CMSIS-RTOS

Overview of CMSIS-RTOS

CMSIS-RTOS (Cortex Microcontroller Software Interface Standard – Real-Time Operating System) is a standard interface for RTOS that provides a common API for software components to interact with the underlying RTOS kernel. The CMSIS-RTOS API provides a standardized way to create, configure, and manage threads, mutexes, semaphores, and other common RTOS constructs. It also supports a range of scheduling policies, including preemption and round-robin scheduling.

Explore our in-depth CMSIS-RTOS tutorial to learn the fundamentals of this powerful, standardized API for real-time operating systems and enhance your embedded development skills.

Introduction to CMSIS-RTOS

CMSIS-RTOS (Cortex Microcontroller Software Interface Standard-Real-Time Operating System) is a standardized API for programming real-time operating systems on ARM Cortex-M microcontrollers. The CMSIS-RTOS provides a generic interface for RTOS kernels and allows for the creation of reusable software components that are portable across different microcontroller vendors and RTOS kernels. It provides a standard interface for configuring the RTOS, managing threads, semaphores, and other synchronization objects, and also includes an optional software timer implementation. CMSIS-RTOS is intended to simplify the development of real-time applications on Cortex-M microcontrollers and promote software reuse across different microcontrollers and RTOS implementations.

History and Inventions of CMSIS-RTOS

CMSIS (Cortex Microcontroller Software Interface Standard) was introduced by ARM in 2008 to provide a unified software layer for Cortex-M processors, allowing developers to write more portable and reusable code across different microcontroller vendors. CMSIS consists of several components, including CMSIS-Core, CMSIS-DSP, CMSIS-SVD, CMSIS-DAP, and CMSIS-RTOS.

CMSIS-RTOS was added as a part of CMSIS to standardize the APIs for RTOS implementations on ARM Cortex-M microcontrollers. The goal was to provide a unified programming model for real-time applications, simplifying the development process and increasing code portability.

CMSIS-RTOS has two main versions: CMSIS-RTOS v1 and CMSIS-RTOS v2.

CMSIS-RTOS v1: The first version of CMSIS-RTOS API was designed to provide a common interface for RTOSes running on Cortex-M processors. It offered a set of standardized APIs for thread management, kernel control, timer management, inter-thread communication (using message queues, mutexes, and semaphores), and more. One of the most widely adopted implementations of CMSIS-RTOS v1 is Keil RTX, developed by Keil, an ARM company.
CMSIS-RTOS v2: In response to the evolving needs of embedded systems developers and the limitations of the first version, ARM introduced CMSIS-RTOS v2. This version provided improvements and refinements to the API, addressing issues related to performance, memory usage, and functionality. CMSIS-RTOS v2 is backward compatible with CMSIS-RTOS v1, allowing developers to migrate their applications with minimal effort. Keil RTX5 is an implementation of CMSIS-RTOS v2.

CMSIS-RTOS is not an RTOS itself, but rather a standardized API that different RTOSes can implement. This standardization allows developers to switch between RTOSes with minimal changes to their application code. Some popular RTOSes that support CMSIS-RTOS include FreeRTOS, Keil RTX, and Micrium µC/OS.

Features of CMSIS-RTOS

CMSIS-RTOS (Cortex Microcontroller Software Interface Standard – Real-Time Operating System) is a standardized API designed to simplify the development of real-time applications on ARM Cortex-M microcontrollers. It provides a consistent interface for various real-time operating systems, improving code portability and allowing developers to switch between different RTOSes with minimal changes to their application code. Here are some of the main features of CMSIS-RTOS:

Thread Management: CMSIS-RTOS provides a standard API for creating, deleting, and controlling threads (also called tasks), which are the basic units of execution in a real-time application. This includes thread prioritization, state management, and the ability to control thread execution by starting, stopping, or waiting for threads.
Kernel Control: The API allows developers to control and query the underlying RTOS kernel, including starting and stopping the scheduler, managing system tick frequency, and obtaining kernel information such as the current system time and version details.
Timer Management: CMSIS-RTOS includes APIs for creating, starting, stopping, and deleting software timers, enabling developers to perform time-based operations and trigger events at specific intervals.
Inter-Thread Communication and Synchronization: The API provides mechanisms for communication and synchronization between threads, including message queues, mutexes, and semaphores. These mechanisms allow threads to share data, coordinate execution, and prevent concurrent access to shared resources.
Memory Management: CMSIS-RTOS supports dynamic memory allocation and deallocation for RTOS objects such as threads, timers, and message queues. This allows developers to create and manage RTOS objects at runtime, adjusting resource usage as needed.
Event Management: The API includes support for event flags, which enable threads to wait for specific events or a combination of events before proceeding with execution. This feature can be used to coordinate actions between multiple threads or react to external events such as interrupts.
ISR (Interrupt Service Routine) Support: CMSIS-RTOS provides a set of functions to support interactions between the RTOS and interrupt service routines, allowing developers to manage RTOS objects and trigger events from within ISRs.
Portability and Adaptability: The standardized API enables code portability across different RTOS implementations and microcontroller vendors, reducing development effort when transitioning between platforms or RTOSes.

Architecture of CMSIS-RTOS

CMSIS-RTOS (Cortex Microcontroller Software Interface Standard – Real-Time Operating System) is a standardized API designed for real-time operating systems (RTOS) running on ARM Cortex-M microcontrollers. It provides a consistent interface across different RTOS implementations, enabling code portability and simplifying the development of real-time applications. The architecture of CMSIS-RTOS can be described in terms of its main components and their relationships:

CMSIS-RTOS API: The core of CMSIS-RTOS is its API, which consists of a set of standardized functions and data structures that developers can use to interact with the underlying RTOS. These functions cover various aspects of real-time application development, such as thread management, kernel control, timer management, inter-thread communication, synchronization, memory management, and event management.
RTOS Implementation: CMSIS-RTOS is an abstraction layer that can be implemented by different RTOSes. Each RTOS implementation provides its own set of services and features while adhering to the standardized CMSIS-RTOS API. Examples of RTOS implementations that support CMSIS-RTOS include FreeRTOS, Keil RTX, and Micrium µC/OS.
Hardware Abstraction Layer (HAL): The underlying RTOS implementation interacts with the hardware through a hardware abstraction layer (HAL). This layer is responsible for providing hardware-specific functions and services, such as interrupt handling and peripheral control, which are utilized by the RTOS to execute real-time applications on the target hardware.
Application Code: Developers write application code using the CMSIS-RTOS API, which remains consistent across different RTOS implementations. This enables code portability and simplifies the development process, as developers can focus on writing application logic without worrying about the specifics of the underlying RTOS or hardware platform.
ARM Cortex-M Processor: The target hardware platform for CMSIS-RTOS is ARM Cortex-M microcontrollers. These microcontrollers provide a set of features and capabilities, such as NVIC (Nested Vectored Interrupt Controller), SysTick (System Timer), and power management, which are leveraged by the RTOS and HAL to execute real-time applications.

Working Principle of CMSIS-RTOS

CMSIS-RTOS (Cortex Microcontroller Software Interface Standard – Real-Time Operating System) is a standardized API for real-time operating systems (RTOS) that run on ARM Cortex-M microcontrollers. The primary goal of CMSIS-RTOS is to provide a consistent interface for various RTOSes, making it easier for developers to create applications that can work with different RTOS implementations. Here’s a high-level overview of how CMSIS-RTOS works:

Standardized API: CMSIS-RTOS provides a set of standardized functions and data structures that developers can use to interact with the underlying RTOS. These functions cover essential aspects of real-time application development, such as thread management, kernel control, timer management, inter-thread communication, synchronization, memory management, and event management.
Application Development: Developers write their application code using the CMSIS-RTOS API, which remains consistent across different RTOS implementations. This enables code portability and simplifies the development process, as developers can focus on writing application logic without worrying about the specifics of the underlying RTOS or hardware platform.
RTOS Implementation: An RTOS that supports CMSIS-RTOS implements the standardized API, providing the actual functionality behind the API functions. Examples of RTOS implementations that support CMSIS-RTOS include FreeRTOS, Keil RTX, and Micrium µC/OS. Each RTOS implementation provides its own set of features and performance characteristics while adhering to the standardized CMSIS-RTOS API.
Hardware Abstraction Layer (HAL): The underlying RTOS implementation interacts with the hardware through a hardware abstraction layer (HAL). This layer is responsible for providing hardware-specific functions and services, such as interrupt handling and peripheral control, which are utilized by the RTOS to execute real-time applications on the target hardware.
ARM Cortex-M Processor: CMSIS-RTOS is designed for ARM Cortex-M microcontrollers, which provide a set of features and capabilities, such as NVIC (Nested Vectored Interrupt Controller), SysTick (System Timer), and power management, that are leveraged by the RTOS and HAL to execute real-time applications.

In practice, when a developer writes an application using the CMSIS-RTOS API, the application code interacts with the RTOS implementation through the standardized API functions. The RTOS implementation, in turn, interacts with the hardware through the HAL to perform tasks such as thread scheduling, interrupt handling, and peripheral control. This layered approach enables code portability and simplifies the development process since the application code remains largely independent of the specific RTOS and hardware platform.

Supported Hardware Platforms by CMSIS-RTOS

CMSIS-RTOS is a standardized API designed for real-time operating systems (RTOS) running on ARM Cortex-M microcontrollers. As such, it is not tied to specific hardware platforms but rather focuses on providing a consistent interface across various RTOS implementations targeting ARM Cortex-M processors.

ARM Cortex-M microcontrollers are a family of 32-bit processors that are widely used in embedded systems due to their low power consumption, high performance, and ease of use. Some of the most popular Cortex-M series processors include:

Cortex-M0
Cortex-M0+
Cortex-M1
Cortex-M3
Cortex-M4
Cortex-M7
Cortex-M23
Cortex-M33
Cortex-M35P
Cortex-M55

These processors are used in a wide range of microcontroller products offered by various semiconductor manufacturers, such as:

STMicroelectronics (STM32 series)
NXP Semiconductors (LPC series, Kinetis series)
Texas Instruments (Tiva C series, MSP432 series)
Microchip (SAM series, PIC32 series)
Nordic Semiconductor (nRF series)
Silicon Labs (EFR32 series, EFM32 series)
Cypress Semiconductor (PSoC 6 series)
Infineon Technologies (XMC series)
Renesas Electronics (RA series, Synergy series)
Analog Devices (ADuCM series)

RTOS implementations that support the CMSIS-RTOS API can run on these ARM Cortex-M-based microcontrollers, enabling developers to create portable real-time applications across different hardware platforms. Some popular RTOSes that support CMSIS-RTOS include FreeRTOS, Keil RTX, and Micrium µC/OS.

Devices used with CMSIS-RTOS

The devices with ARM controller are mostly used CMSIS-RTOS

Applications of CMSIS-RTOS

CMSIS-RTOS is a standardized API for real-time operating systems (RTOS) running on ARM Cortex-M microcontrollers, making it easier for developers to create portable applications across different RTOS implementations. Applications of CMSIS-RTOS span a wide range of industries and use cases where real-time performance, reliability, and portability are crucial. Some of the typical applications include:

Industrial Automation and Control Systems: CMSIS-RTOS can be used in various industrial applications, such as programmable logic controllers (PLCs), motion control systems, and robotics, where real-time performance and deterministic behavior are essential for precise control and coordination.
Automotive Systems: Modern vehicles rely on numerous embedded systems for engine control, advanced driver assistance systems (ADAS), infotainment, and more. CMSIS-RTOS can be utilized in these applications to ensure reliable and real-time operation, as well as portability across different hardware platforms and RTOS implementations.
Medical Devices: CMSIS-RTOS is suitable for use in medical devices, such as patient monitoring systems, infusion pumps, and ventilators, where real-time response, reliability, and safety are critical.
Aerospace and Defense: CMSIS-RTOS can be employed in avionics systems, flight control systems, and other aerospace and defense applications where real-time performance, determinism, and reliability are crucial requirements.
IoT and Smart Devices: The Internet of Things (IoT) encompasses a wide variety of connected devices, such as smart home appliances, wearables, and sensor networks, which often require real-time performance, low power consumption, and code portability. CMSIS-RTOS is well-suited for these applications, providing a standardized interface for RTOS implementations running on ARM Cortex-M microcontrollers.
Consumer Electronics: CMSIS-RTOS can be used in consumer electronic devices, such as gaming consoles, digital cameras, and portable media players, where real-time performance, low power consumption, and a small memory footprint are essential.
Telecommunications: In telecommunications systems, such as base stations and network routers, CMSIS-RTOS can be employed to manage real-time tasks, such as signal processing, protocol handling, and traffic management.
Energy Systems: CMSIS-RTOS is suitable for use in energy systems, such as smart grid infrastructure, energy management systems, and renewable energy controllers, where real-time performance and reliability are crucial for efficient operation.

Advantages of CMSIS-RTOS

CMSIS-RTOS (Cortex Microcontroller Software Interface Standard – Real-Time Operating System) offers several advantages for developers working with real-time applications on ARM Cortex-M microcontrollers. Some of the key benefits include:

Portability: The standardized API provided by CMSIS-RTOS enables developers to write application code that is portable across different RTOS implementations and hardware platforms. This facilitates code reuse, reduces development effort when transitioning between platforms, and simplifies maintenance.
Simplified Development: CMSIS-RTOS provides a consistent set of functions and data structures for essential real-time application development tasks, such as thread management, kernel control, timer management, inter-thread communication, synchronization, memory management, and event management. This simplifies development by allowing developers to focus on application logic without worrying about the specifics of the underlying RTOS or hardware platform.
Wide Industry Support: CMSIS-RTOS is designed for ARM Cortex-M microcontrollers, which are widely used in various industries and embedded applications. Many popular RTOS implementations, such as FreeRTOS, Keil RTX, and Micrium µC/OS, support the CMSIS-RTOS API. This broad support provides developers with a range of choices for selecting the most suitable RTOS for their specific application requirements.
Easier Integration and Migration: The standardized API makes it easier to integrate third-party software components, middleware, and libraries with different RTOS implementations. Additionally, it simplifies the process of migrating an application from one RTOS to another or transitioning between different hardware platforms.
Streamlined Learning Curve: Developers familiar with the CMSIS-RTOS API can more easily adapt to working with different RTOS implementations, reducing the learning curve and making it simpler to switch between various RTOSes and hardware platforms as needed.
Enhanced Collaboration: The use of a standardized API promotes collaboration between developers, middleware providers, and hardware vendors. It also facilitates the sharing of code, expertise, and best practices across the industry.

Disadvantages of CMSIS-RTOS

While CMSIS-RTOS offers several benefits, there are also some disadvantages and limitations to consider:

Limited to ARM Cortex-M: CMSIS-RTOS is designed specifically for ARM Cortex-M microcontrollers. While this covers a wide range of devices and applications, it may not be suitable for developers working with other microcontroller architectures or processor families.
Loss of RTOS-Specific Features: The standardized API provided by CMSIS-RTOS may not expose all features or optimizations available in a specific RTOS implementation. Developers might need to use RTOS-specific APIs or extensions to access these features, which could reduce code portability.
Performance Overhead: Implementing CMSIS-RTOS as an abstraction layer on top of the native RTOS API may introduce a small performance overhead, particularly in terms of function call latency and memory usage. However, this overhead is generally minimal and often outweighed by the benefits of portability and simplified development.
Limited API Scope: The CMSIS-RTOS API covers essential aspects of real-time application development but may not provide all the functionalities required for certain specialized applications. In such cases, developers might need to use additional APIs or custom solutions to meet their specific requirements.
Adoption Challenges: Not all RTOS implementations support the CMSIS-RTOS API, limiting the choices available for developers who want to leverage the benefits of a standardized interface. However, the popularity of ARM Cortex-M microcontrollers and the increasing adoption of CMSIS-RTOS by various RTOS vendors should help mitigate this issue over time.
Learning Curve: Although the standardized API can streamline the learning curve for developers working with different RTOSes, there is still an initial learning curve associated with understanding the CMSIS-RTOS API and its concepts.

Future Development and Enhancement of CMSIS-RTOS

As a widely adopted standard for real-time operating systems (RTOS) running on ARM Cortex-M microcontrollers, CMSIS-RTOS is expected to continue evolving to meet the needs of the embedded systems industry. While it is difficult to predict the exact future development and enhancement of CMSIS-RTOS, some potential areas of focus might include:

Expanded Support for New Hardware and RTOS Implementations: As new ARM Cortex-M microcontrollers and RTOS implementations become available, CMSIS-RTOS will likely need to be updated to support these platforms, ensuring that developers can continue to benefit from its portability and standardized interface.
Enhanced API Functionality: As embedded systems become more complex and sophisticated, there may be a need to expand the CMSIS-RTOS API to include additional functionality or to refine existing functionality. This could involve adding new features for thread management, synchronization, memory management, event handling, or other real-time application development tasks.
Improved Performance and Efficiency: As the performance and efficiency requirements of embedded systems increase, future versions of CMSIS-RTOS may focus on optimizing the API and its underlying implementations to minimize any performance overhead associated with using a standardized interface.
Increased Security Features: Security is an essential aspect of modern embedded systems, particularly with the growing adoption of IoT devices. Future development of CMSIS-RTOS could involve incorporating enhanced security features, such as secure boot, secure storage, or secure communication, to help developers create more secure real-time applications.
Better Integration with Development tools and Middleware: To further simplify the development process, future versions of CMSIS-RTOS could focus on improving integration with various development tools, middleware, and software libraries. This may include better debugging support, more extensive code examples, and improved documentation.
Wider Industry Adoption: As CMSIS-RTOS continues to evolve, it is expected that more RTOS vendors and hardware manufacturers will adopt the standard, further expanding its reach and benefits for developers working with ARM Cortex-M microcontrollers.

CMSIS-RTOS Usage, Availability, Licensing, Pricing and Download Details

CMSIS-RTOS (Cortex Microcontroller Software Interface Standard – Real-Time Operating System) is a standardized API designed for real-time operating systems running on ARM Cortex-M microcontrollers. It is intended to simplify development and increase portability across various RTOS implementations and hardware platforms. Here are some details about its usage, availability, licensing, pricing, and download information:

CMSIS-RTOS Usage

CMSIS-RTOS is used by developers working on real-time applications running on ARM Cortex-M microcontrollers. The standardized API makes it easier for developers to create portable applications across different RTOS implementations, such as FreeRTOS, Keil RTX, Micrium µC/OS, and others. The API provides functions and data structures for tasks such as thread management, kernel control, timer management, inter-thread communication, synchronization, memory management, and event management.

CMSIS-RTOS Availability

CMSIS-RTOS is part of the larger CMSIS (Cortex Microcontroller Software Interface Standard) project, which is maintained by ARM. The API is widely available and supported by various RTOS vendors, and it can be used on a wide range of ARM Cortex-M microcontroller products from different semiconductor manufacturers.

CMSIS-RTOS Licensing

CMSIS-RTOS is typically distributed under permissive open-source licenses, such as the Apache License 2.0 or BSD-3-Clause. This means that developers can freely use, modify, and distribute the CMSIS-RTOS API and its associated files, subject to the terms and conditions of the respective licenses.

CMSIS-RTOS Pricing

CMSIS-RTOS itself is free to use and distribute, as it is an open-source project. However, the RTOS implementations that support the CMSIS-RTOS API may have their own licensing and pricing models. For example, some RTOS implementations are available under open-source licenses (e.g., FreeRTOS), while others may require commercial licenses (e.g., Micrium µC/OS). The specific pricing and licensing details will depend on the chosen RTOS.

CMSIS-RTOS Download Details

The CMSIS-RTOS API and its associated files can be downloaded from the official ARM CMSIS GitHub repository (https://github.com/ARM-software/CMSIS_5) or through the RTOS vendor’s website, as part of the RTOS package. It is essential to consult the documentation and specifications of the chosen RTOS to ensure proper integration and usage of the CMSIS-RTOS API.