ID_ISAR2

Provides information about the instruction sets implemented by the PE in AArch32 state.

For general information about the interpretation of the ID registers see 'Principles of the ID scheme for fields in ID registers'.

Configuration

AArch64 System register ID_ISAR2_EL1 bits [31:0] are architecturally mapped to AArch32 System register ID_ISAR2[31:0].

Attributes

Field descriptions

When AArch32 is supported:

Bits [63:32]

Reversal, bits [31:28]

Indicates the implemented Reversal instructions.

The value of this field is an IMPLEMENTATION DEFINED choice of:

Reversal	Meaning
0b0000	None implemented.
0b0001	Adds the REV, REV16, and REVSH instructions.
0b0010	As for 0b0001, and adds the RBIT instruction.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0010.

Access to this field is RO.

PSR_AR, bits [27:24]

Indicates the implemented A and R-profile instructions to manipulate the PSR.

The value of this field is an IMPLEMENTATION DEFINED choice of:

PSR_AR	Meaning
0b0000	None implemented.
0b0001	Adds the MRS and MSR instructions, and the exception return forms of data-processing instructions.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0001.

The exception return forms of the data-processing instructions are:

In the A32 instruction set, data-processing instructions with the PC as the destination and the S bit set. These instructions might be affected by the WithShifts attribute.
In the T32 instruction set, the SUBS PC,LR,#N instruction.

Access to this field is RO.

MultU, bits [23:20]

Indicates the implemented advanced unsigned Multiply instructions.

The value of this field is an IMPLEMENTATION DEFINED choice of:

MultU	Meaning
0b0000	None implemented.
0b0001	Adds the UMULL and UMLAL instructions.
0b0010	As for 0b0001, and adds the UMAAL instruction.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0010.

Access to this field is RO.

MultS, bits [19:16]

Indicates the implemented advanced signed Multiply instructions.

The value of this field is an IMPLEMENTATION DEFINED choice of:

MultS	Meaning
0b0000	None implemented.
0b0001	Adds the SMULL and SMLAL instructions.
0b0010	As for 0b0001, and adds the SMLABB, SMLABT, SMLALBB, SMLALBT, SMLALTB, SMLALTT, SMLATB, SMLATT, SMLAWB, SMLAWT, SMULBB, SMULBT, SMULTB, SMULTT, SMULWB, and SMULWT instructions. Also adds the Q bit in the PSRs.
0b0011	As for 0b0010, and adds the SMLAD, SMLADX, SMLALD, SMLALDX, SMLSD, SMLSDX, SMLSLD, SMLSLDX, SMMLA, SMMLAR, SMMLS, SMMLSR, SMMUL, SMMULR, SMUAD, SMUADX, SMUSD, and SMUSDX instructions.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0011.

Access to this field is RO.

Mult, bits [15:12]

Indicates the implemented additional Multiply instructions.

The value of this field is an IMPLEMENTATION DEFINED choice of:

Mult	Meaning
0b0000	No additional instructions implemented. This means only MUL is implemented.
0b0001	Adds the MLA instruction.
0b0010	As for 0b0001, and adds the MLS instruction.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0010.

Access to this field is RO.

MultiAccessInt, bits [11:8]

Indicates the support for interruptible multi-access instructions.

The value of this field is an IMPLEMENTATION DEFINED choice of:

MultiAccessInt	Meaning
0b0000	No support. This means the LDM and STM instructions are not interruptible.
0b0001	LDM and STM instructions are restartable.
0b0010	LDM and STM instructions are continuable.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

Access to this field is RO.

MemHint, bits [7:4]

Indicates the implemented Memory Hint instructions.

The value of this field is an IMPLEMENTATION DEFINED choice of:

MemHint	Meaning
0b0000	None implemented.
0b0001	Adds the PLD instruction.
0b0010	Adds the PLD instruction. (0b0001 and 0b0010 have identical effects.)
0b0011	As for 0b0001 (or 0b0010), and adds the PLI instruction.
0b0100	As for 0b0011, and adds the PLDW instruction.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0100.

Access to this field is RO.

LoadStore, bits [3:0]

Indicates the implemented additional load/store instructions.

The value of this field is an IMPLEMENTATION DEFINED choice of:

LoadStore	Meaning
0b0000	No additional load/store instructions implemented.
0b0001	Adds the LDRD and STRD instructions.
0b0010	As for 0b0001, and adds the Load Acquire (LDAB, LDAH, LDA, LDAEXB, LDAEXH, LDAEX, LDAEXD) and Store Release (STLB, STLH, STL, STLEXB, STLEXH, STLEX, STLEXD) instructions.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0010.

Access to this field is RO.

Otherwise:

Bits [63:0]

Accessing ID_ISAR2_EL1

Accesses to this register use the following encodings in the System register encoding space:

MRS <Xt>, ID_ISAR2_EL1

op0	op1	CRn	CRm	op2
0b11	0b000	0b0000	0b0010	0b010

if PSTATE.EL == EL0 then if IsFeatureImplemented(FEAT_IDST) then if EL2Enabled() && HCR_EL2.TGE == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else AArch64.SystemAccessTrap(EL1, 0x18); else UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.TID3 == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else X[t, 64] = ID_ISAR2_EL1; elsif PSTATE.EL == EL2 then X[t, 64] = ID_ISAR2_EL1; elsif PSTATE.EL == EL3 then X[t, 64] = ID_ISAR2_EL1;

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
RES0
Reversal				PSR_AR				MultU				MultS				Mult				MultiAccessInt				MemHint				LoadStore

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
UNKNOWN
UNKNOWN

ID_ISAR2_EL1, AArch32 Instruction Set Attribute Register 2

Purpose

Configuration

Attributes

Field descriptions

When AArch32 is supported:

Bits [63:32]

Reversal, bits [31:28]

PSR_AR, bits [27:24]

MultU, bits [23:20]

MultS, bits [19:16]

Mult, bits [15:12]

MultiAccessInt, bits [11:8]

MemHint, bits [7:4]

LoadStore, bits [3:0]

Otherwise:

Bits [63:0]

Accessing ID_ISAR2_EL1

MRS <Xt>, ID_ISAR2_EL1