer ticks are required before retention entry.

Note

This field is present only if the Advanced SIMD and Floating-point Extension is implemented. Otherwise, it is res0.

Software must not rely on retention state entry when the system counter is in low-power modes where CNTVALUEB increments are greater than 1. Entry to retention state relies on the system counter increments being +1.

[2:0]-

CPU retention control. The possible values are:

0b000

Disable the retention circuit. This is the reset value.

0b001

2 Architectural Timer ticks are required before retention entry.

0b010

8 Architectural Timer ticks are required before retention entry.

0b011

32 Architectural Timer ticks are required before retention entry.

0b100

64 Architectural Timer ticks are required before retention entry.

0b101

128 Architectural Timer ticks are required before retention entry.

0b110

256 Architectural Timer ticks are required before retention entry.

0b111

512 Architectural Timer ticks are required before retention entry.

Note

Software must not rely on retention state entry when the system counter is in low-power modes where CNTVALUEB increments are greater than 1. Entry to retention state relies on the system counter increments being +1.


To access the CPUECTLR_EL1:

MRS <Xt>, S3_1_C15_C2_1; Read EL1 CPU Extended Control Register
MSR S3_1_C15_C2_1, <Xt>; Write EL1 CPU Extended Control Register
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