The ARM Cortex Microcontroller Software Interface Standard (CMSIS) defines a
set of standard interfaces to ARM Cortex-M SOCs. In particular, the CMSIS-CORE
component standardizes the software interface to core and peripheral registers,
as well as exception names and the system clock frequency. Multiple SOC
vendors, including NXP and Nordic Semiconductor, include the CMSIS-CORE header
files in their SOC header files. These SOC header files are in turn used by
the vendor's peripheral drivers.

http://www.arm.com/products/processors/cortex-m/cortex-microcontroller-software-interface-standard.php

The sources in this directory are imported from
https://github.com/ARM-software/CMSIS.git

The current version supported in Zephyr is 
https://github.com/ARM-software/CMSIS/releases/tag/v4.5.0