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更多关于软件时钟处理
在前一篇文章中，我研究了软件中处理时钟的基本知识。在本文中，我们将继续讨论全球时钟恢复、分布式时钟同步和事件同步。
全局时钟恢复
假设一个复杂系统中有几个代理。每一个都有自己的参考时钟，给人一种时间感。一个代理的时间概念是从启动以来有多少个参考时钟滴答通过的。
为了同步操作和共享时钟，代理需要有一个共同的、全局的时间感。这是很容易的总线系统，如USB或火线，因为巴士往往携带自己的时钟。然而，对于分布式的、基于包的互连，情况变得更加困难。IEEE标准1588、1588V2和802.1as和IETF的NTP标准设计的专门针对分布式全局时钟恢复问题。
The first task of the system is to elect one of the agents as the master. It is this agent‘s clock that will become the common global clock. IEEE 1588 and variants use a peer-to-peer leadership elecTIon protocol that tries to elect the highest quality clock amongst the agents. It is guaranteed to elect one， and only one， master.
Once the master is elected， each agent needs to know the following informaTIon：
Is my clock going slower/faster than the global master clock？ If so， by how much？
What is the current TIme now according to the master clock？
The fundamental method used is to regularly transmit synchronizaTIon messages from the master to the other agents. The message contains the global time that the message was sent. The following diagram shows this happening：
