Cyclic functions

The cyclic function execution infrastruture provides a way to periodically execute code, e.g. every 100ms. Examples for such functions might be LED blinking etc. The functions that are hooked into this cyclic list should be small timewise as otherwise the execution of the other code that relies on a high frequent polling (e.g. UART rx char ready check) might be delayed too much. To detect cyclic functions with an excessive execution time, the Kconfig option CONFIG_CYCLIC_MAX_CPU_TIME_US was introduced. It defines the maximum allowable execution time for such a cyclic function. The first time the execution of a cyclic function exceeds this interval, a warning will be displayed indicating the problem to the user.

Registering a cyclic function

To register a cyclic function, use something like this:

struct donkey {
    struct cyclic_info cyclic;
    void (*say)(const char *s);
};

static void cyclic_demo(struct cyclic_info *c)
{
    struct donkey *donkey = container_of(c, struct donkey, cyclic);

    donkey->say("Are we there yet?");
}

int donkey_init(void)
{
    struct donkey *donkey;

    /* Initialize donkey ... */

    /* Register demo cyclic function */
    cyclic_register(&donkey->cyclic, cyclic_demo, 10 * 1000, "cyclic_demo");

    return 0;
}

This will register the function cyclic_demo() to be periodically executed all 10ms.

How is this cyclic functionality integrated / executed?

The cyclic infrastructure integrates cyclic_run(), the main function responsible for calling all registered cyclic functions, into the common schedule() function. This guarantees that cyclic_run() is executed very often, which is necessary for the cyclic functions to get scheduled and executed at their configured periods.