7.2 lwIP Interface Layer

To interface with the rest of the network, the device abstraction layer needs to be glued with a network stack that can form and interpret network packets. The device abstraction hooks into the interface layer of lwIP. This is also referred to as the device-specific "port" or the hdk-interface for lwIP. It defines standard interface entry points and state variables. A network device is represented by struct netif, generically referred to as netif. The netif contains all the information about the interface, including the IP/MAC address(s), TCP/IP options, protocol handlers, link information, and (most importantly) the network device driver entry point callbacks. Every network interface must implement the linkoutput and init callbacks, and all state information is maintained in this structure. The interface layer also implements the core interrupt handling and DMA handling. All the required function calls for initializing the lwIP stack and registering the network interface are performed in lwIP-1.4.1\ports\hdk\lwIPlib.c\lwIPlib.c. For more information about the lwIP stack implementation, see the lwIP documentation under lwip-1.4.1\doc.