1 sys_arch interface for lwIP 0.5
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 amount
64 of time spent waiting for the semaphore to be signaled. If the
65 semaphore wasn't signaled within the specified time, the return
66 value is zero. If the thread didn't have to wait for the semaphore
67 (i.e., it was already signaled), care must be taken to ensure that
68 the function does not return a zero value since this is used to
69 indicate that a timeout occured. A suitable way to implement this is
70 to check if the time spent waiting is zero and if so, the value 1 is
73 Notice that lwIP implements a function with a similar name,
74 sys_sem_wait(), that uses the sys_arch_sem_wait() function.
76 - sys_mbox_t sys_mbox_new(void)
78 Creates an empty mailbox.
80 - void sys_mbox_free(sys_mbox_t mbox)
82 Deallocates a mailbox. If there are messages still present in the
83 mailbox when the mailbox is deallocated, it is an indication of a
84 programming error in lwIP and the developer should be notified.
86 - void sys_mbox_post(sys_mbox_t mbox, void *msg)
88 Posts the "msg" to the mailbox.
90 - u32_t sys_arch_mbox_fetch(sys_mbox_t mbox, void **msg, u32_t timeout)
92 Blocks the thread until a message arrives in the mailbox, but does
93 not block the thread longer than "timeout" milliseconds (similar to
94 the sys_arch_sem_wait() function). The "msg" argument is a result
95 parameter that is set by the function (i.e., by doing "*msg =
96 ptr"). The "msg" parameter maybe NULL to indicate that the message
99 The return values are the same as for the sys_arch_sem_wait()
100 function and the function must not return zero even if a message was
101 present in the mailbox and the time spent waiting was zero
104 Note that a function with a similar name, sys_mbox_fetch(), is
107 - struct sys_timeouts *sys_arch_timeouts(void)
109 Returns a pointer to the per-thread sys_timeouts structure. In lwIP,
110 each thread has a list of timeouts which is repressented as a linked
111 list of sys_timeout structures. The sys_timeouts structure holds a
112 pointer to a linked list of timeouts. This function is called by
113 the lwIP timeout scheduler and must not return a NULL value.
115 In a single threadd sys_arch implementation, this function will
116 simply return a pointer to a global sys_timeouts variable stored in
119 If threads are supported by the underlying operating system and if
120 such functionality is needed in lwIP, the following function will have
121 to be implemented as well:
123 - sys_thread_t sys_thread_new(void (* thread)(void *arg), void *arg, int prio)
125 Starts a new thread with priority "prio" that will begin its execution in the
126 function "thread()". The "arg" argument will be passed as an argument to the
127 thread() function. The id of the new thread is returned.
129 - sys_prot_t sys_arch_protect(void)
131 This optional function does a "fast" critical region protection and returns
132 the previous protection level. This function is only called during very short
133 critical regions. An embedded system which supports ISR-based drivers might
134 want to implement this function by disabling interrupts. Task-based systems
135 might want to implement this by using a mutex or disabling tasking. This
136 function should support recursive calls from the same task or interrupt. In
137 other words, sys_arch_protect() could be called while already protected. In
138 that case the return value indicates that it is already protected.
140 sys_arch_protect() is only required if your port is supporting an operating
143 - void sys_arch_unprotect(sys_prot_t pval)
145 This optional function does a "fast" set of critical region protection to the
146 value specified by pval. See the documentation for sys_arch_protect() for
147 more information. This function is only required if your port is supporting
150 -------------------------------------------------------------------------------
151 Additional files required for the "OS support" emulation layer:
152 -------------------------------------------------------------------------------
154 cc.h - Architecture environment, some compiler specific, some
155 environment specific (probably should move env stuff
158 Typedefs for the types used by lwip -
159 u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t
161 Compiler hints for packing lwip's structures -
167 Platform specific diagnostic output -
168 LWIP_PLATFORM_DIAG(x) - non-fatal, print a message.
169 LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution.
171 "lightweight" synchronization mechanisms -
172 SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable.
173 SYS_ARCH_PROTECT(x) - enter protection mode.
174 SYS_ARCH_UNPROTECT(x) - leave protection mode.
176 If the compiler does not provide memset() this file must include a
177 definition of it, or include a file which defines it.
179 This file must either include a system-local <errno.h> which defines
180 the standard *nix error codes, or it should #define LWIP_PROVIDE_ERRNO
181 to make lwip/arch.h define the codes which are used throughout.
184 perf.h - Architecture specific performance measurement.
185 Measurement calls made throughout lwip, these can be defined to nothing.
186 PERF_START - start measuring something.
187 PERF_STOP(x) - stop measuring something, and record the result.
189 sys_arch.h - Tied to sys_arch.c
191 Arch dependent types for the following objects:
192 sys_sem_t, sys_mbox_t, sys_thread_t,
196 Defines to set vars of sys_mbox_t and sys_sem_t to NULL.