DC ISW, Data or unified Cache line Invalidate by Set/Way
The DC ISW characteristics are:
Invalidate data cache by set/way.
When ARMv8.5-MemTag is implemented, this instruction might invalidate Allocation Tags from caches. When it invalidates Allocation Tags from caches, it also cleans them.
AArch64 System instruction DC ISW performs the same function as AArch32 System instruction DCISW.
DC ISW is a 64-bit System instruction.
The DC ISW 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.
Executing the DC ISW 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:
DC ISW, <Xt>
if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TSW == '1' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EL2Enabled() && !ELUsingAArch32(EL2) && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGITR_EL2.DCISW == '1' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.SWIO == '1' then DC_CISW(X[t]); elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<DC,VM> != '00' then DC_CISW(X[t]); else DC_ISW(X[t]); elsif PSTATE.EL == EL2 then DC_ISW(X[t]); elsif PSTATE.EL == EL3 then DC_ISW(X[t]);