System initialisation

When performing manual initialisation of lwIP for use with the raw API, a variety of lwIP functions need to be called. Th exact functions will depend on the intended configuration, but the following provides an example based on a single Ethernet netif, UDP, TCP, IPv4 and DHCP.

In this example, these functions must be called in the order of appearance:

stats_init()

Clears the structure where runtime statistics are gathered.

sys_init()

Not generally used with raw API, but can be called for ease of compatibility if using sequential API in addition, initialised manually.

mem_init()

Initializes the dynamic memory heap defined by the CDL configuration option CYGNUM_LWIP_MEM_SIZE.

memp_init()

Initializes the memory pools defined by the CDL configuration options CYGNUM_LWIP_MEMP_NUM_*.

pbuf_init()

Initializes the pbuf memory pool defined by the CDL configuration option CYGNUM_LWIP_PBUF_POOL_SIZE.

etharp_init()

Initializes the ARP table and queue. Note: you must call etharp_tmr at a ARP_TMR_INTERVAL (by default, 5 seconds) regular interval after this initialization.

ip_init()

Doesn't do much at present - it should be called to handle future changes.

udp_init()

Clears the UDP PCB list.

tcp_init()

Clears the TCP PCB list and clears some internal TCP timers. Note: as mentioned earlier, you must call tcp_fasttmr() and tcp_slowtmr() at the predefined regular intervals after this initialization.

struct netif *netif_add(struct netif *netif, struct ip_addr *ipaddr, struct ip_addr *netmask, struct ip_addr *gw, void *state, err_t (* init)(struct netif *netif), err_t (* input)(struct pbuf *p, struct netif *netif))

Adds your network interface to the netif_list. Allocate a struct netif and pass a pointer to this structure as the first argument. Give pointers to cleared struct ip_addr structures when using DHCP, or fill them with sane numbers otherwise. The state pointer may be NULL.

The init function pointer must point to a initialization function for your ethernet netif interface. The following code illustrates it's use:

err_t netif_if_init(struct netif *netif)
{
  u8_t i;
  
  for(i = 0; i < 6; i++)
    netif->hwaddr[i] = some_eth_addr[i];
  init_my_eth_device();
  return ERR_OK;
}

The input function pointer must point to the lwIP function ip_input().

netif_set_default(struct netif *netif)

Registers netif as the default network interface.

netif_set_up(struct netif *netif)

When netif is fully configured, this function must be called to allow it to be used.

dhcp_start(struct netif *netif)

Creates a new DHCP client for this interface on the first call. Note: you must call dhcp_fine_tmr() and dhcp_coarse_tmr() at the predefined regular intervals after starting the client.

You can peek in the netif->dhcp struct for the actual DHCP status.