--- /dev/null
+sys_arch interface for lwIP 0.6++
+
+Author: Adam Dunkels
+
+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 and mailboxes 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. Previous versions of lwIP required the sys_arch to
+implement timer scheduling as well but as of lwIP 0.5 this is
+implemented in a higher layer.
+
+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 are used for message passing and can be implemented
+either as a queue which allows multiple messages to be posted to a
+mailbox, or as a rendez-vous point where only one message can be
+posted at a time. lwIP works with both kinds, but the former type will
+be more efficient. 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". lwIP does not place any restrictions on how
+sys_sem_t or sys_mbox_t are represented internally.
+
+The following functions must be implemented by the sys_arch:
+
+- void sys_init(void)
+
+ Is called to initialize the sys_arch layer.
+
+- sys_sem_t sys_sem_new(u8_t count)
+
+ Creates and returns a new semaphore. The "count" argument specifies
+ the initial state of the semaphore.
+
+- 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.
+
+- sys_mbox_t sys_mbox_new(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.
+
+- 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.
+
+- struct sys_timeouts *sys_arch_timeouts(void)
+
+ Returns a pointer to the per-thread sys_timeouts structure. In lwIP,
+ each thread has a list of timeouts which is repressented as a linked
+ list of sys_timeout structures. The sys_timeouts structure holds a
+ pointer to a linked list of timeouts. This function is called by
+ the lwIP timeout scheduler and must not return a NULL value.
+
+ In a single thread sys_arch implementation, this function will
+ simply return a pointer to a global sys_timeouts variable stored in
+ the sys_arch module.
+
+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.
+
+- 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.
+
+Note:
+
+Be carefull 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.
+
+ "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
git.joshuawise.com / netwatch.git / blobdiff