Re: [lwip-users] RTOS Integration

[Freddie Chopin]

On nie, 2016-10-09 at 05:02 +0000, Kenny Koller wrote:
> Hi Everyone,
> 
> I'm starting with some code generated by the ST Cube software for
> FreeRTOS.
> 
> I prefer not to use the FreeRTOS memory manager and the current
> version supports static allocation so I pleased to read this:
> 
> 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).
> 
> Of course I understand what is meant by allocating in place or on the
> stack but in practice how would be be used? It seems that you still
> need to preallocate a number of mailboxes or semaphores. Is creating
> a simple static array in sys_arch.c and doing some book keeping on
> which have been allocated/freed a reasonable approach?

Hello Kenny!

You don't need to preallocate anything, but keep in mind that in case
of mailboxes the memory for the mailbox object is usually separate from
the memory for the mailbox contents. In theory you could have both of
these memories allocated in place or on stack, but this way each
mailbox you create would have to have the same size - not very
flexible...

To use this feature I believe you'd need to
set configSUPPORT_STATIC_ALLOCATION in your configuration and declare
sys_sem_t to be StaticSemaphore_t. The same for mailbox - just
use StaticQueue_t for sys_mbox_t. Then in the *_new() functions you
just "construct" the objects in provided buffers
with xSemaphoreCreateCountingStatic() and xQueueCreateStatic().

Due to the thing I mentioned in the first paragraph this gets tricky
with queues, as you'd need to allocate the storage for contents
(pucQueueStorageBuffer argument for xQueueCreateStatic()) from
somewhere else - heap of preallocated buffers...

Regards,
FCh