doc/services/sensing/index.rst - third_party/github/zephyrproject-rtos/zephyr - Git at Google

 .. _sensing:

 Sensing Subsystem
 ########################

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

 Overview
 ********

 Sensing Subsystem is a high level sensor framework inside the OS user
 space service layer. It is a framework focused on sensor fusion, client
 arbitration, sampling, timing, scheduling and sensor based power management.

 Key concepts in Sensing Subsystem include physical sensor and virtual sensor objects,
 and a scheduling framework over sensor object relationships.
 Physical sensors do not depend on any other sensor objects for input, and
 will directly interact with existing zephyr sensor device drivers.
 Virtual sensors rely on other sensor objects (physical or virtual) as
 report inputs.

 The sensing subsystem relies on Zephyr sensor device APIs (existing version or update in future)
 to leverage Zephyr's large library of sensor device drivers (100+).

 Use of the sensing subsystem is optional. Applications that only need to access simple sensors
 devices can use the Zephyr :ref:`sensor` API directly.

 Since the sensing subsystem is separated from device driver layer or
 kernel space and could support various customizations and sensor
 algorithms in user space with virtual sensor concepts. The existing
 sensor device driver can focus on low layer device side works, can keep
 simple as much as possible, just provide device HW abstraction and
 operations etc. This is very good for system stability.

 The sensing subsystem is decoupled with any sensor expose/transfer
 protocols, the target is to support various up-layer frameworks and
 Applications with different sensor expose/transfer protocols,
 such as `CHRE <https://github.com/zephyrproject-rtos/chre>`_, HID sensors Applications,
 MQTT sensor Applications according different products requirements. Or even support multiple
 Applications with different up-layer sensor protocols at the same time
 with it's multiple clients support design.

 Sensing subsystem can help build a unified Zephyr sensing architecture for
 cross host OSes support and as well as IoT sensor solutions.

 The diagram below illustrates how the Sensing Subsystem integrates with up-layer frameworks.

 .. image:: images/sensing_solution.png
    :align: center
    :alt: Unified Zephyr sensing architecture.

 Configurability
 ***************

 * Reusable and configurable standalone subsystem.
 * Based on Zephyr existing low-level Sensor API (reuse 100+ existing sensor device drivers)
 * Provide Zephyr high-level Sensing Subsystem API for Applications.
 * Separate option CHRE Sensor PAL Implementation module to support CHRE.
 * Decoupled with any host link protocols, it's Zephyr Application's role to handle different
   protocols (MQTT, HID or Private, all configurable)

 Main Features
 *************

 * Scope
     * Focus on framework for sensor fusion, multiple clients, arbitration, data sampling, timing
       management and scheduling.

 * Sensor Abstraction
     * ``Physical sensor``: interacts with Zephyr sensor device drivers, focus on data collecting.
     * ``Virtual sensor``: relies on other sensor(s), ``physical`` or ``virtual``, focus on
       data fusion.

 * Data Driven Model
     * ``Polling mode``: periodical sampling rate
     * ``Interrupt mode``: data ready, threshold interrupt etc.

 * Scheduling
     * single thread main loop for all sensor objects sampling and process.

 * Buffer Mode for Batching

 * Configurable Via Device Tree


 Below diagram shows the API position and scope:

 .. image:: images/sensing_api_org.png
    :align: center
    :alt: Sensing subsystem API organization.

 ``Sensing Subsystem API`` is for Applications.
 ``Sensing Sensor API`` is for development ``sensors``.


 Major Flows
 ***********

 * Sensor Configuration Flow

 .. image:: images/sensor_config_flow.png
    :align: center
    :alt: Sensor Configuration Flow (App set report interval to hinge angel sensor example).

 * Sensor Data Flow

 .. image:: images/sensor_data_flow.png
    :align: center
    :alt: Sensor Data Flow (App receive hinge angel data through data event callback example).

 Sensor Types And Instance
 *************************

 The ``Sensing Subsystem`` supports multiple instances of the same sensor type,
 there're two methods for Applications to identify and open an unique sensor instance:

 * Enumerate all sensor instances

   :c:func:`sensing_get_sensors` returns all current board configuration supported sensor instances'
   information in a :c:struct:`sensing_sensor_info` pointer array .

   Then Applications can use :c:func:`sensing_open_sensor` to
   open specific sensor instance for future accessing, configuration and receive sensor data etc.

   This method is suitable for supporting some up-layer frameworks like ``CHRE``, ``HID`` which need
   to dynamically enumerate the underlying platform's sensor instances.

 * Open the sensor instance by devicetree node directly

   Applications can use :c:func:`sensing_open_sensor_by_dt` to open a sensor instance directly with
   sensor devicetree node identifier.

   For example:

 .. code-block:: c

    sensing_open_sensor_by_dt(DEVICE_DT_GET(DT_NODELABEL(base_accel)), cb_list, handle);
    sensing_open_sensor_by_dt(DEVICE_DT_GET(DT_CHOSEN(zephyr_sensing_base_accel)), cb_list, handle);

 This method is useful and easy use for some simple Application which just want to access specific
 sensor(s).


 ``Sensor type`` follows the
 `HID standard sensor types definition <https://usb.org/sites/default/files/hutrr39b_0.pdf>`_.

 See :zephyr_file:`include/zephyr/sensing/sensing_sensor_types.h`

 Sensor Instance Handler
 ***********************

 Clients using a :c:type:`sensing_sensor_handle_t` type handler to handle a opened sensor
 instance, and all subsequent operations on this sensor instance need use this handler,
 such as set configurations, read sensor sample data, etc.

 For a sensor instance, could have two kinds of clients:
 ``Application clients`` and ``Sensor clients``.

 ``Application clients`` can use :c:func:`sensing_open_sensor` to open a sensor instance
 and get it's handler.

 For ``Sensor clients``, there is no open API for opening a reporter, because the client-report
 relationship is built at the sensor's registration stage with devicetree.

 The ``Sensing Subsystem`` will auto open and create ``handlers`` for client sensor
 to it's reporter sensors.
 ``Sensor clients`` can get it's reporters' handlers via :c:func:`sensing_sensor_get_reporters`.

 .. image:: images/sensor_top.png
    :align: center
    :alt: Sensor Reporting Topology.

 .. note::
    Sensors inside the Sensing Subsystem, the reporting relationship between them are all auto
    generated by Sensing Subsystem according devicetree definitions, handlers between client sensor
    and reporter sensors are auto created.
    Application(s) need to call :c:func:`sensing_open_sensor` to explicitly open the sensor instance.

 Sensor Sample Value
 *******************

 * Data Structure

   Each sensor sample value defines as a common ``header`` + ``readings[]`` data structure, like
   :c:struct:`sensing_sensor_value_3d_q31`, :c:struct:`sensing_sensor_value_q31`, and
   :c:struct:`sensing_sensor_value_uint32`.

   The ``header`` definition :c:func:`sensing_sensor_value_header`.


 * Time Stamp

   Time stamp unit in sensing subsystem is ``micro seconds``.

   The ``header`` defines a **base_timestamp**, and
   each element in the **readings[]** array defines **timestamp_delta**.

   The **timestamp_delta** is in relation to the previous **readings** (or the **base_timestamp**)

   For example:

   * timestamp of ``readings[0]`` is ``header.base_timestamp`` + ``readings[0].timestamp_delta``.

   * timestamp of ``readings[1]`` is ``timestamp of readings[0]`` + ``readings[1].timestamp_delta``.

   Since timestamp unit is micro seconds,
   the max **timestamp_delta** (``uint32_t``) is ``4295`` seconds.

   If a sensor has batched data where two consecutive readings differ by more than ``4295`` seconds,
   the sensing subsystem runtime will split them across multiple instances of the readings structure,
   and send multiple events.

   This concept is referred from `CHRE Sensor API <https://github.com/zephyrproject-rtos/
   chre/blob/zephyr/chre_api/include/chre_api/chre/sensor_types.h>`_.

 * Data Format

   ``Sensing Subsystem`` uses per sensor type defined data format structure,
   and support ``Q Format`` defined in :zephyr_file:`include/zephyr/dsp/types.h`
   for ``zdsp`` lib support.

   For example :c:struct:`sensing_sensor_value_3d_q31` can be used by 3D IMU sensors like
   :c:macro:`SENSING_SENSOR_TYPE_MOTION_ACCELEROMETER_3D`,
   :c:macro:`SENSING_SENSOR_TYPE_MOTION_UNCALIB_ACCELEROMETER_3D`,
   and :c:macro:`SENSING_SENSOR_TYPE_MOTION_GYROMETER_3D`.

   :c:struct:`sensing_sensor_value_uint32` can be used by
   :c:macro:`SENSING_SENSOR_TYPE_LIGHT_AMBIENTLIGHT` sensor,

   and :c:struct:`sensing_sensor_value_q31` can be used by
   :c:macro:`SENSING_SENSOR_TYPE_MOTION_HINGE_ANGLE` sensor

   See :zephyr_file:`include/zephyr/sensing/sensing_datatypes.h`


 Device Tree Configuration
 *************************

 Sensing subsystem using device tree to configuration all sensor instances and their properties,
 reporting relationships.

 See the example :zephyr_file:`samples/subsys/sensing/simple/boards/native_sim.overlay`

 API Reference
 *************

 .. doxygengroup:: sensing_sensor_types
 .. doxygengroup:: sensing_datatypes
 .. doxygengroup:: sensing_api
 .. doxygengroup:: sensing_sensor
	.. _sensing:

	Sensing Subsystem
	########################

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

	Overview
	********

	Sensing Subsystem is a high level sensor framework inside the OS user
	space service layer. It is a framework focused on sensor fusion, client
	arbitration, sampling, timing, scheduling and sensor based power management.

	Key concepts in Sensing Subsystem include physical sensor and virtual sensor objects,
	and a scheduling framework over sensor object relationships.
	Physical sensors do not depend on any other sensor objects for input, and
	will directly interact with existing zephyr sensor device drivers.
	Virtual sensors rely on other sensor objects (physical or virtual) as
	report inputs.

	The sensing subsystem relies on Zephyr sensor device APIs (existing version or update in future)
	to leverage Zephyr's large library of sensor device drivers (100+).

	Use of the sensing subsystem is optional. Applications that only need to access simple sensors
	devices can use the Zephyr :ref:`sensor` API directly.

	Since the sensing subsystem is separated from device driver layer or
	kernel space and could support various customizations and sensor
	algorithms in user space with virtual sensor concepts. The existing
	sensor device driver can focus on low layer device side works, can keep
	simple as much as possible, just provide device HW abstraction and
	operations etc. This is very good for system stability.

	The sensing subsystem is decoupled with any sensor expose/transfer
	protocols, the target is to support various up-layer frameworks and
	Applications with different sensor expose/transfer protocols,
	such as `CHRE <https://github.com/zephyrproject-rtos/chre>`_, HID sensors Applications,
	MQTT sensor Applications according different products requirements. Or even support multiple
	Applications with different up-layer sensor protocols at the same time
	with it's multiple clients support design.

	Sensing subsystem can help build a unified Zephyr sensing architecture for
	cross host OSes support and as well as IoT sensor solutions.

	The diagram below illustrates how the Sensing Subsystem integrates with up-layer frameworks.

	.. image:: images/sensing_solution.png
	:align: center
	:alt: Unified Zephyr sensing architecture.

	Configurability
	***************

	* Reusable and configurable standalone subsystem.
	* Based on Zephyr existing low-level Sensor API (reuse 100+ existing sensor device drivers)
	* Provide Zephyr high-level Sensing Subsystem API for Applications.
	* Separate option CHRE Sensor PAL Implementation module to support CHRE.
	* Decoupled with any host link protocols, it's Zephyr Application's role to handle different
	protocols (MQTT, HID or Private, all configurable)

	Main Features
	*************

	* Scope
	* Focus on framework for sensor fusion, multiple clients, arbitration, data sampling, timing
	management and scheduling.

	* Sensor Abstraction
	* ``Physical sensor``: interacts with Zephyr sensor device drivers, focus on data collecting.
	* ``Virtual sensor``: relies on other sensor(s), ``physical`` or ``virtual``, focus on
	data fusion.

	* Data Driven Model
	* ``Polling mode``: periodical sampling rate
	* ``Interrupt mode``: data ready, threshold interrupt etc.

	* Scheduling
	* single thread main loop for all sensor objects sampling and process.

	* Buffer Mode for Batching

	* Configurable Via Device Tree


	Below diagram shows the API position and scope:

	.. image:: images/sensing_api_org.png
	:align: center
	:alt: Sensing subsystem API organization.

	``Sensing Subsystem API`` is for Applications.
	``Sensing Sensor API`` is for development ``sensors``.


	Major Flows
	***********

	* Sensor Configuration Flow

	.. image:: images/sensor_config_flow.png
	:align: center
	:alt: Sensor Configuration Flow (App set report interval to hinge angel sensor example).

	* Sensor Data Flow

	.. image:: images/sensor_data_flow.png
	:align: center
	:alt: Sensor Data Flow (App receive hinge angel data through data event callback example).

	Sensor Types And Instance
	*************************

	The ``Sensing Subsystem`` supports multiple instances of the same sensor type,
	there're two methods for Applications to identify and open an unique sensor instance:

	* Enumerate all sensor instances

	:c:func:`sensing_get_sensors` returns all current board configuration supported sensor instances'
	information in a :c:struct:`sensing_sensor_info` pointer array .

	Then Applications can use :c:func:`sensing_open_sensor` to
	open specific sensor instance for future accessing, configuration and receive sensor data etc.

	This method is suitable for supporting some up-layer frameworks like ``CHRE``, ``HID`` which need
	to dynamically enumerate the underlying platform's sensor instances.

	* Open the sensor instance by devicetree node directly

	Applications can use :c:func:`sensing_open_sensor_by_dt` to open a sensor instance directly with
	sensor devicetree node identifier.

	For example:

	.. code-block:: c

	sensing_open_sensor_by_dt(DEVICE_DT_GET(DT_NODELABEL(base_accel)), cb_list, handle);
	sensing_open_sensor_by_dt(DEVICE_DT_GET(DT_CHOSEN(zephyr_sensing_base_accel)), cb_list, handle);

	This method is useful and easy use for some simple Application which just want to access specific
	sensor(s).


	``Sensor type`` follows the
	`HID standard sensor types definition <https://usb.org/sites/default/files/hutrr39b_0.pdf>`_.

	See :zephyr_file:`include/zephyr/sensing/sensing_sensor_types.h`

	Sensor Instance Handler
	***********************

	Clients using a :c:type:`sensing_sensor_handle_t` type handler to handle a opened sensor
	instance, and all subsequent operations on this sensor instance need use this handler,
	such as set configurations, read sensor sample data, etc.

	For a sensor instance, could have two kinds of clients:
	``Application clients`` and ``Sensor clients``.

	``Application clients`` can use :c:func:`sensing_open_sensor` to open a sensor instance
	and get it's handler.

	For ``Sensor clients``, there is no open API for opening a reporter, because the client-report
	relationship is built at the sensor's registration stage with devicetree.

	The ``Sensing Subsystem`` will auto open and create ``handlers`` for client sensor
	to it's reporter sensors.
	``Sensor clients`` can get it's reporters' handlers via :c:func:`sensing_sensor_get_reporters`.

	.. image:: images/sensor_top.png
	:align: center
	:alt: Sensor Reporting Topology.

	.. note::
	Sensors inside the Sensing Subsystem, the reporting relationship between them are all auto
	generated by Sensing Subsystem according devicetree definitions, handlers between client sensor
	and reporter sensors are auto created.
	Application(s) need to call :c:func:`sensing_open_sensor` to explicitly open the sensor instance.

	Sensor Sample Value
	*******************

	* Data Structure

	Each sensor sample value defines as a common ``header`` + ``readings[]`` data structure, like
	:c:struct:`sensing_sensor_value_3d_q31`, :c:struct:`sensing_sensor_value_q31`, and
	:c:struct:`sensing_sensor_value_uint32`.

	The ``header`` definition :c:func:`sensing_sensor_value_header`.


	* Time Stamp

	Time stamp unit in sensing subsystem is ``micro seconds``.

	The ``header`` defines a base_timestamp, and
	each element in the readings[] array defines timestamp_delta.

	The timestamp_delta is in relation to the previous readings (or the base_timestamp)

	For example:

	* timestamp of ``readings[0]`` is ``header.base_timestamp`` + ``readings[0].timestamp_delta``.

	* timestamp of ``readings[1]`` is ``timestamp of readings[0]`` + ``readings[1].timestamp_delta``.

	Since timestamp unit is micro seconds,
	the max timestamp_delta (``uint32_t``) is ``4295`` seconds.

	If a sensor has batched data where two consecutive readings differ by more than ``4295`` seconds,
	the sensing subsystem runtime will split them across multiple instances of the readings structure,
	and send multiple events.

	This concept is referred from `CHRE Sensor API <https://github.com/zephyrproject-rtos/
	chre/blob/zephyr/chre_api/include/chre_api/chre/sensor_types.h>`_.

	* Data Format

	``Sensing Subsystem`` uses per sensor type defined data format structure,
	and support ``Q Format`` defined in :zephyr_file:`include/zephyr/dsp/types.h`
	for ``zdsp`` lib support.

	For example :c:struct:`sensing_sensor_value_3d_q31` can be used by 3D IMU sensors like
	:c:macro:`SENSING_SENSOR_TYPE_MOTION_ACCELEROMETER_3D`,
	:c:macro:`SENSING_SENSOR_TYPE_MOTION_UNCALIB_ACCELEROMETER_3D`,
	and :c:macro:`SENSING_SENSOR_TYPE_MOTION_GYROMETER_3D`.

	:c:struct:`sensing_sensor_value_uint32` can be used by
	:c:macro:`SENSING_SENSOR_TYPE_LIGHT_AMBIENTLIGHT` sensor,

	and :c:struct:`sensing_sensor_value_q31` can be used by
	:c:macro:`SENSING_SENSOR_TYPE_MOTION_HINGE_ANGLE` sensor

	See :zephyr_file:`include/zephyr/sensing/sensing_datatypes.h`


	Device Tree Configuration
	*************************

	Sensing subsystem using device tree to configuration all sensor instances and their properties,
	reporting relationships.

	See the example :zephyr_file:`samples/subsys/sensing/simple/boards/native_sim.overlay`

	API Reference
	*************

	.. doxygengroup:: sensing_sensor_types
	.. doxygengroup:: sensing_datatypes
	.. doxygengroup:: sensing_api
	.. doxygengroup:: sensing_sensor