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# HMAIR0, Hyp Memory Attribute Indirection Register 0

The HMAIR0 characteristics are:

## Purpose

Along with HMAIR1, provides the memory attribute encodings corresponding to the possible AttrIndx values in a Long-descriptor format translation table entry for stage 1 translations for memory accesses from Hyp mode.

AttrIndx[2] indicates the HMAIR register to be used:

- When AttrIndx[2] is 0, HMAIR0 is used.
- When AttrIndx[2] is 1, HMAIR1 is used.

## Configuration

AArch32 System register HMAIR0 bits [31:0] are architecturally mapped to AArch64 System register MAIR_EL2[31:0] .

If EL2 is not implemented, this register is RES0 from EL3.

RW fields in this register reset to architecturally UNKNOWN values.

## Attributes

HMAIR0 is a 32-bit register.

## Field descriptions

The HMAIR0 bit assignments are:

### When TTBCR.EAE == 1:

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
Attr3 | Attr2 | Attr1 | Attr0

#### Attr<n>, bits [8n+7:8n], for n = 0 to 3

The memory attribute encoding for an AttrIndx[2:0] entry in a Long descriptor format translation table entry, where:

- AttrIndx[2:0] gives the value of <n> in Attr<n>.
- AttrIndx[2] defines which MAIR to access. Attr7 to Attr4 are in MAIR1, and Attr3 to Attr0 are in MAIR0.

Bits [7:4] are encoded as follows:

Attr<n>[7:4] | Meaning
--- | ---
0b0000 | Device memory. See encoding of Attr<n>[3:0] for the type of Device memory.
0b00RW, RW not 0b00 | Normal memory, Outer Write-Through Transient.
0b0100 | Normal memory, Outer Non-cacheable.
0b01RW, RW not 0b00 | Normal memory, Outer Write-Back Transient.
0b10RW | Normal memory, Outer Write-Through Non-transient.
0b11RW | Normal memory, Outer Write-Back Non-transient.

R = Outer Read-Allocate policy, W = Outer Write-Allocate policy.

The meaning of bits [3:0] depends on the value of bits [7:4]:

Attr<n>[3:0] | Meaning when Attr<n>[7:4] is 0b0000 | Meaning when Attr<n>[7:4] is not 0b0000
--- | --- | ---
0b0000 | Device-nGnRnE memory | UNPREDICTABLE
0b00RW, RW not 0b00 | UNPREDICTABLE | Normal memory, Inner Write-Through Transient
0b0100 | Device-nGnRE memory | Normal memory, Inner Non-cacheable
0b01RW, RW not 0b00 | UNPREDICTABLE | Normal memory, Inner Write-Back Transient
0b1000 | Device-nGRE memory | Normal memory, Inner Write-Through Non-transient (RW=0b00)
0b10RW, RW not 0b00 | UNPREDICTABLE | Normal memory, Inner Write-Through Non-transient
0b1100 | Device-GRE memory | Normal memory, Inner Write-Back Non-transient (RW=0b00)
0b11RW, RW not 0b00 | UNPREDICTABLE | Normal memory, Inner Write-Back Non-transient

R = Inner Read-Allocate policy, W = Inner Write-Allocate policy.

The R and W bits in some Attr<n> fields have the following meanings:

R or W | Meaning
--- | ---
0b0 | No Allocate
0b1 | Allocate

This field resets to an architecturally UNKNOWN value.

## Accessing the HMAIR0

Accesses to this register use the following encodings:

#### MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coproc | opc1 | CRn | CRm | opc2
--- | --- | --- | --- | ---
0b1111 | 0b100 | 0b1010 | 0b0010 | 0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T10 == '1' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T10 == '1' then AArch32.TakeHypTrapException(0x03); else UNDEFINED; elsif PSTATE.EL == EL2 then return HMAIR0; elsif PSTATE.EL == EL3 then if SCR.NS == '0' then UNDEFINED; else return HMAIR0;

#### MCR{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coproc | opc1 | CRn | CRm | opc2
--- | --- | --- | --- | ---
0b1111 | 0b100 | 0b1010 | 0b0010 | 0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T10 == '1' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T10 == '1' then AArch32.TakeHypTrapException(0x03); else UNDEFINED; elsif PSTATE.EL == EL2 then HMAIR0 = R[t]; elsif PSTATE.EL == EL3 then if SCR.NS == '0' then UNDEFINED; else HMAIR0 = R[t];

AArch32 Registers | AArch64 Registers | AArch32 Instructions | AArch64 Instructions | Index by Encoding | External Registers | External Registers by Offset | Registers by Functional Group | Proprietary Notice

27/03/2019 21:59; e5e4db499bf9867a4b93324c4dbac985d3da9376

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