嵌入式固件架构

The concept of an "event bus" is over-complicated. In many cases, the simplest approach is to minimize the number of things that need to happen asynchronously, but instead have a "main poll" routine which runs on an "as often as convenient" basis and calls polling routines for each subsystem. It may be helpful to have such routine in a compilation by itself, so that the essence of that file would simply be a list of all polling functions used by other subsystems, rather than anything with semantics of its own. If one has a "get button push" routine, one can have a loop within that routine which calls the main poll routine until a button is pushed, there's a keyboard timeout, or something else happens that the caller needs to deal with. That would then allow the main UI to be implemented using code like:

void maybe_do_something_fun(void)
{
  while(1)
  {
    show_message("Do something fun?");
    wait_for_button();
    if (button_hit(YES_BUTTON))
    {
      ... do something fun
      return;
    }
    else if (button_hit(NO_BUTTON))
    {
      ... do something boring
      return;
    }
  } while(1);
}

这通常比尝试拥有巨型状态机要方便得多，后者说如果代码是STATE_MAYBE_DO_SOMETHING_FUN状态，并且按下yes或no按钮，则需要前进到STATE_START_DOING_SOMETHING_FUN或STATE_START_DOING_SOMETHING_BORING状态。

请注意，如果使用这种方法，则需要确保两次调用main_poll之间的最坏情况之间的时间始终满足通过处理的轮询操作的及时性要求main_poll，但是在可以满足该要求的情况下，可以采用这种方法比抢先调度多线程代码所需的一切，以及使其可靠运行所需的锁和其他防护措施，要方便和高效得多。