ID_MMFR1

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_MMFR1_EL1 bits [31:0] are architecturally mapped to AArch32 System register ID_MMFR1[31:0].

Attributes

Field descriptions

When AArch32 is supported:

Bits [63:32]

BPred, bits [31:28]

Branch Predictor. Indicates branch predictor management requirements. Defined values are:

BPred	Meaning
0b0000	No branch predictor, or no MMU present. Implies a fixed MPU configuration.
0b0001	Branch predictor requires flushing on: Enabling or disabling a stage of address translation. Writing new data to instruction locations. Writing new mappings to the translation tables. Changes to the TTBR0, TTBR1, or TTBCR registers. Changes to the ContextID or ASID, or to the FCSE ProcessID if this is supported.
0b0010	Branch predictor requires flushing on: Enabling or disabling a stage of address translation. Writing new data to instruction locations. Writing new mappings to the translation tables. Any change to the TTBR0, TTBR1, or TTBCR registers without a change to the corresponding ContextID or ASID, or FCSE ProcessID if this is supported.
0b0011	Branch predictor requires flushing only on writing new data to instruction locations.
0b0100	For execution correctness, branch predictor requires no flushing at any time.

All other values are reserved.

In Armv8-A, the permitted values are 0b0010, 0b0011, and 0b0100. For values other than 0b0000 and 0b0100 the Arm Architecture Reference Manual, or the product documentation, might give more information about the required maintenance.

L1TstCln, bits [27:24]

Level 1 cache Test and Clean. Indicates the supported Level 1 data cache test and clean operations, for Harvard or unified cache implementations. Defined values are:

L1TstCln

Meaning

0b0000

None supported.

0b0001

Supported Level 1 data cache test and clean operations are:

Test and clean data cache.

0b0010

As for 0b0001, and adds:

Test, clean, and invalidate data cache.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

L1Uni, bits [23:20]

Level 1 Unified cache. Indicates the supported entire Level 1 cache maintenance operations for a unified cache implementation. Defined values are:

L1Uni

Meaning

0b0000

None supported.

0b0001

Supported entire Level 1 cache operations are:

Invalidate cache, including branch predictor if appropriate.
Invalidate branch predictor, if appropriate.

0b0010

As for 0b0001, and adds:

Clean cache, using a recursive model that uses the cache dirty status bit.
Clean and invalidate cache, using a recursive model that uses the cache dirty status bit.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

L1Hvd, bits [19:16]

Level 1 Harvard cache. Indicates the supported entire Level 1 cache maintenance operations for a Harvard cache implementation. Defined values are:

L1Hvd	Meaning
0b0000	None supported.
0b0001	Supported entire Level 1 cache operations are: Invalidate instruction cache, including branch predictor if appropriate. Invalidate branch predictor, if appropriate.
0b0010	As for 0b0001, and adds: Invalidate data cache. Invalidate data cache and instruction cache, including branch predictor if appropriate.
0b0011	As for 0b0010, and adds: Clean data cache, using a recursive model that uses the cache dirty status bit. Clean and invalidate data cache, using a recursive model that uses the cache dirty status bit.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

L1UniSW, bits [15:12]

Level 1 Unified cache by Set/Way. Indicates the supported Level 1 cache line maintenance operations by set/way, for a unified cache implementation. Defined values are:

L1UniSW	Meaning
0b0000	None supported.
0b0001	Supported Level 1 unified cache line maintenance operations by set/way are: Clean cache line by set/way.
0b0010	As for 0b0001, and adds: Clean and invalidate cache line by set/way.
0b0011	As for 0b0010, and adds: Invalidate cache line by set/way.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

L1HvdSW, bits [11:8]

Level 1 Harvard cache by Set/Way. Indicates the supported Level 1 cache line maintenance operations by set/way, for a Harvard cache implementation. Defined values are:

L1HvdSW	Meaning
0b0000	None supported.
0b0001	Supported Level 1 Harvard cache line maintenance operations by set/way are: Clean data cache line by set/way. Clean and invalidate data cache line by set/way.
0b0010	As for 0b0001, and adds: Invalidate data cache line by set/way.
0b0011	As for 0b0010, and adds: Invalidate instruction cache line by set/way.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

L1UniVA, bits [7:4]

Level 1 Unified cache by Virtual Address. Indicates the supported Level 1 cache line maintenance operations by VA, for a unified cache implementation. Defined values are:

L1UniVA

Meaning

0b0000

None supported.

0b0001

Supported Level 1 unified cache line maintenance operations by VA are:

Clean cache line by VA.
Invalidate cache line by VA.
Clean and invalidate cache line by VA.

0b0010

As for 0b0001, and adds:

Invalidate branch predictor by VA, if branch predictor is implemented.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

L1HvdVA, bits [3:0]

Level 1 Harvard cache by Virtual Address. Indicates the supported Level 1 cache line maintenance operations by VA, for a Harvard cache implementation. Defined values are:

L1HvdVA

Meaning

0b0000

None supported.

0b0001

Supported Level 1 Harvard cache line maintenance operations by VA are:

Clean data cache line by VA.
Invalidate data cache line by VA.
Clean and invalidate data cache line by VA.
Clean instruction cache line by VA.

0b0010

As for 0b0001, and adds:

Invalidate branch predictor by VA, if branch predictor is implemented.

All other values are reserved.

In Armv8-A, the only permitted value is 0b0000.

Otherwise:

Bits [63:0]

Accessing ID_MMFR1_EL1

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

MRS <Xt>, ID_MMFR1_EL1

op0	op1	CRn	CRm	op2
0b11	0b000	0b0000	0b0001	0b101

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_MMFR1_EL1; elsif PSTATE.EL == EL2 then X[t, 64] = ID_MMFR1_EL1; elsif PSTATE.EL == EL3 then X[t, 64] = ID_MMFR1_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
BPred				L1TstCln				L1Uni				L1Hvd				L1UniSW				L1HvdSW				L1UniVA				L1HvdVA

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_MMFR1_EL1, AArch32 Memory Model Feature Register 1

Purpose

Configuration

Attributes

Field descriptions

When AArch32 is supported:

Bits [63:32]

BPred, bits [31:28]

L1TstCln, bits [27:24]

L1Uni, bits [23:20]

L1Hvd, bits [19:16]

L1UniSW, bits [15:12]

L1HvdSW, bits [11:8]

L1UniVA, bits [7:4]

L1HvdVA, bits [3:0]

Otherwise:

Bits [63:0]

Accessing ID_MMFR1_EL1

MRS <Xt>, ID_MMFR1_EL1