doc: nrf-bm: libraries: add bm_storage documentation

Adds `bm_storage` library documentation.

Signed-off-by: Mirko Covizzi <[email protected]>

Author: MirkoCovizzi

doc/nrf-bm/api/api.rst

@@ -68,6 +68,8 @@ Bare Metal Low Power UART with EasyDMA driver
 Bare Metal Storage library
 ==========================
 
+.. _api_storage:
+
 .. doxygengroup:: bm_storage
    :inner:
    :members:

doc/nrf-bm/libraries/bm_storage.rst

@@ -0,0 +1,105 @@
+.. _lib_storage:
+
+Storage Library
+###############
+
+.. contents::
+   :local:
+   :depth: 2
+
+Overview
+********
+
+The Storage library provides abstractions for reading, writing, and erasing non-volatile memory (NVM).
+It supports multiple storage instances, each bound to a specific memory region, and reports operation results through user-defined event handlers.
+Depending on the backend and runtime state, operations may be synchronous or asynchronous.
+
+Configuration
+*************
+
+The library is enabled and configured entirely using the Kconfig system.
+Set the :kconfig:option:`CONFIG_BM_STORAGE` Kconfig option to enable the library.
+
+Select a backend using :kconfig:option:`CONFIG_BM_STORAGE_BACKEND`:
+
+* :kconfig:option:`CONFIG_BM_STORAGE_BACKEND_RRAM` – RRAM backend. The events reported are synchronous.
+* :kconfig:option:`CONFIG_BM_STORAGE_BACKEND_SD` – SoftDevice backend. The events reported are asynchronous.
+
+SoftDevice backend options:
+
+* :kconfig:option:`CONFIG_BM_STORAGE_BACKEND_SD_QUEUE_SIZE` – Queue size for pending operations.
+* :kconfig:option:`CONFIG_BM_STORAGE_BACKEND_SD_MAX_RETRIES` – Maximum retries if the SoftDevice is busy.
+
+Initialization
+==============
+
+Each storage instance is represented by a :c:struct:`bm_storage` structure.
+
+Initialize an instance with the :c:func:`bm_storage_init` function, providing:
+
+* :c:member:`bm_storage.evt_handler` – Event callback.
+* :c:member:`bm_storage.start_addr` and :c:member:`bm_storage.end_addr` – Accessible address range.
+
+Uninitialize with the :c:func:`bm_storage_uninit` function.
+
+Usage
+*****
+
+Read
+====
+
+Use the :c:func:`bm_storage_read` function to copy data from NVM into RAM.
+The data length must be a multiple of the backend’s program unit and within the configured region.
+
+Write
+=====
+
+Use the :c:func:`bm_storage_write` function to write data to NVM.
+Writes are validated against alignment and range, and completion is reported through :c:member:`bm_storage.evt_handler`.
+
+Erase
+=====
+
+Use the :c:func:`bm_storage_erase` function to erase a region in NVM.
+``len`` must be a multiple of the erase unit. If not supported by the backend, the call may return ``NRF_ERROR_NOT_SUPPORTED``.
+This means that the backend does not require the region to be erased before another write operation.
+
+Busy state
+==========
+
+Use the :c:func:`bm_storage_is_busy` function to check whether a backend is executing an operation.
+
+Events
+======
+
+The following events may be reported to the user callback:
+
+* :c:enum:`BM_STORAGE_EVT_WRITE_RESULT` – Write operation completed.
+* :c:enum:`BM_STORAGE_EVT_ERASE_RESULT` – Erase operation completed.
+
+Each event includes the result code, information about the address range of the associated operation, and if the operation is synchronous or asynchronous.
+
+Dependencies
+************
+
+* :kconfig:option:`CONFIG_BM_STORAGE_BACKEND_RRAM`:
+
+  This backend requires the following Kconfig options to be disabled:
+
+  * :kconfig:option:`CONFIG_SOFTDEVICE`
+
+* :kconfig:option:`CONFIG_BM_STORAGE_BACKEND_SD`:
+
+  This backend requires the following Kconfig options to be enabled:
+
+  * :kconfig:option:`CONFIG_SOFTDEVICE`
+  * :kconfig:option:`CONFIG_NRF_SDH`
+  * :kconfig:option:`CONFIG_RING_BUFFER`
+
+API documentation
+*****************
+
+| Header file: :file:`include/bm_storage.h`
+| Source files: :file:`lib/bm_storage/`
+
+:ref:`Storage library API reference <api_storage>`