|Home > Register descriptions > AArch64 system registers > CPUACTLR_EL1, CPU Auxiliary Control Register, EL1|
The CPUACTLR_EL1 provides IMPLEMENTATION DEFINED configuration and control options for the core.
CPUACTLR_EL1 is a 64-bit register, and is part of the IMPLEMENTATION DEFINED registers functional group.
|Reserved for Arm® internal use.|
CPUACTLR_EL1 is common to the Secure and Non-secure states.
The CPU Auxiliary Control Register can be written only when the system is idle. Arm recommends that you write to this register after a powerup reset, before the MMU is enabled.
Setting many of these bits can cause significantly lower performance on your code. Therefore, Arm strongly recommends that you do not modify this register unless directed by Arm.
This register is accessible as follows:
This register can be read with the MRS instruction using the following syntax:
This register can be written with the MSR instruction using the following syntax:
MSR <systemreg>, <Xt>
This syntax is encoded with the following settings in the instruction encoding:
This register is accessible in software as follows:
'n/a' Not accessible. The core cannot be executing at this Exception level, so this access is not possible.
For a description of the prioritization of any generated exceptions, see Synchronous exception prioritization in the Arm® Architecture Reference Manual Armv8, for Armv8-A architecture profile.