Mailboxes
[OS abstraction layer]

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.

Parameters:

mbox	mbox to get a message from
msg	pointer where the message is stored
timeout	maximum time (in milliseconds) to wait for a message (0 = wait forever)

Returns:

SYS_ARCH_TIMEOUT on timeout, any other value if a message has been received

Definition at line 293 of file sys_arch.c.

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.

Parameters:

mbox	mbox to get a message from
msg	pointer where the message is stored

Returns:

0 (milliseconds) if a message has been received or SYS_MBOX_EMPTY if the mailbox is empty

Definition at line 343 of file sys_arch.c.

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.

Parameters:

mbox	mbox to delete

Definition at line 228 of file sys_arch.c.

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.

Parameters:

mbox	pointer to the mbox to create
size	(minimum) number of messages in this mbox

Returns:

ERR_OK if successful, another err_t otherwise

Definition at line 209 of file sys_arch.c.

Post a message to an mbox - may not fail -> blocks if full, only to be used from tasks NOT from ISR!

Parameters:

mbox	mbox to posts the message
msg	message to post (ATTENTION: can be NULL)

Definition at line 250 of file sys_arch.c.

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.

Definition at line 241 of file sys_arch.c.

Try to post a message to an mbox - may fail if full.

Can be used from ISR (if the sys arch layer allows this). Returns ERR_MEM if it is full, else, ERR_OK if the "msg" is posted.

Parameters:

mbox	mbox to posts the message
msg	message to post (ATTENTION: can be NULL)

Definition at line 270 of file sys_arch.c.

Try to post a message to an mbox - may fail if full.

To be be used from ISR. Returns ERR_MEM if it is full, else, ERR_OK if the "msg" is posted.

Parameters:

mbox	mbox to posts the message
msg	message to post (ATTENTION: can be NULL)

Definition at line 287 of file sys_arch.c.

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.