← Home

PRFUM

Prefetch memory (unscaled offset)

This instruction signals to the memory system that memory accesses to a location are likely to occur soon. The memory system can respond by taking actions that are expected to speed up the memory access when it does occur, such as making the cache line containing the specified address available at the level of cache specified by the instruction.

The address for memory accesses is calculated from a base register value and a signed, unscaled immediate offset.

The <prfop> operand specifies the prefetch hint as follows:

The effect of a PRFUM instruction is IMPLEMENTATION DEFINED. For more information, see Prefetch memory.

For information about addressing modes, see Load/Store addressing modes.

313029282726252423222120191817161514131211109876543210
11111000100imm900RnRt
sizeVRopc

Encoding

PRFUM (<prfop>|#<imm5>), [<Xn|SP>{, #<simm>}]

Decode

let offset : bits(64) = SignExtend{}(imm9); let n : integer = UInt(Rn); let t : integer = UInt(Rt); let nontemporal : boolean = FALSE; let tagchecked : boolean = FALSE;

Assembler Symbols

<prfop>

Is the prefetch operation, encoded in Rt:

Rt <prfop> Architectural Feature
00000 PLDL1KEEP -
00001 PLDL1STRM -
00010 PLDL2KEEP -
00011 PLDL2STRM -
00100 PLDL3KEEP -
00101 PLDL3STRM -
00110 PLDSLCKEEP FEAT_PRFMSLC
00111 PLDSLCSTRM FEAT_PRFMSLC
01000 PLIL1KEEP -
01001 PLIL1STRM -
01010 PLIL2KEEP -
01011 PLIL2STRM -
01100 PLIL3KEEP -
01101 PLIL3STRM -
01110 PLISLCKEEP FEAT_PRFMSLC
01111 PLISLCSTRM FEAT_PRFMSLC
10000 PSTL1KEEP -
10001 PSTL1STRM -
10010 PSTL2KEEP -
10011 PSTL2STRM -
10100 PSTL3KEEP -
10101 PSTL3STRM -
10110 PSTSLCKEEP FEAT_PRFMSLC
10111 PSTSLCSTRM FEAT_PRFMSLC
For other encodings of the "Rt" field, use <imm5>.
<imm5>

Is the prefetch operation encoding as an immediate, in the range 0 to 31, encoded in the "Rt" field.

This syntax is only for encodings that are not accessible using <prfop>.

<Xn|SP>

Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

<simm>

Is the optional signed immediate byte offset, in the range -256 to 255, defaulting to 0 and encoded in the "imm9" field.

Operation

var address : bits(64); let privileged : boolean = PSTATE.EL != EL0; let accdesc : AccessDescriptor = CreateAccDescGPR(MemOp_PREFETCH, nontemporal, privileged, tagchecked, t); if n == 31 then address = SP{64}(); else address = X{64}(n); end; address = AddressAdd(address, offset, accdesc); let supports_ir : boolean = FALSE; Prefetch(address, t[4:0], supports_ir);

Version 2026.06 — Copyright © 2010-2026 Arm Limited or its affiliates.

This site is provided as a community resource and is NOT affiliated with nor endorsed by Arm Limited.