Improve system abstraction layer doxygen docs by moving documentation from sys_arch.txt to the corresponding functions

src/include/lwip/sys.h

@@ -125,39 +125,51 @@ typedef void (*lwip_thread_fn)(void *arg);
  * Create a new mutex.
  * Note that mutexes are expected to not be taken recursively by the lwIP code,
  * so both implementation types (recursive or non-recursive) should work.
+ * 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.
+ * 
  * @param mutex pointer to the mutex to create
  * @return ERR_OK if successful, another err_t otherwise
  */
 err_t sys_mutex_new(sys_mutex_t *mutex);
 /**
  * @ingroup sys_mutex
- * Lock a mutex
+ * Blocks the thread until the mutex can be grabbed.
  * @param mutex the mutex to lock
  */
 void sys_mutex_lock(sys_mutex_t *mutex);
 /**
  * @ingroup sys_mutex
- * Unlock a mutex
+ * Releases the mutex previously locked through 'sys_mutex_lock()'.
  * @param mutex the mutex to unlock
  */
 void sys_mutex_unlock(sys_mutex_t *mutex);
 /**
  * @ingroup sys_mutex
- * Delete a semaphore
+ * Deallocates a mutex.
  * @param mutex the mutex to delete
  */
 void sys_mutex_free(sys_mutex_t *mutex);
 #ifndef sys_mutex_valid
 /**
  * @ingroup sys_mutex
- * Check if a mutex is valid/allocated: return 1 for valid, 0 for invalid
+ * 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.
  */
 int sys_mutex_valid(sys_mutex_t *mutex);
 #endif
 #ifndef sys_mutex_set_invalid
 /**
  * @ingroup sys_mutex
- * Set a mutex invalid so that sys_mutex_valid returns 0
+ * 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.
  */
 void sys_mutex_set_invalid(sys_mutex_t *mutex);
 #endif
@@ -168,6 +180,14 @@ void sys_mutex_set_invalid(sys_mutex_t *mutex);
 /**
  * @ingroup sys_sem
  * Create a new semaphore
+ * 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.
+ *
  * @param sem pointer to the semaphore to create
  * @param count initial count of the semaphore
  * @return ERR_OK if successful, another err_t otherwise
@@ -181,7 +201,17 @@ err_t sys_sem_new(sys_sem_t *sem, u8_t count);
 void sys_sem_signal(sys_sem_t *sem);
 /**
  * @ingroup sys_sem
- * Wait for a semaphore for the specified 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.
+ * 
+ * The return value is SYS_ARCH_TIMEOUT if the semaphore wasn't signaled within
+ * the specified time or any other value if it was signaled (with or without
+ * waiting).
+ * Notice that lwIP implements a function with a similar name,
+ * sys_sem_wait(), that uses the sys_arch_sem_wait() function.
+ * 
  * @param sem the semaphore to wait for
  * @param timeout timeout in milliseconds to wait (0 = wait forever)
  * @return SYS_ARCH_TIMEOUT on timeout, any other value on success
@@ -189,7 +219,7 @@ void sys_sem_signal(sys_sem_t *sem);
 u32_t sys_arch_sem_wait(sys_sem_t *sem, u32_t timeout);
 /**
  * @ingroup sys_sem
- * Delete a semaphore
+ * Deallocates a semaphore.
  * @param sem semaphore to delete
  */
 void sys_sem_free(sys_sem_t *sem);
@@ -198,14 +228,20 @@ void sys_sem_free(sys_sem_t *sem);
 #ifndef sys_sem_valid
 /**
  * @ingroup sys_sem
- * Check if a semaphore is valid/allocated: return 1 for valid, 0 for invalid
+ * 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.
  */
 int sys_sem_valid(sys_sem_t *sem);
 #endif
 #ifndef sys_sem_set_invalid
 /**
  * @ingroup sys_sem
- * Set a semaphore invalid so that sys_sem_valid returns 0
+ * 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_sem_set_invalid(sys_sem_t *sem);
 #endif
@@ -234,7 +270,14 @@ void sys_msleep(u32_t ms); /* only has a (close to) 1 ms resolution. */
 
 /**
  * @ingroup sys_mbox
- * Create a new mbox of specified 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.
+ * 
  * @param mbox pointer to the mbox to create
  * @param size (minimum) number of messages in this mbox
  * @return ERR_OK if successful, another err_t otherwise
@@ -243,21 +286,38 @@ err_t sys_mbox_new(sys_mbox_t *mbox, int size);
 /**
  * @ingroup sys_mbox
  * Post a message to an mbox - may not fail
- * -> blocks if full, only used from tasks not from ISR
+ * -> blocks if full, only to be used from tasks NOT from ISR!
+ * 
  * @param mbox mbox to posts the message
  * @param msg message to post (ATTENTION: can be NULL)
  */
 void sys_mbox_post(sys_mbox_t *mbox, void *msg);
 /**
  * @ingroup sys_mbox
- * Try to post a message to an mbox - may fail if full or ISR
+ * Try to post a message to an mbox - may fail if full.
+ * Can be used from ISR.
+ * Returns ERR_MEM if it is full, else, ERR_OK if the "msg" is posted.
+ * 
  * @param mbox mbox to posts the message
  * @param msg message to post (ATTENTION: can be NULL)
  */
 err_t sys_mbox_trypost(sys_mbox_t *mbox, void *msg);
 /**
  * @ingroup sys_mbox
- * Wait for a new message to arrive in the mbox
+ * 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:
+ * SYS_ARCH_TIMEOUT if there was a timeout, any other value if a messages
+ * is received.
+ * 
+ * Note that a function with a similar name, sys_mbox_fetch(), is
+ * implemented by lwIP. 
+ * 
  * @param mbox mbox to get a message from
  * @param msg pointer where the message is stored
  * @param timeout maximum time (in milliseconds) to wait for a message (0 = wait forever)
@@ -268,7 +328,15 @@ u32_t sys_arch_mbox_fetch(sys_mbox_t *mbox, void **msg, u32_t timeout);
 #ifndef sys_arch_mbox_tryfetch
 /**
  * @ingroup sys_mbox
- * Wait for a new message to arrive in the mbox
+ * 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.
+ * 
  * @param mbox mbox to get a message from
  * @param msg pointer where the message is stored
  * @return 0 (milliseconds) if a message has been received
@@ -282,7 +350,10 @@ u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg);
 #define sys_mbox_tryfetch(mbox, msg) sys_arch_mbox_tryfetch(mbox, msg)
 /**
  * @ingroup sys_mbox
- * Delete an 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.
+ * 
  * @param mbox mbox to delete
  */
 void sys_mbox_free(sys_mbox_t *mbox);
@@ -290,14 +361,20 @@ void sys_mbox_free(sys_mbox_t *mbox);
 #ifndef sys_mbox_valid
 /**
  * @ingroup sys_mbox
- * Check if an mbox is valid/allocated: return 1 for valid, 0 for invalid
+ * 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.
  */
 int sys_mbox_valid(sys_mbox_t *mbox);
 #endif
 #ifndef sys_mbox_set_invalid
 /**
  * @ingroup sys_mbox
- * Set an mbox invalid so that sys_mbox_valid returns 0
+ * 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.
  */
 void sys_mbox_set_invalid(sys_mbox_t *mbox);
 #endif
@@ -318,8 +395,13 @@ void sys_mbox_set_invalid(sys_mbox_t *mbox);
 /**
  * @ingroup sys_misc
  * The only thread function:
- * Creates a new thread
+ * 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.
  * ATTENTION: although this function returns a value, it MUST NOT FAIL (ports have to assert this!)
+ * 
  * @param name human-readable name for the thread (used for debugging purposes)
  * @param thread thread-function
  * @param arg parameter passed to 'thread'
@@ -329,7 +411,11 @@ sys_thread_t sys_thread_new(const char *name, lwip_thread_fn thread, void *arg,
 
 #endif /* NO_SYS */
 
-/* sys_init() must be called before anything else. */
+/**
+ * @ingroup sys_misc
+ * sys_init() must be called before anything else.
+ * Initialize the sys_arch layer.
+ */
 void sys_init(void);
 
 #ifndef sys_jiffies
@@ -343,6 +429,9 @@ u32_t sys_jiffies(void);
  * @ingroup sys_time
  * Returns the current time in milliseconds,
  * may be the same as sys_jiffies or at least based on it.
+ * 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).
  */
 u32_t sys_now(void);