Miscellaneous System APIs
=========================

:link_to_translation:`zh_CN:[中文]`

{IDF_TARGET_BASE_MAC_BLOCK: default="BLK1", esp32="BLK0"}
{IDF_TARGET_CPU_RESET_DES: default="the CPU is reset", esp32="both CPUs are reset", esp32s3="both CPUs are reset", esp32p4="both CPUs are reset"}

Software Reset
--------------

To perform software reset of the chip, the :cpp:func:`esp_restart` function is provided. When the function is called, execution of the program stops, {IDF_TARGET_CPU_RESET_DES}, the application is loaded by the bootloader and starts execution again.

Additionally, the :cpp:func:`esp_register_shutdown_handler` function can register a routine that will be automatically called before a restart (that is triggered by :cpp:func:`esp_restart`) occurs. This is similar to the functionality of ``atexit`` POSIX function.

Reset Reason
------------

ESP-IDF applications can be started or restarted due to a variety of reasons. To get the last reset reason, call :cpp:func:`esp_reset_reason` function. See description of :cpp:type:`esp_reset_reason_t` for the list of possible reset reasons.

Heap Memory
-----------

Two heap-memory-related functions are provided:

* :cpp:func:`esp_get_free_heap_size` returns the current size of free heap memory.
* :cpp:func:`esp_get_minimum_free_heap_size` returns the minimum size of free heap memory that has ever been available (i.e., the smallest size of free heap memory in the application's lifetime).

Note that ESP-IDF supports multiple heaps with different capabilities. The functions mentioned in this section return the size of heap memory that can be allocated using the ``malloc`` family of functions. For further information about heap memory, see :doc:`Heap Memory Allocation <mem_alloc>`.

.. _MAC-Address-Allocation:

MAC Address
-----------

These APIs allow querying and customizing MAC addresses for different supported network interfaces (e.g., Wi-Fi, Bluetooth, Ethernet).

To fetch the MAC address for a specific network interface (e.g., Wi-Fi, Bluetooth, Ethernet), call the function :cpp:func:`esp_read_mac`.

In ESP-IDF, the MAC addresses for the various network interfaces are calculated from a single **base MAC address**. By default, the Espressif base MAC address is used. This base MAC address is pre-programmed into the {IDF_TARGET_NAME} eFuse in the factory during production.

.. only:: not esp32s2

    .. list-table::
        :widths: 20 40 40
        :header-rows: 1

        * - Interface
          - MAC Address (4 universally administered, default)
          - MAC Address (2 universally administered)
        * - Wi-Fi Station
          - base_mac
          - base_mac
        * - Wi-Fi SoftAP
          - base_mac, +1 to the last octet
          - :ref:`Local MAC <local-mac-addresses>` (derived from Wi-Fi Station MAC)
        * - Bluetooth
          - base_mac, +2 to the last octet
          - base_mac, +1 to the last octet
        * - Ethernet
          - base_mac, +3 to the last octet
          - :ref:`Local MAC <local-mac-addresses>` (derived from Bluetooth MAC)

    .. note::

        The :ref:`configuration <CONFIG_{IDF_TARGET_CFG_PREFIX}_UNIVERSAL_MAC_ADDRESSES>` configures the number of universally administered MAC addresses that are provided by Espressif.

.. only:: esp32s2

    .. list-table::
        :widths: 20 40 40
        :header-rows: 1

        * - Interface
          - MAC Address (2 universally administered, default)
          - MAC Address (1 universally administered)
        * - Wi-Fi Station
          - base_mac
          - base_mac
        * - Wi-Fi SoftAP
          - base_mac, +1 to the last octet
          - :ref:`Local MAC <local-mac-addresses>` (derived from Wi-Fi Station MAC)
        * - Ethernet
          - :ref:`Local MAC <local-mac-addresses>` (derived from Wi-Fi SoftAP MAC)
          - :ref:`Local MAC <local-mac-addresses>` (derived from base_mac with +1 to last octet. Not recommended.)

    .. note::

        The :ref:`configuration <CONFIG_{IDF_TARGET_CFG_PREFIX}_UNIVERSAL_MAC_ADDRESSES>` configures the number of universally administered MAC addresses that are provided by Espressif.

.. only:: not SOC_EMAC_SUPPORTED

    .. note::

      Although {IDF_TARGET_NAME} has no integrated Ethernet MAC, it is still possible to calculate an Ethernet MAC address. However, this MAC address can only be used with an external ethernet interface such as an SPI-Ethernet device. See :doc:`/api-reference/network/esp_eth`.

Custom Interface MAC
^^^^^^^^^^^^^^^^^^^^

Sometimes you may need to define custom MAC addresses that are not generated from the base MAC address. To set a custom interface MAC address, use the :cpp:func:`esp_iface_mac_addr_set` function. This function allows you to overwrite the MAC addresses of interfaces set (or not yet set) by the base MAC address. Once a MAC address has been set for a particular interface, it will not be affected when the base MAC address is changed.

Custom Base MAC
^^^^^^^^^^^^^^^

The default base MAC is pre-programmed by Espressif in eFuse {IDF_TARGET_BASE_MAC_BLOCK}. To set a custom base MAC instead, call the function :cpp:func:`esp_iface_mac_addr_set` with the ``ESP_MAC_BASE`` argument (or :cpp:func:`esp_base_mac_addr_set`) before initializing any network interfaces or calling the :cpp:func:`esp_read_mac` function. The custom MAC address can be stored in any supported storage device (e.g., flash, NVS).

The custom base MAC addresses should be allocated such that derived MAC addresses will not overlap. Based on the table above, users can configure the option :ref:`CONFIG_{IDF_TARGET_CFG_PREFIX}_UNIVERSAL_MAC_ADDRESSES` to set the number of valid universal MAC addresses that can be derived from the custom base MAC.

.. note::

    It is also possible to call the function :cpp:func:`esp_netif_set_mac` to set the specific MAC used by a network interface after network initialization. But it is recommended to use the base MAC approach documented here to avoid the possibility of the original MAC address briefly appearing on the network before being changed.


Custom MAC Address in eFuse
@@@@@@@@@@@@@@@@@@@@@@@@@@@

When reading custom MAC addresses from eFuse, ESP-IDF provides a helper function :cpp:func:`esp_efuse_mac_get_custom`. Users can also use :cpp:func:`esp_read_mac` with the ``ESP_MAC_EFUSE_CUSTOM`` argument. This loads the MAC address from eFuse BLK3. The :cpp:func:`esp_efuse_mac_get_custom` function assumes that the custom base MAC address is stored in the following format:

.. only:: esp32

    .. list-table::
        :widths: 20 15 20 45
        :header-rows: 1

        * - Field
          - # of bits
          - Range of bits
          - Notes
        * - Version
          - 8
          - 191:184
          - 0: invalid, others — valid
        * - Reserved
          - 128
          - 183:56
          -
        * - MAC address
          - 48
          - 55:8
          -
        * - MAC address CRC
          - 8
          - 7:0
          - CRC-8-CCITT, polynomial 0x07

    .. note::

        If the 3/4 coding scheme is enabled, all eFuse fields in this block must be burnt at the same time.

.. only:: not esp32

    .. list-table::
        :widths: 30 30 30
        :header-rows: 1

        * - Field
          - # of bits
          - Range of bits
        * - MAC address
          - 48
          - 200:248

    .. note::

        The eFuse BLK3 uses RS-coding during burning, which means that all eFuse fields in this block must be burnt at the same time.

Once custom eFuse MAC address has been obtained (using :cpp:func:`esp_efuse_mac_get_custom` or :cpp:func:`esp_read_mac`), you need to set it as the base MAC address. There are two ways to do it:

1. Use an old API: call :cpp:func:`esp_base_mac_addr_set`.
2. Use a new API: call :cpp:func:`esp_iface_mac_addr_set` with the ``ESP_MAC_BASE`` argument.


.. _local-mac-addresses:

Local Versus Universal MAC Addresses
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

{IDF_TARGET_NAME} comes pre-programmed with enough valid Espressif universally administered MAC addresses for all internal interfaces. The table above shows how to calculate and derive the MAC address for a specific interface according to the base MAC address.

When using a custom MAC address scheme, it is possible that not all interfaces can be assigned with a universally administered MAC address. In these cases, a locally administered MAC address is assigned. Note that these addresses are intended for use on a single local network only.

See `this article <https://en.wikipedia.org/wiki/MAC_address#Universal_vs._local_(U/L_bit)>`_ for the definition of locally and universally administered MAC addresses.

Function :cpp:func:`esp_derive_local_mac` is called internally to derive a local MAC address from a universal MAC address. The process is as follows:

1. The U/L bit (bit value 0x2) is set in the first octet of the universal MAC address, creating a local MAC address.
2. If this bit is already set in the supplied universal MAC address (i.e., the supplied "universal" MAC address was in fact already a local MAC address), then the first octet of the local MAC address is XORed with 0x4.

Chip Version
------------

:cpp:func:`esp_chip_info` function fills :cpp:class:`esp_chip_info_t` structure with information about the chip. This includes the chip revision, number of CPU cores, and a bit mask of features enabled in the chip.

.. _idf-version-h:

SDK Version
-----------

:cpp:func:`esp_get_idf_version` returns a string describing the ESP-IDF version which is used to compile the application. This is the same value as the one available through ``IDF_VER`` variable of the build system. The version string generally has the format of ``git describe`` output.

To get the version at build time, additional version macros are provided. They can be used to enable or disable parts of the program depending on the ESP-IDF version.

* :c:macro:`ESP_IDF_VERSION_MAJOR`, :c:macro:`ESP_IDF_VERSION_MINOR`, :c:macro:`ESP_IDF_VERSION_PATCH` are defined to integers representing major, minor, and patch version.

* :c:macro:`ESP_IDF_VERSION_VAL` and :c:macro:`ESP_IDF_VERSION` can be used when implementing version checks:

  .. code-block:: c

      #include "esp_idf_version.h"

      #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(4, 0, 0)
          // enable functionality present in ESP-IDF v4.0
      #endif


.. _app-version:

App Version
-----------

The application version is stored in :cpp:class:`esp_app_desc_t` structure. It is located in DROM sector and has a fixed offset from the beginning of the binary file. The structure is located after :cpp:class:`esp_image_header_t` and :cpp:class:`esp_image_segment_header_t` structures. The type of the field version is string and it has a maximum length of 32 chars.

To set the version in your project manually, you need to set the ``PROJECT_VER`` variable in the ``CMakeLists.txt`` of your project. In application ``CMakeLists.txt``, put ``set(PROJECT_VER "0.1.0.1")`` before including ``project.cmake``.

If the :ref:`CONFIG_APP_PROJECT_VER_FROM_CONFIG` option is set, the value of :ref:`CONFIG_APP_PROJECT_VER` will be used. Otherwise, if the ``PROJECT_VER`` variable is not set in the project, it will be retrieved either from the ``$(PROJECT_PATH)/version.txt`` file (if present) or using git command ``git describe``. If neither is available, ``PROJECT_VER`` will be set to "1". Application can make use of this by calling :cpp:func:`esp_app_get_description` or :cpp:func:`esp_ota_get_partition_description` functions.

Application Examples
--------------------

- :example:`system/base_mac_address` demonstrates how to retrieve, set, and derive the base MAC address for each network interface on {IDF_TARGET_NAME} from non-volatile memory, using either the eFuse blocks or external storage.

API Reference
-------------

.. include-build-file:: inc/esp_system.inc
.. include-build-file:: inc/esp_idf_version.inc
.. include-build-file:: inc/esp_mac.inc
.. include-build-file:: inc/esp_chip_info.inc
.. include-build-file:: inc/esp_cpu.inc
.. include-build-file:: inc/esp_app_desc.inc
