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ID_MMFR0, Memory Model Feature Register 0

The ID_MMFR0 characteristics are:

Purpose

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

Must be interpreted with ID_MMFR1, ID_MMFR2, ID_MMFR3, and ID_MMFR4.

For general information about the interpretation of the ID registers see 'Principles of the ID scheme for fields in ID registers' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G7.1.3.

Configuration

AArch32 System register ID_MMFR0 bits [31:0] are architecturally mapped to AArch64 System register ID_MMFR0_EL1[31:0] .

Attributes

ID_MMFR0 is a 32-bit register.

Field descriptions

The ID_MMFR0 bit assignments are:

313029282726252423222120191817161514131211109876543210
InnerShrFCSEAuxRegTCMShareLvlOuterShrPMSAVMSA

InnerShr, bits [31:28]

Innermost Shareability. Indicates the innermost shareability domain implemented. Defined values are:

InnerShrMeaning
0b0000

Implemented as Non-cacheable.

0b0001

Implemented with hardware coherency support.

0b1111

Shareability ignored.

All other values are reserved.

In Armv8 the permitted values are 0b0000, 0b0001, and 0b1111.

This field is valid only if the implementation supports two levels of shareability, as indicated by ID_MMFR0.ShareLvl having the value 0b0001.

When ID_MMFR0.ShareLvl is zero, this field is UNK.

FCSE, bits [27:24]

Indicates whether the implementation includes the FCSE. Defined values are:

FCSEMeaning
0b0000

Not supported.

0b0001

Support for FCSE.

All other values are reserved.

In Armv8 the only permitted value is 0b0000.

AuxReg, bits [23:20]

Auxiliary Registers. Indicates support for Auxiliary registers. Defined values are:

AuxRegMeaning
0b0000

None supported.

0b0001

Support for Auxiliary Control Register only.

0b0010

Support for Auxiliary Fault Status Registers (AIFSR and ADFSR) and Auxiliary Control Register.

All other values are reserved.

In Armv8 the only permitted value is 0b0010.

Note

Accesses to unimplemented Auxiliary registers are UNDEFINED.

TCM, bits [19:16]

Indicates support for TCMs and associated DMAs. Defined values are:

TCMMeaning
0b0000

Not supported.

0b0001

Support is IMPLEMENTATION DEFINED. Armv7 requires this setting.

0b0010

Support for TCM only, Armv6 implementation.

0b0011

Support for TCM and DMA, Armv6 implementation.

All other values are reserved.

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

ShareLvl, bits [15:12]

Shareability Levels. Indicates the number of shareability levels implemented. Defined values are:

ShareLvlMeaning
0b0000

One level of shareability implemented.

0b0001

Two levels of shareability implemented.

All other values are reserved.

In Armv8 the only permitted value is 0b0001.

OuterShr, bits [11:8]

Outermost Shareability. Indicates the outermost shareability domain implemented. Defined values are:

OuterShrMeaning
0b0000

Implemented as Non-cacheable.

0b0001

Implemented with hardware coherency support.

0b1111

Shareability ignored.

All other values are reserved.

In Armv8 the permitted values are 0b0000, 0b0001, and 0b1111.

PMSA, bits [7:4]

Indicates support for a PMSA. Defined values are:

PMSAMeaning
0b0000

Not supported.

0b0001

Support for IMPLEMENTATION DEFINED PMSA.

0b0010

Support for PMSAv6, with a Cache Type Register implemented.

0b0011

Support for PMSAv7, with support for memory subsections. Armv7-R profile.

All other values are reserved.

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

VMSA, bits [3:0]

Indicates support for a VMSA. Defined values are:

VMSAMeaning
0b0000

Not supported.

0b0001

Support for IMPLEMENTATION DEFINED VMSA.

0b0010

Support for VMSAv6, with Cache and TLB Type Registers implemented.

0b0011

Support for VMSAv7, with support for remapping and the Access flag. ARMv7-A profile.

0b0100

As for 0b0011, and adds support for the PXN bit in the Short-descriptor translation table format descriptors.

0b0101

As for 0b0100, and adds support for the Long-descriptor translation table format.

All other values are reserved.

In Armv8-A the only permitted value is 0b0101.

Accessing the ID_MMFR0

Accesses to this register use the following encodings:

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

opc1opc2CRncoprocCRm
0b0000b1000b00000b11110b0001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T0 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T0 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID3 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TID3 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        return ID_MMFR0;
elsif PSTATE.EL == EL2 then
    return ID_MMFR0;
elsif PSTATE.EL == EL3 then
    return ID_MMFR0;
              


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