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DCCSW, Data Cache line Clean by Set/Way

The DCCSW characteristics are:


Clean data or unified cache line by set/way.


AArch32 System instruction DCCSW performs the same function as AArch64 System instruction DC CSW.

This instruction is present only when AArch32 is supported at any Exception level. Otherwise, direct accesses to DCCSW are UNDEFINED.


DCCSW is a 32-bit System instruction.

Field descriptions

The DCCSW input value bit assignments are:


SetWay, bits [31:4]

Contains two fields:

  • Way, bits[31:32-A], the number of the way to operate on.
  • Set, bits[B-1:L], the number of the set to operate on.

Bits[L-1:4] are RES0.

A = Log2(ASSOCIATIVITY), L = Log2(LINELEN), B = (L + S), S = Log2(NSETS).

ASSOCIATIVITY, LINELEN (line length, in bytes), and NSETS (number of sets) have their usual meanings and are the values for the cache level being operated on. The values of A and S are rounded up to the next integer.

Level, bits [3:1]

Cache level to operate on, minus 1. For example, this field is 0 for operations on L1 cache, or 1 for operations on L2 cache.

Bit [0]

Reserved, RES0.

Executing the DCCSW instruction

If this instruction is executed with a set, way or level argument that is larger than the value supported by the implementation then the behavior is CONSTRAINED UNPREDICTABLE and one of the following occurs:

  • The instruction is UNDEFINED
  • The instruction performs cache maintenance on one of:
    • No cache lines.
    • A single arbitrary cache line.
    • Multiple arbitrary cache lines.

Accesses to this instruction use the following encodings:

MCR{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

if PSTATE.EL == EL0 then
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T7 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T7 == '1' then
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TSW == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TSW == '1' then
elsif PSTATE.EL == EL2 then
elsif PSTATE.EL == EL3 then