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CLIDR_EL1, Cache Level ID Register

The CLIDR_EL1 characteristics are:

Purpose

Identifies the type of cache, or caches, that are implemented at each level and can be managed using the architected cache maintenance instructions that operate by set/way, up to a maximum of seven levels. Also identifies the Level of Coherence (LoC) and Level of Unification (LoU) for the cache hierarchy.

Configuration

AArch64 System register CLIDR_EL1 bits [31:0] are architecturally mapped to AArch32 System register CLIDR[31:0] .

Attributes

CLIDR_EL1 is a 64-bit register.

Field descriptions

The CLIDR_EL1 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0Ttype<n>, bits [2(n-1)+34:2(n-1)+33], for n = 1 to 7ICB
ICBLoUULoCLoUISCtype7Ctype6Ctype5Ctype4Ctype3Ctype2Ctype1
313029282726252423222120191817161514131211109876543210

Bits [63:47]

Reserved, RES0.

Ttype<n>, bits [2(n-1)+34:2(n-1)+33], for n = 1 to 7

When ARMv8.5-MemTag is implemented:

Tag cache type. Indicate the type of cache that is implemented and can be managed using the architected cache maintenance instructions that operate by set/way at each level, from Level 1 up to a maximum of seven levels of cache hierarchy.

Ttype<n>Meaning
0b00

No Tag Cache.

0b01

Separate Allocation Tag Cache.

0b10

Unified Allocation Tag and Data cache, Allocation Tags and Data in unified lines.

0b11

Unified Allocation Tag and Data cache, Allocation Tags and Data in separate lines.


Otherwise:

Reserved, RES0.

ICB, bits [32:30]

Inner cache boundary. This field indicates the boundary for caching Inner Cacheable memory regions.

The possible values are:

ICBMeaning
0b000

Not disclosed by this mechanism.

0b001

L1 cache is the highest Inner Cacheable level.

0b010

L2 cache is the highest Inner Cacheable level.

0b011

L3 cache is the highest Inner Cacheable level.

0b100

L4 cache is the highest Inner Cacheable level.

0b101

L5 cache is the highest Inner Cacheable level.

0b110

L6 cache is the highest Inner Cacheable level.

0b111

L7 cache is the highest Inner Cacheable level.

LoUU, bits [29:27]

Level of Unification Uniprocessor for the cache hierarchy.

LoC, bits [26:24]

Level of Coherence for the cache hierarchy.

LoUIS, bits [23:21]

Level of Unification Inner Shareable for the cache hierarchy.

Ctype<n>, bits [3(n-1)+2:3(n-1)], for n = 1 to 7

Cache Type fields. Indicate the type of cache that is implemented and can be managed using the architected cache maintenance instructions that operate by set/way at each level, from Level 1 up to a maximum of seven levels of cache hierarchy. Possible values of each field are:

Ctype<n>Meaning
0b000

No cache.

0b001

Instruction cache only.

0b010

Data cache only.

0b011

Separate instruction and data caches.

0b100

Unified cache.

All other values are reserved.

If software reads the Cache Type fields from Ctype1 upwards, once it has seen a value of 000, no caches that can be managed using the architected cache maintenance instructions that operate by set/way exist at further-out levels of the hierarchy. So, for example, if Ctype3 is the first Cache Type field with a value of 000, the values of Ctype4 to Ctype7 must be ignored.

Accessing the CLIDR_EL1

Accesses to this register use the following encodings:

MRS <Xt>, CLIDR_EL1

op0op1CRnCRmop2
0b110b0010b00000b00000b001
if PSTATE.EL == EL0 then
    if IsFeatureImplemented("ARMv8.4-IDST") then
        if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TGE == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            AArch64.SystemAccessTrap(EL1, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID2 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID4 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGRTR_EL2.CLIDR_EL1 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        return CLIDR_EL1;
elsif PSTATE.EL == EL2 then
    return CLIDR_EL1;
elsif PSTATE.EL == EL3 then
    return CLIDR_EL1;
              


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