RNDRRS

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RNDRRS, Random Number Full Entropy

Purpose

Random Number with fresh full entropy. Returns a 64-bit random number from an approved Random Bit Generator, using either a Non-deterministic Random Bit Generator or one where the Deterministic Random Bit Generator is reseeded, where possible, from an approved entropy source before the return of the random number. See 'Properties of the generated random number'.

If the instruction cannot return a genuine random number in a reasonable period of time, PSTATE.NZCV is set to 0b0100 and the data value returned is 0.

When FEAT_RNG_TRAP is implemented and SCR_EL3.TRNDR is 1, reads of this register are trapped to EL3.

Configuration

This register is present only when (FEAT_RNG is implemented or FEAT_RNG_TRAP is implemented) and FEAT_AA64 is implemented. Otherwise, direct accesses to RNDRRS are UNDEFINED.

Attributes

Field descriptions

RNDRRS, bits [63:0]

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Accessing RNDRRS

Accesses to this register use the following encodings in the System register encoding space:

MRS <Xt>, RNDRRS

op0	op1	CRn	CRm	op2
0b11	0b011	0b0010	0b0100	0b001

if !((IsFeatureImplemented(FEAT_RNG) || IsFeatureImplemented(FEAT_RNG_TRAP)) && IsFeatureImplemented(FEAT_AA64)) then Undefined(); elsif PSTATE.EL == EL0 then if IsFeatureImplemented(FEAT_RNG_TRAP) && SCR_EL3().TRNDR == '1' then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; elsif !IsFeatureImplemented(FEAT_RNG) then Undefined(); else X{64}(t) = RNDRRS(); end; elsif PSTATE.EL == EL1 then if IsFeatureImplemented(FEAT_RNG_TRAP) && SCR_EL3().TRNDR == '1' then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; elsif !IsFeatureImplemented(FEAT_RNG) then Undefined(); else X{64}(t) = RNDRRS(); end; elsif PSTATE.EL == EL2 then if IsFeatureImplemented(FEAT_RNG_TRAP) && SCR_EL3().TRNDR == '1' then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; elsif !IsFeatureImplemented(FEAT_RNG) then Undefined(); else X{64}(t) = RNDRRS(); end; elsif PSTATE.EL == EL3 then if IsFeatureImplemented(FEAT_RNG_TRAP) && SCR_EL3().TRNDR == '1' then AArch64_SystemAccessTrap(EL3, 0x18); elsif !IsFeatureImplemented(FEAT_RNG) then Undefined(); else X{64}(t) = RNDRRS(); end; end;

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RNDRRS
RNDRRS