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DSB

Data Synchronization Barrier is a memory barrier that ensures the completion of memory accesses, see Data Synchronization Barrier.

313029282726252423222120191817161514131211109876543210
11010101000000110011!= 0x0010011111
CRmopc

System

DSB <option>|#<imm>

MemBarrierOp op;
MBReqDomain domain;
MBReqTypes types;

op = MemBarrierOp_DSB;
case CRm<3:2> of
    when '00' domain = MBReqDomain_OuterShareable;
    when '01' domain = MBReqDomain_Nonshareable;
    when '10' domain = MBReqDomain_InnerShareable;
    when '11' domain = MBReqDomain_FullSystem;

case CRm<1:0> of
    when '01' types = MBReqTypes_Reads;
    when '10' types = MBReqTypes_Writes;
    when '11' types = MBReqTypes_All;
    otherwise
        if CRm<3:2> == '01' then
            op = MemBarrierOp_PSSBB;
        elsif CRm<3:2> == '00' then
            op = MemBarrierOp_SSBB;
        elsif HaveSBExt() && FALSE then
            op = MemBarrierOp_SB;
        else
            types = MBReqTypes_All;
            domain = MBReqDomain_FullSystem;

Assembler Symbols

<option>

Specifies the 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. This option is referred to as the full system barrier. Encoded as CRm = 0b1111.
ST
Full system is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 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 CRm = 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 CRm = 0b1011.
ISHST
Inner Shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 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 CRm = 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 CRm = 0b0111.
NSHST
Non-shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 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 CRm = 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 CRm = 0b0011.
OSHST
Outer Shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 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 CRm = 0b0001.

All other encodings of CRm that are not listed above are reserved, and can be encoded using the #<imm> syntax. It is implementation defined whether options other than SY are implemented. All unsupported and reserved options must execute as a full system barrier operation, but software must not rely on this behavior. For more information on whether an access is before or after a barrier instruction, see Data Memory Barrier (DMB) or see Data Synchronization Barrier (DSB).

<imm>

Is a 4-bit unsigned immediate, in the range 0 to 15, encoded in the "CRm" field.

Operation

case op of
    when MemBarrierOp_DSB
        DataSynchronizationBarrier(domain, types);
    when MemBarrierOp_DMB
        DataMemoryBarrier(domain, types);
    when MemBarrierOp_ISB
        InstructionSynchronizationBarrier();
    when MemBarrierOp_SSBB
        SpeculativeStoreBypassBarrierToVA();
    when MemBarrierOp_PSSBB
        SpeculativeStoreBypassBarrierToPA();
    when MemBarrierOp_SB
        SpeculationBarrier();
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