B1.72 ID_MMFR4, Memory Model Feature Register 4

The ID_MMFR4 provides information about the memory model and memory management support in AArch32.

Bit field descriptions

ID_MMFR4 is a 32-bit register, and is part of the Identification registers functional group.

This register is Read Only.

Figure B1-57 ID_MMFR4 bit assignments
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RAZ, [31:24]
LSM, [23:20]
Load/Store Multiple. Indicates whether adjacent loads or stores can be combined. The value is:
0x0LSMAOE and nTLSMD bit not supported.
HD, [19:16]
Hierarchical Disables. Enables an operating system or hypervisor to hand over up to 4 bits of the last level page table descriptor (bits[62:59] of the page table entry) for use by hardware for implementation defined usage. The value is:
0x2Hierarchical Permission Disables and Hardware allocation of bits[62:59] supported.
CNP, [15:12]
Common Not Private. Indicates support for selective sharing of TLB entries across multiple cores. The value is:
0x1CnP bit supported.
XNX, [11:8]
Execute Never. Indicates whether the stage 2 translation tables allows the stage 2 control of whether memory is executable at EL1 independent of whether memory is executable at EL0. The value is:
0x1EL0/EL1 execute control distinction at stage2 bit supported.
AC2, [7:4]
Indicates the extension of the ACTLR and HACTLR registers using ACTLR2 and HACTLR2. The value is:
0x1ACTLR2 and HACTLR2 are implemented.
SpecSEI, [3:0]
Describes whether the core can generate SError interrupt exceptions from speculative reads of memory, including speculative instruction fetches. The value is:
0x0The core never generates an SError interrupt due to an external abort on a speculative read.

ID_MMFR4 is architecturally mapped to AArch64 register ID_MMFR4_EL1. See B2.78 ID_MMFR4_EL1, AArch32 Memory Model Feature Register 4, EL1.

There is one copy of this register that is used in both Secure and Non-secure states.

Must be interpreted with ID_MMFR0, ID_MMFR1, ID_MMFR2, and ID_MMFR3. See:

Bit fields and details not provided in this description are architecturally defined. See the Arm® Architecture Reference Manual Armv8, for Armv8-A architecture profile.

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