DIT, Data Independent Timing

The DIT characteristics are:

Purpose

Allows access to the Data Independent Timing bit.

Configuration

This register is present only when FEAT_DIT is implemented. Otherwise, direct accesses to DIT are UNDEFINED.

Attributes

DIT is a 64-bit register.

Field descriptions

The DIT bit assignments are:

Bits [63:25]

Reserved, RES0.

DIT, bit [24]

Data Independent Timing.

The data processing instructions affected by this bit are:

• All cryptographic instructions. These instructions are:

  • AESD, AESE, AESIMC, AESMC, SHA1C, SHA1H, SHA1M, SHA1P, SHA1SU0, SHA1SU1, SHA256H, SHA256H2, SHA256SU0, SHA256SU1, SHA512H, SHA512H2, SHA512SU0, SHA512SU1, EOR3, RAX1, XAR, BCAX, SM3SS1, SM3TT1A, SM3TT1B, SM3TT2A, SM3TT2B, SM3PARTW1, SM3PARTW2, SM4E, and SM4EKEY.

• A subset of those instructions which use the general-purpose register file. These instructions are:

  • ADC, ADCS, ADD, ADDS, AND, ANDS, ASR, ASRV, BFC, BFI, BFM, BFXIL, BIC, BICS, CCMN, CCMP, CFINV, CINC, CINV, CLS, CLZ, CMN, CMP, CNEG, CSEL, CSET, CSETM, CSINC, CSINV, CSNEG, EON, EOR, EXTR, LSL, LSLV, LSR, LSRV, MADD, MNEG, MOV, MOVK, MOVN, MOVZ, MSUB, MUL, MVN, NEG, NEGS, NGC, NGCS, NOP, ORN, ORR, RBIT, RET, REV, REV16, REV32, REV64, RMIF, ROR, RORV, SBC, SBCS, SBFIZ, SBFM, SBFX, SETF8, SETF16, SMADDL, SMNEGL, SMSUBL, SMULH, SMULL, SUB, SUBS, SXTB, SXTH, SXTW, TST, UBFIZ, UBFM, UBFX, UMADDL, UMNEGL, UMSUBL, UMULH, UMULL, UXTB, and UXTH.

• A subset of those instuctions which use the SIMD&FP register file. These instructions are:

  • ABS, ADD, ADDHN, ADDHN2, ADDP, ADDV, AND, BIC, BIF, BIT, BSL, CLS, CLZ, CMEQ, CMGE, CMGT, CMHI, CMHS, CMLE, CMLT, CMTST, CNT, CRC32B, CRC32H, CRC32W, CRC32X, CRC32CB, CRC32CH, CRC32CW, CRC32CX, DUP, EOR, EXT, FCSEL, INS, MLA, MLS, MOV, MOVI, MUL, MVN, MVNI, NEG, NOT, ORN, ORR, PMUL, PMULL, PMULL2, RADDHN, RADDHN2, RBIT, REV16, REV32, RSHRN, RSHRN2, RSUBHN, RSUBHN2, SABA, SABD, SABAL, SABAL2, SABDL, SABDL2, SADALP, SADDL, SADDL2, SADDLP, SADDLV, SADDW, SADDW2, SHADD, SHL, SHLL, SHLL2, SHRN, SHRN2, SHSUB, SLI, SMAX, SMAXP, SMAXV, SMIN, SMINP, SMINV, SMLAL, SMLAL2, SMLSL, SMLSL2, SMOV, SMULL, SMULL2, SRI, SSHL, SSHLL, SSHLL2, SSHR, SSRA, SSUBL, SSUBL2, SSUBW, SSUBW2, SUB, SUBHN, SUBHN2, SXTL, SXTL2, TBL, TBX, TRN1, TRN2, UABA, UABAL, UABAL2, UABD, UABDL, UABDL2, UADALP, UADDL, UADDL2, UADDLP, UADDLV, UADDW, UADDW2, UHADD, UHSUB, UMAX, UMAXP, UMAXV, UMIN, UMINP, UMINV, UMLAL, UMLAL2, UMLSL, UMOV, UMLSL2, UMULL, UMULL2, USHL, USHLL, USHLL2, USHR, USRA, USUBL, USUBL2, USUBW, USUBW2, UXTL, UXTL2, UZP1, UZP2, XTN, XTN2, ZIP1, and ZIP2.

This field resets to 0.

Bits [23:0]

Reserved, RES0.

if PSTATE.EL == EL0 then
    return Zeros(39):PSTATE.DIT:Zeros(24);
elsif PSTATE.EL == EL1 then
    return Zeros(39):PSTATE.DIT:Zeros(24);
elsif PSTATE.EL == EL2 then
    return Zeros(39):PSTATE.DIT:Zeros(24);
elsif PSTATE.EL == EL3 then
    return Zeros(39):PSTATE.DIT:Zeros(24);
              

if PSTATE.EL == EL0 then
    PSTATE.DIT = X[t]<24>;
elsif PSTATE.EL == EL1 then
    PSTATE.DIT = X[t]<24>;
elsif PSTATE.EL == EL2 then
    PSTATE.DIT = X[t]<24>;
elsif PSTATE.EL == EL3 then
    PSTATE.DIT = X[t]<24>;