WRFFR Write the first-fault register Read the source predicate register and place in the first-fault register (FFR). This instruction is intended to restore a saved FFR and is not recommended for general use by applications. This instruction requires that the source predicate contains a monotonic predicate value, in which starting from bit 0 there are zero or more 1 bits, followed only by 0 bits in any remaining bit positions. If the source is not a monotonic predicate value, then the resulting value in the FFR will be UNPREDICTABLE. It is not possible to generate a non-monotonic value in FFR when using SETFFR followed by first-fault or non-fault loads. This instruction is illegal when executed in Streaming SVE mode, unless FEAT_SME_FA64 is implemented and enabled. Green False True SM_0_only 0 0 1 0 0 1 0 1 0 0 1 0 1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 WRFFR <Pn>.B if !IsFeatureImplemented(FEAT_SVE) then UNDEFINED; constant integer n = UInt(Pn); <Pn> Is the name of the source scalable predicate register, encoded in the "Pn" field. CheckNonStreamingSVEEnabled(); constant integer VL = CurrentVL; constant integer PL = VL DIV 8; constant bits(PL) operand = P[n, PL]; constant integer hsb = HighestSetBit(operand); if hsb < 0 || IsOnes(operand<hsb:0>) then FFR[PL] = operand; else // not a monotonic predicate FFR[PL] = bits(PL) UNKNOWN;