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

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

This register is present only when EL1 is capable of using AArch32. Otherwise, direct accesses to ID_ISAR2 are UNDEFINED.

Attributes

Field descriptions

Reversal, bits [31:28]

Indicates the implemented Reversal instructions. Defined values are:

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.

PSR_AR, bits [27:24]

Indicates the implemented A and R-profile instructions to manipulate the PSR. Defined values are:

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.

MultU, bits [23:20]

Indicates the implemented advanced unsigned Multiply instructions. Defined values are:

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.

MultS, bits [19:16]

Indicates the implemented advanced signed Multiply instructions. Defined values are:

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.

Mult, bits [15:12]

Indicates the implemented additional Multiply instructions. Defined values are:

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.

MultiAccessInt, bits [11:8]

Indicates the support for interruptible multi-access instructions. Defined values are:

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.

MemHint, bits [7:4]

Indicates the implemented Memory Hint instructions. Defined values are:

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.

LoadStore, bits [3:0]

Indicates the implemented additional load/store instructions. Defined values are:

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.

Accessing ID_ISAR2

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

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

coproc	opc1	CRn	CRm	opc2
0b1111	0b000	0b0000	0b0010	0b010

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.TID3 == '1' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TID3 == '1' then AArch32.TakeHypTrapException(0x03); else R[t] = ID_ISAR2; elsif PSTATE.EL == EL2 then R[t] = ID_ISAR2; elsif PSTATE.EL == EL3 then R[t] = ID_ISAR2;

ID_ISAR2, Instruction Set Attribute Register 2

Purpose

Configuration

Attributes

Field descriptions

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]

Accessing ID_ISAR2

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