B2.76 ID_MMFR4_EL1, AArch32 Memory Model Feature Register 4, EL1
The ID_MMFR4_EL1 provides information about the memory model and memory management support
in AArch32.
Bit field descriptions
ID_MMFR4_EL1 is a 32-bit register, and is part of the Identification registers functional group.
This register is Read Only.
31 8 7 04 3
RAZ AC2 SpecSEIHD CNPLSM XNX
1112151619202324
Figure B2-60 ID_MMFR4_EL1 bit assignments
RAZ, [31:24]
Read-As-Zero.
LSM, [23:20]
Load/Store Multiple. Indicates whether adjacent loads or stores can be combined. The value is:
0x0 LSMAOE and nTLSMD bit not supported.
HD, [19:16]
Presence of 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:
0x2 Hierarchical 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
PEs. The value is:
0x1 CnP 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:
0x1 EL0/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:
0x1 ACTLR2 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:
0x0 The core never generates an SError interrupt due to an external abort on a speculative
read.
B2 AArch64 system registers
B2.76 ID_MMFR4_EL1, AArch32 Memory Model Feature Register 4, EL1
100798_0300_00_en Copyright © 2016–2018 Arm Limited or its affiliates. All rights
reserved.
B2-254
Non-Confidential
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