ARM R4 Manuale Utente

ARM DDI 0363E

4-32

ID013010

To access the Instruction Set Attributes Register 4 read CP15 with:

MRC p15, 0, <Rd>, c0, c2, 4 ; Read Instruction Set Attributes Register 4

The Instruction Set Attributes Registers 5-7 provide additional information about the properties 
of the processor.

The Instruction Set Attributes Register 5 is:
•

a read-only register

•

accessible in Privileged mode only.

In the processor, Instruction Set Attributes Register 5 is read as 

0x00000000

.

To access the Instruction Set Attributes Register 5, read CP15 with:

MRC p15, 0, <Rd>, c0, c2, 5 ; Read Instruction Set Attribute Register 5

Instruction Set Attributes Registers 6 and 7 are not implemented, and their positions in the 
register map are Reserved. They correspond to CP15 accesses with:

MRC p15, 0, <Rd>, c0, c2, 6 ; Read Instruction Set Attribute Register 6
MRC p15, 0, <Rd>, c0, c2, 7 ; Read Instruction Set Attribute Register 7

These registers are read-only, and are accessible in Privileged mode only.

The Current Cache Size Identification Register provides the current cache size information for 
the instruction and data caches. Architecturally, there can be up to eight levels of cache, 
containing instruction, data, or unified caches. This processor contains L1 instruction and data 
caches. The Cache Size Selection Register determines which Current Cache Size Identification 
Register to select, see c0, Cache Size Selection Register on page 4-35.

The Current Cache Size Identification Register is:
•

a read-only register

•

accessible in Privileged mode only.

Figure 4-24 on page 4-33 shows the bit arrangement for the Current Cache Size Identification 
Register.

[15:12]

SMC instructions

Indicates support for Secure Monitor Call (

SMC

) (formerly 

SMI

) instructions.

0x0

, no support.

[11:8]

Write-back instructions

Indicates support for write-back instructions.

0x1

, supports all the writeback addressing modes defined in ARMv7.

[7:4]

With shift instructions

Indicates support for with-shift instructions.

0x4

, the processor supports:

•

the full range of constant shift options, on load/store and other instructions

•

register-controlled shift options.

[3:0]

Unprivileged instructions

Indicates support for Unprivileged instructions.

0x2

, the processor supports 

LDR{SB|B|SH|H}T

 and 

STR{B|H}T

.