ZCR_EL3, SVE Control Register for EL3

The ZCR_EL3 characteristics are:

Purpose

The SVE Control Register for EL3 is used to control aspects of SVE visible at all Exception levels.

Configuration

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

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

ZCR_EL3 is a 64-bit register.

Field descriptions

The ZCR_EL3 bit assignments are:

Bits [63:9]

Reserved, RES0.

Bits [8:4]

Reserved, RAZ/WI.

LEN, bits [3:0]

Constrains the scalable vector register length for all Exception levels to (LEN+1)x128 bits. For all purposes other than returning the result of a direct read of ZCR_EL3 then this field behaves as if rounded down to the nearest implemented vector 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.

This field resets to an architecturally UNKNOWN value.

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;
              

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];