doc: lib: bluetooth: add GATT queue documentation

Add documentation for BLE GATT queue.

Signed-off-by: Eivind Jølsgard <[email protected]>

Author: eivindj-nordic

doc/nrf-bm/api/api.rst

@@ -95,6 +95,8 @@ Bare Metal Zephyr Memory Storage (ZMS)
    :inner:
    :members:
 
+.. _api_gatt_queue:
+
 GATT Queue
 ==========
 

doc/nrf-bm/libraries/bluetooth/ble_gatt_queue.rst

@@ -0,0 +1,76 @@
+.. _lib_ble_gatt_queue:
+
+Bluetooth: GATT Queue
+#####################
+
+.. contents::
+   :local:
+   :depth: 2
+
+The Bluetooth Low Energy® GATT Queue library can be used to buffer BLE GATT requests if the SoftDevice is not able to handle them at the moment.
+
+Overview
+********
+
+If the SoftDevice is not able to handle the GATT request at the moment, the BLE GATT Queue library buffers the request.
+Later on, when the corresponding BLE event indicates that the SoftDevice may be free, the request is retried.
+This library can be used in multiple connections scenario.
+
+The library currently handles the following types of GATT requests:
+
+* Read Characteristic or Descriptor (See ``sd_ble_gattc_read``)
+* Write Characteristic Value or Descriptor (See ``sd_ble_gattc_write``)
+* Primary Service Discovery (See ``sd_ble_gattc_primary_services_discover``)
+* Characteristic Discovery (See ``sd_ble_gattc_characteristics_discover``)
+* Descriptor Discovery (See ``sd_ble_gattc_descriptors_discover``)
+* Notify or Indicate an attribute value. (See ``sd_ble_gatts_hvx``)
+
+The BLE GATT Queue can be used with BLE service clients and other BLE libraries that issue GATT requests to the SoftDevice.
+
+Configuration
+*************
+
+The library is enabled and configured using the Kconfig system.
+Set the :kconfig:option:`CONFIG_BLE_GATT_QUEUE` Kconfig option to enable the library.
+
+You can add an instance of the library to your application using the :c:macro:`BLE_GQ_DEF` macro.
+If you need an instance that does not use the default parameters, it can be added with the :c:macro:`BLE_GQ_CUSTOM_DEF` macro.
+
+The library exposes the following Kconfig options for the default configuration:
+
+* :kconfig:option:`CONFIG_BLE_GQ_MAX_CONNECTIONS` - Sets the maximum simultaneous connections the GATT queue instance can manage.
+* :kconfig:option:`CONFIG_BLE_GQ_QUEUE_SIZE` - Sets the max number of requests that can be queued for each connection that have been registered to the GATT queue instance.
+* :kconfig:option:`CONFIG_BLE_GQ_HEAP_SIZE` - Sets the heap size for storing additional data that can be of variable size.
+  The heap is used for storing the data of write, notify and indicate requests.
+
+Initialization
+==============
+
+The module does not require other initialization than adding the library instance as described above.
+
+Usage
+*****
+
+Once defined, you can register a connection handle in the BLE Gatt Queue (BLE GQ) instance by calling the :c:func:`ble_gq_conn_handle_register` function.
+From this point forward, the BLE GQ instance can handle GATT requests associated with the handle until the connection is no longer valid (for example when a disconnect event occurs).
+
+To add a GATT request to the BLE GQ instance, call the :c:func:`ble_gq_item_add` function.
+This function adds a request to the BLE GQ instance and allocates the necessary memory for data that can be held within the request descriptor.
+If the SoftDevice is free and the queue is empty, the request will be processed immediately.
+Otherwise, the request is queued and processed later.
+
+Dependencies
+************
+
+This library uses the following |BMshort| libraries:
+
+* SoftDevice - :kconfig:option:`CONFIG_SOFTDEVICE`
+* SoftDevice handler - :kconfig:option:`CONFIG_NRF_SDH`
+
+API documentation
+*****************
+
+| Header file: :file:`include/ble_gq.h`
+| Source files: :file:`lib/ble_gq/`
+
+:ref:`Bluetooth LE GATT Queue library API reference <api_ble_gatt_queue>`