Load unprivileged pair of SIMD&FP registers
This instruction loads a pair of SIMD&FP registers from memory. The address that is used for the load is calculated from a base register value and an optional immediate offset.
Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.
Explicit Memory effects produced by the instruction behave as if the instruction was executed at EL0 if the Effective value of PSTATE.UAO is 0 and either:
Otherwise, the Explicit Memory effects operate with the restrictions determined by the Exception level at which the instruction is executed.
It has encodings from 3 classes: Post-index , Pre-index and Signed offset
| 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 |
| 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | imm7 | Rt2 | Rn | Rt | ||||||||||||||||||
| opc | VR | L | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_FP) || !IsFeatureImplemented(FEAT_LSUI) then EndOfDecode(Decode_UNDEF); constant boolean wback = TRUE; constant boolean postindex = TRUE;
| 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 |
| 1 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | imm7 | Rt2 | Rn | Rt | ||||||||||||||||||
| opc | VR | L | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_FP) || !IsFeatureImplemented(FEAT_LSUI) then EndOfDecode(Decode_UNDEF); constant boolean wback = TRUE; constant boolean postindex = FALSE;
| 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 |
| 1 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | imm7 | Rt2 | Rn | Rt | ||||||||||||||||||
| opc | VR | L | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_FP) || !IsFeatureImplemented(FEAT_LSUI) then EndOfDecode(Decode_UNDEF); constant boolean wback = FALSE; constant boolean postindex = FALSE;
LDTP has the same CONSTRAINED UNPREDICTABLE behavior as LDP (SIMD&FP). See Architectural Constraints on UNPREDICTABLE behaviors, and particularly LDP (SIMD&FP).
| <Qt1> |
Is the 128-bit name of the first SIMD&FP register to be transferred, encoded in the "Rt" field. |
| <Qt2> |
Is the 128-bit name of the second SIMD&FP register to be transferred, encoded in the "Rt2" field. |
| <Xn|SP> |
Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field. |
constant integer t = UInt(Rt); constant integer t2 = UInt(Rt2); constant integer n = UInt(Rn); constant boolean nontemporal = FALSE; constant integer datasize = 128; constant bits(64) offset = LSL(SignExtend(imm7, 64), 4); constant boolean tagchecked = wback || n != 31; boolean rt_unknown = FALSE; if t == t2 then constant Constraint c = ConstrainUnpredictable(Unpredictable_LDPOVERLAP); assert c IN {Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_UNKNOWN rt_unknown = TRUE; // Result is UNKNOWN when Constraint_UNDEF EndOfDecode(Decode_UNDEF); when Constraint_NOP EndOfDecode(Decode_NOP);
AArch64.CheckFPEnabled(); bits(64) address; constant integer dbytes = datasize DIV 8; constant boolean privileged = AArch64.IsUnprivAccessPriv(); constant boolean ispair = TRUE; constant AccessDescriptor accdesc = CreateAccDescASIMD(MemOp_LOAD, nontemporal, tagchecked, privileged, ispair); if n == 31 then CheckSPAlignment(); address = SP[64]; else address = X[n, 64]; if !postindex then address = AddressAdd(address, offset, accdesc); constant bits(2*datasize) data = Mem[address, 2*dbytes, accdesc]; if rt_unknown then V[t , datasize] = bits(datasize) UNKNOWN; elsif BigEndian(accdesc.acctype) then V[t2, datasize] = data<(datasize-1):0>; V[t , datasize] = data<(2*datasize-1):datasize>; else V[t , datasize] = data<(datasize-1):0>; V[t2, datasize] = data<(2*datasize-1):datasize>; if wback then if postindex then address = AddressAdd(address, offset, accdesc); if n == 31 then SP[64] = address; else X[n, 64] = address;
This instruction is a data-independent-time instruction as described in About PSTATE.DIT.
Version 2025.09 — Copyright © 2010-2025 Arm Limited or its affiliates.
This site is provided as a community resource and is NOT affiliated with nor endorsed by Arm Limited.