/* \method callback(fun) Set the function to be called when the timer triggers.  */
STATIC mp_obj_t pyb_timer_callback(mp_obj_t self_in, mp_obj_t callback)
/* \method callback(fun) Set the function to be called when the timer triggers.  */
STATIC mp_obj_t pyb_timer_callback(mp_obj_t self_in, mp_obj_t callback)
{
        self->callback = mp_const_none;
    } else if (mp_obj_is_callable(callback)) {
        self->callback = callback;
    } else {
        mp_raise_ValueError(MP_ERROR_TEXT("callback must be None or a callable object"));
    }
    return mp_const_none;
}