diff options
Diffstat (limited to 'thirdparty/nRF5_SDK_15.0.0_a53641a/external/lwip/doc/sys_arch.txt')
| -rw-r--r-- | thirdparty/nRF5_SDK_15.0.0_a53641a/external/lwip/doc/sys_arch.txt | 303 |
1 files changed, 303 insertions, 0 deletions
diff --git a/thirdparty/nRF5_SDK_15.0.0_a53641a/external/lwip/doc/sys_arch.txt b/thirdparty/nRF5_SDK_15.0.0_a53641a/external/lwip/doc/sys_arch.txt new file mode 100644 index 0000000..4dc727b --- /dev/null +++ b/thirdparty/nRF5_SDK_15.0.0_a53641a/external/lwip/doc/sys_arch.txt @@ -0,0 +1,303 @@ +sys_arch interface for lwIP + +Author: Adam Dunkels + Simon Goldschmidt + +The operating system emulation layer provides a common interface +between the lwIP code and the underlying operating system kernel. The +general idea is that porting lwIP to new architectures requires only +small changes to a few header files and a new sys_arch +implementation. It is also possible to do a sys_arch implementation +that does not rely on any underlying operating system. + +The sys_arch provides semaphores, mailboxes and mutexes to lwIP. For the full +lwIP functionality, multiple threads support can be implemented in the +sys_arch, but this is not required for the basic lwIP +functionality. Timer scheduling is implemented in lwIP, but can be implemented +by the sys_arch port (LWIP_TIMERS_CUSTOM==1). + +In addition to the source file providing the functionality of sys_arch, +the OS emulation layer must provide several header files defining +macros used throughout lwip. The files required and the macros they +must define are listed below the sys_arch description. + +Semaphores can be either counting or binary - lwIP works with both +kinds. Mailboxes should be implemented as a queue which allows multiple messages +to be posted (implementing as a rendez-vous point where only one message can be +posted at a time can have a highly negative impact on performance). A message +in a mailbox is just a pointer, nothing more. + +Semaphores are represented by the type "sys_sem_t" which is typedef'd +in the sys_arch.h file. Mailboxes are equivalently represented by the +type "sys_mbox_t". Mutexes are represented by the type "sys_mutex_t". +lwIP does not place any restrictions on how these types are represented +internally. + +Since lwIP 1.4.0, semaphore, mutexes and mailbox functions are prototyped in a way that +allows both using pointers or actual OS structures to be used. This way, memory +required for such types can be either allocated in place (globally or on the +stack) or on the heap (allocated internally in the "*_new()" functions). + +The following functions must be implemented by the sys_arch: + +- void sys_init(void) + + Is called to initialize the sys_arch layer. + +- err_t sys_sem_new(sys_sem_t *sem, u8_t count) + + Creates a new semaphore. The semaphore is allocated to the memory that 'sem' + points to (which can be both a pointer or the actual OS structure). + The "count" argument specifies the initial state of the semaphore (which is + either 0 or 1). + If the semaphore has been created, ERR_OK should be returned. Returning any + other error will provide a hint what went wrong, but except for assertions, + no real error handling is implemented. + +- void sys_sem_free(sys_sem_t *sem) + + Deallocates a semaphore. + +- void sys_sem_signal(sys_sem_t *sem) + + Signals a semaphore. + +- u32_t sys_arch_sem_wait(sys_sem_t *sem, u32_t timeout) + + Blocks the thread while waiting for the semaphore to be + signaled. If the "timeout" argument is non-zero, the thread should + only be blocked for the specified time (measured in + milliseconds). If the "timeout" argument is zero, the thread should be + blocked until the semaphore is signalled. + + If the timeout argument is non-zero, the return value is the number of + milliseconds spent waiting for the semaphore to be signaled. If the + semaphore wasn't signaled within the specified time, the return value is + SYS_ARCH_TIMEOUT. If the thread didn't have to wait for the semaphore + (i.e., it was already signaled), the function may return zero. + + Notice that lwIP implements a function with a similar name, + sys_sem_wait(), that uses the sys_arch_sem_wait() function. + +- int sys_sem_valid(sys_sem_t *sem) + + Returns 1 if the semaphore is valid, 0 if it is not valid. + When using pointers, a simple way is to check the pointer for != NULL. + When directly using OS structures, implementing this may be more complex. + This may also be a define, in which case the function is not prototyped. + +- void sys_sem_set_invalid(sys_sem_t *sem) + + Invalidate a semaphore so that sys_sem_valid() returns 0. + ATTENTION: This does NOT mean that the semaphore shall be deallocated: + sys_sem_free() is always called before calling this function! + This may also be a define, in which case the function is not prototyped. + +- void sys_mutex_new(sys_mutex_t *mutex) + + Creates a new mutex. The mutex is allocated to the memory that 'mutex' + points to (which can be both a pointer or the actual OS structure). + If the mutex has been created, ERR_OK should be returned. Returning any + other error will provide a hint what went wrong, but except for assertions, + no real error handling is implemented. + +- void sys_mutex_free(sys_mutex_t *mutex) + + Deallocates a mutex. + +- void sys_mutex_lock(sys_mutex_t *mutex) + + Blocks the thread until the mutex can be grabbed. + +- void sys_mutex_unlock(sys_mutex_t *mutex) + + Releases the mutex previously locked through 'sys_mutex_lock()'. + +- void sys_mutex_valid(sys_mutex_t *mutex) + + Returns 1 if the mutes is valid, 0 if it is not valid. + When using pointers, a simple way is to check the pointer for != NULL. + When directly using OS structures, implementing this may be more complex. + This may also be a define, in which case the function is not prototyped. + +- void sys_mutex_set_invalid(sys_mutex_t *mutex) + + Invalidate a mutex so that sys_mutex_valid() returns 0. + ATTENTION: This does NOT mean that the mutex shall be deallocated: + sys_mutex_free() is always called before calling this function! + This may also be a define, in which case the function is not prototyped. + +- err_t sys_mbox_new(sys_mbox_t *mbox, int size) + + Creates an empty mailbox for maximum "size" elements. Elements stored + in mailboxes are pointers. You have to define macros "_MBOX_SIZE" + in your lwipopts.h, or ignore this parameter in your implementation + and use a default size. + If the mailbox has been created, ERR_OK should be returned. Returning any + other error will provide a hint what went wrong, but except for assertions, + no real error handling is implemented. + +- void sys_mbox_free(sys_mbox_t *mbox) + + Deallocates a mailbox. If there are messages still present in the + mailbox when the mailbox is deallocated, it is an indication of a + programming error in lwIP and the developer should be notified. + +- void sys_mbox_post(sys_mbox_t *mbox, void *msg) + + Posts the "msg" to the mailbox. This function have to block until + the "msg" is really posted. + +- err_t sys_mbox_trypost(sys_mbox_t *mbox, void *msg) + + Try to post the "msg" to the mailbox. Returns ERR_MEM if this one + is full, else, ERR_OK if the "msg" is posted. + +- u32_t sys_arch_mbox_fetch(sys_mbox_t *mbox, void **msg, u32_t timeout) + + Blocks the thread until a message arrives in the mailbox, but does + not block the thread longer than "timeout" milliseconds (similar to + the sys_arch_sem_wait() function). If "timeout" is 0, the thread should + be blocked until a message arrives. The "msg" argument is a result + parameter that is set by the function (i.e., by doing "*msg = + ptr"). The "msg" parameter maybe NULL to indicate that the message + should be dropped. + + The return values are the same as for the sys_arch_sem_wait() function: + Number of milliseconds spent waiting or SYS_ARCH_TIMEOUT if there was a + timeout. + + Note that a function with a similar name, sys_mbox_fetch(), is + implemented by lwIP. + +- u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg) + + This is similar to sys_arch_mbox_fetch, however if a message is not + present in the mailbox, it immediately returns with the code + SYS_MBOX_EMPTY. On success 0 is returned. + + To allow for efficient implementations, this can be defined as a + function-like macro in sys_arch.h instead of a normal function. For + example, a naive implementation could be: + #define sys_arch_mbox_tryfetch(mbox,msg) \ + sys_arch_mbox_fetch(mbox,msg,1) + although this would introduce unnecessary delays. + +- int sys_mbox_valid(sys_mbox_t *mbox) + + Returns 1 if the mailbox is valid, 0 if it is not valid. + When using pointers, a simple way is to check the pointer for != NULL. + When directly using OS structures, implementing this may be more complex. + This may also be a define, in which case the function is not prototyped. + +- void sys_mbox_set_invalid(sys_mbox_t *mbox) + + Invalidate a mailbox so that sys_mbox_valid() returns 0. + ATTENTION: This does NOT mean that the mailbox shall be deallocated: + sys_mbox_free() is always called before calling this function! + This may also be a define, in which case the function is not prototyped. + +If threads are supported by the underlying operating system and if +such functionality is needed in lwIP, the following function will have +to be implemented as well: + +- sys_thread_t sys_thread_new(char *name, void (* thread)(void *arg), void *arg, int stacksize, int prio) + + Starts a new thread named "name" with priority "prio" that will begin its + execution in the function "thread()". The "arg" argument will be passed as an + argument to the thread() function. The stack size to used for this thread is + the "stacksize" parameter. The id of the new thread is returned. Both the id + and the priority are system dependent. + +When lwIP is used from more than one context (e.g. from multiple threads OR from +main-loop and from interrupts), the SYS_LIGHTWEIGHT_PROT protection SHOULD be enabled! + +- sys_prot_t sys_arch_protect(void) + + This optional function does a "fast" critical region protection and returns + the previous protection level. This function is only called during very short + critical regions. An embedded system which supports ISR-based drivers might + want to implement this function by disabling interrupts. Task-based systems + might want to implement this by using a mutex or disabling tasking. This + function should support recursive calls from the same task or interrupt. In + other words, sys_arch_protect() could be called while already protected. In + that case the return value indicates that it is already protected. + + sys_arch_protect() is only required if your port is supporting an operating + system. + +- void sys_arch_unprotect(sys_prot_t pval) + + This optional function does a "fast" set of critical region protection to the + value specified by pval. See the documentation for sys_arch_protect() for + more information. This function is only required if your port is supporting + an operating system. + +For some configurations, you also need: + +- u32_t sys_now(void) + + This optional function returns the current time in milliseconds (don't care + for wraparound, this is only used for time diffs). + Not implementing this function means you cannot use some modules (e.g. TCP + timestamps, internal timeouts for NO_SYS==1). + + +Note: + +Be careful with using mem_malloc() in sys_arch. When malloc() refers to +mem_malloc() you can run into a circular function call problem. In mem.c +mem_init() tries to allcate a semaphore using mem_malloc, which of course +can't be performed when sys_arch uses mem_malloc. + +------------------------------------------------------------------------------- +Additional files required for the "OS support" emulation layer: +------------------------------------------------------------------------------- + +cc.h - Architecture environment, some compiler specific, some + environment specific (probably should move env stuff + to sys_arch.h.) + + Typedefs for the types used by lwip - + u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t + + Compiler hints for packing lwip's structures - + PACK_STRUCT_FIELD(x) + PACK_STRUCT_STRUCT + PACK_STRUCT_BEGIN + PACK_STRUCT_END + + Platform specific diagnostic output - + LWIP_PLATFORM_DIAG(x) - non-fatal, print a message. + LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution. + Portability defines for printf formatters: + U16_F, S16_F, X16_F, U32_F, S32_F, X32_F, SZT_F + + "lightweight" synchronization mechanisms - + SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable. + SYS_ARCH_PROTECT(x) - enter protection mode. + SYS_ARCH_UNPROTECT(x) - leave protection mode. + + If the compiler does not provide memset() this file must include a + definition of it, or include a file which defines it. + + This file must either include a system-local <errno.h> which defines + the standard *nix error codes, or it should #define LWIP_PROVIDE_ERRNO + to make lwip/arch.h define the codes which are used throughout. + + +perf.h - Architecture specific performance measurement. + Measurement calls made throughout lwip, these can be defined to nothing. + PERF_START - start measuring something. + PERF_STOP(x) - stop measuring something, and record the result. + +sys_arch.h - Tied to sys_arch.c + + Arch dependent types for the following objects: + sys_sem_t, sys_mbox_t, sys_thread_t, + And, optionally: + sys_prot_t + + Defines to set vars of sys_mbox_t and sys_sem_t to NULL. + SYS_MBOX_NULL NULL + SYS_SEM_NULL NULL |