先来参考别人的
https://www.jianshu.com/p/09b91b9a778f
https://www.jianshu.com/p/ab47f613e8c6
https://blog.csdn.net/hailangtuteng/article/details/87690056
博客与解释心跳原理的
https://www.cnblogs.com/tugenhua0707/p/8648044.html
