SETPT, SETMT, SETET

Memory set, unprivileged

These instructions set a required number of bytes in memory to the value in the least significant byte of the source data register. The prologue, main, and epilogue instructions are expected to be run in succession and to appear consecutively in memory: SETPT, then SETMT, and then SETET.

SETPT performs some preconditioning of the arguments suitable for using the SETMT instruction, and sets an IMPLEMENTATION DEFINED portion of the requested number of bytes. SETMT sets a further IMPLEMENTATION DEFINED portion of the remaining bytes. SETET sets any final remaining bytes.

For more information on exceptions specific to memory set instructions, see Memory Copy and Memory Set exceptions.

The architecture supports two algorithms for the memory set: option A and option B. Which algorithm is used is IMPLEMENTATION DEFINED.

For SETPT:

• If Xn[63] == '1', the set size is saturated to 0x7FFFFFFFFFFFFFFF.

On completion of SETPT, option A:

• Xn holds -1 times the number of bytes in the saturated set size remaining to be set.
• Xd holds the original Xd + saturated set size.
• PSTATE.{N,Z,C,V} are set to {0,0,0,0}.

On completion of SETPT, option B:

• Xn holds the number of bytes in the saturated set size remaining to be set.
• Xd holds the lowest address that has not been set.
• PSTATE.{N,Z,C,V} are set to {0,0,1,0}.

For SETMT, option A, when PSTATE.C = '0':

• Xn holds a signed 64-bit integer.
• Xn holds -1 times the number of bytes remaining to be set.
• Xd holds the lowest address to be set - Xn.
• On completion of the instruction, Xn holds -1 times the number of bytes remaining to be set.

For SETMT, option B, when PSTATE.C = '1':

• Xn holds the number of bytes remaining to be set.
• Xd holds the lowest address to be set.
• On completion of the instruction:
  • Xn holds the number of bytes remaining to be set.
  • Xd holds the lowest address that has not been set.

For SETET, option A, when PSTATE.C = '0':

• Xn holds a signed 64-bit integer.
• Xn holds -1 times the number of bytes remaining to be set.
• Xd holds the lowest address to be set - Xn.
• On completion of the instruction, Xn holds 0.

For SETET, option B, when PSTATE.C = '1':

• Xn holds the number of bytes remaining to be set.
• Xd holds the lowest address to be set.
• On completion of the instruction:
  • Xn holds 0.
  • Xd holds the lowest address that has not been set.

Explicit Memory Write 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:

• The instruction is executed at EL1.
• The instruction is executed at EL2 when the Effective value of HCR_EL2().{E2H, TGE} is '11'.

Otherwise, the Explicit Memory Write effects operate with the restrictions determined by the Exception level at which the instruction is executed.

Integer
(FEAT_MOPS)

Decode for all variants of this encoding

if !IsFeatureImplemented(FEAT_MOPS) || sz != '00' then EndOfDecode(Decode_UNDEF); end; var memset : SETParams; memset.d = UInt(Rd); memset.s = UInt(Rs); memset.n = UInt(Rn); let options : bits(2) = op2[1:0]; let nontemporal : boolean = options[1] == '1'; case op2[3:2] of when '00' => memset.stage = MOPSStage_Prologue; when '01' => memset.stage = MOPSStage_Main; when '10' => memset.stage = MOPSStage_Epilogue; otherwise => EndOfDecode(Decode_UNDEF); end;

Assembler Symbols