Cortex Microcontroller System Interface Standard

CMSIS enables consistent device support and simple software interfaces to the processor and its peripherals, simplifying software reuse, reducing the learning curve for microcontroller developers, and reducing the time to market for new devices.


Starting from CMSIS-CORE, a vendor-independent hardware abstraction layer for Cortex-M processors, CMSIS has since expanded into areas such as software component management and reference debugger interfaces. Creation of software is a major cost factor in the embedded industry. Standardizing the software interfaces across all Cortex-M silicon vendor products, especially when creating new projects or migrating existing software to a new device, means significant cost reductions. 

CMSIS is defined in close cooperation with various silicon and software vendors and provides a common approach to interface to peripherals, real-time operating systems, and middleware components. It simplifies software reuse, reducing the learning curve for new microcontroller developers and cutting the time-to market for devices.

CMSIS Components

CMSIS-CORE: Consistent system startup and peripheral access

System startup, processor core access, and peripheral definitions are essential for every embedded application. The standardized CMSIS-CORE is implemented for over 3900 different devices and makes it easy to get started with a new device or migrate software across microcontrollers.

CMSIS version 5

CMSIS is publicly developed on GitHub. The latest version can be downloaded here:

CMSIS-RTOS: Deterministic Real-Time Software Execution

A super-loop concept is only adequate for simple embedded applications. Cortex-M microcontrollers are designed for real-time operating systems that give you resource and time control.

CMSIS-RTOS is an API that enables consistent software layers with middleware and library components. CMSIS-RTOS RTX runs on every Cortex-M device and is the proven reference implementation that is easy to learn and use.

CMSIS-DSP: Fast implementation of digital signal processing 

Developing a real-time digital signal processing (DSP) system is not trivial as the DSP algorithms rely heavily on complex mathematical operations that are even time-critical.

CMSIS-DSP library is a rich collection of DSP functions that ARM has optimized for the various Cortex-M processor cores. CMSIS-DSP is widely used in the industry and enables also optimized C code generation from various third-party tools.

CMSIS-Driver: Generic peripheral interfaces for middleware and application code 

Interfacing microcontroller peripherals with middleware or generic application code can be challenging as each device is different. Ready-to use CMSIS-Driver interfaces are today available for many microcontroller families and avoid cumbersome and time consuming driver porting.

CMSIS-Pack: Easy access to reusable software components

Previously, software modules were hard to integrate as the source and header files had unclear requirements, inconsistent documentation, or missing license information.

Because CMSIS-Pack defines the structure of a software pack containing software components, these issues are addressed. Software components are easily selectable, and any dependencies on other software are highlighted.

CMSIS-SVD: Consistent view to device and peripherals

For every supported microcontroller, debuggers can provide detailed views to the device peripherals that display the current register state.

CMSIS-SVD files enable these views, and ensure that the debugger view matches the actual implementation of the device peripherals.

CMSIS-DAP: Connectivity to low-cost evaluation hardware

Inexpensive development boards are available from many microcontroller vendors. Frequently, a low-cost debug unit is included, but different interfaces need a specific tool setup.

CMSIS-DAP is a standardized interface to the Cortex Debug Access Port (DAP) and is used by many starter kits and supported by various debuggers.