ZCR_EL3

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ZCR_EL3, SVE Control Register (EL3)

Purpose

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

Field descriptions

Bits [63:9]

Bits [8:4]

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:

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

Accessing ZCR_EL3

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

MRS <Xt>, ZCR_EL3

op0	op1	CRn	CRm	op2
0b11	0b110	0b0001	0b0010	0b000

if !IsFeatureImplemented(FEAT_SVE) then Undefined(); elsif 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{64}(t) = ZCR_EL3(); end; end;

MSR ZCR_EL3, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b110	0b0001	0b0010	0b000

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
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																							RAZ/WI					LEN