1sys_arch interface for lwIP 2 3Author: Adam Dunkels 4 Simon Goldschmidt 5 6The operating system emulation layer provides a common interface 7between the lwIP code and the underlying operating system kernel. The 8general idea is that porting lwIP to new architectures requires only 9small changes to a few header files and a new sys_arch 10implementation. It is also possible to do a sys_arch implementation 11that does not rely on any underlying operating system. 12 13The sys_arch provides semaphores, mailboxes and mutexes to lwIP. For the full 14lwIP functionality, multiple threads support can be implemented in the 15sys_arch, but this is not required for the basic lwIP 16functionality. Timer scheduling is implemented in lwIP, but can be implemented 17by the sys_arch port (LWIP_TIMERS_CUSTOM==1). 18 19In addition to the source file providing the functionality of sys_arch, 20the OS emulation layer must provide several header files defining 21macros used throughout lwip. The files required and the macros they 22must define are listed below the sys_arch description. 23 24Semaphores can be either counting or binary - lwIP works with both 25kinds. Mailboxes should be implemented as a queue which allows multiple messages 26to be posted (implementing as a rendez-vous point where only one message can be 27posted at a time can have a highly negative impact on performance). A message 28in a mailbox is just a pointer, nothing more. 29 30Semaphores are represented by the type "sys_sem_t" which is typedef'd 31in the sys_arch.h file. Mailboxes are equivalently represented by the 32type "sys_mbox_t". Mutexes are represented by the type "sys_mutex_t". 33lwIP does not place any restrictions on how these types are represented 34internally. 35 36Since lwIP 1.4.0, semaphore, mutexes and mailbox functions are prototyped in a way that 37allows both using pointers or actual OS structures to be used. This way, memory 38required for such types can be either allocated in place (globally or on the 39stack) or on the heap (allocated internally in the "*_new()" functions). 40 41The following functions must be implemented by the sys_arch: 42 43- void sys_init(void) 44 45 Is called to initialize the sys_arch layer. 46 47- err_t sys_sem_new(sys_sem_t *sem, u8_t count) 48 49 Creates a new semaphore. The semaphore is allocated to the memory that 'sem' 50 points to (which can be both a pointer or the actual OS structure). 51 The "count" argument specifies the initial state of the semaphore (which is 52 either 0 or 1). 53 If the semaphore has been created, ERR_OK should be returned. Returning any 54 other error will provide a hint what went wrong, but except for assertions, 55 no real error handling is implemented. 56 57- void sys_sem_free(sys_sem_t *sem) 58 59 Deallocates a semaphore. 60 61- void sys_sem_signal(sys_sem_t *sem) 62 63 Signals a semaphore. 64 65- u32_t sys_arch_sem_wait(sys_sem_t *sem, u32_t timeout) 66 67 Blocks the thread while waiting for the semaphore to be 68 signaled. If the "timeout" argument is non-zero, the thread should 69 only be blocked for the specified time (measured in 70 milliseconds). If the "timeout" argument is zero, the thread should be 71 blocked until the semaphore is signalled. 72 73 If the timeout argument is non-zero, the return value is the number of 74 milliseconds spent waiting for the semaphore to be signaled. If the 75 semaphore wasn't signaled within the specified time, the return value is 76 SYS_ARCH_TIMEOUT. If the thread didn't have to wait for the semaphore 77 (i.e., it was already signaled), the function may return zero. 78 79 Notice that lwIP implements a function with a similar name, 80 sys_sem_wait(), that uses the sys_arch_sem_wait() function. 81 82- int sys_sem_valid(sys_sem_t *sem) 83 84 Returns 1 if the semaphore is valid, 0 if it is not valid. 85 When using pointers, a simple way is to check the pointer for != NULL. 86 When directly using OS structures, implementing this may be more complex. 87 This may also be a define, in which case the function is not prototyped. 88 89- void sys_sem_set_invalid(sys_sem_t *sem) 90 91 Invalidate a semaphore so that sys_sem_valid() returns 0. 92 ATTENTION: This does NOT mean that the semaphore shall be deallocated: 93 sys_sem_free() is always called before calling this function! 94 This may also be a define, in which case the function is not prototyped. 95 96- void sys_mutex_new(sys_mutex_t *mutex) 97 98 Creates a new mutex. The mutex is allocated to the memory that 'mutex' 99 points to (which can be both a pointer or the actual OS structure). 100 If the mutex has been created, ERR_OK should be returned. Returning any 101 other error will provide a hint what went wrong, but except for assertions, 102 no real error handling is implemented. 103 104- void sys_mutex_free(sys_mutex_t *mutex) 105 106 Deallocates a mutex. 107 108- void sys_mutex_lock(sys_mutex_t *mutex) 109 110 Blocks the thread until the mutex can be grabbed. 111 112- void sys_mutex_unlock(sys_mutex_t *mutex) 113 114 Releases the mutex previously locked through 'sys_mutex_lock()'. 115 116- void sys_mutex_valid(sys_mutex_t *mutex) 117 118 Returns 1 if the mutes is valid, 0 if it is not valid. 119 When using pointers, a simple way is to check the pointer for != NULL. 120 When directly using OS structures, implementing this may be more complex. 121 This may also be a define, in which case the function is not prototyped. 122 123- void sys_mutex_set_invalid(sys_mutex_t *mutex) 124 125 Invalidate a mutex so that sys_mutex_valid() returns 0. 126 ATTENTION: This does NOT mean that the mutex shall be deallocated: 127 sys_mutex_free() is always called before calling this function! 128 This may also be a define, in which case the function is not prototyped. 129 130- err_t sys_mbox_new(sys_mbox_t *mbox, int size) 131 132 Creates an empty mailbox for maximum "size" elements. Elements stored 133 in mailboxes are pointers. You have to define macros "_MBOX_SIZE" 134 in your lwipopts.h, or ignore this parameter in your implementation 135 and use a default size. 136 If the mailbox has been created, ERR_OK should be returned. Returning any 137 other error will provide a hint what went wrong, but except for assertions, 138 no real error handling is implemented. 139 140- void sys_mbox_free(sys_mbox_t *mbox) 141 142 Deallocates a mailbox. If there are messages still present in the 143 mailbox when the mailbox is deallocated, it is an indication of a 144 programming error in lwIP and the developer should be notified. 145 146- void sys_mbox_post(sys_mbox_t *mbox, void *msg) 147 148 Posts the "msg" to the mailbox. This function have to block until 149 the "msg" is really posted. 150 151- err_t sys_mbox_trypost(sys_mbox_t *mbox, void *msg) 152 153 Try to post the "msg" to the mailbox. Returns ERR_MEM if this one 154 is full, else, ERR_OK if the "msg" is posted. 155 156- u32_t sys_arch_mbox_fetch(sys_mbox_t *mbox, void **msg, u32_t timeout) 157 158 Blocks the thread until a message arrives in the mailbox, but does 159 not block the thread longer than "timeout" milliseconds (similar to 160 the sys_arch_sem_wait() function). If "timeout" is 0, the thread should 161 be blocked until a message arrives. The "msg" argument is a result 162 parameter that is set by the function (i.e., by doing "*msg = 163 ptr"). The "msg" parameter maybe NULL to indicate that the message 164 should be dropped. 165 166 The return values are the same as for the sys_arch_sem_wait() function: 167 Number of milliseconds spent waiting or SYS_ARCH_TIMEOUT if there was a 168 timeout. 169 170 Note that a function with a similar name, sys_mbox_fetch(), is 171 implemented by lwIP. 172 173- u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg) 174 175 This is similar to sys_arch_mbox_fetch, however if a message is not 176 present in the mailbox, it immediately returns with the code 177 SYS_MBOX_EMPTY. On success 0 is returned. 178 179 To allow for efficient implementations, this can be defined as a 180 function-like macro in sys_arch.h instead of a normal function. For 181 example, a naive implementation could be: 182 #define sys_arch_mbox_tryfetch(mbox,msg) \ 183 sys_arch_mbox_fetch(mbox,msg,1) 184 although this would introduce unnecessary delays. 185 186- int sys_mbox_valid(sys_mbox_t *mbox) 187 188 Returns 1 if the mailbox is valid, 0 if it is not valid. 189 When using pointers, a simple way is to check the pointer for != NULL. 190 When directly using OS structures, implementing this may be more complex. 191 This may also be a define, in which case the function is not prototyped. 192 193- void sys_mbox_set_invalid(sys_mbox_t *mbox) 194 195 Invalidate a mailbox so that sys_mbox_valid() returns 0. 196 ATTENTION: This does NOT mean that the mailbox shall be deallocated: 197 sys_mbox_free() is always called before calling this function! 198 This may also be a define, in which case the function is not prototyped. 199 200If threads are supported by the underlying operating system and if 201such functionality is needed in lwIP, the following function will have 202to be implemented as well: 203 204- sys_thread_t sys_thread_new(char *name, void (* thread)(void *arg), void *arg, int stacksize, int prio) 205 206 Starts a new thread named "name" with priority "prio" that will begin its 207 execution in the function "thread()". The "arg" argument will be passed as an 208 argument to the thread() function. The stack size to used for this thread is 209 the "stacksize" parameter. The id of the new thread is returned. Both the id 210 and the priority are system dependent. 211 212When lwIP is used from more than one context (e.g. from multiple threads OR from 213main-loop and from interrupts), the SYS_LIGHTWEIGHT_PROT protection SHOULD be enabled! 214 215- sys_prot_t sys_arch_protect(void) 216 217 This optional function does a "fast" critical region protection and returns 218 the previous protection level. This function is only called during very short 219 critical regions. An embedded system which supports ISR-based drivers might 220 want to implement this function by disabling interrupts. Task-based systems 221 might want to implement this by using a mutex or disabling tasking. This 222 function should support recursive calls from the same task or interrupt. In 223 other words, sys_arch_protect() could be called while already protected. In 224 that case the return value indicates that it is already protected. 225 226 sys_arch_protect() is only required if your port is supporting an operating 227 system. 228 229- void sys_arch_unprotect(sys_prot_t pval) 230 231 This optional function does a "fast" set of critical region protection to the 232 value specified by pval. See the documentation for sys_arch_protect() for 233 more information. This function is only required if your port is supporting 234 an operating system. 235 236For some configurations, you also need: 237 238- u32_t sys_now(void) 239 240 This optional function returns the current time in milliseconds (don't care 241 for wraparound, this is only used for time diffs). 242 Not implementing this function means you cannot use some modules (e.g. TCP 243 timestamps, internal timeouts for NO_SYS==1). 244 245 246Note: 247 248Be careful with using mem_malloc() in sys_arch. When malloc() refers to 249mem_malloc() you can run into a circular function call problem. In mem.c 250mem_init() tries to allcate a semaphore using mem_malloc, which of course 251can't be performed when sys_arch uses mem_malloc. 252 253------------------------------------------------------------------------------- 254Additional files required for the "OS support" emulation layer: 255------------------------------------------------------------------------------- 256 257cc.h - Architecture environment, some compiler specific, some 258 environment specific (probably should move env stuff 259 to sys_arch.h.) 260 261 Typedefs for the types used by lwip - 262 u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t 263 264 Compiler hints for packing lwip's structures - 265 PACK_STRUCT_FIELD(x) 266 PACK_STRUCT_STRUCT 267 PACK_STRUCT_BEGIN 268 PACK_STRUCT_END 269 270 Platform specific diagnostic output - 271 LWIP_PLATFORM_DIAG(x) - non-fatal, print a message. 272 LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution. 273 Portability defines for printf formatters: 274 U16_F, S16_F, X16_F, U32_F, S32_F, X32_F, SZT_F 275 276 "lightweight" synchronization mechanisms - 277 SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable. 278 SYS_ARCH_PROTECT(x) - enter protection mode. 279 SYS_ARCH_UNPROTECT(x) - leave protection mode. 280 281 If the compiler does not provide memset() this file must include a 282 definition of it, or include a file which defines it. 283 284 This file must either include a system-local <errno.h> which defines 285 the standard *nix error codes (or define LWIP_ERRNO_INCLUDE to that file name), 286 or it should #define LWIP_PROVIDE_ERRNO to make lwip/arch.h define the codes 287 which are used throughout. 288 289 290perf.h - Architecture specific performance measurement. 291 Measurement calls made throughout lwip, these can be defined to nothing. 292 PERF_START - start measuring something. 293 PERF_STOP(x) - stop measuring something, and record the result. 294 295sys_arch.h - Tied to sys_arch.c 296 297 Arch dependent types for the following objects: 298 sys_sem_t, sys_mbox_t, sys_thread_t, 299 And, optionally: 300 sys_prot_t 301 302 Defines to set vars of sys_mbox_t and sys_sem_t to NULL. 303 SYS_MBOX_NULL NULL 304 SYS_SEM_NULL NULL 305