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[reactos.git] / sdk / lib / drivers / lwip / doc / rawapi.txt
1 Raw TCP/IP interface for lwIP
2
3 Authors: Adam Dunkels, Leon Woestenberg, Christiaan Simons
4
5 lwIP provides three Application Program's Interfaces (APIs) for programs
6 to use for communication with the TCP/IP code:
7 * low-level "core" / "callback" or "raw" API.
8 * higher-level "sequential" API.
9 * BSD-style socket API.
10
11 The sequential API provides a way for ordinary, sequential, programs
12 to use the lwIP stack. It is quite similar to the BSD socket API. The
13 model of execution is based on the blocking open-read-write-close
14 paradigm. Since the TCP/IP stack is event based by nature, the TCP/IP
15 code and the application program must reside in different execution
16 contexts (threads).
17
18 The socket API is a compatibility API for existing applications,
19 currently it is built on top of the sequential API. It is meant to
20 provide all functions needed to run socket API applications running
21 on other platforms (e.g. unix / windows etc.). However, due to limitations
22 in the specification of this API, there might be incompatibilities
23 that require small modifications of existing programs.
24
25 ** Threading
26
27 lwIP started targeting single-threaded environments. When adding multi-
28 threading support, instead of making the core thread-safe, another
29 approach was chosen: there is one main thread running the lwIP core
30 (also known as the "tcpip_thread"). The raw API may only be used from
31 this thread! Application threads using the sequential- or socket API
32 communicate with this main thread through message passing.
33
34 As such, the list of functions that may be called from
35 other threads or an ISR is very limited! Only functions
36 from these API header files are thread-safe:
37 - api.h
38 - netbuf.h
39 - netdb.h
40 - netifapi.h
41 - sockets.h
42 - sys.h
43
44 Additionaly, memory (de-)allocation functions may be
45 called from multiple threads (not ISR!) with NO_SYS=0
46 since they are protected by SYS_LIGHTWEIGHT_PROT and/or
47 semaphores.
48
49 Only since 1.3.0, if SYS_LIGHTWEIGHT_PROT is set to 1
50 and LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT is set to 1,
51 pbuf_free() may also be called from another thread or
52 an ISR (since only then, mem_free - for PBUF_RAM - may
53 be called from an ISR: otherwise, the HEAP is only
54 protected by semaphores).
55
56
57 ** The remainder of this document discusses the "raw" API. **
58
59 The raw TCP/IP interface allows the application program to integrate
60 better with the TCP/IP code. Program execution is event based by
61 having callback functions being called from within the TCP/IP
62 code. The TCP/IP code and the application program both run in the same
63 thread. The sequential API has a much higher overhead and is not very
64 well suited for small systems since it forces a multithreaded paradigm
65 on the application.
66
67 The raw TCP/IP interface is not only faster in terms of code execution
68 time but is also less memory intensive. The drawback is that program
69 development is somewhat harder and application programs written for
70 the raw TCP/IP interface are more difficult to understand. Still, this
71 is the preferred way of writing applications that should be small in
72 code size and memory usage.
73
74 Both APIs can be used simultaneously by different application
75 programs. In fact, the sequential API is implemented as an application
76 program using the raw TCP/IP interface.
77
78 --- Callbacks
79
80 Program execution is driven by callbacks. Each callback is an ordinary
81 C function that is called from within the TCP/IP code. Every callback
82 function is passed the current TCP or UDP connection state as an
83 argument. Also, in order to be able to keep program specific state,
84 the callback functions are called with a program specified argument
85 that is independent of the TCP/IP state.
86
87 The function for setting the application connection state is:
88
89 - void tcp_arg(struct tcp_pcb *pcb, void *arg)
90
91 Specifies the program specific state that should be passed to all
92 other callback functions. The "pcb" argument is the current TCP
93 connection control block, and the "arg" argument is the argument
94 that will be passed to the callbacks.
95
96
97 --- TCP connection setup
98
99 The functions used for setting up connections is similar to that of
100 the sequential API and of the BSD socket API. A new TCP connection
101 identifier (i.e., a protocol control block - PCB) is created with the
102 tcp_new() function. This PCB can then be either set to listen for new
103 incoming connections or be explicitly connected to another host.
104
105 - struct tcp_pcb *tcp_new(void)
106
107 Creates a new connection identifier (PCB). If memory is not
108 available for creating the new pcb, NULL is returned.
109
110 - err_t tcp_bind(struct tcp_pcb *pcb, ip_addr_t *ipaddr,
111 u16_t port)
112
113 Binds the pcb to a local IP address and port number. The IP address
114 can be specified as IP_ADDR_ANY in order to bind the connection to
115 all local IP addresses.
116
117 If another connection is bound to the same port, the function will
118 return ERR_USE, otherwise ERR_OK is returned.
119
120 - struct tcp_pcb *tcp_listen(struct tcp_pcb *pcb)
121
122 Commands a pcb to start listening for incoming connections. When an
123 incoming connection is accepted, the function specified with the
124 tcp_accept() function will be called. The pcb will have to be bound
125 to a local port with the tcp_bind() function.
126
127 The tcp_listen() function returns a new connection identifier, and
128 the one passed as an argument to the function will be
129 deallocated. The reason for this behavior is that less memory is
130 needed for a connection that is listening, so tcp_listen() will
131 reclaim the memory needed for the original connection and allocate a
132 new smaller memory block for the listening connection.
133
134 tcp_listen() may return NULL if no memory was available for the
135 listening connection. If so, the memory associated with the pcb
136 passed as an argument to tcp_listen() will not be deallocated.
137
138 - struct tcp_pcb *tcp_listen_with_backlog(struct tcp_pcb *pcb, u8_t backlog)
139
140 Same as tcp_listen, but limits the number of outstanding connections
141 in the listen queue to the value specified by the backlog argument.
142 To use it, your need to set TCP_LISTEN_BACKLOG=1 in your lwipopts.h.
143
144 - void tcp_accepted(struct tcp_pcb *pcb)
145
146 Inform lwIP that an incoming connection has been accepted. This would
147 usually be called from the accept callback. This allows lwIP to perform
148 housekeeping tasks, such as allowing further incoming connections to be
149 queued in the listen backlog.
150 ATTENTION: the PCB passed in must be the listening pcb, not the pcb passed
151 into the accept callback!
152
153 - void tcp_accept(struct tcp_pcb *pcb,
154 err_t (* accept)(void *arg, struct tcp_pcb *newpcb,
155 err_t err))
156
157 Specified the callback function that should be called when a new
158 connection arrives on a listening connection.
159
160 - err_t tcp_connect(struct tcp_pcb *pcb, ip_addr_t *ipaddr,
161 u16_t port, err_t (* connected)(void *arg,
162 struct tcp_pcb *tpcb,
163 err_t err));
164
165 Sets up the pcb to connect to the remote host and sends the
166 initial SYN segment which opens the connection.
167
168 The tcp_connect() function returns immediately; it does not wait for
169 the connection to be properly setup. Instead, it will call the
170 function specified as the fourth argument (the "connected" argument)
171 when the connection is established. If the connection could not be
172 properly established, either because the other host refused the
173 connection or because the other host didn't answer, the "err"
174 callback function of this pcb (registered with tcp_err, see below)
175 will be called.
176
177 The tcp_connect() function can return ERR_MEM if no memory is
178 available for enqueueing the SYN segment. If the SYN indeed was
179 enqueued successfully, the tcp_connect() function returns ERR_OK.
180
181
182 --- Sending TCP data
183
184 TCP data is sent by enqueueing the data with a call to
185 tcp_write(). When the data is successfully transmitted to the remote
186 host, the application will be notified with a call to a specified
187 callback function.
188
189 - err_t tcp_write(struct tcp_pcb *pcb, const void *dataptr, u16_t len,
190 u8_t apiflags)
191
192 Enqueues the data pointed to by the argument dataptr. The length of
193 the data is passed as the len parameter. The apiflags can be one or more of:
194 - TCP_WRITE_FLAG_COPY: indicates whether the new memory should be allocated
195 for the data to be copied into. If this flag is not given, no new memory
196 should be allocated and the data should only be referenced by pointer. This
197 also means that the memory behind dataptr must not change until the data is
198 ACKed by the remote host
199 - TCP_WRITE_FLAG_MORE: indicates that more data follows. If this is given,
200 the PSH flag is set in the last segment created by this call to tcp_write.
201 If this flag is given, the PSH flag is not set.
202
203 The tcp_write() function will fail and return ERR_MEM if the length
204 of the data exceeds the current send buffer size or if the length of
205 the queue of outgoing segment is larger than the upper limit defined
206 in lwipopts.h. The number of bytes available in the output queue can
207 be retrieved with the tcp_sndbuf() function.
208
209 The proper way to use this function is to call the function with at
210 most tcp_sndbuf() bytes of data. If the function returns ERR_MEM,
211 the application should wait until some of the currently enqueued
212 data has been successfully received by the other host and try again.
213
214 - void tcp_sent(struct tcp_pcb *pcb,
215 err_t (* sent)(void *arg, struct tcp_pcb *tpcb,
216 u16_t len))
217
218 Specifies the callback function that should be called when data has
219 successfully been received (i.e., acknowledged) by the remote
220 host. The len argument passed to the callback function gives the
221 amount bytes that was acknowledged by the last acknowledgment.
222
223
224 --- Receiving TCP data
225
226 TCP data reception is callback based - an application specified
227 callback function is called when new data arrives. When the
228 application has taken the data, it has to call the tcp_recved()
229 function to indicate that TCP can advertise increase the receive
230 window.
231
232 - void tcp_recv(struct tcp_pcb *pcb,
233 err_t (* recv)(void *arg, struct tcp_pcb *tpcb,
234 struct pbuf *p, err_t err))
235
236 Sets the callback function that will be called when new data
237 arrives. The callback function will be passed a NULL pbuf to
238 indicate that the remote host has closed the connection. If
239 there are no errors and the callback function is to return
240 ERR_OK, then it must free the pbuf. Otherwise, it must not
241 free the pbuf so that lwIP core code can store it.
242
243 - void tcp_recved(struct tcp_pcb *pcb, u16_t len)
244
245 Must be called when the application has received the data. The len
246 argument indicates the length of the received data.
247
248
249 --- Application polling
250
251 When a connection is idle (i.e., no data is either transmitted or
252 received), lwIP will repeatedly poll the application by calling a
253 specified callback function. This can be used either as a watchdog
254 timer for killing connections that have stayed idle for too long, or
255 as a method of waiting for memory to become available. For instance,
256 if a call to tcp_write() has failed because memory wasn't available,
257 the application may use the polling functionality to call tcp_write()
258 again when the connection has been idle for a while.
259
260 - void tcp_poll(struct tcp_pcb *pcb,
261 err_t (* poll)(void *arg, struct tcp_pcb *tpcb),
262 u8_t interval)
263
264 Specifies the polling interval and the callback function that should
265 be called to poll the application. The interval is specified in
266 number of TCP coarse grained timer shots, which typically occurs
267 twice a second. An interval of 10 means that the application would
268 be polled every 5 seconds.
269
270
271 --- Closing and aborting connections
272
273 - err_t tcp_close(struct tcp_pcb *pcb)
274
275 Closes the connection. The function may return ERR_MEM if no memory
276 was available for closing the connection. If so, the application
277 should wait and try again either by using the acknowledgment
278 callback or the polling functionality. If the close succeeds, the
279 function returns ERR_OK.
280
281 The pcb is deallocated by the TCP code after a call to tcp_close().
282
283 - void tcp_abort(struct tcp_pcb *pcb)
284
285 Aborts the connection by sending a RST (reset) segment to the remote
286 host. The pcb is deallocated. This function never fails.
287
288 ATTENTION: When calling this from one of the TCP callbacks, make
289 sure you always return ERR_ABRT (and never return ERR_ABRT otherwise
290 or you will risk accessing deallocated memory or memory leaks!
291
292
293 If a connection is aborted because of an error, the application is
294 alerted of this event by the err callback. Errors that might abort a
295 connection are when there is a shortage of memory. The callback
296 function to be called is set using the tcp_err() function.
297
298 - void tcp_err(struct tcp_pcb *pcb, void (* err)(void *arg,
299 err_t err))
300
301 The error callback function does not get the pcb passed to it as a
302 parameter since the pcb may already have been deallocated.
303
304
305 --- Lower layer TCP interface
306
307 TCP provides a simple interface to the lower layers of the
308 system. During system initialization, the function tcp_init() has
309 to be called before any other TCP function is called. When the system
310 is running, the two timer functions tcp_fasttmr() and tcp_slowtmr()
311 must be called with regular intervals. The tcp_fasttmr() should be
312 called every TCP_FAST_INTERVAL milliseconds (defined in tcp.h) and
313 tcp_slowtmr() should be called every TCP_SLOW_INTERVAL milliseconds.
314
315
316 --- UDP interface
317
318 The UDP interface is similar to that of TCP, but due to the lower
319 level of complexity of UDP, the interface is significantly simpler.
320
321 - struct udp_pcb *udp_new(void)
322
323 Creates a new UDP pcb which can be used for UDP communication. The
324 pcb is not active until it has either been bound to a local address
325 or connected to a remote address.
326
327 - void udp_remove(struct udp_pcb *pcb)
328
329 Removes and deallocates the pcb.
330
331 - err_t udp_bind(struct udp_pcb *pcb, ip_addr_t *ipaddr,
332 u16_t port)
333
334 Binds the pcb to a local address. The IP-address argument "ipaddr"
335 can be IP_ADDR_ANY to indicate that it should listen to any local IP
336 address. The function currently always return ERR_OK.
337
338 - err_t udp_connect(struct udp_pcb *pcb, ip_addr_t *ipaddr,
339 u16_t port)
340
341 Sets the remote end of the pcb. This function does not generate any
342 network traffic, but only set the remote address of the pcb.
343
344 - err_t udp_disconnect(struct udp_pcb *pcb)
345
346 Remove the remote end of the pcb. This function does not generate
347 any network traffic, but only removes the remote address of the pcb.
348
349 - err_t udp_send(struct udp_pcb *pcb, struct pbuf *p)
350
351 Sends the pbuf p. The pbuf is not deallocated.
352
353 - void udp_recv(struct udp_pcb *pcb,
354 void (* recv)(void *arg, struct udp_pcb *upcb,
355 struct pbuf *p,
356 ip_addr_t *addr,
357 u16_t port),
358 void *recv_arg)
359
360 Specifies a callback function that should be called when a UDP
361 datagram is received.
362
363
364 --- System initalization
365
366 A truly complete and generic sequence for initializing the lwip stack
367 cannot be given because it depends on the build configuration (lwipopts.h)
368 and additional initializations for your runtime environment (e.g. timers).
369
370 We can give you some idea on how to proceed when using the raw API.
371 We assume a configuration using a single Ethernet netif and the
372 UDP and TCP transport layers, IPv4 and the DHCP client.
373
374 Call these functions in the order of appearance:
375
376 - stats_init()
377
378 Clears the structure where runtime statistics are gathered.
379
380 - sys_init()
381
382 Not of much use since we set the NO_SYS 1 option in lwipopts.h,
383 to be called for easy configuration changes.
384
385 - mem_init()
386
387 Initializes the dynamic memory heap defined by MEM_SIZE.
388
389 - memp_init()
390
391 Initializes the memory pools defined by MEMP_NUM_x.
392
393 - pbuf_init()
394
395 Initializes the pbuf memory pool defined by PBUF_POOL_SIZE.
396
397 - etharp_init()
398
399 Initializes the ARP table and queue.
400 Note: you must call etharp_tmr at a ARP_TMR_INTERVAL (5 seconds) regular interval
401 after this initialization.
402
403 - ip_init()
404
405 Doesn't do much, it should be called to handle future changes.
406
407 - udp_init()
408
409 Clears the UDP PCB list.
410
411 - tcp_init()
412
413 Clears the TCP PCB list and clears some internal TCP timers.
414 Note: you must call tcp_fasttmr() and tcp_slowtmr() at the
415 predefined regular intervals after this initialization.
416
417 - netif_add(struct netif *netif, ip_addr_t *ipaddr,
418 ip_addr_t *netmask, ip_addr_t *gw,
419 void *state, err_t (* init)(struct netif *netif),
420 err_t (* input)(struct pbuf *p, struct netif *netif))
421
422 Adds your network interface to the netif_list. Allocate a struct
423 netif and pass a pointer to this structure as the first argument.
424 Give pointers to cleared ip_addr structures when using DHCP,
425 or fill them with sane numbers otherwise. The state pointer may be NULL.
426
427 The init function pointer must point to a initialization function for
428 your ethernet netif interface. The following code illustrates it's use.
429
430 err_t netif_if_init(struct netif *netif)
431 {
432 u8_t i;
433
434 for(i = 0; i < ETHARP_HWADDR_LEN; i++) netif->hwaddr[i] = some_eth_addr[i];
435 init_my_eth_device();
436 return ERR_OK;
437 }
438
439 For ethernet drivers, the input function pointer must point to the lwip
440 function ethernet_input() declared in "netif/etharp.h". Other drivers
441 must use ip_input() declared in "lwip/ip.h".
442
443 - netif_set_default(struct netif *netif)
444
445 Registers the default network interface.
446
447 - netif_set_up(struct netif *netif)
448
449 When the netif is fully configured this function must be called.
450
451 - dhcp_start(struct netif *netif)
452
453 Creates a new DHCP client for this interface on the first call.
454 Note: you must call dhcp_fine_tmr() and dhcp_coarse_tmr() at
455 the predefined regular intervals after starting the client.
456
457 You can peek in the netif->dhcp struct for the actual DHCP status.
458
459
460 --- Optimalization hints
461
462 The first thing you want to optimize is the lwip_standard_checksum()
463 routine from src/core/inet.c. You can override this standard
464 function with the #define LWIP_CHKSUM <your_checksum_routine>.
465
466 There are C examples given in inet.c or you might want to
467 craft an assembly function for this. RFC1071 is a good
468 introduction to this subject.
469
470 Other significant improvements can be made by supplying
471 assembly or inline replacements for htons() and htonl()
472 if you're using a little-endian architecture.
473 #define LWIP_PLATFORM_BYTESWAP 1
474 #define LWIP_PLATFORM_HTONS(x) <your_htons>
475 #define LWIP_PLATFORM_HTONL(x) <your_htonl>
476
477 Check your network interface driver if it reads at
478 a higher speed than the maximum wire-speed. If the
479 hardware isn't serviced frequently and fast enough
480 buffer overflows are likely to occur.
481
482 E.g. when using the cs8900 driver, call cs8900if_service(ethif)
483 as frequently as possible. When using an RTOS let the cs8900 interrupt
484 wake a high priority task that services your driver using a binary
485 semaphore or event flag. Some drivers might allow additional tuning
486 to match your application and network.
487
488 For a production release it is recommended to set LWIP_STATS to 0.
489 Note that speed performance isn't influenced much by simply setting
490 high values to the memory options.
491
492 For more optimization hints take a look at the lwIP wiki.
493
494 --- Zero-copy MACs
495
496 To achieve zero-copy on transmit, the data passed to the raw API must
497 remain unchanged until sent. Because the send- (or write-)functions return
498 when the packets have been enqueued for sending, data must be kept stable
499 after that, too.
500
501 This implies that PBUF_RAM/PBUF_POOL pbufs passed to raw-API send functions
502 must *not* be reused by the application unless their ref-count is 1.
503
504 For no-copy pbufs (PBUF_ROM/PBUF_REF), data must be kept unchanged, too,
505 but the stack/driver will/must copy PBUF_REF'ed data when enqueueing, while
506 PBUF_ROM-pbufs are just enqueued (as ROM-data is expected to never change).
507
508 Also, data passed to tcp_write without the copy-flag must not be changed!
509
510 Therefore, be careful which type of PBUF you use and if you copy TCP data
511 or not!