.. _nrf_desktop_dev_descr:

Device description module
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The device description module defines the custom GATT Service that contains:

* Information about whether the peripheral supports the Low Latency Packet Mode (LLPM).
* Hardware ID (HW ID) of the peripheral.

To support the LLPM, the peripheral must use the SoftDevice Link Layer.
This means that you must enable both the :kconfig:option:`CONFIG_BT_LL_SOFTDEVICE` and the :kconfig:option:`CONFIG_CAF_BLE_USE_LLPM` Kconfig options.

.. note::
   HID Shorter Connection Intervals (SCI) support is not part of the device description service.
   The nRF Desktop central determines HID SCI capability from the HID Service during GATT discovery.
   See the :ref:`nrf_desktop_ble_discovery` and :ref:`nrf_desktop_hid_forward` documentation pages for details.

The Service is mandatory for all nRF Desktop peripherals that connect to the nRF Desktop centrals.

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

The ``dev_descr`` module does not submit nor subscribe to any events.

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

The module requires the basic Bluetooth® configuration, as described in the :ref:`nrf_desktop_bluetooth_guide` documentation.
Make sure that both :option:`CONFIG_DESKTOP_ROLE_HID_PERIPHERAL` and :option:`CONFIG_DESKTOP_BT_PERIPHERAL` Kconfig options are enabled.
The device description application module is enabled by the :option:`CONFIG_DESKTOP_DEV_DESCR_ENABLE` option, which is implied by :option:`CONFIG_DESKTOP_BT_PERIPHERAL` together with other features used by a Bluetooth LE HID peripheral device.

The module selects the :option:`CONFIG_DESKTOP_HWID` option to make sure that the nRF Desktop Hardware ID utility is enabled.
The utility uses Zephyr's :ref:`zephyr:hwinfo_api` to obtain the hardware ID and selects the :kconfig:option:`CONFIG_HWINFO` Kconfig option to automatically enable the required driver.

The :file:`dev_descr.h` file contains the UUIDs used by the custom GATT Service.
The file is located in the :file:`configuration/common` directory.
The UUIDs must be the same for all devices to ensure that the central can read the provided information.

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

The module uses :c:macro:`BT_GATT_SERVICE_DEFINE` to define the custom GATT Service.
More detailed information regarding GATT is available in Zephyr's :ref:`zephyr:bt_gatt` documentation.