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(void)
74 Creates an empty mailbox.
76 - void sys_mbox_free(sys_mbox_t mbox)
78 Deallocates a mailbox. If there are messages still present in the
79 mailbox when the mailbox is deallocated, it is an indication of a
80 programming error in lwIP and the developer should be notified.
82 - void sys_mbox_post(sys_mbox_t mbox, void *msg)
84 Posts the "msg" to the mailbox.
86 - u32_t sys_arch_mbox_fetch(sys_mbox_t mbox, void **msg, u32_t timeout)
88 Blocks the thread until a message arrives in the mailbox, but does
89 not block the thread longer than "timeout" milliseconds (similar to
90 the sys_arch_sem_wait() function). The "msg" argument is a result
91 parameter that is set by the function (i.e., by doing "*msg =
92 ptr"). The "msg" parameter maybe NULL to indicate that the message
95 The return values are the same as for the sys_arch_sem_wait() function:
96 Number of milliseconds spent waiting or SYS_ARCH_TIMEOUT if there was a
99 Note that a function with a similar name, sys_mbox_fetch(), is
102 - u32_t sys_arch_mbox_tryfetch(sys_mbox_t mbox, void **msg)
104 This is similar to sys_arch_mbox_fetch, however if a message is not
105 present in the mailbox, it immediately returns with the code
108 To allow for efficient implementations, this can be defined as a
109 function-like macro in sys_arch.h instead of a normal function. For
110 example, a naive implementation could be:
111 #define sys_arch_mbox_tryfetch(mbox,msg) \
112 sys_arch_mbox_fetch(mbox,msg,1)
113 although this would introduce unnecessary delays.
115 - struct sys_timeouts *sys_arch_timeouts(void)
117 Returns a pointer to the per-thread sys_timeouts structure. In lwIP,
118 each thread has a list of timeouts which is repressented as a linked
119 list of sys_timeout structures. The sys_timeouts structure holds a
120 pointer to a linked list of timeouts. This function is called by
121 the lwIP timeout scheduler and must not return a NULL value.
123 In a single threadd sys_arch implementation, this function will
124 simply return a pointer to a global sys_timeouts variable stored in
127 If threads are supported by the underlying operating system and if
128 such functionality is needed in lwIP, the following function will have
129 to be implemented as well:
131 - sys_thread_t sys_thread_new(void (* thread)(void *arg), void *arg, int prio)
133 Starts a new thread with priority "prio" that will begin its execution in the
134 function "thread()". The "arg" argument will be passed as an argument to the
135 thread() function. The id of the new thread is returned. Both the id and
136 the priority are system dependent.
138 - sys_prot_t sys_arch_protect(void)
140 This optional function does a "fast" critical region protection and returns
141 the previous protection level. This function is only called during very short
142 critical regions. An embedded system which supports ISR-based drivers might
143 want to implement this function by disabling interrupts. Task-based systems
144 might want to implement this by using a mutex or disabling tasking. This
145 function should support recursive calls from the same task or interrupt. In
146 other words, sys_arch_protect() could be called while already protected. In
147 that case the return value indicates that it is already protected.
149 sys_arch_protect() is only required if your port is supporting an operating
152 - void sys_arch_unprotect(sys_prot_t pval)
154 This optional function does a "fast" set of critical region protection to the
155 value specified by pval. See the documentation for sys_arch_protect() for
156 more information. This function is only required if your port is supporting
161 Be carefull with using mem_malloc() in sys_arch. When malloc() refers to
162 mem_malloc() you can run into a circular function call problem. In mem.c
163 mem_init() tries to allcate a semaphore using mem_malloc, which of course
164 can't be performed when sys_arch uses mem_malloc.
166 -------------------------------------------------------------------------------
167 Additional files required for the "OS support" emulation layer:
168 -------------------------------------------------------------------------------
170 cc.h - Architecture environment, some compiler specific, some
171 environment specific (probably should move env stuff
174 Typedefs for the types used by lwip -
175 u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t
177 Compiler hints for packing lwip's structures -
183 Platform specific diagnostic output -
184 LWIP_PLATFORM_DIAG(x) - non-fatal, print a message.
185 LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution.
187 "lightweight" synchronization mechanisms -
188 SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable.
189 SYS_ARCH_PROTECT(x) - enter protection mode.
190 SYS_ARCH_UNPROTECT(x) - leave protection mode.
192 If the compiler does not provide memset() this file must include a
193 definition of it, or include a file which defines it.
195 This file must either include a system-local <errno.h> which defines
196 the standard *nix error codes, or it should #define LWIP_PROVIDE_ERRNO
197 to make lwip/arch.h define the codes which are used throughout.
200 perf.h - Architecture specific performance measurement.
201 Measurement calls made throughout lwip, these can be defined to nothing.
202 PERF_START - start measuring something.
203 PERF_STOP(x) - stop measuring something, and record the result.
205 sys_arch.h - Tied to sys_arch.c
207 Arch dependent types for the following objects:
208 sys_sem_t, sys_mbox_t, sys_thread_t,
212 Defines to set vars of sys_mbox_t and sys_sem_t to NULL.