+++ /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.
-
-Since lwIP 1.4.0, semaphore 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.
-
-- 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.
-
-- 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 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.
- 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
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