OpenThread
==========

:link_to_translation:`zh_CN:[中文]`

`OpenThread <https://github.com/openthread/openthread>`_ is an IP stack running on the 802.15.4 MAC layer which features mesh network and low power consumption.

Modes of the OpenThread stack
-----------------------------

OpenThread can run under the following modes on Espressif chips:

Standalone Node
+++++++++++++++

The full OpenThread stack and the application layer run on the same chip. This mode is available on chips with 15.4 radio such as ESP32-H2 and ESP32-C6.

Radio Co-Processor (RCP)
++++++++++++++++++++++++

The chip is connected to another host running the OpenThread IP stack. It sends and receives 15.4 packets on behalf of the host. This mode is available on chips with 15.4 radio such as ESP32-H2 and ESP32-C6. The underlying transport between the chip and the host can be SPI or UART. For the sake of latency, we recommend using SPI as the underlying transport.

OpenThread Host
+++++++++++++++

For chips without a 15.4 radio, it can be connected to an RCP and run OpenThread under host mode. This mode enables OpenThread on Wi-Fi chips such as ESP32, ESP32-S2, ESP32-S3, and ESP32-C3. The following diagram shows how devices work under different modes:

.. blockdiag::
    :caption: OpenThread device modes
    :align: center

    blockdiag openthread-device-modes {

        # global attributes
        node_height = 90;
        node_width = 220;
        span_width = 100
        default_shape = roundedbox;
        default_group_color = none;

        # node labels
        HOST_NODE [label="OpenThread \nhost\n(ESP32)", fontsize=14];
        RCP [label="Radio \nCo-Processor\n(ESP32-H2)", fontsize=14];
        STANDALONE [label="Standalone \nnode\n (ESP32-H2)", fontsize=14];

        # node connections + labels
        RCP -> STANDALONE [label="15.4 radio", dir=both, style=dashed];

        # arrange nodes vertically
        group {
           orientation = portrait;
           HOST_NODE -> RCP [label="SPI", dir=both];
        }
    }


How to Write an OpenThread Application
--------------------------------------

The OpenThread :example:`openthread/ot_cli` example is a good place to start at. It demonstrates basic OpenThread initialization and simple socket-based server and client.

Before OpenThread Initialization
++++++++++++++++++++++++++++++++

- s1.1: The main task calls :cpp:func:`esp_vfs_eventfd_register` to initialize the eventfd virtual file system. The eventfd file system is used for task notification in the OpenThread driver.

- s1.2: The main task calls :cpp:func:`nvs_flash_init` to initialize the NVS where the Thread network data is stored.

- s1.3: **Optional**. The main task calls :cpp:func:`esp_netif_init` only when it wants to create the network interface for Thread.

- s1.4: The main task calls :cpp:func:`esp_event_loop_create` to create the system Event task and initialize an application event's callback function.

OpenThread Stack Initialization
+++++++++++++++++++++++++++++++

- s2.1: Call :cpp:func:`esp_openthread_init` to initialize the OpenThread stack.

OpenThread Network Interface Initialization
+++++++++++++++++++++++++++++++++++++++++++

The whole stage is **optional** and only required if the application wants to create the network interface for Thread.

- s3.1: Call :cpp:func:`esp_netif_new` with ``ESP_NETIF_DEFAULT_OPENTHREAD`` to create the interface.
- s3.2: Call :cpp:func:`esp_openthread_netif_glue_init` to create the OpenThread interface handlers.
- s3.3: Call :cpp:func:`esp_netif_attach` to attach the handlers to the interface.

The OpenThread Main Loop
++++++++++++++++++++++++

- s4.3: Call :cpp:func:`esp_openthread_launch_mainloop` to launch the OpenThread main loop. Note that this is a busy loop and does not return until the OpenThread stack is terminated.

Calling OpenThread APIs
++++++++++++++++++++++++

The OpenThread APIs are not thread-safe. When calling OpenThread APIs from other tasks, make sure to hold the lock with :cpp:func:`esp_openthread_lock_acquire` and release the lock with :cpp:func:`esp_openthread_lock_release` afterwards.

Deinitialization
++++++++++++++++

The following steps are required to deinitialize the OpenThread stack:

- Call :cpp:func:`esp_netif_destroy` and :cpp:func:`esp_openthread_netif_glue_deinit` to deinitialize the OpenThread network interface if you have created one.
- Call :cpp:func:`esp_openthread_deinit` to deinitialize the OpenThread stack.

The OpenThread Border Router
----------------------------

The OpenThread border router connects the Thread network with other IP networks. It provides IPv6 connectivity, service registration, and commission functionality.

To launch an OpenThread border router on an ESP chip, you need to connect an RCP to a Wi-Fi capable chip such as ESP32.

Calling :cpp:func:`esp_openthread_border_router_init` during the initialization launches all the border routing functionalities.

You may refer to the :example:`openthread/ot_br` example and the README for further border router details.