ID_MMFR3

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

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

Field descriptions

When AArch32 is supported:

Bits [63:32]

Supersec, bits [31:28]

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

Supersec	Meaning
0b0000	Supersections supported.
0b1111	Supersections not supported.

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:

CMemSz	Meaning
0b0000	4GB, corresponding to a 32-bit physical address range.
0b0001	64GB, corresponding to a 36-bit physical address range.
0b0010	1TB or more, corresponding to a 40-bit or larger physical address range.

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:

CohWalk	Meaning
0b0000	Updates to the translation tables require a clean to the Point of Unification to ensure visibility by subsequent translation table walks.
0b0001	Updates to the translation tables do not require a clean to the Point of Unification to ensure visibility by subsequent translation table walks.

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:

PAN	Meaning
0b0000	PAN not supported.
0b0001	PAN supported.
0b0010	PAN supported and ATS1CPRP and ATS1CPWP instructions supported.

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:

MaintBcst	Meaning
0b0000	Cache, TLB, and branch predictor operations only affect local structures.
0b0001	Cache and branch predictor operations affect structures according to shareability and defined behavior of instructions. TLB operations only affect local structures.
0b0010	Cache, TLB, and branch predictor operations affect structures according to shareability and defined behavior of instructions.

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:

BPMaint	Meaning
0b0000	None supported.
0b0001	Supported branch predictor maintenance operations are: Invalidate all branch predictors.
0b0010	As for 0b0001, and adds: Invalidate branch predictors by VA.

BPMaint

Meaning

0b0000

None supported.

0b0001

Supported branch predictor maintenance operations are:

Invalidate all branch predictors.

0b0010

As for 0b0001, and adds:

Invalidate branch predictors by VA.

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:

CMaintSW	Meaning
0b0000	None supported.
0b0001	Supported hierarchical cache maintenance instructions by set/way are: Invalidate data cache by set/way. Clean data cache by set/way. Clean and invalidate data cache by set/way.

CMaintSW

Meaning

0b0000

None supported.

0b0001

Supported hierarchical cache maintenance instructions by set/way are:

Invalidate data cache by set/way.
Clean data cache by set/way.
Clean and invalidate data cache by set/way.

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:

CMaintVA	Meaning
0b0000	None supported.
0b0001	Supported hierarchical cache maintenance operations by VA are: Invalidate data cache by VA. Clean data cache by VA. Clean and invalidate data cache by VA. Invalidate instruction cache by VA. Invalidate all instruction cache entries.

CMaintVA

Meaning

0b0000

None supported.

0b0001

Supported hierarchical cache maintenance operations by VA are:

Invalidate data cache by VA.
Clean data cache by VA.
Clean and invalidate data cache by VA.
Invalidate instruction cache by VA.
Invalidate all instruction cache entries.

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:

Bits [63:0]

Accessing ID_MMFR3_EL1

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

MRS <Xt>, ID_MMFR3_EL1

op0	op1	CRn	CRm	op2
0b11	0b000	0b0000	0b0001	0b111

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 X[t, 64] = ID_MMFR3_EL1; elsif PSTATE.EL == EL2 then X[t, 64] = ID_MMFR3_EL1; elsif PSTATE.EL == EL3 then X[t, 64] = ID_MMFR3_EL1;

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
Supersec				CMemSz				CohWalk				PAN				MaintBcst				BPMaint				CMaintSW				CMaintVA

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
UNKNOWN
UNKNOWN

ID_MMFR3_EL1, AArch32 Memory Model Feature Register 3

Purpose

Configuration

Attributes

Field descriptions

When AArch32 is supported:

Bits [63:32]

Supersec, bits [31:28]

CMemSz, bits [27:24]

CohWalk, bits [23:20]

PAN, bits [19:16]

MaintBcst, bits [15:12]

BPMaint, bits [11:8]

CMaintSW, bits [7:4]

CMaintVA, bits [3:0]

Otherwise:

Bits [63:0]

Accessing ID_MMFR3_EL1

MRS <Xt>, ID_MMFR3_EL1