好的链接

uboot启动流程：

http://www.elecfans.com/emb/xitong/20171212601280.html

https://blog.csdn.net/kernel_yx/article/details/53045424

https://www.cnblogs.com/heaad/archive/2010/07/17/1779829.html

 

Linux内部时钟：

https://www.cnblogs.com/hoys/archive/2012/02/21/2361675.html

 

Linux ARM MMU：

https://blog.csdn.net/xiaojsj111/article/details/11065717

 something good：

http://www.wayland-informatics.com/The%20Seven%20Stages%20of%20Expertise%20in%20Software.htm