2 级和3 级（L2 和L3）互连子系统

Hi Wei,

    你说的应该是安全手册的5.11.6中的内容吧？

    这段的英文原文如下:

5.11.6 Software Test of Basic Functionality Including Error Tests
A software test can be utilized to test for basic functionality as well as to inject diagnostic errors and check
for proper error response. Such a test can be executed at boot or periodically. Software requirements
necessary are defined by the software implemented by the system integrator. The use of a boot time
software test of basic functionality is highly recommended. The use of a periodic software test of basic
functionality reporting is recommended.

    这里说的L2和L3是指MCU内部的系统，一般被成为Subsystem，这个Sub是跟CPU相对应的。

    5.11开篇有这样的描述:

The system interconnect is composed of a number of bridges, gaskets, communications crossbars, and

routing logic, which connects the bus masters (DMA, CPU, TUs, and so forth) to L2 slaves and L3

peripherals.

    一般来说，用户不用特别关心和理解L2和L3的区别，但是需要知道在MCU构架下，外设是如何与CPU建立连接的。

    了解了这个架构，就能更好的预估哪里有可能出问题，从而设计系统来规避或不断检测是否有问题存在。

    所以L2，L3应该是MCU的概念，而不是CPU的概念，ARM的手册应该不会提及。

    “基本功能性的引导时间软件测试”..........

    我觉得还是建议中英文对照来看文档，这句在英文原文里是"The use of a boot time software test of basic functionality is highly recommended."

    即"我们非常建议用户在系统启动时，对基本功能进行软件测试。"