.. _nrf_desktop_hfclk_lock:

High frequency clock lock hotfix module
#######################################

.. contents::
   :local:
   :depth: 2

Use the high frequency clock lock hotfix module to keep the high frequency clock enabled.
This reduces the latency before the first packet in a row is transmitted over Bluetooth®, but it also increases the power consumption.
If this module is disabled, a startup delay of around 1.4 ms (0.85 ms in case of nRF54L Series SoCs) will be added to the overall latency of the first packet.

.. note::
   The module is deprecated.
   Use the :option:`CONFIG_DESKTOP_BLE_LOW_LATENCY_LOCK` Kconfig option instead for LLPM connections.
   For HID SCI connections, set :kconfig:option:`CONFIG_BT_HIDS_SCI_FAST_MAX_LATENCY` to ``0``.
   Setting the peripheral latency Bluetooth LE connection parameter to ``0`` for a connection that uses Low Latency Packet Mode connection interval on the peripheral keeps the high frequency clock enabled.
   That mitigates the extra HID report latency caused by the high frequency clock startup delay.

Module events
*************

.. include:: ../../../../../../applications/nrf_desktop/doc/event_propagation.rst
    :start-after: table_hfclk_lock_start
    :end-before: table_hfclk_lock_end

.. note::
    |nrf_desktop_module_event_note|

Configuration
*************

To enable the module, use the :option:`CONFIG_DESKTOP_HFCLK_LOCK_ENABLE` Kconfig option.

Make sure that you have enabled the Bluetooth LE Low Latency Packet Mode (LLPM) (:kconfig:option:`CONFIG_CAF_BLE_USE_LLPM`).
Using LLPM connection parameters reduces HID data latency more than enabling the module.

Implementation details
**********************

The high frequency clock is disabled on a :c:struct:`power_down_event` and re-enabled on a :c:struct:`wake_up_event`.
This is done to reduce the power consumption.