Raw TCP/IP interface for lwIP
Authors: Adam Dunkels, Leon Woestenberg, Christiaan Simons
lwIP provides three Application Program's Interfaces (APIs) for programs
to use for communication with the TCP/IP code:
* low-level "core" / "callback" or "raw" API.
* higher-level "sequential" API.
* BSD-style socket API.
The sequential API provides a way for ordinary, sequential, programs
to use the lwIP stack. It is quite similar to the BSD socket API. The
model of execution is based on the blocking open-read-write-close
paradigm. Since the TCP/IP stack is event based by nature, the TCP/IP
code and the application program must reside in different execution
contexts (threads).
The socket API is a compatibility API for existing applications,
currently it is built on top of the sequential API. It is meant to
provide all functions needed to run socket API applications running
on other platforms (e.g. unix / windows etc.). However, due to limitations
in the specification of this API, there might be incompatibilities
that require small modifications of existing programs.
** Threading
lwIP started targeting single-threaded environments. When adding multi-
threading support, instead of making the core thread-safe, another
approach was chosen: there is one main thread running the lwIP core
(also known as the "tcpip_thread"). The raw API may only be used from
this thread! Application threads using the sequential- or socket API
communicate with this main thread through message passing.
As such, the list of functions that may be called from
other threads or an ISR is very limited! Only functions
from these API header files are thread-safe:
- api.h
- netbuf.h
- netdb.h
- netifapi.h
- sockets.h
- sys.h
Additionaly, memory (de-)allocation functions may be
called from multiple threads (not ISR!) with NO_SYS=0
since they are protected by SYS_LIGHTWEIGHT_PROT and/or
semaphores.
Only since 1.3.0, if SYS_LIGHTWEIGHT_PROT is set to 1
and LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT is set to 1,
pbuf_free() may also be called from another thread or
an ISR (since only then, mem_free - for PBUF_RAM - may
be called from an ISR: otherwise, the HEAP is only
protected by semaphores).
** The remainder of this document discusses the "raw" API. **
The raw TCP/IP interface allows the application program to integrate
better with the TCP/IP code. Program execution is event based by
having callback functions being called from within the TCP/IP
code. The TCP/IP code and the application program both run in the same
thread. The sequential API has a much higher overhead and is not very
well suited for small systems since it forces a multithreaded paradigm
on the application.
The raw TCP/IP interface is not only faster in terms of code execution
time but is also less memory intensive. The drawback is that program
development is somewhat harder and application programs written for
the raw TCP/IP interface are more difficult to understand. Still, this
is the preferred way of writing applications that should be small in
code size and memory usage.
Both APIs can be used simultaneously by different application
programs. In fact, the sequential API is implemented as an application
program using the raw TCP/IP interface.
--- Callbacks
Program execution is driven by callbacks. Each callback is an ordinary
C function that is called from within the TCP/IP code. Every callback
function is passed the current TCP or UDP connection state as an
argument. Also, in order to be able to keep program specific state,
the callback functions are called with a program specified argument
that is independent of the TCP/IP state.
The function for setting the application connection state is:
- void tcp_arg(struct tcp_pcb *pcb, void *arg)
Specifies the program specific state that should be passed to all
other callback functions. The "pcb" argument is the current TCP
connection control block, and the "arg" argument is the argument
that will be passed to the callbacks.
--- TCP connection setup
The functions used for setting up connections is similar to that of
the sequential API and of the BSD socket API. A new TCP connection
identifier (i.e., a protocol control block - PCB) is created with the
tcp_new() function. This PCB can then be either set to listen for new
incoming connections or be explicitly connected to another host.
- struct tcp_pcb *tcp_new(void)
Creates a new connection identifier (PCB). If memory is not
available for creating the new pcb, NULL is returned.
- err_t tcp_bind(struct tcp_pcb *pcb, ip_addr_t *ipaddr,
u16_t port)
Binds the pcb to a local IP address and port number. The IP address
can be specified as IP_ADDR_ANY in order to bind the connection to
all local IP addresses.
If another connection is bound to the same port, the function will
return ERR_USE, otherwise ERR_OK is returned.
- struct tcp_pcb *tcp_listen(struct tcp_pcb *pcb)
Commands a pcb to start listening for incoming connections. When an
incoming connection is accepted, the function specified with the
tcp_accept() function will be called. The pcb will have to be bound
to a local port with the tcp_bind() function.
The tcp_listen() function returns a new connection identifier, and
the one passed as an argument to the function will be
deallocated. The reason for this behavior is that less memory is
needed for a connection that is listening, so tcp_listen() will
reclaim the memory needed for the original connection and allocate a
new smaller memory block for the listening connection.
tcp_listen() may return NULL if no memory was available for the
listening connection. If so, the memory associated with the pcb
passed as an argument to tcp_listen() will not be deallocated.
- struct tcp_pcb *tcp_listen_with_backlog(struct tcp_pcb *pcb, u8_t backlog)
Same as tcp_listen, but limits the number of outstanding connections
in the listen queue to the value specified by the backlog argument.
To use it, your need to set TCP_LISTEN_BACKLOG=1 in your lwipopts.h.
- void tcp_accepted(struct tcp_pcb *pcb)
Inform lwIP that an incoming connection has been accepted. This would
usually be called from the accept callback. This allows lwIP to perform
housekeeping tasks, such as allowing further incoming connections to be
queued in the listen backlog.
ATTENTION: the PCB passed in must be the listening pcb, not the pcb passed
into the accept callback!
- void tcp_accept(struct tcp_pcb *pcb,
err_t (* accept)(void *arg, struct tcp_pcb *newpcb,
err_t err))
Specified the callback function that should be called when a new
connection arrives on a listening connection.
- err_t tcp_connect(struct tcp_pcb *pcb, ip_addr_t *ipaddr,
u16_t port, err_t (* connected)(void *arg,
struct tcp_pcb *tpcb,
err_t err));
Sets up the pcb to connect to the remote host and sends the
initial SYN segment which opens the connection.
The tcp_connect() function returns immediately; it does not wait for
the connection to be properly setup. Instead, it will call the
function specified as the fourth argument (the "connected" argument)
when the connection is established. If the connection could not be
properly established, either because the other host refused the
connection or because the other host didn't answer, the "err"
callback function of this pcb (registered with tcp_err, see below)
will be called.
The tcp_connect() function can return ERR_MEM if no memory is
available for enqueueing the SYN segment. If the SYN indeed was
enqueued successfully, the tcp_connect() function returns ERR_OK.
--- Sending TCP data
TCP data is sent by enqueueing the data with a call to
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基于C语言+stm32f4的modbus tcp上下位机通信项目+上位机由LabVIEW编写+源码+开发文档+视频教程(高分项目 (350个子文件)
os_cpu_a.asm 8KB
keilkilll.bat 372B
stm32f4xx_tim.c 119KB
mib2.c 103KB
stm32f4x7_eth.c 98KB
stm32f4xx_rtc.c 98KB
stm32f4xx_rcc.c 94KB
os_core.c 85KB
lcd.c 83KB
sockets.c 68KB
stm32f4xx_adc.c 66KB
dhcp.c 63KB
stm32f4xx_flash.c 60KB
tcp_in.c 59KB
ppp.c 57KB
stm32f4xx_can.c 57KB
lcp.c 56KB
os_task.c 55KB
stm32f4xx_usart.c 55KB
stm32f4xx_cryp_aes.c 55KB
os_flag.c 55KB
stm32f4xx_fmc.c 54KB
tcp.c 52KB
stm32f4xx_i2c.c 52KB
etharp.c 51KB
stm32f4xx_dma.c 50KB
stm32f4xx_spi.c 50KB
tcp_out.c 49KB
system_stm32f4xx.c 46KB
api_msg.c 45KB
stm32f4xx_sai.c 44KB
os_tmr.c 44KB
msg_in.c 43KB
os_q.c 41KB
stm32f4xx_fsmc.c 40KB
pbuf.c 38KB
ipcp.c 38KB
stm32f4xx_ltdc.c 38KB
stm32f4xx_sdio.c 37KB
os_mutex.c 36KB
stm32f4xx_pwr.c 36KB
auth.c 35KB
stm32f4xx_cryp.c 34KB
udp.c 33KB
ppp_oe.c 33KB
ip.c 32KB
test_tcp_oos.c 31KB
dns.c 30KB
os_mbox.c 30KB
os_sem.c 30KB
mib_structs.c 29KB
ip_frag.c 28KB
igmp.c 26KB
stm32f4xx_dma2d.c 26KB
stm32f4xx_dac.c 25KB
stm32f4xx_hash.c 25KB
chap.c 24KB
stm32f4xx_gpio.c 24KB
api_lib.c 23KB
fsm.c 23KB
mem.c 23KB
netif.c 22KB
msg_out.c 21KB
test_tcp.c 21KB
os_mem.c 19KB
vj.c 18KB
stm32f4xx_dcmi.c 18KB
autoip.c 18KB
asn1_dec.c 16KB
pap.c 16KB
mbascii.c 15KB
slipif.c 14KB
usmart.c 14KB
tcpip.c 14KB
asn1_enc.c 14KB
memp.c 14KB
init.c 14KB
stm32f4xx_rng.c 13KB
os_cpu_c.c 13KB
timers.c 13KB
inet_chksum.c 13KB
os_dbg_r.c 12KB
icmp.c 12KB
mbfuncholding.c 12KB
md5.c 11KB
chpms.c 11KB
os_dbg.c 11KB
mb.c 11KB
ip6.c 11KB
mbrtu.c 11KB
netdb.c 11KB
misc.c 11KB
usmart_str.c 11KB
os_time.c 11KB
lan8720.c 11KB
raw.c 10KB
user_mb_app.c 10KB
porttcp.c 10KB
stm32f4xx_cryp_tdes.c 10KB
stm32f4xx_wwdg.c 10KB
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