ZCR_EL3, SVE Control Register (EL3)

The ZCR_EL3 characteristics are:

Purpose

This register controls aspects of SVE visible at all Exception levels.

Configuration

This register is present only when FEAT_SVE is implemented. Otherwise, direct accesses to ZCR_EL3 are UNDEFINED.

This register has no effect when FEAT_SME is implemented and the PE is in Streaming SVE mode.

Attributes

ZCR_EL3 is a 64-bit register.

Field descriptions

6362616059585756555453525150494847464544434241403938373635343332
313029282726252423222120191817161514131211109876543210
RES0
RES0RAZ/WILEN

Bits [63:9]

Reserved, RES0.

Bits [8:4]

Reserved, RAZ/WI.

LEN, bits [3:0]

Requests an Effective Non-streaming SVE vector length at EL3 of (LEN+1)*128 bits.

The Non-streaming SVE vector length can be any power of two from 128 bits to 2048 bits inclusive. An implementation can support a subset of the architecturally permitted lengths. An implementation is required to support all lengths that are powers of two, from 128 bits up to its maximum implemented Non-streaming SVE vector length.

When FEAT_SME is not implemented, or the PE is not in Streaming SVE mode, the Effective SVE vector length (VL) is equal to the Effective Non-streaming SVE vector length.

When FEAT_SME is implemented and the PE is in Streaming SVE mode, VL is equal to the Effective Streaming SVE vector length. See SMCR_EL3.

For all purposes other than returning the result of a direct read of ZCR_EL3, the PE selects the highest supported Non-streaming SVE vector length that is less than or equal to the requested length.

An indirect read of ZCR_EL3.LEN appears to occur in program order relative to a direct write of the same register, without the need for explicit synchronization.

The reset behavior of this field is:

Accessing ZCR_EL3

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

MRS <Xt>, ZCR_EL3

op0op1CRnCRmop2
0b110b1100b00010b00100b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then UNDEFINED; elsif PSTATE.EL == EL2 then UNDEFINED; elsif PSTATE.EL == EL3 then if CPTR_EL3.EZ == '0' then AArch64.SystemAccessTrap(EL3, 0x19); else X[t, 64] = ZCR_EL3;

MSR ZCR_EL3, <Xt>

op0op1CRnCRmop2
0b110b1100b00010b00100b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then UNDEFINED; elsif PSTATE.EL == EL2 then UNDEFINED; elsif PSTATE.EL == EL3 then if CPTR_EL3.EZ == '0' then AArch64.SystemAccessTrap(EL3, 0x19); else ZCR_EL3 = X[t, 64];


26/03/2024 09:49; 67c0ae5282a7629ba0ea0ba7267b43cd4f7939f6

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