cpu/esp8266: doc extended for esp_wifi

cpu/esp8266/doc.txt

@@ -27,14 +27,17 @@
     6. [Timers](#esp8266_timers)
     7. [SPIFFS Device](#esp8266_spiffs_device)
     8. [Other Peripherals](#esp8266_other_peripherals)
-6. [Preconfigured Devices](#esp8266_preconfigured_devices)
+6. [Network Interfaces](#esp8266_network_interfaces)
+    1. [WiFi Network Interface](#esp8266_wifi_network_interface)
+    2. [ESP-NOW Network Interface](#esp8266_esp_now_network_interface)
+7. [Preconfigured Devices](#esp8266_preconfigured_devices)
     1. [Network Devices](#esp8266_network_devices)
     2. [SD-Card Device](#esp8266_sd_card_device)
-7. [Application-Specific Configurations](#esp8266_application_specific_configurations)
+8. [Application-Specific Configurations](#esp8266_application_specific_configurations)
     1. [Application-Specific Board Configuration](#esp8266_application_specific_board_configuration)
     2. [Application-Specific Driver Configuration](#esp8266_application_specific_driver_configuration)
-8. [SDK Task Handling](#esp8266_sdk_task_handling)
+9. [SDK Task Handling](#esp8266_sdk_task_handling)
-9. [QEMU Mode and GDB](#esp8266_qemu_mode_and_gdb)
+10. [QEMU Mode and GDB](#esp8266_qemu_mode_and_gdb)
 
 # <a name="esp8266_overview"> Overview </a> &nbsp;&nbsp; [[TOC](#esp8266_toc)]
 
@@ -353,9 +356,11 @@ Optional features of ESP8266 can be enabled by ```USEMODULE``` definitions in th
 Module | Description
 -------|------------
 [esp_gdb](#esp8266_qemu_mode_and_gdb) | Enable the compilation with debug information, which is equivalent to using ```ENABLE_GDB=1```
+[esp_now](#esp8266_esp_now_network_interface) | Enable the built-in WiFi module with the ESP-NOW protocol as `netdev` network device
 [esp_sdk](#esp8266_sdk_task_handling) | Enable the SDK version, which is equivalent to using ```USE_SDK=1```
 [esp_spiffs](#esp8266_spiffs_device) | Enable the SPIFFS drive in on-board flash memory
 [esp_sw_timer](#esp8266_timers) | Enable software timer implementation, implies the setting ```USE_SDK=1``` (module ```esp_sdk```)
+[esp_wifi](#esp8266_wifi_network_interface) | Use the built-in WiFi module as `netdev` network device
 
 </center><br>
 
@@ -563,6 +568,104 @@ The ESP8266 port of RIOT also supports
 
 RTC is not yet implemented.
 
+# <a name="esp8266_network_interfaces"> Network Interfaces </a> &nbsp;[[TOC](#esp8266_toc)]
+
+ESP8266 provides different built-in possibilities to realize network devices:
+
+- <b>ESP WiFi</b>, usual AP-based wireless LAN (not yet supported)
+- <b>ESP-NOW</b>, a WiFi based AP-less and connectionless peer to peer communication protocol
+
+\anchor esp8266_wifi_network_interface
+## <a name="esp8266_wifi_network_interface"> WiFi Network Interface </a> &nbsp;[[TOC](#esp8266_toc)]
+
+The RIOT port for ESP8266 implements in module `esp_wifi` a `netdev` driver for
+the built-in WiFi interface.
+
+@note Due to symbol conflicts with the `crypto` and `hash` modules of RIOT
+in vendor library `libwpa.so`, which is required by module
+`esp_wifi`, `esp_wifi` cannot be used for applications that use these modules.
+Therefore, module `esp_wifi` is not automatically enabled when module
+`netdev_default` is used. Instead, if necessary, the application has to add
+the module `esp_wifi` in the Makefile.
+
+```
+USEMODULE += esp_wifi
+```
+
+Furthermore, the following configuration parameters have to be defined:
+
+<center>
+
+Parameter          | Default                   | Description
+:------------------|:--------------------------|:------------
+ESP_WIFI_SSID      | "RIOT_AP"                 | SSID of the AP to be used.
+ESP_WIFI_PASS      | "ThisistheRIOTporttoESP"  | Passphrase used for the AP as clear text (max. 64 chars).
+ESP_WIFI_STACKSIZE | #THREAD_STACKSIZE_DEFAULT |Stack size used for the WiFi netdev driver thread.
+
+</center>
+
+These configuration parameter definitions, as well as enabling the `esp_wifi`
+module, can be done either in the makefile of the project or at make command
+line, e.g.:
+
+```
+USEMODULE=esp_wifi \
+CFLAGS='-DESP_WIFI_SSID=\"MySSID\" -DESP_WIFI_PASS=\"MyPassphrase\"' \
+make -C examples/gnrc_networking BOARD=...
+```
+
+@note The Wifi network interface (module `esp_wifi`) and the
+[ESP-NOW network interface](#esp8266_esp_now_network_interface)
+(module `esp_now`) can be used simultaneously, for example, to realize a
+border router for a mesh network which uses ESP-NOW.
+
+\anchor esp8266_esp_now_network_interface
+## <a name="esp8266_esp_now_network_interface"> ESP-NOW Network Interface </a> &nbsp;[[TOC](#esp8266_toc)]
+
+With ESP-NOW, the ESP8266 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 ESP8266 implements in module `esp_now` a `netdev` driver
+which uses ESP-NOW to provide a link layer interface to a meshed network of
+ESP8266 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 vendor library `libwpa.so` 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, ESP8266 nodes are used in WiFi SoftAP + Station mode to advertise
+their SSID and become visible to other ESP8266 nodes. The SSID of an ESP8266
+node is the concatenation of the prefix `RIOT_ESP_` with the MAC address of
+its SoftAP WiFi interface. The driver periodically scans all visible ESP8266
+nodes.
+
+The following parameters are defined for ESP-NOW nodes. These parameters can
+be overriden by [application-specific board configurations](#esp8266_application_specific_board_configuration).
+
+<center>
+
+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_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.
+
+</center>
+
+@note The ESP-NOW network interface (module `esp_now`) and the
+[Wifi network interface](#esp8266_wifi_network_interface) (module `esp_wifi`)
+can be used simultaneously, for example, to realize a border router for
+a mesh network which uses ESP-NOW.
+
 # <a name="esp8266_preconfigured_devices"> Preconfigured Devices </a> &nbsp;[[TOC](#esp8266_toc)]
 
 The ESP8266 port of RIOT has been tested with several common external devices that can be connected to ESP8266 boards and are preconfigured accordingly.