Development Studio installs with the latest Arm Compiler for Embedded version available at the time of its release. It may be that you need to use a specific compiler version for your project (particularly common if the Arm Compiler for Embedded FuSa is needed).
Refer to the Arm Compiler for Embedded install guide to learn how to install different versions of the compiler.
To change the compiler version used for a project, right-click on the project, and select Properties (or from the menu, select Project > Properties), then C/C++ Build > Tool Chain Editor, and select the appropriate compiler version from the Current toolchain pulldown. Click Apply and Close, and rebuild the project.
CMSIS is a vendor-independent abstraction layer for microcontrollers that are based on Arm Cortex processors.
Cortex-M users can import projects from the library of CMSIS Packs. It is generally recommended to use Keil MDK for such projects, which has more robust support for such packs.
For more information, see the Development Studio documentation .