说明：  ARMv7-M架构参考手册，Cortex-M系列处理面向嵌入式应用，而Cortex-R系列则面向实时应用，Cortex-A，则面向广大的手机用户。这是M系列参考手册。
(ARM v7-M Architecture, Application Level, Reference Manual. Cortex-M series processing is oriented to embedded applications, while Cortex-R series is oriented to real-time applications, and Cortex-A is oriented to the majority of mobile phone users. This is the M series reference manual.)