| lwIP
    2.1.2
    Lightweight IP stack | 
| Functions | |
| err_t | slipif_init (struct netif *netif) | 
| void | slipif_poll (struct netif *netif) | 
| void | slipif_process_rxqueue (struct netif *netif) | 
| void | slipif_received_byte (struct netif *netif, u8_t data) | 
| void | slipif_received_bytes (struct netif *netif, u8_t *data, u8_t len) | 
This is an arch independent SLIP netif. The specific serial hooks must be provided by another file. They are sio_open, sio_read/sio_tryread and sio_send
Usage: This netif can be used in three ways:
 1) For NO_SYS==0, an RX thread can be used which blocks on sio_read() until data is received.
 2) In your main loop, call slipif_poll() to check for new RX bytes, completed packets are fed into netif->input().
 3) Call slipif_received_byte[s]() from your serial RX ISR and slipif_process_rxqueue() from your main loop. ISR level decodes packets and puts completed packets on a queue which is fed into the stack from the main loop (needs SYS_LIGHTWEIGHT_PROT for pbuf_alloc to work on ISR level!). 
SLIP netif initialization
Call the arch specific sio_open and remember the opened device in the state field of the netif.
| netif | the lwip network interface structure for this slipif | 
| void slipif_poll | ( | struct netif * | netif | ) | 
Polls the serial device and feeds the IP layer with incoming packets.
| netif | The lwip network interface structure for this slipif | 
| void slipif_process_rxqueue | ( | struct netif * | netif | ) | 
Feeds the IP layer with incoming packets that were receive
| netif | The lwip network interface structure for this slipif | 
| void slipif_received_byte | ( | struct netif * | netif, | 
| u8_t | data | ||
| ) | 
Process a received byte, completed packets are put on a queue that is fed into IP through slipif_process_rxqueue().
This function can be called from ISR if SYS_LIGHTWEIGHT_PROT is enabled.
| netif | The lwip network interface structure for this slipif | 
| data | received character | 
| void slipif_received_bytes | ( | struct netif * | netif, | 
| u8_t * | data, | ||
| u8_t | len | ||
| ) | 
Process multiple received byte, completed packets are put on a queue that is fed into IP through slipif_process_rxqueue().
This function can be called from ISR if SYS_LIGHTWEIGHT_PROT is enabled.
| netif | The lwip network interface structure for this slipif | 
| data | received character | 
| len | Number of received characters |