System Control
ARM DDI 0500D
Copyright © 2013-2014 ARM. All rights reserved.
4-35
ID021414
Non-Confidential
Usage constraints
This register is accessible as follows:
Configurations
ID_ISAR4_EL1 is architecturally mapped to AArch32 register
ID_ISAR4. See
Instruction Set Attribute Register 4
on page 4-179
.
Attributes
ID_ISAR4_EL1 is a 32-bit register.
Figure 4-15
shows the ID_ISAR4_EL1 bit assignments.
Figure 4-15 ID_ISAR4_EL1 bit assignments
Table 4-41
shows the ID_ISAR4_EL1 bit assignments.
To access the ID_ISAR4_EL1:
EL0
EL1
(NS)
EL1
(S)
EL2
EL3
(SCR.NS = 1)
EL3
(SCR.NS = 0)
-
RO
RO
RO
RO
RO
31
24 23
20 19
16 15
12 11
8 7
4 3
0
SynchPrim_frac
SWP_frac
28 27
PSR_M
Barrier
SMC
Writeback
WithShifts
Unpriv
Table 4-41 ID_ISAR4_EL1 bit assignments
Bits
Name
Function
[31:28]
SWP_frac
Indicates support for the memory system locking the bus for
SWP
or
SWPB
instructions:
0x0
SWP
and
SWPB
instructions not implemented.
[27:24]
PSR_M
Indicates the implemented M profile instructions to modify the PSRs:
0x0
None implemented.
[23:20]
SynchPrim_frac
This field is used with the ID_ISAR3.SynchPrim field to indicate the implemented Synchronization
Primitive instructions:
0x0
•
The
LDREX
and
STREX
instructions.
•
The
CLREX
,
LDREXB
,
LDREXH
,
STREXB
, and
STREXH
instructions.
•
The
LDREXD
and
STREXD
instructions.
[19:16]
Barrier
Indicates the supported Barrier instructions in the A32 and T32 instruction sets:
0x1
The
DMB
,
DSB
, and
ISB
barrier instructions.
[15:12]
SMC
Indicates the implemented
SMC
instructions:
0x1
The
SMC
instruction.
[11:8]
WriteBack
Indicates the support for Write-Back addressing modes:
0x1
Processor supports all of the Write-Back addressing modes defined in ARMv8.
[7:4]
WithShifts
Indicates the support for instructions with shifts.
0x4
•
Support for shifts of loads and stores over the range LSL 0-3.
•
Support for other constant shift options, both on load/store and other instructions.
•
Support for register-controlled shift options.
[3:0]
Unpriv
Indicates the implemented unprivileged instructions.
0x2
•
The
LDRBT
,
LDRT
,
STRBT
, and
STRT
instructions.
•
The
LDRHT
,
LDRSBT
,
LDRSHT
, and
STRHT
instructions.