Introduction to the features of some EOS

1、μClinux

μClinux is an excellent version of embedded Linux, and its full name is micro-control Linux, which means micro-control Linux.

Compared with standard Linux, μClinux's kernel is very small. However, it still inherits the main features of the Linux operating system, including good stability and portability, powerful networking features, excellent file system support, standard rich API, and TCP/IP network protocols. Because there is no MMU memory management unit, its multitasking implementation requires some skills.

μClinux inherits the standard Linux multitasking implementation in structure, divided into real-time processes and ordinary processes, using first-come, first-served and time-slice rotation scheduling, respectively, which is only improved for low- and mid-range embedded CPU features, and does not support kernel preemption, with average real-time performance.

In summary, it can be seen that the biggest feature of μClinux is designed for no MMU processor, which is suitable for stm32f103 without MMU function, but transplanting this system requires at least 512KB of RAM space, 1MB of ROM/FLASH space, and stmf103 has 256K of FLASH, which requires external memory, which increases the cost of hardware design.

μClinux structure is complex and relatively difficult to port, the kernel is also larger, and its real-time performance is also poor. If the development of embedded products focuses on the file system and network applications, then μClinux is a good choice.

2、μC/OS-II

μC/OS-II is developed based on μC/OS, a compact, preemptive multitasking real-time kernel written in C. μC/OS-II can manage 64 tasks and provides task scheduling and management, memory management, inter-task synchronization and communication, time management and interrupt services, etc., with high execution efficiency, small footprint, excellent real-time performance and It is characterized by high execution efficiency, small footprint, excellent real-time performance and high scalability.

In terms of file system support, since μC/OS-II is designed for small and medium-sized embedded systems, the compiled kernel is less than 10 KB even with all the features included, so the system itself does not provide support for file systems. However, μC/OS-II has good extensibility and can add file system content if needed.

Regarding hardware support, μC/OS-II can support most of the current popular CPUs. μC/OS-II has a small kernel and can be trimmed down to a minimum of 2 KB of code and requires a minimum of 4 KB of data RAM space. μC/OS-II is relatively easy to port, requiring only processor-related code changes.

In summary, μC/OS-II is a simple, full-featured and real-time embedded operating system kernel, which is very suitable for CPUs without MMU functionality. It requires very little kernel code space and data storage space, has good real-time performance and scalability, and is open source with many information and examples available on the Internet. Hence, it is very suitable for porting to STM32F103C4.

3、eCos

eCos (embedded Configurable operating system) is an open-source configurable, portable, real-time operating system for deeply embedded applications.

The biggest feature is flexible configuration, modular design, and the core part of the same small components, including the kernel, C language library and the underlying runtime package.

Each component can be provided with many configuration options (the real-time kernel is also available as an optional configuration), which can be easily configured using the configuration tools provided by eCos, and the different configurations enable eCos to meet the requirements of different embedded applications.

The configurability of eCos OS is very powerful, and users can add the required file system by themselves. eCos OS also supports most of the current popular embedded CPUs. eCos OS can be ported between different architectures such as 16-bit, 32-bit and 64-bit.

Due to its small kernel, eCos can be trimmed down to a minimum of 10 KB of code and requires a minimum of 10 KB of data RAM space.

Regarding system portability, eCos OS is portable and easier than µC/OS-II and µClinux.

In summary, eCos is characterized by its flexible configuration and supports porting to CPUs without MMU, is open source and has good portability, and is also more suitable for porting to CPUs on the stm32 platform. But the application of eCOS is not too widespread, not yet as common as μC/OS-II, and the information is not as much as μC/OS-II. eCos is suitable for some commercial or industrial cost-sensitive embedded systems, such as some applications in the field of consumer electronics.

4、FreeRTOS

Because RTOS needs to occupy a certain amount of system resources (especially RAM), only μC/OS-II, embOS, salvo, FreeRTOS and a few other real-time operating systems can run on small RAM microcontrollers.

Compared to commercial operating systems such as C/OS-II and embOS, the FreeRTOS system is free with open source, portable, resizable, and flexible scheduling policies. It can be easily ported to run on various microcontrollers, with its latest version being version 6.0.

As a lightweight operating system, FreeRTOS provides task management, time management, semaphore, message queue, memory management, logging functions, etc., which can meet the needs of smaller systems.

The FreeRTOS kernel supports a priority scheduling algorithm, where each task is given a certain priority according to its importance. The CPU always lets the task run first in the ready state with the highest priority.

The FreeRT0S kernel also supports a rotating scheduling algorithm, which allows different tasks to use the same priority, and tasks of the same priority share the CPU time if no higher priority task is ready.

Shortcomings of FreeRTOS: Compared to the common μC/OS-II operating system, FreeRTOS has both advantages and shortcomings. For example, FreeRTOS only provides the implementation of message queues and semaphores, which cannot send messages to message queues in a last-in-first-out order; on the other hand, FreeRTOS is only an operating system kernel, which needs to be extended with third-party GUIs (graphical user interfaces), TCP/IP protocol stacks, FS (file systems), etc. to implement a more complex system. Unlike μC/OS-II, which can be seamlessly integrated with μC/GUI, μC/FS, and μC/TCP-IP, FreeRTOS is only an operating system kernel. It needs to be extended with a third-party GUI, TCP/IP stack, and FS (file system) to achieve a more complex system.

5、mbed OS

Open source embedded operating system, ARM will embed OS free for all manufacturers to use, embed provides a relatively more systematic and comprehensive intelligent hardware development environment.

Main features

Provides a common operating system foundation for developing IoT devices to address the fragmentation of embedded designs. Supports all important open standards for connectivity and device management to enable future-proof designs. Enables secure and scalable edge devices to support added processing power and functionality. Addresses complex energy consumption issues through automated power management.

Key features

Fast development, powerful and secure, designed for mass production, can be developed offline or edited on the web.

6、RTX

RTX is an embedded real-time operating system from ARM, written in standard C architecture and compiled using the RealView compiler. It is not only a real-time kernel but also has rich middle layer components, which are not only free but also the code is open.

Main functions

Starting and stopping tasks (processes), supporting process communication, such as synchronising tasks, managing shared resources (peripherals or memory), and passing messages between tasks. Developers can use basic functions to open real-time runners, start and end tasks, and pass control between tasks (rotational scheduling). Developers can assign task priorities.

Main features

Support for time-slice, preemptive and cooperative scheduling. An unrestricted number of tasks, each with a priority of 254. An unlimited number of mutually exclusive semaphores, message mailboxes and soft timers. Support for multi-threading and thread-safe operation. MDK configuration can be easily done using MDK's dialogue-based configuration wizard.

7、VxWorks

WindRiver, a U.S. company designed and developed in 1983, is an embedded real-time operating system (RTOS) with hard real-time, deterministic and stable, but also has the scalability and security required by aviation and defence, industrial, medical, automotive, consumer electronics, networking and other industries.

Key Features

Support for predictable task synchronization mechanisms, inter-multitask communication, memory optimization management, and OS (interrupt latency, task switching, driver latency, etc.) behaviour is known and predictable. Real-time clock service + interrupt management service.

Main features

Has a high-performance operating system kernel Wind (good real-time, reducible) friendly development and debugging environment, better compatibility, support for a variety of development and operating environments

8、QNX

Born in 1980, it is a commercial Unix-like embedded RTOS that complies with the POSIX specification.

Key features

Supports scheduling and execution of multiple tasks on the same computer; also allows multiple users to share a single computer. These users can submit tasks to the system and interact with QNX through multiple terminals.

Key features

The core provides only four services: process scheduling, inter-process communication, underlying network communication, and interrupt handling, with its processes running in a separate address space. All other OS services are implemented as collaborative user processes, making the QNX core very small (QNX4.x is about 12Kb) and very fast.

9. NuttX

NuttX is a real-time embedded operating system (Embedded RTOS), the first version released by Gregory Nutt in 2007 under a liberal BSD license.

Key features

It can be built as an open, flat embedded RTOS or separately as a microkernel with a system call interface. Easily extensible to new processor architectures, SoC architectures, or board-level architectures. Real-time, deterministic, priority inheritance supports the BSD socket interface. Priority management extensions Optional tasks (processes) with address environment.

Main features

Flexible configuration and modular design, with the core consisting of small homogeneous components, including the kernel, C library and underlying runtime packages. Each component can provide many configuration options (real-time kernel is also available as an optional configuration), which can be easily configured using the configuration tools provided by eCos, and different configurations make eCos able to meet the requirements of different embedded applications.

10、DJYOS

Unlike traditional operating systems, djyos does not use threads but events as the core of scheduling. This scheduling algorithm enables programmers to get rid of the way of thinking of writing programs that simulate the execution process of computers, but to write applications in the way of the human cognitive world, just like the introduction of VC in embedded programming.

The scheduling algorithm of days allows programmers to eliminate threads and processes. djyos has no API about threads, and a programmer with no knowledge of threads can write applications under DJYOS without any problem.

The DJYOS operating system is event-centric scheduling, and this scheduling strategy allows programmers to program as humans are used to perceiving things rather than as computers are used to.

11、Alios Things

According to the famous media-embedded operating system RTOS, AliOS Things is a highly scalable IoT operating system for the IoT domain under the AliOS family. aliOS Things will be dedicated to building cloud-integrated IoT infrastructure with key capabilities such as ultimate performance, minimal development, cloud-integrated, rich components, security protection, and support AliOS Things can be widely used in smart homes, smart city, the new travel and other fields.

12、Huawei LiteOS

Huawei LiteOS is a lightweight IoT operating system built by Huawei for the IoT field. It provides developers with a "one-stop" complete software platform with key capabilities such as low power consumption, fast startup, interoperability, and security, effectively reducing the development threshold and shortening the development cycle.

13、RT-Thread

RT-Thread is a real-time operating system (RTOS) kernel, middleware components and developer community in one technology platform, led by Mr Xiong Puxiang and gathered the strength of the open source community; RT-Thread is also a complete rich component, highly scalable, easy to develop, ultra-low power consumption, high security of the Internet of Things operating system.

RT-Thread has all the key components needed for an IoT OS platform, such as GUI, network protocol stack, secure transmission, and low-power components. After 11 years of cumulative development, RT-Thread already has one of the largest embedded open source communities in China and is widely used in many industries, such as energy, automotive, medical, and consumer electronics, with a cumulative installed base of over 20 million units.