ID_MMFR3_EL1, AArch32 Memory Model Feature Register 3

The ID_MMFR3_EL1 characteristics are:

Purpose

Provides information about the implemented memory model and memory management support in AArch32 state.

Must be interpreted with ID_MMFR0_EL1, ID_MMFR1_EL1, ID_MMFR2_EL1, and ID_MMFR4_EL1.

For general information about the interpretation of the ID registers see 'Principles of the ID scheme for fields in ID registers'.

Configuration

AArch64 System register ID_MMFR3_EL1 bits [31:0] are architecturally mapped to AArch32 System register ID_MMFR3[31:0] .

Attributes

ID_MMFR3_EL1 is a 64-bit register.

Field descriptions

The ID_MMFR3_EL1 bit assignments are:

When AArch32 is supported at any Exception level:

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
RES0
Supersec				CMemSz				CohWalk				PAN				MaintBcst				BPMaint				CMaintSW				CMaintVA

Bits [63:32]

Reserved, RES0.

Supersec, bits [31:28]

Supersections. On a VMSA implementation, indicates whether Supersections are supported. Defined values are:

All other values are reserved.

In Armv8-A, the permitted values are 0b0000 and 0b1111.

CMemSz, bits [27:24]

Cached Memory Size. Indicates the physical memory size supported by the caches. Defined values are:

All other values are reserved.

In Armv8-A, the permitted values are 0b0000, 0b0001, and 0b0010.

CohWalk, bits [23:20]

Coherent Walk. Indicates whether Translation table updates require a clean to the Point of Unification. Defined values are:

All other values are reserved.

In Armv8-A, the only permitted value is 0b0001.

PAN, bits [19:16]

Privileged Access Never. Indicates support for the PAN bit in CPSR, SPSR, and DSPSR in AArch32 state. Defined values are:

All other values are reserved.

FEAT_PAN implements the functionality identified by the value 0b0001.

FEAT_PAN2 implements the functionality added by the value 0b0010.

In Armv8.1, the value 0b0000 is not permitted.

From Armv8.2, the only permitted value is 0b0010.

MaintBcst, bits [15:12]

Maintenance Broadcast. Indicates whether Cache, TLB, and branch predictor operations are broadcast. Defined values are:

All other values are reserved.

In Armv8-A, the only permitted value is 0b0010.

BPMaint, bits [11:8]

Branch Predictor Maintenance. Indicates the supported branch predictor maintenance operations in an implementation with hierarchical cache maintenance operations. Defined values are:

All other values are reserved.

In Armv8-A, the only permitted value is 0b0010.

CMaintSW, bits [7:4]

Cache Maintenance by Set/Way. Indicates the supported cache maintenance operations by set/way, in an implementation with hierarchical caches. Defined values are:

All other values are reserved.

In Armv8-A, the only permitted value is 0b0001.

In a unified cache implementation, the data cache maintenance operations apply to the unified caches.

CMaintVA, bits [3:0]

Cache Maintenance by Virtual Address. Indicates the supported cache maintenance operations by VA, in an implementation with hierarchical caches. Defined values are:

All other values are reserved.

In Armv8-A, the only permitted value is 0b0001.

In a unified cache implementation, data cache maintenance operations apply to the unified caches, and the instruction cache maintenance instructions are not implemented.

Otherwise:

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
UNKNOWN
UNKNOWN
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
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

Bits [63:0]

Reserved, UNKNOWN.

if PSTATE.EL == EL0 then
    if IsFeatureImplemented("FEAT_IDST") then
        if EL2Enabled() && HCR_EL2.TGE == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            AArch64.SystemAccessTrap(EL1, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.TID3 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        return ID_MMFR3_EL1;
elsif PSTATE.EL == EL2 then
    return ID_MMFR3_EL1;
elsif PSTATE.EL == EL3 then
    return ID_MMFR3_EL1;