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ISB

Instruction Synchronization Barrier.

Syntax

ISB {option|#imm}

Where:

option

Specifies an optional limitation on the barrier operation. Values are:

SY
Full system barrier operation. Can be omitted.
The instructions corresponding to options other than SY execute as full system barrier operations, but your code must not rely on this.
imm

Is an optional 4-bit unsigned immediate, in the range 0 to 15, defaulting to 15.

Usage

Instruction Synchronization Barrier flushes the pipeline in the PE, so that all instructions following the ISB are fetched from cache or memory, after the instruction has been completed. It ensures that the effects of context changing operations executed before the ISB instruction are visible to the instructions fetched after the ISB. Context changing operations include changing the ASID, TLB maintenance instructions, and all changes to the System registers. In addition, any branches that appear in program order after the ISB instruction are written into the branch prediction logic with the context that is visible after the ISB instruction. This is needed to ensure correct execution of the instruction stream. For more information, see Instruction Synchronization Barrier (ISB) in the ARMv8-A Architecture Reference Manual.

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