1 sys_arch interface for lwIP 0.6++
5 The operating system emulation layer provides a common interface
6 between the lwIP code and the underlying operating system kernel. The
7 general idea is that porting lwIP to new architectures requires only
8 small changes to a few header files and a new sys_arch
9 implementation. It is also possible to do a sys_arch implementation
10 that does not rely on any underlying operating system.
12 The sys_arch provides semaphores and mailboxes to lwIP. For the full
13 lwIP functionality, multiple threads support can be implemented in the
14 sys_arch, but this is not required for the basic lwIP
15 functionality. Previous versions of lwIP required the sys_arch to
16 implement timer scheduling as well but as of lwIP 0.5 this is
17 implemented in a higher layer.
19 In addition to the source file providing the functionality of sys_arch,
20 the OS emulation layer must provide several header files defining
21 macros used throughout lwip. The files required and the macros they
22 must define are listed below the sys_arch description.
24 Semaphores can be either counting or binary - lwIP works with both
25 kinds. Mailboxes are used for message passing and can be implemented
26 either as a queue which allows multiple messages to be posted to a
27 mailbox, or as a rendez-vous point where only one message can be
28 posted at a time. lwIP works with both kinds, but the former type will
29 be more efficient. A message in a mailbox is just a pointer, nothing
32 Semaphores are represented by the type "sys_sem_t" which is typedef'd
33 in the sys_arch.h file. Mailboxes are equivalently represented by the
34 type "sys_mbox_t". lwIP does not place any restrictions on how
35 sys_sem_t or sys_mbox_t are represented internally.
37 The following functions must be implemented by the sys_arch:
41 Is called to initialize the sys_arch layer.
43 - sys_sem_t sys_sem_new(u8_t count)
45 Creates and returns a new semaphore. The "count" argument specifies
46 the initial state of the semaphore.
48 - void sys_sem_free(sys_sem_t sem)
50 Deallocates a semaphore.
52 - void sys_sem_signal(sys_sem_t sem)
56 - u32_t sys_arch_sem_wait(sys_sem_t sem, u32_t timeout)
58 Blocks the thread while waiting for the semaphore to be
59 signaled. If the "timeout" argument is non-zero, the thread should
60 only be blocked for the specified time (measured in
63 If the timeout argument is non-zero, the return value is the number of
64 milliseconds spent waiting for the semaphore to be signaled. If the
65 semaphore wasn't signaled within the specified time, the return value is
66 SYS_ARCH_TIMEOUT. If the thread didn't have to wait for the semaphore
67 (i.e., it was already signaled), the function may return zero.
69 Notice that lwIP implements a function with a similar name,
70 sys_sem_wait(), that uses the sys_arch_sem_wait() function.
72 - sys_mbox_t sys_mbox_new(int size)
74 Creates an empty mailbox for maximum "size" elements. Elements stored
75 in mailboxes are pointers. You have to define macros "_MBOX_SIZE"
76 in your lwipopts.h, or ignore this parameter in your implementation
77 and use a default size.
79 - void sys_mbox_free(sys_mbox_t mbox)
81 Deallocates a mailbox. If there are messages still present in the
82 mailbox when the mailbox is deallocated, it is an indication of a
83 programming error in lwIP and the developer should be notified.
85 - void sys_mbox_post(sys_mbox_t mbox, void *msg)
87 Posts the "msg" to the mailbox. This function have to block until
88 the "msg" is really posted.
90 - err_t sys_mbox_trypost(sys_mbox_t mbox, void *msg)
92 Try to post the "msg" to the mailbox. Returns ERR_MEM if this one
93 is full, else, ERR_OK if the "msg" is posted.
95 - u32_t sys_arch_mbox_fetch(sys_mbox_t mbox, void **msg, u32_t timeout)
97 Blocks the thread until a message arrives in the mailbox, but does
98 not block the thread longer than "timeout" milliseconds (similar to
99 the sys_arch_sem_wait() function). The "msg" argument is a result
100 parameter that is set by the function (i.e., by doing "*msg =
101 ptr"). The "msg" parameter maybe NULL to indicate that the message
104 The return values are the same as for the sys_arch_sem_wait() function:
105 Number of milliseconds spent waiting or SYS_ARCH_TIMEOUT if there was a
108 Note that a function with a similar name, sys_mbox_fetch(), is
111 - u32_t sys_arch_mbox_tryfetch(sys_mbox_t mbox, void **msg)
113 This is similar to sys_arch_mbox_fetch, however if a message is not
114 present in the mailbox, it immediately returns with the code
115 SYS_MBOX_EMPTY. On success 0 is returned.
117 To allow for efficient implementations, this can be defined as a
118 function-like macro in sys_arch.h instead of a normal function. For
119 example, a naive implementation could be:
120 #define sys_arch_mbox_tryfetch(mbox,msg) \
121 sys_arch_mbox_fetch(mbox,msg,1)
122 although this would introduce unnecessary delays.
124 - struct sys_timeouts *sys_arch_timeouts(void)
126 Returns a pointer to the per-thread sys_timeouts structure. In lwIP,
127 each thread has a list of timeouts which is repressented as a linked
128 list of sys_timeout structures. The sys_timeouts structure holds a
129 pointer to a linked list of timeouts. This function is called by
130 the lwIP timeout scheduler and must not return a NULL value.
132 In a single thread sys_arch implementation, this function will
133 simply return a pointer to a global sys_timeouts variable stored in
136 If threads are supported by the underlying operating system and if
137 such functionality is needed in lwIP, the following function will have
138 to be implemented as well:
140 - sys_thread_t sys_thread_new(char *name, void (* thread)(void *arg), void *arg, int stacksize, int prio)
142 Starts a new thread named "name" with priority "prio" that will begin its
143 execution in the function "thread()". The "arg" argument will be passed as an
144 argument to the thread() function. The stack size to used for this thread is
145 the "stacksize" parameter. The id of the new thread is returned. Both the id
146 and the priority are system dependent.
148 - sys_prot_t sys_arch_protect(void)
150 This optional function does a "fast" critical region protection and returns
151 the previous protection level. This function is only called during very short
152 critical regions. An embedded system which supports ISR-based drivers might
153 want to implement this function by disabling interrupts. Task-based systems
154 might want to implement this by using a mutex or disabling tasking. This
155 function should support recursive calls from the same task or interrupt. In
156 other words, sys_arch_protect() could be called while already protected. In
157 that case the return value indicates that it is already protected.
159 sys_arch_protect() is only required if your port is supporting an operating
162 - void sys_arch_unprotect(sys_prot_t pval)
164 This optional function does a "fast" set of critical region protection to the
165 value specified by pval. See the documentation for sys_arch_protect() for
166 more information. This function is only required if your port is supporting
171 Be carefull with using mem_malloc() in sys_arch. When malloc() refers to
172 mem_malloc() you can run into a circular function call problem. In mem.c
173 mem_init() tries to allcate a semaphore using mem_malloc, which of course
174 can't be performed when sys_arch uses mem_malloc.
176 -------------------------------------------------------------------------------
177 Additional files required for the "OS support" emulation layer:
178 -------------------------------------------------------------------------------
180 cc.h - Architecture environment, some compiler specific, some
181 environment specific (probably should move env stuff
184 Typedefs for the types used by lwip -
185 u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t
187 Compiler hints for packing lwip's structures -
193 Platform specific diagnostic output -
194 LWIP_PLATFORM_DIAG(x) - non-fatal, print a message.
195 LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution.
197 "lightweight" synchronization mechanisms -
198 SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable.
199 SYS_ARCH_PROTECT(x) - enter protection mode.
200 SYS_ARCH_UNPROTECT(x) - leave protection mode.
202 If the compiler does not provide memset() this file must include a
203 definition of it, or include a file which defines it.
205 This file must either include a system-local <errno.h> which defines
206 the standard *nix error codes, or it should #define LWIP_PROVIDE_ERRNO
207 to make lwip/arch.h define the codes which are used throughout.
210 perf.h - Architecture specific performance measurement.
211 Measurement calls made throughout lwip, these can be defined to nothing.
212 PERF_START - start measuring something.
213 PERF_STOP(x) - stop measuring something, and record the result.
215 sys_arch.h - Tied to sys_arch.c
217 Arch dependent types for the following objects:
218 sys_sem_t, sys_mbox_t, sys_thread_t,
222 Defines to set vars of sys_mbox_t and sys_sem_t to NULL.