ID_ISAR0_EL1, AArch32 Instruction Set Attribute Register 0

The ID_ISAR0_EL1 characteristics are:

Purpose

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

Must be interpreted with ID_ISAR1_EL1, ID_ISAR2_EL1, ID_ISAR3_EL1, ID_ISAR4_EL1, and ID_ISAR5_EL1.

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_ISAR0_EL1 bits [31:0] are architecturally mapped to AArch32 System register ID_ISAR0[31:0] .

Attributes

ID_ISAR0_EL1 is a 64-bit register.

Field descriptions

The ID_ISAR0_EL1 bit assignments are:

When AArch32 is supported at any Exception level:

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
RES0
RES0				Divide				Debug				Coproc				CmpBranch				BitField				BitCount				Swap

Bits [63:28]

Reserved, RES0.

Divide, bits [27:24]

Indicates the implemented Divide instructions. Defined values are:

All other values are reserved.

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

Debug, bits [23:20]

Indicates the implemented Debug instructions. Defined values are:

All other values are reserved.

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

Coproc, bits [19:16]

Indicates the implemented System register access instructions. Defined values are:

All other values are reserved.

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

CmpBranch, bits [15:12]

Indicates the implemented combined Compare and Branch instructions in the T32 instruction set. Defined values are:

All other values are reserved.

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

BitField, bits [11:8]

Indicates the implemented BitField instructions. Defined values are:

All other values are reserved.

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

BitCount, bits [7:4]

Indicates the implemented Bit Counting instructions. Defined values are:

All other values are reserved.

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

Swap, bits [3:0]

Indicates the implemented Swap instructions in the A32 instruction set. Defined values are:

All other values are reserved.

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

Otherwise:

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
UNKNOWN
UNKNOWN
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
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

Bits [63:0]

Reserved, UNKNOWN.

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
        return ID_ISAR0_EL1;
elsif PSTATE.EL == EL2 then
    return ID_ISAR0_EL1;
elsif PSTATE.EL == EL3 then
    return ID_ISAR0_EL1;