1Activity Monitors
2=================
3
4FEAT_AMUv1 of the Armv8-A architecture introduces the Activity Monitors
5extension. This extension describes the architecture for the Activity Monitor
6Unit (|AMU|), an optional non-invasive component for monitoring core events
7through a set of 64-bit counters.
8
9When the ``ENABLE_AMU=1`` build option is provided, Trusted Firmware-A sets up
10the |AMU| prior to its exit from EL3, and will save and restore architected
11|AMU| counters as necessary upon suspend and resume.
12
13.. _Activity Monitor Auxiliary Counters:
14
15Auxiliary counters
16------------------
17
18FEAT_AMUv1 describes a set of implementation-defined auxiliary counters (also
19known as group 1 counters), controlled by the ``ENABLE_AMU_AUXILIARY_COUNTERS``
20build option.
21
22As a security precaution, Trusted Firmware-A does not enable these by default.
23Instead, platforms may configure their auxiliary counters through one of two
24possible mechanisms:
25
26- |FCONF|, controlled by the ``ENABLE_AMU_FCONF`` build option.
27- A platform implementation of the ``plat_amu_topology`` function (the default).
28
29See :ref:`Activity Monitor Unit (AMU) Bindings` for documentation on the |FCONF|
30device tree bindings.
31
32--------------
33
34*Copyright (c) 2021, Arm Limited. All rights reserved.*
35