DMB Data Memory Barrier Data Memory Barrier is a memory barrier that ensures the ordering of observations of memory accesses, see Data Memory Barrier (DMB). For more information about the CONSTRAINED UNPREDICTABLE behavior, see Architectural Constraints on UNPREDICTABLE behaviors. It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) . 1 1 1 1 0 1 0 1 0 1 1 1 (1) (1) (1) (1) (1) (1) (1) (1) (0) (0) (0) (0) 0 1 0 1 DMB{<c>}{<q>} {<option>} // No additional decoding required 1 1 1 1 0 0 1 1 1 0 1 1 (1) (1) (1) (1) 1 0 (0) 0 (1) (1) (1) (1) 0 1 0 1 DMB{<c>}{<q>} {<option>} // No additional decoding required <c> For the "A1" variant: see Standard assembler syntax fields. Must be AL or omitted. <c> For the "T1" variant: see Standard assembler syntax fields. <q> See Standard assembler syntax fields. <option> Specifies an optional limitation on the barrier operation. Values are: SY Full system is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. Can be omitted. This option is referred to as the full system barrier. Encoded as option = 0b1111. ST Full system is the required shareability domain, writes are the required access type, both before and after the barrier instruction. SYST is a synonym for ST. Encoded as option = 0b1110. LD Full system is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as option = 0b1101. ISH Inner Shareable is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. Encoded as option = 0b1011. ISHST Inner Shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as option = 0b1010. ISHLD Inner Shareable is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as option = 0b1001. NSH Non-shareable is the required shareability domain, reads and writes are the required access, both before and after the barrier instruction. Encoded as option = 0b0111. NSHST Non-shareable is the required shareability domain, writes are the required access type both before and after the barrier instruction. Encoded as option = 0b0110. NSHLD Non-shareable is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as option = 0b0101. OSH Outer Shareable is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. Encoded as option = 0b0011. OSHST Outer Shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as option = 0b0010. OSHLD Outer Shareable is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as option = 0b0001. For more information on whether an access is before or after a barrier instruction, see Data Memory Barrier (DMB). All other encodings of option are reserved. All unsupported and reserved options must execute as a full system DMB operation, but software must not rely on this behavior. The instruction supports the following alternative <option> values, but Arm recommends that software does not use these alternative values: SH as an alias for ISH. SHST as an alias for ISHST. UN as an alias for NSH. UNST as an alias for NSHST. if ConditionPassed() then EncodingSpecificOperations(); var domain : MBReqDomain; var types : MBReqTypes; case option of when '0001' => domain = MBReqDomain_OuterShareable; types = MBReqTypes_Reads; when '0010' => domain = MBReqDomain_OuterShareable; types = MBReqTypes_Writes; when '0011' => domain = MBReqDomain_OuterShareable; types = MBReqTypes_All; when '0101' => domain = MBReqDomain_Nonshareable; types = MBReqTypes_Reads; when '0110' => domain = MBReqDomain_Nonshareable; types = MBReqTypes_Writes; when '0111' => domain = MBReqDomain_Nonshareable; types = MBReqTypes_All; when '1001' => domain = MBReqDomain_InnerShareable; types = MBReqTypes_Reads; when '1010' => domain = MBReqDomain_InnerShareable; types = MBReqTypes_Writes; when '1011' => domain = MBReqDomain_InnerShareable; types = MBReqTypes_All; when '1101' => domain = MBReqDomain_FullSystem; types = MBReqTypes_Reads; when '1110' => domain = MBReqDomain_FullSystem; types = MBReqTypes_Writes; otherwise => domain = MBReqDomain_FullSystem; types = MBReqTypes_All; end; if PSTATE.EL IN {EL0, EL1} && EL2Enabled() then if HCR().BSU == '11' then domain = MBReqDomain_FullSystem; end; if HCR().BSU == '10' && domain != MBReqDomain_FullSystem then domain = MBReqDomain_OuterShareable; end; if HCR().BSU == '01' && domain == MBReqDomain_Nonshareable then domain = MBReqDomain_InnerShareable; end; end; DataMemoryBarrier(domain, types); end; 2026-03-12 12:23:09 2025-09_rel_asl1