Activity Monitors
=================

FEAT_AMUv1 of the Armv8-A architecture introduces the Activity Monitors
extension. This extension describes the architecture for the Activity Monitor
Unit (|AMU|), an optional non-invasive component for monitoring core events
through a set of 64-bit counters.

When the ``ENABLE_FEAT_AMU=1`` build option is provided, Trusted Firmware-A
sets up the |AMU| prior to its exit from EL3, and will save and restore
architected |AMU| counters as necessary upon suspend and resume.

.. _Activity Monitor Auxiliary Counters:

Auxiliary counters
------------------

FEAT_AMUv1 describes a set of implementation-defined auxiliary counters (also
known as group 1 counters), controlled by the ``ENABLE_AMU_AUXILIARY_COUNTERS``
build option.

As a security precaution, Trusted Firmware-A does not enable these by default.
Instead, platforms must configure their auxiliary counters through the
``plat_amu_aux_enables`` platform hook.

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