Call function with external stack
=================================

Overview
--------

A given function can be executed with a user allocated stack space
which is independent of current task stack, this mechanism can be
used to save stack space wasted by tasks which call a common function
with intensive stack usage such as `printf`. The given function can
be called inside the shared stack space which is a callback function
deferred by calling :cpp:func:`esp_execute_shared_stack_function`, 
passing that function as parameter

Usage
-----

:cpp:func:`esp_execute_shared_stack_function` takes four arguments, 
a mutex object allocated by the caller, which is used to protect if 
the same function shares its allocated stack, a pointer to the top 
of stack used to that fuction, the size in bytes of stack and, a pointer
to a user function where the shared stack space will reside, after calling
the function, the user defined function will be deferred as a callback
where functions can be called using the user allocated space without
taking space from current task stack. 

The usage may looks like the code below:

.. code-block:: c

    void external_stack_function(void)
    {
        printf("Executing this printf from external stack! \n");
    }

    //Let's suppose we wanting to call printf using a separated stack space
    //allowing app to reduce its stack size.
    void app_main()
    {
        //Allocate a stack buffer, from heap or as a static form:
        portSTACK_TYPE *shared_stack = malloc(8192 * sizeof(portSTACK_TYPE));
        assert(shared_stack != NULL);

        //Allocate a mutex to protect its usage:
        SemaphoreHandle_t printf_lock = xSemaphoreCreateMutex();
        assert(printf_lock != NULL);
     
        //Call the desired function using the macro helper:
        esp_execute_shared_stack_function(printf_lock, 
                                        shared_stack,
                                        8192,
                                        external_stack_function);
        
        vSemaphoreDelete(printf_lock);    
        free(shared_stack); 
    }

.. _esp-call-with-stack-basic_usage:

API Reference
-------------

.. include:: /_build/inc/esp_expression_with_stack.inc