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CCSIDR, Current Cache Size ID Register

The CCSIDR characteristics are:

Purpose

Provides information about the architecture of the currently selected cache.

When ARMv8.3-CCIDX is implemented, this register is used in conjunction with CCSIDR2.

Configuration

AArch32 System register CCSIDR bits [31:0] are architecturally mapped to AArch64 System register CCSIDR_EL1[31:0] .

The implementation includes one CCSIDR for each cache that it can access. CSSELR and the Security state select which Cache Size ID Register is accessible.

Attributes

CCSIDR is a 32-bit register.

Field descriptions

The CCSIDR bit assignments are:

When ARMv8.3-CCIDX is implemented:
313029282726252423222120191817161514131211109876543210
00000000AssociativityLineSize

Note

The parameters NumSets, Associativity, and LineSize in these registers define the architecturally visible parameters that are required for the cache maintenance by Set/Way instructions. They are not guaranteed to represent the actual microarchitectural features of a design. You cannot make any inference about the actual sizes of caches based on these parameters.

Bits [31:24]

Reserved, RES0.

Associativity, bits [23:3]

(Associativity of cache) - 1, therefore a value of 0 indicates an associativity of 1. The associativity does not have to be a power of 2.

LineSize, bits [2:0]

(Log2(Number of bytes in cache line)) - 4. For example:

For a line length of 16 bytes: Log2(16) = 4, LineSize entry = 0. This is the minimum line length.

For a line length of 32 bytes: Log2(32) = 5, LineSize entry = 1.

Otherwise:
313029282726252423222120191817161514131211109876543210
UNKNOWNNumSetsAssociativityLineSize

Note

The parameters NumSets, Associativity, and LineSize in these registers define the architecturally visible parameters that are required for the cache maintenance by Set/Way instructions. They are not guaranteed to represent the actual microarchitectural features of a design. You cannot make any inference about the actual sizes of caches based on these parameters.

UNKNOWN, bits [31:28]

Reserved, UNKNOWN.

NumSets, bits [27:13]

(Number of sets in cache) - 1, therefore a value of 0 indicates 1 set in the cache. The number of sets does not have to be a power of 2.

Associativity, bits [12:3]

(Associativity of cache) - 1, therefore a value of 0 indicates an associativity of 1. The associativity does not have to be a power of 2.

LineSize, bits [2:0]

(Log2(Number of bytes in cache line)) - 4. For example:

For a line length of 16 bytes: Log2(16) = 4, LineSize entry = 0. This is the minimum line length.

For a line length of 32 bytes: Log2(32) = 5, LineSize entry = 1.

Accessing the CCSIDR

If CSSELR.Level is programmed to a cache level that is not implemented, then on a read of the CCSIDR the behavior is CONSTRAINED UNPREDICTABLE, and can be one of the following:

  • The CCSIDR read is treated as NOP.
  • The CCSIDR read is UNDEFINED.
  • The CCSIDR read returns an UNKNOWN value.

Accesses to this register use the following encodings:

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

opc1opc2CRncoprocCRm
0b0010b0000b00000b11110b0000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T0 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T0 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID2 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID4 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TID2 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR2.TID4 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        return CCSIDR;
elsif PSTATE.EL == EL2 then
    return CCSIDR;
elsif PSTATE.EL == EL3 then
    return CCSIDR;
              


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