AN2282

Firmware

13/19

The uIP main features are as follows:

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Very small code size

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Very low RAM usage, configurable at compile time

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ARP, SLIP, IP, UDP, ICMP (ping) and TCP protocols

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Includes a set of example applications: web server, web client, e-mail sender (SMTP

client), Telnet server, DNS hostname resolver

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Any number of concurrently active TCP connections, maximum amount configurable at

compile time

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Any number of passively listening (server) TCP connections, maximum amount

configurable at compile time

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Free for both commercial and non-commercial use

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RFC compliant TCP and IP protocol implementations, including flow control, fragment

reassembly and retransmission time-out estimation

The total memory requirement (ROM+RAM) is less then 21.3 KB. The uIP stack does not

use explicit dynamic memory allocation. Instead, it uses a single global buffer (uip_buf) for

holding packets and has a fixed table for holding connection states. The global packet buffer

is large enough to contain one packet of maximum size. When a packet is received, the

device driver places it in the global buffer, updates the global variable uip_len with the value

of the received packet dimension and calls the TCP/IP stack. If the packet contains data, the

TCP/IP stack will notify the corresponding application. In uIP, the same global packet buffer

is also used for the TCP/IP headers of outgoing data. If the application sends dynamic data,

it may use the parts of the global packet buffer that are not used for headers as a temporary

storage buffer.

To send the data, the application passes a pointer to the data as well as the length of the

data to the stack. The data is not queued for retransmissions; instead, the application has to

reproduce the data if a retransmission is necessary. uIP uses an event driven interface

where the application is invoked in response to certain events. The application must be

implemented as a C function, UIP_APPCALL(), that uIP calls whenever an event occurs.

uIP calls the application when data is received, when data has been successfully delivered

to the other end of the connection, when a new connection has been set up, or when data

has to be retransmitted. The application is also periodically polled for new data. The

application provides only one callback function; it is up to the application to deal with

mapping different network services to different ports and connections. Figure 8 shows the

uIP main control loop flow diagram.