esp-idf/components/esp_netif/README.md

ESP-NETIF architecture

                 |          (A) USER CODE                 |
                 |                                        |
    .............| init          settings      events     |
    .            +----------------------------------------+          
    .               .                |           *
    .               .                V           *                                   
--------+        +===========================+   *     +-----------------------+
        |        | new/config     get/set    |   *     |                       |
        |        |                           |...*.....| init                  |
        |        |---------------------------|   *     |                       |
  init  |        |                           |****     |                       |
  start |********|  event handler            |*********|  DHCP                 |
  stop  |        |                           |         |                       |
        |        |---------------------------|         |                       | 
        |        |                           |         |    NETIF              |
  +-----|        |                           |         +-----------------+     |   
  | glue|----<---|  esp_netif_transmit       |--<------| netif_output    |     |
  |     |        |                           |         |                 |     |
  |     |---->---|  esp_netif_receive        |-->------| netif_input     |     |
  |     |        |                           |         + ----------------+     |
  |     |....<...|  esp_netif_free_rx_buffer |...<.....| packet buffer         |
  +-----|        |                           |         |                       |  
        |        |                           |         |                       |  
  (B)   |        |                           |         +-----------------------+
--------+        +===========================+
communication                                                NETWORK STACK
DRIVER                   ESP-NETIF                          

Components:

A) User code, boiler plate

Overall application interaction with communication media and network stack

• initialization code
  • create a new instance of ESP-NETIF
  • configure the object with 1) netif specific options (flags, behaviour, name) 2) network stack options (netif init and input functions, not publicly available) 3) IO driver specific options (transmit, tx_free functions, IO driver handle)
  • setup event handlers
  • use default handlers for common interfaces defined in IO drivers; or define a specific handlers for customised behaviour/new interfaces
  • register handlers for app related events (such as IP lost/acquired)
• interact with network interfaces using ESP-NETIF API

B) Communication driver, IO driver, media driver

• event handler
  • define behaviour patterns of interaction with ESP-NETIF (example: ehternet link-up -> turn netif on)
• glue IO layer: adapt the input/output functions to use esp-netif transmit/input/free_rx
  • install driver_transmit to appropriate ESP-NETIF object, so that outgoing packets from network stack are passed to the IO driver
  • calls esp_netif_receive to pass incoming data to network stack

C) ESP-NETIF, former tcpip_adapter

• init API (new, configure)
• IO API: for passing data between IO driver and network stack
• event/action API (esp-netif lifecycle management)
  • building blocks for designing event handlers
• setters, getters
• network stack abstraction: enabling user interaction with TCP/IP stack
  • netif up/down
  • DHCP server, client
  • DNS API
• driver conversion utilities

D) Network stack: no public interaction with user code (wrtt interfaces)

Data/event flow:

• ........ Initialization line from user code to esp-netif and comm driver

• --<--->-- Data packets going from communication media to TCP/IP stack and back

• ******** Events agregated in ESP-NETIP propagates to driver, user code and network stack

• | User settings and runtime configuration