The ZCR_EL3 characteristics are:
This register controls aspects of SVE visible at all Exception levels.
This register is present only when FEAT_SVE is implemented. Otherwise, direct accesses to ZCR_EL3 are UNDEFINED.
ZCR_EL3 is a 64-bit register.
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 |
Reserved, RES0.
Reserved, RAZ/WI.
Effective SVE Vector Length (VL).
Constrains the effective scalable vector register length for all Exception levels to (LEN+1)*128 bits.
An implementation is permitted to include any set of vector lengths that are multiples of 128 bits, from 128 bits to 2048 bits inclusive, and required to support all vector lengths that are powers of two, from 128 bits up to its maximum implemented vector length.
For all purposes other than returning the result of a direct read of ZCR_EL3, this field selects the effective vector length as follows:
If the requested length is not implemented, then the requested length rounded down to the nearest implemented scalable vector length is used.
Otherwise, the requested length is used.
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:
Accesses to this register use the following encodings in the System register encoding space:
op0 | op1 | CRn | CRm | op2 |
---|---|---|---|---|
0b11 | 0b110 | 0b0001 | 0b0010 | 0b000 |
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 return ZCR_EL3;
op0 | op1 | CRn | CRm | op2 |
---|---|---|---|---|
0b11 | 0b110 | 0b0001 | 0b0010 | 0b000 |
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];
30/09/2021 15:34; 092b4e1bbfbb45a293b198f9330c5f529ead2b0f
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