SMPRI_EL1

Configures the streaming execution priority for instructions executed on a shared Streaming Mode Compute Unit (SMCU) when the PE is in Streaming SVE mode at any Exception level.

Configuration

This register is present only when FEAT_SME is implemented. Otherwise, direct accesses to SMPRI_EL1 are UNDEFINED.

Attributes

Field descriptions

Bits [63:4]

Priority, bits [3:0]

Streaming execution priority value.

Either this value is used directly, or it is mapped into an effective priority value using SMPRIMAP_EL2.

This value is used directly when any of the following are true:

The current Exception level is EL3 or EL2.
The current Exception level is EL1 or EL0, if EL2 is implemented and enabled in the current Security state and HCRX_EL2.SMPME is '0'.
The current Exception level is EL1 or EL0, if EL2 is either not implemented or not enabled in the current Security state.

The precise meaning and behavior of each streaming execution priority value is IMPLEMENTATION DEFINED.

In an implementation that shares execution resources between PEs, higher priority values are allocated more processing resource than other PEs configured with lower priority values in the same Priority domain.

The reset behavior of this field is:

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

Accessing SMPRI_EL1

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

MRS <Xt>, SMPRI_EL1

op0	op1	CRn	CRm	op2
0b11	0b000	0b0001	0b0010	0b100

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.ESM == '0' then UNDEFINED; elsif EL2Enabled() && IsFeatureImplemented(FEAT_FGT) && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGRTR_EL2.nSMPRI_EL1 == '0' then AArch64.SystemAccessTrap(EL2, 0x18); elsif HaveEL(EL3) && CPTR_EL3.ESM == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else X[t, 64] = SMPRI_EL1; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.ESM == '0' then UNDEFINED; elsif HaveEL(EL3) && CPTR_EL3.ESM == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else X[t, 64] = SMPRI_EL1; elsif PSTATE.EL == EL3 then if CPTR_EL3.ESM == '0' then AArch64.SystemAccessTrap(EL3, 0x18); else X[t, 64] = SMPRI_EL1;

MSR SMPRI_EL1, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b000	0b0001	0b0010	0b100

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.ESM == '0' then UNDEFINED; elsif EL2Enabled() && IsFeatureImplemented(FEAT_FGT) && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGWTR_EL2.nSMPRI_EL1 == '0' then AArch64.SystemAccessTrap(EL2, 0x18); elsif HaveEL(EL3) && CPTR_EL3.ESM == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else SMPRI_EL1 = X[t, 64]; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.ESM == '0' then UNDEFINED; elsif HaveEL(EL3) && CPTR_EL3.ESM == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else SMPRI_EL1 = X[t, 64]; elsif PSTATE.EL == EL3 then if CPTR_EL3.ESM == '0' then AArch64.SystemAccessTrap(EL3, 0x18); else SMPRI_EL1 = X[t, 64];

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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
RES0
RES0																												Priority

SMPRI_EL1, Streaming Mode Priority Register

Purpose