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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' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D7.1.3.

Configuration

AArch64 System register ID_ISAR0_EL1 bits [31:0] are architecturally mapped to AArch32 System register ID_ISAR0[31:0] .

In an implementation that supports only AArch64 state, this register is UNKNOWN.

Attributes

ID_ISAR0_EL1 is a 64-bit register.

Field descriptions

The ID_ISAR0_EL1 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
00000000000000000000000000000000
0000DivideDebugCoprocCmpBranchBitFieldBitCountSwap
313029282726252423222120191817161514131211109876543210

Bits [63:28]

Reserved, RES0.

Divide, bits [27:24]

Indicates the implemented Divide instructions. Defined values are:

DivideMeaning
0b0000

None implemented.

0b0001

Adds SDIV and UDIV in the T32 instruction set.

0b0010

As for 0b0001, and adds SDIV and UDIV in the A32 instruction set.

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:

DebugMeaning
0b0000

None implemented.

0b0001

Adds BKPT.

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:

CoprocMeaning
0b0000

None implemented, except for instructions separately attributed by the architecture to provide access to AArch32 System registers and System instructions.

0b0001

Adds generic CDP, LDC, MCR, MRC, and STC.

0b0010

As for 0b0001, and adds generic CDP2, LDC2, MCR2, MRC2, and STC2.

0b0011

As for 0b0010, and adds generic MCRR and MRRC.

0b0100

As for 0b0011, and adds generic MCRR2 and MRRC2.

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:

CmpBranchMeaning
0b0000

None implemented.

0b0001

Adds CBNZ and CBZ.

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:

BitFieldMeaning
0b0000

None implemented.

0b0001

Adds BFC, BFI, SBFX, and UBFX.

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:

BitCountMeaning
0b0000

None implemented.

0b0001

Adds CLZ.

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:

SwapMeaning
0b0000

None implemented.

0b0001

Adds SWP and SWPB.

All other values are reserved.

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

Accessing the ID_ISAR0_EL1

Accesses to this register use the following encodings:

MRS <Xt>, ID_ISAR0_EL1

op0CRnop1op2CRm
0b110b00000b0000b0000b0010
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && 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;
              


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