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DMB

Data Memory Barrier.

Syntax

DMB{cond} {option}

where:

cond

is an optional condition code.

Note

cond is permitted only in T32 code. This is an unconditional instruction in A32.
option

is an optional limitation on the operation of the hint. Permitted values are:

SY

Full system DMB operation. This is the default and can be omitted.

LD

DMB operation that waits only for loads to complete.

ST

DMB operation that waits only for stores to complete.

ISH

DMB operation only to the inner shareable domain.

ISHLD

DMB operation that waits only for loads to complete, and only applies to the inner shareable domain.

ISHST

DMB operation that waits only for stores to complete, and only to the inner shareable domain.

NSH

DMB operation only out to the point of unification.

NSHLD

DMB operation that waits only for loads to complete and only applies out to the point of unification.

NSHST

DMB operation that waits only for stores to complete and only out to the point of unification.

OSH

DMB operation only to the outer shareable domain.

OSHLD

DMB operation that waits only for loads to complete, and only applies to the outer shareable domain.

OSHST

DMB operation that waits only for stores to complete, and only to the outer shareable domain.

Note

The options LD, ISHLD, NSHLD, and OSHLD are supported only in ARMv8.

Operation

Data Memory Barrier acts as a memory barrier. It ensures that all explicit memory accesses that appear in program order before the DMB instruction are observed before any explicit memory accesses that appear in program order after the DMB instruction. It does not affect the ordering of any other instructions executing on the processor.

Alias

The following alternative values of option are supported, but ARM recommends that you do not use them:

  • SH is an alias for ISH.
  • SHST is an alias for ISHST.
  • UN is an alias for NSH.
  • UNST is an alias for NSHST.

Architectures

This 32-bit instruction is available in A32 and T32.

There is no 16-bit version of this instruction in T32.

Related reference

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