看到USOS官方和网上很多基于Cortex-M3内核的移植，任务都运行于特权级，并没有充分发挥Cortex-M3用户级和特权级的保护功能，本文件的移植用户级和特权级是分开的，用户任务程序完全运行在用户级，用户级下需要操作中断等特殊要求，都在SVC系统调用函数中实，也可以方便的添加自己的SVC系统调用。-Many official and on-line to see USOS Cortex-M3 core-based migration, the task runs in the privileged class, and did not give full play to Cortex-M3 user-level and privilege level of protection, user-level migration of this document is a separate and privileged class the user task program completely run in user level, users need to operate under the interruption level special requirements, call the function in SVC 系统 of Real, They can also add your own in the SVC system calls.