A5.5
MMU memory accesses
During a translation table walk, the MMU generates accesses. This section describes the specific
behaviors of the core for MMU memory accesses.
A5.5.1
Configuring MMU accesses
By programming the IRGN and ORGN bits, you can configure the MMU to perform translation table
walks in cacheable or non-cacheable regions:
AArch64
Appropriate TCR_EL
x
register.
If the encoding of both the ORGN and IRGN bits is Write-Back, the data cache lookup is performed and
data is read from the data cache. External memory is accessed, if the ORGN and IRGN bit contain
different attributes, or if the encoding of the ORGN and IRGN bits is Write-Through or Non-cacheable.
A5.5.2
Descriptor hardware update
The core supports hardware update in AArch64 state using hardware management of the access flag and
hardware management of dirty state.
These features are enabled in registers TCR_ELx and VTCR_EL2.
Hardware management of the Access flag is enabled by the following configuration fields:
• TCR_ELx.HA for stage 1 translations.
• VTCR_EL2.HA for stage 2 translations.
Hardware management of dirty state is enabled by the following configuration fields:
• TCR_ELx.HD for stage 1 translations.
• VTCR_EL2.HD for stage 2 translations.
Note
Hardware management of dirty state can only be enabled if hardware management of the Access flag is
enabled.
To support the hardware management of dirty state, the DBM field is added to the translation table
descriptors as part of Armv8.1 architecture.
The core supports hardware update only in outer Write-Back and inner Write-Back memory regions.
If software requests a hardware update in a memory region that is not inner Write-Back or not outer
Write-Back, then the core returns an abort with the following encoding:
• ESR.ELx.DFSC =
0b110001
for Data Aborts in AArch64.
• ESR.ELx.IFSC =
0b110001
for Instruction Aborts in AArch64.
A5 Memory Management Unit
A5.5 MMU memory accesses
100798_0300_00_en
Copyright © 2016–2018 Arm Limited or its affiliates. All rights
reserved.
A5-67
Non-Confidential
Summary of Contents for Cortex-A76 Core
Page 4: ......
Page 22: ......
Page 23: ...Part A Functional description ...
Page 24: ......
Page 119: ...Part B Register descriptions ...
Page 120: ......
Page 363: ...Part C Debug descriptions ...
Page 364: ......
Page 401: ...Part D Debug registers ...
Page 402: ......
Page 589: ...Part E Appendices ...
Page 590: ......