[reactos.git] / reactos / lib / drivers / lwip / doc / sys_arch.txt
1 sys_arch interface for lwIP 0.6++
3 Author: Adam Dunkels
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
30 more.
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:
39 - void sys_init(void)
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)
54 Signals a semaphore.
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
61 milliseconds). If the "timeout" argument is zero, the thread should be
62 blocked until the semaphore is signalled.
64 If the timeout argument is non-zero, the return value is the number of
65 milliseconds spent waiting for the semaphore to be signaled. If the
66 semaphore wasn't signaled within the specified time, the return value is
67 SYS_ARCH_TIMEOUT. If the thread didn't have to wait for the semaphore
68 (i.e., it was already signaled), the function may return zero.
70 Notice that lwIP implements a function with a similar name,
71 sys_sem_wait(), that uses the sys_arch_sem_wait() function.
73 - sys_mbox_t sys_mbox_new(int size)
75 Creates an empty mailbox for maximum "size" elements. Elements stored
76 in mailboxes are pointers. You have to define macros "_MBOX_SIZE"
77 in your lwipopts.h, or ignore this parameter in your implementation
78 and use a default size.
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. This function have to block until
89 the "msg" is really posted.
91 - err_t sys_mbox_trypost(sys_mbox_t mbox, void *msg)
93 Try to post the "msg" to the mailbox. Returns ERR_MEM if this one
94 is full, else, ERR_OK if the "msg" is posted.
96 - u32_t sys_arch_mbox_fetch(sys_mbox_t mbox, void **msg, u32_t timeout)
98 Blocks the thread until a message arrives in the mailbox, but does
99 not block the thread longer than "timeout" milliseconds (similar to
100 the sys_arch_sem_wait() function). If "timeout" is 0, the thread should
101 be blocked until a message arrives. The "msg" argument is a result
102 parameter that is set by the function (i.e., by doing "*msg =
103 ptr"). The "msg" parameter maybe NULL to indicate that the message
104 should be dropped.
106 The return values are the same as for the sys_arch_sem_wait() function:
107 Number of milliseconds spent waiting or SYS_ARCH_TIMEOUT if there was a
108 timeout.
110 Note that a function with a similar name, sys_mbox_fetch(), is
111 implemented by lwIP.
113 - u32_t sys_arch_mbox_tryfetch(sys_mbox_t mbox, void **msg)
115 This is similar to sys_arch_mbox_fetch, however if a message is not
116 present in the mailbox, it immediately returns with the code
117 SYS_MBOX_EMPTY. On success 0 is returned.
119 To allow for efficient implementations, this can be defined as a
120 function-like macro in sys_arch.h instead of a normal function. For
121 example, a naive implementation could be:
122 #define sys_arch_mbox_tryfetch(mbox,msg) \
123 sys_arch_mbox_fetch(mbox,msg,1)
124 although this would introduce unnecessary delays.
126 - struct sys_timeouts *sys_arch_timeouts(void)
128 Returns a pointer to the per-thread sys_timeouts structure. In lwIP,
129 each thread has a list of timeouts which is repressented as a linked
130 list of sys_timeout structures. The sys_timeouts structure holds a
131 pointer to a linked list of timeouts. This function is called by
132 the lwIP timeout scheduler and must not return a NULL value.
134 In a single thread sys_arch implementation, this function will
135 simply return a pointer to a global sys_timeouts variable stored in
136 the sys_arch module.
138 If threads are supported by the underlying operating system and if
139 such functionality is needed in lwIP, the following function will have
140 to be implemented as well:
142 - sys_thread_t sys_thread_new(char *name, void (* thread)(void *arg), void *arg, int stacksize, int prio)
144 Starts a new thread named "name" with priority "prio" that will begin its
145 execution in the function "thread()". The "arg" argument will be passed as an
146 argument to the thread() function. The stack size to used for this thread is
147 the "stacksize" parameter. The id of the new thread is returned. Both the id
148 and the priority are system dependent.
150 - sys_prot_t sys_arch_protect(void)
152 This optional function does a "fast" critical region protection and returns
153 the previous protection level. This function is only called during very short
154 critical regions. An embedded system which supports ISR-based drivers might
155 want to implement this function by disabling interrupts. Task-based systems
156 might want to implement this by using a mutex or disabling tasking. This
157 function should support recursive calls from the same task or interrupt. In
158 other words, sys_arch_protect() could be called while already protected. In
159 that case the return value indicates that it is already protected.
161 sys_arch_protect() is only required if your port is supporting an operating
162 system.
164 - void sys_arch_unprotect(sys_prot_t pval)
166 This optional function does a "fast" set of critical region protection to the
167 value specified by pval. See the documentation for sys_arch_protect() for
168 more information. This function is only required if your port is supporting
169 an operating system.
171 Note:
173 Be carefull with using mem_malloc() in sys_arch. When malloc() refers to
174 mem_malloc() you can run into a circular function call problem. In mem.c
175 mem_init() tries to allcate a semaphore using mem_malloc, which of course
176 can't be performed when sys_arch uses mem_malloc.
178 -------------------------------------------------------------------------------
179 Additional files required for the "OS support" emulation layer:
180 -------------------------------------------------------------------------------
182 cc.h - Architecture environment, some compiler specific, some
183 environment specific (probably should move env stuff
184 to sys_arch.h.)
186 Typedefs for the types used by lwip -
187 u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t
189 Compiler hints for packing lwip's structures -
195 Platform specific diagnostic output -
196 LWIP_PLATFORM_DIAG(x) - non-fatal, print a message.
197 LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution.
198 Portability defines for printf formatters:
199 U16_F, S16_F, X16_F, U32_F, S32_F, X32_F, SZT_F
201 "lightweight" synchronization mechanisms -
202 SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable.
203 SYS_ARCH_PROTECT(x) - enter protection mode.
204 SYS_ARCH_UNPROTECT(x) - leave protection mode.
206 If the compiler does not provide memset() this file must include a
207 definition of it, or include a file which defines it.
209 This file must either include a system-local <errno.h> which defines
210 the standard *nix error codes, or it should #define LWIP_PROVIDE_ERRNO
211 to make lwip/arch.h define the codes which are used throughout.
214 perf.h - Architecture specific performance measurement.
215 Measurement calls made throughout lwip, these can be defined to nothing.
216 PERF_START - start measuring something.
217 PERF_STOP(x) - stop measuring something, and record the result.
219 sys_arch.h - Tied to sys_arch.c
221 Arch dependent types for the following objects:
222 sys_sem_t, sys_mbox_t, sys_thread_t,
223 And, optionally:
224 sys_prot_t
226 Defines to set vars of sys_mbox_t and sys_sem_t to NULL.