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Cache Size ID Register

The CCSIDR characteristics are:

Purpose

Provides information about the architecture of the caches.

Usage constraints

This register is accessible as follows:

EL0

(NS)

EL0

(S)

EL1

(NS)

EL1

(S)

 EL2

EL3

(SCR.NS = 1)

EL3

(SCR.NS = 0)
- - RO RO RO RO RO

If CSSELR indicates a cache 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 (preferred).

Configurations

CCSIDR is architecturally mapped to AArch64 register CCSIDR_EL1. See Cache Size ID Register.

There is one copy of this register that is used in both Secure and Non-secure states.

The implementation includes one CCSIDR for each cache that it can access. CSSELR selects which Cache Size ID Register is accessible.

Attributes

CCSIDR is a 32-bit register.

Figure 4.92 shows the CCSIDR bit assignments.

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Table 4.190 shows the CCSIDR bit assignments.

Table 4.190. CCSIDR bit assignments
Bits Name Function
[31] WT

Indicates support for Write-Through:

0

Cache level does not support Write-Through.

[30] WB

Indicates support for Write-Back:

0

Cache level does not support Write-Back.

1

Cache level supports Write-Back.

[29] RA

Indicates support for Read-Allocation:

0

Cache level does not support Read-Allocation.

1

Cache level supports Read-Allocation.

[28] WA

Indicates support for Write-Allocation:

0

Cache level does not support Write-Allocation.

1

Cache level supports Write-Allocation.

[27:13] NumSets[a]

Indicates the 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.

[12:3] Associativity[a]

Indicates the 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.

[2:0] LineSize[a]

Indicates the (log2 (number of words in cache line)) - 2:

0b010

16 words per line.

[a] For more information about encoding, see Table 4.191.


Table 4.191 shows the individual bit field and complete register encodings for the CCSIDR. The CSSELR determines which CCSIDR to select.

Table 4.191. CCSIDR encodings
CSSELR Cache Size Complete register encoding Register bit field encoding
WT WB RA WA NumSets Associativity LineSize
0x0 L1 Data cache 8KB 0x7003E01A 0 1 1 1 0x001F 0x003 0x2
16KB 0x7007E01A 0x003F 0x003 0x2
32KB 0x700FE01A 0x007F 0x003 0x2
64KB 0x701FE01A 0x00FF 0x003 0x2
0x1 L1 Instruction cache 8KB 0x2007E00A 0 0 1 0 0x003F 0x001 0x2
16KB 0x200FE00A 0x007F 0x001 0x2
32KB 0x201FE00A 0x00FF 0x001 0x2
64KB 0x203FE00A 0x001F 0x001 0x2
0x2 L2 cache 128KB 0x700FE07A 0 1 1 1 0x007F 0x00F 0x2
256KB 0x701FE07A 0x00FF 0x00F 0x2
512KB 0x703FE07A 0x01FF 0x00F 0x2
1024KB 0x707FE07A 0x03FF 0x00F 0x2
2048KB 0x70FFE07A 0x07FF 0x00F 0x2
0x3-0xF Reserved - - - - - - - - -

To access the CCSIDR:

	
MRC p15, 1, <Rt>, c0, c0, 0 ; Read CCSIDR into Rt

Register access is encoded as follows:

Table 4.192. CCSIDR access encoding
coproc opc1 CRn CRm opc2
1111 001 0000 0000 000

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