随机应变——可裁剪性
从硬件环境来看,桌面操作系统具有标准化的、存储和I/O架构,而嵌入式环境中的RTOS的硬件环境只有标准化的,没有标准化的存储、I/O和显示器架构。
从应用环境来看,桌面操作系统面向复杂多变的应用,而RTOS面向单一设备的单一应用。
从开发界面来看,桌面操作系统试图给开发人员提供一个“黑箱”,让开发人员通过一系列标准的系统调用来使用操作系统中的功能,而嵌入式试图为开发人员提供一个“白箱”,让开发人员可以自主控制系统的所有资源。
桌面操作系统的研究开发指导思想是尽可能在不改变自身的前提下具有广泛的适应性。也就是说:不论应用环境怎么变化,好都不要对自身内部产生什么影响,也不要求自身做太多的变化。反过来,应用于嵌入式环境的RTOS,在研发的时候就必须立足于改变自身、开放自身,让开发人员可以根据硬件环境和应用环境的不同而对操作系统进行灵活的裁剪和配置,因为对于任何一个具体的嵌入式设备,它的功能是确定的,因此只要从原有操作系统中把这个特定应用所需的功能拿进来即可。
应当指出的是:如果一个操作系统平台只能依靠手工的方式去掉一些代码,这根本就不是可裁剪性。所谓可裁剪性是在软件工程阶段利用软件配置方法实现软件构件的“即插即用”。
可裁剪性带给用户的一个直接的好处是硬件成本降低,这对于成本敏感的应用,如消费电子类设备,具有重要的现实意义。由于设备中只包含应用程序用到的那部分操作系统功能,这就使得系统变得简单、易把握,从而提高系统的可靠性。
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