This module realizes a netdev interface using Espressif's ESP-NOW technology which uses the built-in WiFi module.
With ESP-NOW, the ESP32 provides a connectionless communication technology, featuring short packet transmission. It applies the IEEE802.11 Action Vendor frame technology, along with the IE function developed by Espressif, and CCMP encryption technology, realizing a secure, connectionless communication solution.
The RIOT port for ESP32 implements in module ```esp_now``` a ```netdev``` driver which uses ESP-NOW to provide a link layer interface to a meshed network of ESP32 nodes. In this network, each node can send short packets with up to 250 data bytes to all other nodes that are visible in its range.
@note Due to symbol conflicts in the ```esp_idf_wpa_supplicant_crypto``` module used by the ```esp_now``` with RIOT's ```crypto``` and ```hashes``` modules, ESP-NOW cannot be used for application that use these modules. Therefore, the module ```esp_now``` is not enabled automatically if the ```netdev_default``` module is used. Instead, the application has to add the ```esp_now``` module in its makefile when needed.<br>
```
USEMODULE += esp_now
```
For ESP-NOW, ESP32 nodes are used in WiFi SoftAP + Station mode to advertise their SSID and become visible to other ESP32 nodes. The SSID of an ESP32 node is the concatenation of the prefix ```RIOT_ESP_``` with the MAC address of its SoftAP WiFi interface. The driver periodically scans all visible ESP32 nodes.
The following parameters are defined for ESP-NOW nodes. These parameters can be overriden by [application-specific board configurations](#esp32_application_specific_board_configuration).
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Parameter | Default | Description
:---------|:--------|:-----------
ESP_NOW_SCAN_PERIOD | 10000000UL | Defines the period in us at which an node scans for other nodes in its range. The default period is 10 s.
ESP_NOW_SOFT_AP_PASSPHRASE | ThisistheRIOTporttoESP | Defines the passphrase (max. 64 chars) that is used for the SoftAP interface of an nodes. It has to be same for all nodes in one network.
ESP_NOW_CHANNEL | 6 | Defines the channel that is used as the broadcast medium by all nodes together.
ESP_NOW_KEY | NULL | Defines a key that is used for encrypted communication between nodes. If it is NULL, encryption is disabled. The key has to be of type ```uint8_t[16]``` and has to be exactly 16 bytes long.
