The ARM? Cortex? Microcontroller Software Interface Standard （CMSIS） is a vendor-independent hardware abstractionlayer for the Cortex-M processor series. The CMSIS enables consistent and simple software interfaces to the processor andperipherals. It simplifies software re-use by reducing the learning curve for new microcontroller developers and reducing thetime to market for new device

　　The lowest level defines addresses and accesses methods for common components and functions in every Cortex-M system.Access to core registers， NVIC， and the debug subsystem is provided by this layer. Tool specific access to special purposeregisters （for example CONTROL， xPSR）， is provided in the form of inline functions or compiler intrinsics. This layer isprovided by AR