479 lines
19 KiB
Plaintext
479 lines
19 KiB
Plaintext
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, struct ip_addr *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.
|
|
|
|
- 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, struct ip_addr *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
|
|
tcp_write(). When the data is successfully transmitted to the remote
|
|
host, the application will be notified with a call to a specified
|
|
callback function.
|
|
|
|
- err_t tcp_write(struct tcp_pcb *pcb, void *dataptr, u16_t len,
|
|
u8_t copy)
|
|
|
|
Enqueues the data pointed to by the argument dataptr. The length of
|
|
the data is passed as the len parameter. The copy argument is either
|
|
0 or 1 and indicates whether the new memory should be allocated for
|
|
the data to be copied into. If the argument is 0, no new memory
|
|
should be allocated and the data should only be referenced by
|
|
pointer.
|
|
|
|
The tcp_write() function will fail and return ERR_MEM if the length
|
|
of the data exceeds the current send buffer size or if the length of
|
|
the queue of outgoing segment is larger than the upper limit defined
|
|
in lwipopts.h. The number of bytes available in the output queue can
|
|
be retrieved with the tcp_sndbuf() function.
|
|
|
|
The proper way to use this function is to call the function with at
|
|
most tcp_sndbuf() bytes of data. If the function returns ERR_MEM,
|
|
the application should wait until some of the currently enqueued
|
|
data has been successfully received by the other host and try again.
|
|
|
|
- void tcp_sent(struct tcp_pcb *pcb,
|
|
err_t (* sent)(void *arg, struct tcp_pcb *tpcb,
|
|
u16_t len))
|
|
|
|
Specifies the callback function that should be called when data has
|
|
successfully been received (i.e., acknowledged) by the remote
|
|
host. The len argument passed to the callback function gives the
|
|
amount bytes that was acknowledged by the last acknowledgment.
|
|
|
|
|
|
--- Receiving TCP data
|
|
|
|
TCP data reception is callback based - an application specified
|
|
callback function is called when new data arrives. When the
|
|
application has taken the data, it has to call the tcp_recved()
|
|
function to indicate that TCP can advertise increase the receive
|
|
window.
|
|
|
|
- void tcp_recv(struct tcp_pcb *pcb,
|
|
err_t (* recv)(void *arg, struct tcp_pcb *tpcb,
|
|
struct pbuf *p, err_t err))
|
|
|
|
Sets the callback function that will be called when new data
|
|
arrives. The callback function will be passed a NULL pbuf to
|
|
indicate that the remote host has closed the connection. If
|
|
there are no errors and the callback function is to return
|
|
ERR_OK, then it must free the pbuf. Otherwise, it must not
|
|
free the pbuf so that lwIP core code can store it.
|
|
|
|
- void tcp_recved(struct tcp_pcb *pcb, u16_t len)
|
|
|
|
Must be called when the application has received the data. The len
|
|
argument indicates the length of the received data.
|
|
|
|
|
|
--- Application polling
|
|
|
|
When a connection is idle (i.e., no data is either transmitted or
|
|
received), lwIP will repeatedly poll the application by calling a
|
|
specified callback function. This can be used either as a watchdog
|
|
timer for killing connections that have stayed idle for too long, or
|
|
as a method of waiting for memory to become available. For instance,
|
|
if a call to tcp_write() has failed because memory wasn't available,
|
|
the application may use the polling functionality to call tcp_write()
|
|
again when the connection has been idle for a while.
|
|
|
|
- void tcp_poll(struct tcp_pcb *pcb, u8_t interval,
|
|
err_t (* poll)(void *arg, struct tcp_pcb *tpcb))
|
|
|
|
Specifies the polling interval and the callback function that should
|
|
be called to poll the application. The interval is specified in
|
|
number of TCP coarse grained timer shots, which typically occurs
|
|
twice a second. An interval of 10 means that the application would
|
|
be polled every 5 seconds.
|
|
|
|
|
|
--- Closing and aborting connections
|
|
|
|
- err_t tcp_close(struct tcp_pcb *pcb)
|
|
|
|
Closes the connection. The function may return ERR_MEM if no memory
|
|
was available for closing the connection. If so, the application
|
|
should wait and try again either by using the acknowledgment
|
|
callback or the polling functionality. If the close succeeds, the
|
|
function returns ERR_OK.
|
|
|
|
The pcb is deallocated by the TCP code after a call to tcp_close().
|
|
|
|
- void tcp_abort(struct tcp_pcb *pcb)
|
|
|
|
Aborts the connection by sending a RST (reset) segment to the remote
|
|
host. The pcb is deallocated. This function never fails.
|
|
|
|
If a connection is aborted because of an error, the application is
|
|
alerted of this event by the err callback. Errors that might abort a
|
|
connection are when there is a shortage of memory. The callback
|
|
function to be called is set using the tcp_err() function.
|
|
|
|
- void tcp_err(struct tcp_pcb *pcb, void (* err)(void *arg,
|
|
err_t err))
|
|
|
|
The error callback function does not get the pcb passed to it as a
|
|
parameter since the pcb may already have been deallocated.
|
|
|
|
|
|
--- Lower layer TCP interface
|
|
|
|
TCP provides a simple interface to the lower layers of the
|
|
system. During system initialization, the function tcp_init() has
|
|
to be called before any other TCP function is called. When the system
|
|
is running, the two timer functions tcp_fasttmr() and tcp_slowtmr()
|
|
must be called with regular intervals. The tcp_fasttmr() should be
|
|
called every TCP_FAST_INTERVAL milliseconds (defined in tcp.h) and
|
|
tcp_slowtmr() should be called every TCP_SLOW_INTERVAL milliseconds.
|
|
|
|
|
|
--- UDP interface
|
|
|
|
The UDP interface is similar to that of TCP, but due to the lower
|
|
level of complexity of UDP, the interface is significantly simpler.
|
|
|
|
- struct udp_pcb *udp_new(void)
|
|
|
|
Creates a new UDP pcb which can be used for UDP communication. The
|
|
pcb is not active until it has either been bound to a local address
|
|
or connected to a remote address.
|
|
|
|
- void udp_remove(struct udp_pcb *pcb)
|
|
|
|
Removes and deallocates the pcb.
|
|
|
|
- err_t udp_bind(struct udp_pcb *pcb, struct ip_addr *ipaddr,
|
|
u16_t port)
|
|
|
|
Binds the pcb to a local address. The IP-address argument "ipaddr"
|
|
can be IP_ADDR_ANY to indicate that it should listen to any local IP
|
|
address. The function currently always return ERR_OK.
|
|
|
|
- err_t udp_connect(struct udp_pcb *pcb, struct ip_addr *ipaddr,
|
|
u16_t port)
|
|
|
|
Sets the remote end of the pcb. This function does not generate any
|
|
network traffic, but only set the remote address of the pcb.
|
|
|
|
- err_t udp_disconnect(struct udp_pcb *pcb)
|
|
|
|
Remove the remote end of the pcb. This function does not generate
|
|
any network traffic, but only removes the remote address of the pcb.
|
|
|
|
- err_t udp_send(struct udp_pcb *pcb, struct pbuf *p)
|
|
|
|
Sends the pbuf p. The pbuf is not deallocated.
|
|
|
|
- void udp_recv(struct udp_pcb *pcb,
|
|
void (* recv)(void *arg, struct udp_pcb *upcb,
|
|
struct pbuf *p,
|
|
struct ip_addr *addr,
|
|
u16_t port),
|
|
void *recv_arg)
|
|
|
|
Specifies a callback function that should be called when a UDP
|
|
datagram is received.
|
|
|
|
|
|
--- System initalization
|
|
|
|
A truly complete and generic sequence for initializing the lwip stack
|
|
cannot be given because it depends on the build configuration (lwipopts.h)
|
|
and additional initializations for your runtime environment (e.g. timers).
|
|
|
|
We can give you some idea on how to proceed when using the raw API.
|
|
We assume a configuration using a single Ethernet netif and the
|
|
UDP and TCP transport layers, IPv4 and the DHCP client.
|
|
|
|
Call these functions in the order of appearance:
|
|
|
|
- stats_init()
|
|
|
|
Clears the structure where runtime statistics are gathered.
|
|
|
|
- sys_init()
|
|
|
|
Not of much use since we set the NO_SYS 1 option in lwipopts.h,
|
|
to be called for easy configuration changes.
|
|
|
|
- mem_init()
|
|
|
|
Initializes the dynamic memory heap defined by MEM_SIZE.
|
|
|
|
- memp_init()
|
|
|
|
Initializes the memory pools defined by MEMP_NUM_x.
|
|
|
|
- pbuf_init()
|
|
|
|
Initializes the pbuf memory pool defined by PBUF_POOL_SIZE.
|
|
|
|
- etharp_init()
|
|
|
|
Initializes the ARP table and queue.
|
|
Note: you must call etharp_tmr at a ARP_TMR_INTERVAL (5 seconds) regular interval
|
|
after this initialization.
|
|
|
|
- ip_init()
|
|
|
|
Doesn't do much, 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: you must call tcp_fasttmr() and tcp_slowtmr() at the
|
|
predefined regular intervals after this initialization.
|
|
|
|
- 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 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 < ETHARP_HWADDR_LEN; i++) netif->hwaddr[i] = some_eth_addr[i];
|
|
init_my_eth_device();
|
|
return ERR_OK;
|
|
}
|
|
|
|
For ethernet drivers, the input function pointer must point to the lwip
|
|
function ethernet_input() declared in "netif/etharp.h". Other drivers
|
|
must use ip_input() declared in "lwip/ip.h".
|
|
|
|
- netif_set_default(struct netif *netif)
|
|
|
|
Registers the default network interface.
|
|
|
|
- netif_set_up(struct netif *netif)
|
|
|
|
When the netif is fully configured this function must be called.
|
|
|
|
- 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.
|
|
|
|
|
|
--- Optimalization hints
|
|
|
|
The first thing you want to optimize is the lwip_standard_checksum()
|
|
routine from src/core/inet.c. You can override this standard
|
|
function with the #define LWIP_CHKSUM <your_checksum_routine>.
|
|
|
|
There are C examples given in inet.c or you might want to
|
|
craft an assembly function for this. RFC1071 is a good
|
|
introduction to this subject.
|
|
|
|
Other significant improvements can be made by supplying
|
|
assembly or inline replacements for htons() and htonl()
|
|
if you're using a little-endian architecture.
|
|
#define LWIP_PLATFORM_BYTESWAP 1
|
|
#define LWIP_PLATFORM_HTONS(x) <your_htons>
|
|
#define LWIP_PLATFORM_HTONL(x) <your_htonl>
|
|
|
|
Check your network interface driver if it reads at
|
|
a higher speed than the maximum wire-speed. If the
|
|
hardware isn't serviced frequently and fast enough
|
|
buffer overflows are likely to occur.
|
|
|
|
E.g. when using the cs8900 driver, call cs8900if_service(ethif)
|
|
as frequently as possible. When using an RTOS let the cs8900 interrupt
|
|
wake a high priority task that services your driver using a binary
|
|
semaphore or event flag. Some drivers might allow additional tuning
|
|
to match your application and network.
|
|
|
|
For a production release it is recommended to set LWIP_STATS to 0.
|
|
Note that speed performance isn't influenced much by simply setting
|
|
high values to the memory options.
|