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savannah.txt - How to obtain the current development source code.
contrib.txt - How to contribute to lwIP as a developer.
rawapi.txt - The documentation for the core API of lwIP.
Also provides an overview about the other APIs and multithreading.
snmp_agent.txt - The documentation for the lwIP SNMP agent.
sys_arch.txt - The documentation for a system abstraction layer of lwIP.

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1 Introduction
This document describes some guidelines for people participating
in lwIP development.
2 How to contribute to lwIP
Here is a short list of suggestions to anybody working with lwIP and
trying to contribute bug reports, fixes, enhancements, platform ports etc.
First of all as you may already know lwIP is a volunteer project so feedback
to fixes or questions might often come late. Hopefully the bug and patch tracking
features of Savannah help us not lose users' input.
2.1 Source code style:
1. do not use tabs.
2. indentation is two spaces per level (i.e. per tab).
3. end debug messages with a trailing newline (\n).
4. one space between keyword and opening bracket.
5. no space between function and opening bracket.
6. one space and no newline before opening curly braces of a block.
7. closing curly brace on a single line.
8. spaces surrounding assignment and comparisons.
9. don't initialize static and/or global variables to zero, the compiler takes care of that.
10. use current source code style as further reference.
2.2 Source code documentation style:
1. JavaDoc compliant and Doxygen compatible.
2. Function documentation above functions in .c files, not .h files.
(This forces you to synchronize documentation and implementation.)
3. Use current documentation style as further reference.
2.3 Bug reports and patches:
1. Make sure you are reporting bugs or send patches against the latest
sources. (From the latest release and/or the current CVS sources.)
2. If you think you found a bug make sure it's not already filed in the
bugtracker at Savannah.
3. If you have a fix put the patch on Savannah. If it is a patch that affects
both core and arch specific stuff please separate them so that the core can
be applied separately while leaving the other patch 'open'. The prefered way
is to NOT touch archs you can't test and let maintainers take care of them.
This is a good way to see if they are used at all - the same goes for unix
netifs except tapif.
4. Do not file a bug and post a fix to it to the patch area. Either a bug report
or a patch will be enough.
If you correct an existing bug then attach the patch to the bug rather than creating a new entry in the patch area.
5. Trivial patches (compiler warning, indentation and spelling fixes or anything obvious which takes a line or two)
can go to the lwip-users list. This is still the fastest way of interaction and the list is not so crowded
as to allow for loss of fixes. Putting bugs on Savannah and subsequently closing them is too much an overhead
for reporting a compiler warning fix.
6. Patches should be specific to a single change or to related changes.Do not mix bugfixes with spelling and other
trivial fixes unless the bugfix is trivial too.Do not reorganize code and rename identifiers in the same patch you
change behaviour if not necessary.A patch is easier to read and understand if it's to the point and short than
if it's not to the point and long :) so the chances for it to be applied are greater.
2.4 Platform porters:
1. If you have ported lwIP to a platform (an OS, a uC/processor or a combination of these) and
you think it could benefit others[1] you might want discuss this on the mailing list. You
can also ask for CVS access to submit and maintain your port in the contrib CVS module.

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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.

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Daily Use Guide for using Savannah for lwIP
Table of Contents:
1 - Obtaining lwIP from the CVS repository
2 - Committers/developers CVS access using SSH (to be written)
3 - Merging from DEVEL branch to main trunk (stable branch)
4 - How to release lwIP
1 Obtaining lwIP from the CVS repository
----------------------------------------
To perform an anonymous CVS checkout of the main trunk (this is where
bug fixes and incremental enhancements occur), do this:
cvs -z3 -d:pserver:anonymous@cvs.sv.gnu.org:/sources/lwip checkout lwip
Or, obtain a stable branch (updated with bug fixes only) as follows:
cvs -z3 -d:pserver:anonymous@cvs.sv.gnu.org:/sources/lwip checkout \
-r STABLE-0_7 -d lwip-0.7 lwip
Or, obtain a specific (fixed) release as follows:
cvs -z3 -d:pserver:anonymous@cvs.sv.gnu.org:/sources/lwip checkout \
-r STABLE-0_7_0 -d lwip-0.7.0 lwip
3 Committers/developers CVS access using SSH
--------------------------------------------
The Savannah server uses SSH (Secure Shell) protocol 2 authentication and encryption.
As such, CVS commits to the server occur through a SSH tunnel for project members.
To create a SSH2 key pair in UNIX-like environments, do this:
ssh-keygen -t dsa
Under Windows, a recommended SSH client is "PuTTY", freely available with good
documentation and a graphic user interface. Use its key generator.
Now paste the id_dsa.pub contents into your Savannah account public key list. Wait
a while so that Savannah can update its configuration (This can take minutes).
Try to login using SSH:
ssh -v your_login@cvs.sv.gnu.org
If it tells you:
Authenticating with public key "your_key_name"...
Server refused to allocate pty
then you could login; Savannah refuses to give you a shell - which is OK, as we
are allowed to use SSH for CVS only. Now, you should be able to do this:
export CVS_RSH=ssh
cvs -z3 -d:ext:your_login@cvs.sv.gnu.org:/sources/lwip co lwip
after which you can edit your local files with bug fixes or new features and
commit them. Make sure you know what you are doing when using CVS to make
changes on the repository. If in doubt, ask on the lwip-members mailing list.
(If SSH asks about authenticity of the host, you can check the key
fingerprint against http://savannah.nongnu.org/cvs/?group=lwip)
3 Merging from DEVEL branch to main trunk (stable)
--------------------------------------------------
Merging is a delicate process in CVS and requires the
following disciplined steps in order to prevent conflicts
in the future. Conflicts can be hard to solve!
Merging from branch A to branch B requires that the A branch
has a tag indicating the previous merger. This tag is called
'merged_from_A_to_B'. After merging, the tag is moved in the
A branch to remember this merger for future merge actions.
IMPORTANT: AFTER COMMITTING A SUCCESFUL MERGE IN THE
REPOSITORY, THE TAG MUST BE SET ON THE SOURCE BRANCH OF THE
MERGE ACTION (REPLACING EXISTING TAGS WITH THE SAME NAME).
Merge all changes in DEVEL since our last merge to main:
In the working copy of the main trunk:
cvs update -P -jmerged_from_DEVEL_to_main -jDEVEL
(This will apply the changes between 'merged_from_DEVEL_to_main'
and 'DEVEL' to your work set of files)
We can now commit the merge result.
cvs commit -R -m "Merged from DEVEL to main."
If this worked out OK, we now move the tag in the DEVEL branch
to this merge point, so we can use this point for future merges:
cvs rtag -F -r DEVEL merged_from_DEVEL_to_main lwip
4 How to release lwIP
---------------------
First, checkout a clean copy of the branch to be released. Tag this set with
tag name "STABLE-0_6_3". (I use release number 0.6.3 throughout this example).
Login CVS using pserver authentication, then export a clean copy of the
tagged tree. Export is similar to a checkout, except that the CVS metadata
is not created locally.
export CVS_RSH=ssh
cvs -z3 -d:pserver:anonymous@cvs.sv.gnu.org:/sources/lwip checkout \
-r STABLE-0_6_3 -d lwip-0.6.3 lwip
Archive this directory using tar, gzip'd, bzip2'd and zip'd.
tar czvf lwip-0.6.3.tar.gz lwip-0.6.3
tar cjvf lwip-0.6.3.tar.bz2 lwip-0.6.3
zip -r lwip-0.6.3.zip lwip-0.6.3
Now, sign the archives with a detached GPG binary signature as follows:
gpg -b lwip-0.6.3.tar.gz
gpg -b lwip-0.6.3.tar.bz2
gpg -b lwip-0.6.3.zip
Upload these files using anonymous FTP:
ncftp ftp://savannah.gnu.org/incoming/savannah/lwip
ncftp>mput *0.6.3.*
Additionally, you may post a news item on Savannah, like this:
A new 0.6.3 release is now available here:
http://savannah.nongnu.org/files/?group=lwip&highlight=0.6.3
You will have to submit this via the user News interface, then approve
this via the Administrator News interface.

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SNMPv1 agent for lwIP
Author: Christiaan Simons
This is a brief introduction how to use and configure the SNMP agent.
Note the agent uses the raw-API UDP interface so you may also want to
read rawapi.txt to gain a better understanding of the SNMP message handling.
0 Agent Capabilities
====================
SNMPv1 per RFC1157
This is an old(er) standard but is still widely supported.
For SNMPv2c and v3 have a greater complexity and need many
more lines of code. IMHO this breaks the idea of "lightweight IP".
Note the S in SNMP stands for "Simple". Note that "Simple" is
relative. SNMP is simple compared to the complex ISO network
management protocols CMIP (Common Management Information Protocol)
and CMOT (CMip Over Tcp).
MIB II per RFC1213
The standard lwIP stack management information base.
This is a required MIB, so this is always enabled.
When builing lwIP without TCP, the mib-2.tcp group is omitted.
The groups EGP, CMOT and transmission are disabled by default.
Most mib-2 objects are not writable except:
sysName, sysLocation, sysContact, snmpEnableAuthenTraps.
Writing to or changing the ARP and IP address and route
tables is not possible.
Note lwIP has a very limited notion of IP routing. It currently
doen't have a route table and doesn't have a notion of the U,G,H flags.
Instead lwIP uses the interface list with only one default interface
acting as a single gateway interface (G) for the default route.
The agent returns a "virtual table" with the default route 0.0.0.0
for the default interface and network routes (no H) for each
network interface in the netif_list.
All routes are considered to be up (U).
Loading additional MIBs
MIBs can only be added in compile-time, not in run-time.
There is no MIB compiler thus additional MIBs must be hand coded.
Large SNMP message support
The packet decoding and encoding routines are designed
to use pbuf-chains. Larger payloads then the minimum
SNMP requirement of 484 octets are supported if the
PBUF_POOL_SIZE and IP_REASS_BUFSIZE are set to match your
local requirement.
1 Building the Agent
====================
First of all you'll need to add the following define
to your local lwipopts.h:
#define LWIP_SNMP 1
and add the source files in lwip/src/core/snmp
and some snmp headers in lwip/src/include/lwip to your makefile.
Note you'll might need to adapt you network driver to update
the mib2 variables for your interface.
2 Running the Agent
===================
The following function calls must be made in your program to
actually get the SNMP agent running.
Before starting the agent you should supply pointers
to non-volatile memory for sysContact, sysLocation,
and snmpEnableAuthenTraps. You can do this by calling
snmp_set_syscontact()
snmp_set_syslocation()
snmp_set_snmpenableauthentraps()
Additionally you may want to set
snmp_set_sysdescr()
snmp_set_sysobjid() (if you have a private MIB)
snmp_set_sysname()
Also before starting the agent you need to setup
one or more trap destinations using these calls:
snmp_trap_dst_enable();
snmp_trap_dst_ip_set();
In the lwIP initialisation sequence call snmp_init() just after
the call to udp_init().
Exactly every 10 msec the SNMP uptime timestamp must be updated with
snmp_inc_sysuptime(). You should call this from a timer interrupt
or a timer signal handler depending on your runtime environment.
An alternative way to update the SNMP uptime timestamp is to do a call like
snmp_add_sysuptime(100) each 1000ms (which is bigger "step", but call to
a lower frequency). Another one is to not call snmp_inc_sysuptime() or
snmp_add_sysuptime(), and to define the SNMP_GET_SYSUPTIME(sysuptime) macro.
This one is undefined by default in mib2.c. SNMP_GET_SYSUPTIME is called inside
snmp_get_sysuptime(u32_t *value), and enable to change "sysuptime" value only
when it's queried (any function which need "sysuptime" have to call
snmp_get_sysuptime).
3 Private MIBs
==============
If want to extend the agent with your own private MIB you'll need to
add the following define to your local lwipopts.h:
#define SNMP_PRIVATE_MIB 1
You must provide the private_mib.h and associated files yourself.
Note we don't have a "MIB compiler" that generates C source from a MIB,
so you're required to do some serious coding if you enable this!
Note the lwIP enterprise ID (26381) is assigned to the lwIP project,
ALL OBJECT IDENTIFIERS LIVING UNDER THIS ID ARE ASSIGNED BY THE lwIP
MAINTAINERS!
If you need to create your own private MIB you'll need
to apply for your own enterprise ID with IANA: http://www.iana.org/numbers.html
You can set it by passing a struct snmp_obj_id to the agent
using snmp_set_sysobjid(&my_object_id), just before snmp_init().
Note the object identifiers for thes MIB-2 and your private MIB
tree must be kept in sorted ascending (lexicographical) order.
This to ensure correct getnext operation.
An example for a private MIB is part of the "minimal Unix" project:
contrib/ports/unix/proj/minimal/lwip_prvmib.c
The next chapter gives a more detailed description of the
MIB-2 tree and the optional private MIB.
4 The Gory Details
==================
4.0 Object identifiers and the MIB tree.
We have three distinct parts for all object identifiers:
The prefix
.iso.org.dod.internet
the middle part
.mgmt.mib-2.ip.ipNetToMediaTable.ipNetToMediaEntry.ipNetToMediaPhysAddress
and the index part
.1.192.168.0.1
Objects located above the .internet hierarchy aren't supported.
Currently only the .mgmt sub-tree is available and
when the SNMP_PRIVATE_MIB is enabled the .private tree
becomes available too.
Object identifiers from incoming requests are checked
for a matching prefix, middle part and index part
or are expanded(*) for GetNext requests with short
or inexisting names in the request.
(* we call this "expansion" but this also
resembles the "auto-completion" operation)
The middle part is usually located in ROM (const)
to preserve precious RAM on small microcontrollers.
However RAM location is possible for an dynamically
changing private tree.
The index part is handled by functions which in
turn use dynamically allocated index trees from RAM.
These trees are updated by e.g. the etharp code
when new entries are made or removed form the ARP cache.
/** @todo more gory details */

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bertos/net/lwip/doc/sys_arch.txt Normal file
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@ -0,0 +1,228 @@
sys_arch interface for lwIP 0.6++
Author: Adam Dunkels
The operating system emulation layer provides a common interface
between the lwIP code and the underlying operating system kernel. The
general idea is that porting lwIP to new architectures requires only
small changes to a few header files and a new sys_arch
implementation. It is also possible to do a sys_arch implementation
that does not rely on any underlying operating system.
The sys_arch provides semaphores and mailboxes to lwIP. For the full
lwIP functionality, multiple threads support can be implemented in the
sys_arch, but this is not required for the basic lwIP
functionality. Previous versions of lwIP required the sys_arch to
implement timer scheduling as well but as of lwIP 0.5 this is
implemented in a higher layer.
In addition to the source file providing the functionality of sys_arch,
the OS emulation layer must provide several header files defining
macros used throughout lwip. The files required and the macros they
must define are listed below the sys_arch description.
Semaphores can be either counting or binary - lwIP works with both
kinds. Mailboxes are used for message passing and can be implemented
either as a queue which allows multiple messages to be posted to a
mailbox, or as a rendez-vous point where only one message can be
posted at a time. lwIP works with both kinds, but the former type will
be more efficient. A message in a mailbox is just a pointer, nothing
more.
Semaphores are represented by the type "sys_sem_t" which is typedef'd
in the sys_arch.h file. Mailboxes are equivalently represented by the
type "sys_mbox_t". lwIP does not place any restrictions on how
sys_sem_t or sys_mbox_t are represented internally.
The following functions must be implemented by the sys_arch:
- void sys_init(void)
Is called to initialize the sys_arch layer.
- sys_sem_t sys_sem_new(u8_t count)
Creates and returns a new semaphore. The "count" argument specifies
the initial state of the semaphore.
- void sys_sem_free(sys_sem_t sem)
Deallocates a semaphore.
- void sys_sem_signal(sys_sem_t sem)
Signals a semaphore.
- u32_t sys_arch_sem_wait(sys_sem_t sem, u32_t timeout)
Blocks the thread while waiting for the semaphore to be
signaled. If the "timeout" argument is non-zero, the thread should
only be blocked for the specified time (measured in
milliseconds). If the "timeout" argument is zero, the thread should be
blocked until the semaphore is signalled.
If the timeout argument is non-zero, the return value is the number of
milliseconds spent waiting for the semaphore to be signaled. If the
semaphore wasn't signaled within the specified time, the return value is
SYS_ARCH_TIMEOUT. If the thread didn't have to wait for the semaphore
(i.e., it was already signaled), the function may return zero.
Notice that lwIP implements a function with a similar name,
sys_sem_wait(), that uses the sys_arch_sem_wait() function.
- sys_mbox_t sys_mbox_new(int size)
Creates an empty mailbox for maximum "size" elements. Elements stored
in mailboxes are pointers. You have to define macros "_MBOX_SIZE"
in your lwipopts.h, or ignore this parameter in your implementation
and use a default size.
- void sys_mbox_free(sys_mbox_t mbox)
Deallocates a mailbox. If there are messages still present in the
mailbox when the mailbox is deallocated, it is an indication of a
programming error in lwIP and the developer should be notified.
- void sys_mbox_post(sys_mbox_t mbox, void *msg)
Posts the "msg" to the mailbox. This function have to block until
the "msg" is really posted.
- err_t sys_mbox_trypost(sys_mbox_t mbox, void *msg)
Try to post the "msg" to the mailbox. Returns ERR_MEM if this one
is full, else, ERR_OK if the "msg" is posted.
- u32_t sys_arch_mbox_fetch(sys_mbox_t mbox, void **msg, u32_t timeout)
Blocks the thread until a message arrives in the mailbox, but does
not block the thread longer than "timeout" milliseconds (similar to
the sys_arch_sem_wait() function). If "timeout" is 0, the thread should
be blocked until a message arrives. The "msg" argument is a result
parameter that is set by the function (i.e., by doing "*msg =
ptr"). The "msg" parameter maybe NULL to indicate that the message
should be dropped.
The return values are the same as for the sys_arch_sem_wait() function:
Number of milliseconds spent waiting or SYS_ARCH_TIMEOUT if there was a
timeout.
Note that a function with a similar name, sys_mbox_fetch(), is
implemented by lwIP.
- u32_t sys_arch_mbox_tryfetch(sys_mbox_t mbox, void **msg)
This is similar to sys_arch_mbox_fetch, however if a message is not
present in the mailbox, it immediately returns with the code
SYS_MBOX_EMPTY. On success 0 is returned.
To allow for efficient implementations, this can be defined as a
function-like macro in sys_arch.h instead of a normal function. For
example, a naive implementation could be:
#define sys_arch_mbox_tryfetch(mbox,msg) \
sys_arch_mbox_fetch(mbox,msg,1)
although this would introduce unnecessary delays.
- struct sys_timeouts *sys_arch_timeouts(void)
Returns a pointer to the per-thread sys_timeouts structure. In lwIP,
each thread has a list of timeouts which is repressented as a linked
list of sys_timeout structures. The sys_timeouts structure holds a
pointer to a linked list of timeouts. This function is called by
the lwIP timeout scheduler and must not return a NULL value.
In a single thread sys_arch implementation, this function will
simply return a pointer to a global sys_timeouts variable stored in
the sys_arch module.
If threads are supported by the underlying operating system and if
such functionality is needed in lwIP, the following function will have
to be implemented as well:
- sys_thread_t sys_thread_new(char *name, void (* thread)(void *arg), void *arg, int stacksize, int prio)
Starts a new thread named "name" with priority "prio" that will begin its
execution in the function "thread()". The "arg" argument will be passed as an
argument to the thread() function. The stack size to used for this thread is
the "stacksize" parameter. The id of the new thread is returned. Both the id
and the priority are system dependent.
- sys_prot_t sys_arch_protect(void)
This optional function does a "fast" critical region protection and returns
the previous protection level. This function is only called during very short
critical regions. An embedded system which supports ISR-based drivers might
want to implement this function by disabling interrupts. Task-based systems
might want to implement this by using a mutex or disabling tasking. This
function should support recursive calls from the same task or interrupt. In
other words, sys_arch_protect() could be called while already protected. In
that case the return value indicates that it is already protected.
sys_arch_protect() is only required if your port is supporting an operating
system.
- void sys_arch_unprotect(sys_prot_t pval)
This optional function does a "fast" set of critical region protection to the
value specified by pval. See the documentation for sys_arch_protect() for
more information. This function is only required if your port is supporting
an operating system.
Note:
Be carefull with using mem_malloc() in sys_arch. When malloc() refers to
mem_malloc() you can run into a circular function call problem. In mem.c
mem_init() tries to allcate a semaphore using mem_malloc, which of course
can't be performed when sys_arch uses mem_malloc.
-------------------------------------------------------------------------------
Additional files required for the "OS support" emulation layer:
-------------------------------------------------------------------------------
cc.h - Architecture environment, some compiler specific, some
environment specific (probably should move env stuff
to sys_arch.h.)
Typedefs for the types used by lwip -
u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t
Compiler hints for packing lwip's structures -
PACK_STRUCT_FIELD(x)
PACK_STRUCT_STRUCT
PACK_STRUCT_BEGIN
PACK_STRUCT_END
Platform specific diagnostic output -
LWIP_PLATFORM_DIAG(x) - non-fatal, print a message.
LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution.
Portability defines for printf formatters:
U16_F, S16_F, X16_F, U32_F, S32_F, X32_F, SZT_F
"lightweight" synchronization mechanisms -
SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable.
SYS_ARCH_PROTECT(x) - enter protection mode.
SYS_ARCH_UNPROTECT(x) - leave protection mode.
If the compiler does not provide memset() this file must include a
definition of it, or include a file which defines it.
This file must either include a system-local <errno.h> which defines
the standard *nix error codes, or it should #define LWIP_PROVIDE_ERRNO
to make lwip/arch.h define the codes which are used throughout.
perf.h - Architecture specific performance measurement.
Measurement calls made throughout lwip, these can be defined to nothing.
PERF_START - start measuring something.
PERF_STOP(x) - stop measuring something, and record the result.
sys_arch.h - Tied to sys_arch.c
Arch dependent types for the following objects:
sys_sem_t, sys_mbox_t, sys_thread_t,
And, optionally:
sys_prot_t
Defines to set vars of sys_mbox_t and sys_sem_t to NULL.
SYS_MBOX_NULL NULL
SYS_SEM_NULL NULL