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Four Embedded Operating Systems

Embedded operating systems play a vital role in today's technology field, providing key software support for various embedded systems and devices. Selecting the right embedded operating system for a specific application is a critical task in a wide variety of markets. In this article, we will compare several representative embedded operating systems, VxWorks, Windows CE, Embedded Linux and µC/OS-Ⅱ, to help readers better understand their characteristics, advantages and applicable scenarios.

VxWorks

The VxWorks operating system is an embedded real-time operating system (RTOS) designed and developed by WindRiver Corporation of the United States in 1983. It is a key component of the Tornado embedded development environment. Good sustainable development ability, high-performance kernel and friendly user development environment gradually occupy a place in the field of embedded real-time operating system. VxWorks has a tailorable microkernel structure; efficient task management; flexible inter-task communication; microsecond-level interrupt processing; supports POSIX 1003.1b real-time extension standards; supports multiple physical media and standard, complete TCP/IP networks agreement etc.

However, it is expensive. Since the operating system itself and the development environment are proprietary, the price is generally relatively high. It usually takes more than 100,000 RMB to build a usable development environment, and an additional royalty is generally charged for each application. Generally, the source code is not available, only the binary code is provided. Since they are all dedicated operating systems, specialized technicians are required to master development techniques and maintenance, so the cost of software development and maintenance is very high. The amount of supported hardware is limited.

Windows CE

Windows CE has good compatibility with Windows series, which is undoubtedly a major advantage of Windows CE promotion. Among them, WinCE3.0 is a modular real-time embedded operating system for small-capacity, mobile, intelligent, 32-bit, and understanding devices. Provides a feature-rich operating system platform for building dynamic applications and services for handheld devices, wireless devices, it can run on a variety of processor architectures, and is generally suitable for those with limited memory footprint equipment. It is a multi-threaded, full-priority, multi-tasking operating system designed as a whole for limited-resource platforms. Its modular design allows it to be customized for consumer electronics ranging from PDAs to specialized industrial controllers. The basic kernel of the operating system requires at least 200KB of ROM. Due to the stricter requirements on the size and cost of embedded products, the space occupied by the processor part should be as small as possible. The amount of available memory and external memory of the system is also limited, and the embedded operating system runs in limited memory (usually in ROM or flash memory), so higher requirements are put forward for the scale and efficiency of the operating system. Require. From a technical point of view, Windows CE has many defects as an embedded operating system: there is no open source code, which makes it difficult for application developers to realize product customization; the performance in terms of efficiency and power consumption is not outstanding, and it is the same as Windows. Excessive system memory is used, and the application program is huge; copyright licensing fees are also factors that manufacturers have to consider.

Embedded Linux

This is a new member of the embedded operating system. Its biggest feature is that the source code is open and follows the GPL agreement. It has become a research hotspot in the past year. According to IDG, embedded Linux will account for the embedded operating system in the next two years. 50% of the share.

Since its source code is open, people can modify it arbitrarily to meet their own applications, and it is easy to check for errors. Comply with GPL, no need to pay license fee for each application. There are a large number of application software available. Most of them are GPL compliant, open source and free. Can be slightly modified and applied to the user's own system. There are a large number of free and excellent development tools, and they all comply with the GPL and are open source. There is a huge developer community. No special talents are needed, as long as you know Unix/Linux and C language. With the popularity of Linux in China, there are more and more such talents. So software development and maintenance costs are low. Excellent network function, which is especially important in the Internet era. Stability - this is a great advantage of Linux itself. The core is powerful and requires less resources to run, which is very suitable for embedded applications.

The number of supported hardware is huge. There is no essential difference between embedded Linux and ordinary Linux, and almost all hardware embedded Linux used on PCs supports it. Moreover, the driver program source codes of various hardware can be obtained, which brings great convenience for users to write their own proprietary hardware driver programs.

One disadvantage of running Linux on an embedded system is that the real-time performance of the Linux architecture requires the addition of real-time software modules. The kernel space where these modules run is the part of the operating system that implements scheduling policies, hardware interrupt exceptions, and program execution. Since these real-time software modules run in the kernel space, code errors may destroy the operating system and affect the reliability of the entire system, which will be a very serious weakness for real-time applications.

µC/OS-II

µC/OS-II is a well-known real-time kernel whose source code is open. It is specially designed for embedded applications and can be used for 8-bit, 16-bit and 32-bit microcontrollers or digital signal processors (DSP). It has been greatly improved and upgraded on the basis of the original version of µC/OS, and has been used for nearly ten years, and there are many examples of successful application of this real-time kernel. Its main features are as follows:

1. The open source code makes it easy to port the operating system to various hardware platforms.

2. Portability, most of the source code is written in C language, easy to port to other microprocessors.

3. Can be cured.

4. Tailorability, selective use of required system services to reduce storage space required for buckets.

5. Preemptive, completely preemptive real-time kernel, that is, always run the highest priority task under the ready condition.

6. Multi-tasking, can manage 64 tasks, the priority of tasks must be different, does not support time slice round-robin scheduling method.

7. Deterministic, the execution time of function calls and services is deterministic and does not depend on the number of tasks.

8. Practicability and reliability, the successful application of the real-time kernel instance is the best evidence of its practicality and reliability.

Since µC/OS-II is only a real-time kernel, it means that unlike other real-time systems, what it provides to users is only some API function interfaces, and there are still a lot of work to be done by users themselves.

To sum up, VxWorks, Windows CE, embedded Linux and µC/OS-II are all representative embedded operating systems, which play an important role in different application fields and specific requirements. By comparing these operating systems, we can see their respective advantages and applicable scenarios.

VxWorks performs well in embedded applications with high reliability and real-time requirements, and provides reliable solutions for aerospace, medical equipment, and industrial automation. Windows CE focuses on providing a user experience and development environment similar to the desktop Windows operating system, and is suitable for embedded systems that require graphical interfaces and multimedia functions. Embedded Linux has become the preferred operating system for many embedded devices with its flexibility, customizability and extensive hardware support. However, µC/OS-II is suitable for applications that require high system resources and real-time performance, providing efficient task scheduling and memory management mechanisms.

When selecting an embedded operating system suitable for a specific application, it is necessary to comprehensively consider the project's functional requirements, resource constraints, development team experience, and industry-specific standards and requirements. Additionally, development tools, supported hardware platforms, and community support also factor into the decision-making process.

With the rapid development of embedded systems and the Internet of Things, the choice of embedded operating system becomes more and more important. With an in-depth knowledge of different embedded operating systems, we can provide the basis and support for a successful project implementation. Whether you are pursuing high reliability and real-time performance, or focusing on user experience and multimedia functions, you can find a suitable embedded operating system.

It is hoped that the comparison and overview provided in this article can help readers better understand the characteristics and applicable scenarios of embedded operating systems such as VxWorks, Windows CE, embedded Linux, and µC/OS-II. When selecting an embedded operating system, readers are advised to further research and evaluate the documentation, case studies, and user communities for a particular operating system to ensure that the final selection meets project needs and provides a solid solution.

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