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:
InnerShr, bits [31:28]
Innermost Shareability. Indicates the innermost shareability domain implemented. Defined values are:
| InnerShr | Meaning |
|---|---|
| 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:
| FCSE | Meaning |
|---|---|
| 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:
| AuxReg | Meaning |
|---|---|
| 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.
Accesses to unimplemented Auxiliary registers are UNDEFINED.
TCM, bits [19:16]
Indicates support for TCMs and associated DMAs. Defined values are:
| TCM | Meaning |
|---|---|
| 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:
| ShareLvl | Meaning |
|---|---|
| 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:
| OuterShr | Meaning |
|---|---|
| 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:
| PMSA | Meaning |
|---|---|
| 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:
| VMSA | Meaning |
|---|---|
| 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>}
| opc1 | opc2 | CRn | coproc | CRm |
|---|---|---|---|---|
| 0b000 | 0b100 | 0b0000 | 0b1111 | 0b0001 |
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;