Software reset¶

To perform software reset of the chip, esp_restart() function is provided. When the function is called, execution of the program will stop, both CPUs will be reset, application will be loaded by the bootloader and started again.

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Additionally, esp_register_shutdown_handler() function is provided to register a routine which needs to be called prior to restart (when done by esp_restart()). This is similar to the functionality of atexit POSIX function.

Reset reason¶

ESP-IDF application can be started or restarted due to a variety of reasons. To get the last reset reason, call esp_reset_reason() function. See description of esp_reset_reason_t for the list of possible reset reasons.

Heap memory¶

Two heap memory related functions are provided:

esp_get_free_heap_size() returns the current size of free heap memory
esp_get_minimum_free_heap_size() returns the minimum size of free heap memory that was available during program execution.

Note that ESP-IDF supports multiple heaps with different capabilities. Functions mentioned in this section return the size of heap memory which can be allocated using malloc family of functions. For further information about heap memory see Heap Memory Allocation.

Random number generation¶

ESP32 contains a hardware random number generator, values from it can be obtained using esp_random().

When Wi-Fi or Bluetooth are enabled, numbers returned by hardware random number generator (RNG) can be considered true random numbers. Without Wi-Fi or Bluetooth enabled, hardware RNG is a pseudo-random number generator. At startup, ESP-IDF bootloader seeds the hardware RNG with entropy, but care must be taken when reading random values between the start of app_main and initialization of Wi-Fi or Bluetooth drivers.

MAC Address¶

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

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

In ESP-IDF these addresses are calculated from a single Base MAC address. By default, the Espressif base MAC address is used. This MAC is pre-programmed into ESP32 eFuse from the factory.

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	Local MACderived 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	Local MAC(derived from Bluetooth MAC)

Note

The default configurationis 4 universally administered MAC addresses, and this is recommended when usingEspressif-provided MAC addresses.

Custom Base MAC¶

The default Base MAC is pre-programmed by Espressif in eFuse BLK0. To set a custom Base MAC instead, call the function esp_base_mac_addr_set() before initializing any network interfaces or calling the esp_read_mac() function. The customized MAC address can be stored in any supported storage device (e.g. Flash, NVS, etc).

The custom base MAC addresses should be allocated such that derived MAC addresses will not overlap. Configure the option CONFIG_ESP32_UNIVERSAL_MAC_ADDRESSES to set the number of valid universal MAC addresses that can be derived from the custom base MAC, according to the table above.

Note

It is also possible to call the function esp_netif_set_mac() to set the specific MAC used by a network interface, after network initialization. It’s recommended to use the Base MAC approach documented here instead, to avoid the possibility of the original MAC address briefly appearing on the network before it is changed.

Custom MAC address in eFuse¶

When reading custom MAC addresses from eFuse, ESP-IDF provides a helper function esp_efuse_mac_get_custom(). This loads the MAC address from eFuse BLK3. This function assumes that the custom base MAC address is stored in the following format:

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

Once MAC address has been obtained using esp_efuse_mac_get_custom(), call esp_base_mac_addr_set() to set this MAC address as base MAC address.

Local vs Universal MAC addresses¶

ESP32 comes pre-programmed with enough valid Espressif universally administered MAC addresses for all internal interfaces. The specific calculations to derive an interface’s MAC address from the base MAC address is shown in the table above.

When using a custom MAC address scheme, it’s possible that not all interfaces can be assigned 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 for the definition of local and universally administered MAC addresses.

Function esp_derive_local_mac() is called internally to derive a local MAC address from a universal MAC address. The process is as follows:

The U/L bit (bit value 0x2) is set in the first octet of the universal MAC address, creating a local MAC address.
If this bit is already set in the supplied universal MAC address (meaning: 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¶

esp_chip_info() function fills 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.

SDK version¶

esp_get_idf_version() returns a string describing the IDF version which was 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 gitdescribe 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 IDF version.

ESP_IDF_VERSION_MAJOR, ESP_IDF_VERSION_MINOR, ESP_IDF_VERSION_PATCH are defined to integers representing major, minor, and patch version.
ESP_IDF_VERSION_VAL and ESP_IDF_VERSION<

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