With ESP-NOW, the ESP nodes (ESP32 and ESP8266) provide 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 ESP implements in module ```esp_now``` a ```netdev``` driver which uses ESP-NOW to provide a link layer interface to a meshed network of ESP 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>
For ESP-NOW, ESP nodes are used in WiFi SoftAP + Station mode to advertise their SSID and become visible to other ESP nodes. The SSID of an ESP node is the concatenation of the prefix ```RIOT_ESP_``` with the MAC address of its SoftAP WiFi interface. The driver periodically scans all visible ESP nodes.
ESP_NOW_SOFT_AP_PASS | "ThisistheRIOTporttoESP" | Defines the passphrase as clear text (max. 64 chars) that is used for the SoftAP interface of ESP-NOW 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.
