四、几种代表性嵌入式操作系统比较
（一）VxWorks
VxWorks操作系统是美国WindRiver公司于1983年设计开发的一种嵌入式实时操作系统（RTOS），是Tornado嵌入式开发环境的关键组成部分。良好的持续发展能力、高性能的内核以及友好的用户开发环境，在嵌人式实时操作系统领域逐渐占据一席之地。VxWorks具有可裁剪微内核结构；高效的任务管理；灵活的任务间通讯；微秒级的中断处理；支持POSIX 1003．1b实时扩展标准；支持多种物理介质及标准的、完整的TCP/IP网络协议等。
然而其价格昂贵。由于操作系统本身以及开发环境都是专有的，价格一般都比较高，通常需花费10万元人民币以上才能建起一个可用的开发环境，对每一个应用一般还要另外收取版税。一般不通供源代码，只提供二进制代码。由于它们都是专用操作系统，需要专门的技术人员掌握开发技术和维护，所以软件的开发和维护成本都非常高。支持的硬件数量有限。
（二）Windows CE
Windows CE与Windows系列有较好的兼容性，无疑是Windows CE推广的一大优势。其中WinCE3.0是一种针对小容量、移动式、智能化、32位、了解设备的模块化实时嵌人式操作系统。为建立针对掌上设备、无线设备的动态应用程序和服务提供了一种功能丰富的操作系统平台，它能在多种处理器体系结构上运行，并且通常适用于那些对内存占用空间具有一定限制的设备。它是从整体上为有限资源的平台设计的多线程、完整优先权、多任务的操作系统。它的模块化设计允许它对从掌上电脑到专用的工业控制器的用户电子设备进行定制。操作系统的基本内核需要至少200KB的ROM。由于嵌入式产品的体积、成本等方面有较严格的要求，所以处理器部分占用空间应尽可能的小。系统的可用内存和外存数量也要受限制，而嵌入式操作系统就运行在有限的内存（一般在ROM或快闪存储器）中，因此就对操作系统的规模、效率等提出了较高的要求。从技术角度上讲，Windows CE作为嵌入式操作系统有很多的缺陷：没有开放源代码，使应用开发人员很难实现产品的定制；在效率、功耗方面的表现并不出色，而且和Windows一样占用过的系统内存，运用程序庞大；版权许可费也是厂商不得不考虑的因素。
（三）嵌入式Linux
这是嵌入式操作系统的一个新成员，其最大的特点是源代码公开并且遵循GPL协议，在近一年多以来成为研究热点，据IDG预测嵌入式Linux将占未来两年的嵌入式操作系统份额的50%。
由于其源代码公开，人们可以任意修改，以满足自己的应用，并且查错也很容易。遵从GPL，无须为每例应用交纳许可证费。有大量的应用软件可用。其中大部分都遵从GPL，是开放源代码和免费的。可以稍加修改后应用于用户自己的系统。 有大量的免费的优秀的开发工具，且都遵从GPL，是开放源代码的。有庞大的开发人员群体。无需专门的人才，只要懂Unix/Linux和C语言即可。随着Linux在中国的普及，这类人才越来越多。所以软件的开发和维护成本很低。优秀的网络功能，这在Internet时代尤其重要。稳定——这是Linux本身具备的一个很大优点。内核精悍，运行所需资源少，十分适合嵌入式应用。
支持的硬件数量庞大。嵌入式Linux和普通Linux并无本质区别，PC上用到的硬件嵌入式Linux几乎都支持。而且各种硬件的驱动程序源代码都可以得到，为用户编写自己专有硬件的驱动程序带来很大方便。
在嵌入式系统上运行Linux的一个缺点是Linux体系提供实时性能需要添加实时软件模块。而这些模块运行的内核空间正是操作系统实现调度策略、硬件中断异常和执行程序的部分。由于这些实时软件模块是在内核空间运行的，因此代码错误可能会破坏操作系统从而影响整个系统的可靠性，这对于实时应用将是一个非常严重的弱点。
(1) VxWorks
WindRiver VxWorks operating system companies in the United States in 1983 the design and development of an embedded real-time operating systems (RTOS), Tornado embedded development is a key component of the environment. Good sustainable development capacity, high-performance core and user-friendly development environment, in the embedded real-time operating system fields occupy a place gradually. VxWorks can be cut with micro-kernel structure; efficient task management; flexible mandate communication; microsecond interrupt handling; support POSIX 1003.1b real-time extensions to support multiple physical media and standards, and complete TCP / IP network protocols.
But its high price. The operating system itself is proprietary, as well as the development environment, a higher than normal price, and typically costs more than 100,000 yuan to set up a development environment available for general application to every other charge royalties. General unreasonable for the source code, binary code only. Because they are dedicated operating system, the need for specialized technical staff in the development of technology and maintenance, software development and maintenance costs are very high. A limited number of hardware support.
(B) Windows CE
Windows CE and Windows series better compatibility, Windows CE is a big advantage of the promotion. WinCE3.0 which is a capacity for small, mobile, intelligent, 32, understand the modular equipment for real-time embedded operating system. For the establishment for handheld devices, wireless devices dynamic applications and services provides a feature-rich operating system platforms, it can in a variety of processor architecture on the run, and usually applies to those who have some memory space restrictions equipment. It is from the limited resources for the overall design of the platform's multi-threading, complete priority, multi-task operating system. Its modular design allows it to the Pocket PC controller for industrial users customized electronic equipment. The basic core operating system needs at least 200 KB of ROM. As the volume of embedded products, the costs have more stringent requirements, processor space should be part of the small as possible. System Disk and the number of available memory to the limit, and embedded operating system running on the limited memory (usually in the ROM or flash memory), and therefore on the size of the operating system, and put forward a high efficiency requirements . From a technical standpoint, as an embedded operating system Windows CE has a lot of shortcomings: no open-source code, application developers to be very difficult to achieve product customization; efficiency, power consumption performance is not outstanding, and in Windows Like the occupation of the system memory, using procedures huge; copyright licensing fees to companies is taken into account.
(3) Embedded Linux
This is the embedded operating system a new member of its greatest feature of the source code is open and follow the GPL agreement, in the past year or so become a hotspot, according to IDG forecasts Embedded Linux will account for the next two years embedded operating system share of 50 per cent.
Because of its open source code, it can be modified to meet their applications, and Chaxi also very easy. Comply with the GPL, the need for the application of each pay permit fees. A large number of applications available. Most of them follow the GPL, the open source and free of charge. Little can be modified for the user's own system. A large number of outstanding free development tools, and follow the GPL is the open-source. A large group of developers. Without specialized personnel, as long as understood Unix / Linux and C language can be. With the popularity of Linux in China, more and more such talents. Therefore, software development and maintenance costs low. Excellent networking capabilities, which is particularly important in the Internet era. Stability - this is Linux itself have a great advantage. Jinghan core operation for less resources, and is very suitable for embedded applications.
The large number of hardware support. Embedded Linux, and there is no essential difference between ordinary Linux, PC hardware used on virtually all embedded Linux support. Various hardware and driver source code can be for users to prepare their own proprietary hardware drivers have a great convenience.
In the embedded Linux operating system is a shortcoming of the Linux system to provide real-time performance need to add real-time software modules. These modules run the operating system kernel space is the realization of scheduling strategy, the hardware interrupt abnormal and part of the implementation process. As a result of these real-time software module is the core of the operating room, coding errors could undermine the entire operating system thereby affecting the reliability of the system, which will be for real-time applications is a very serious weakness.
好多啊,累人,下次记得悬赏多点.
