ITR: Advanced Programming Languages for Embedded Systems

Mark P.Jones和Richard B.KieburtzCCR-0205737《用于嵌入式系统的高级编程语言》在过去的几十年里，我们见证了计算机使用和编程方式的显著变化。例如，今天使用的许多计算机都隐藏在嵌入式系统中。从日常家用电器--如洗衣机和电视--到安全和安保关键系统--如车辆导航和控制、国防应用程序或医疗设备--嵌入式计算机的使用使制造商能够构建比以往任何时候都更具灵活性、功能性和复杂性的系统。与此同时，新的编程语言已经开发出来，具有提高开发人员生产力的功能，并允许构建更可靠和灵活的系统。例如，模块系统有助于管理大型项目的复杂性，类型系统可用于在编译时检测错误，自动存储管理技术消除了常见的错误来源。然而，在工业中，今天正在开发的许多嵌入式软件仍然使用较旧的语言或较低级别的汇编语言编写，没有现代语言所能提供的好处。问题是，最近编程语言研究的结果和重点并不能很好地与嵌入式系统开发的挑战和背景相匹配。因此，一些人可能会期望嵌入式系统开发人员接受现代编程语言，但似乎许多人选择了忽略它们！问题的一个来源是难以捕获行为的所谓非功能方面-例如执行时间、功耗和适应性--这些都是许多嵌入式系统的关键要求。不幸的是，这些正是语言设计者为了提高生产率和可移植性而抽象出来的东西。其他困难是对诸如并发和事件处理等特性的复杂处理的结果，这些特性在许多嵌入式应用程序中再次扮演核心角色。如果程序员在使用这些功能时不遵守精心制定的编码规则，则可能会出现严重的错误，但底层类型系统或语义几乎无法帮助检测这些问题。该项目致力于弥合这两个重要领域之间的差距，并演示嵌入式系统开发如何从编程语言研究中受益并为其提供信息。特别是，该项目正在关注一种称为Timber的高级语言的持续开发和使用，该语言支持并发、异步通信和非阻塞、反应式编程的隐含概念。所有这些功能都与嵌入式系统设计环境直接相关。此外，该项目正在开发新的分析和编译技术，允许使用高级约束和策略指定行为的非功能方面，以实现优雅的降级。因为它们是在高级别指定的，所以这些约束可以继续作为对所需行为的有意义的描述，即使程序为了适应新功能或支持新平台而发展。成功的关键是一种说明性的方法，在这种方法中，程序员专注于需要什么，而编译器则确定应该如何实现它，使用分析结果来指导选择适当的低级实现策略。考虑到从研究到工业的过渡，该项目将重点放在PC/104系统的工具上，这是行业标准，也是当今嵌入式系统市场的重要部分。从长远来看，该项目正在推动态度的转变和编程语言技术在交付更广泛、更灵活、更可靠和更安全的嵌入式系统方面所发挥的作用的有益变化。

Mark P. Jones and Richard B. KieburtzCCR-0205737"Advanced Programming Languages for Embedded Systems"Over the last few decades we have witnessed remarkable changes in the way that computers are both used and programmed. For example, many of the computers in use today are hidden in embedded systems. From everyday appliances---such as washing machines and televisions---to safety and security critical systems---such as vehicle navigation and control, defense applications, or medical devices---the use of embedded computers allows manufacturers to build systems with much greater flexibility,functionality, and sophistication than has ever been possible before.During the same time, new programming languages have been developed with features that increase developer productivity and allow the construction of produce more reliable and flexible systems. For example, module systems help to manage the complexity of large projects, type systems can be used to detect bugs at compile-time, and automatic storage management techniques eliminate a common source of errors.In industry, however, much of the embedded software that is being developed today is still written using older languages, or lower-level assembly languages, without the benefits that modern languages can provide. The problem is that the results and focus of recent programming language research have not been a good match for the challenges and context of embedded systems development. As a result, where some might have expected embedded systems developers to embrace modern programming languages, it might seem instead that many have chosen to ignore them!One source of problems arises from difficulties in capturing so-called non-functional aspects of behavior---such as execution time, power consumption, and adaptivity---that are critical requirements for many embedded systems. Unfortunately, these are exactly the kinds of things that language designers have abstracted away from in the hope of increasing productivity and portability. Other difficulties occur as the result of complicated treatments of features such as concurrency and event handling, which again play a central role in many embedded applications. Significant bugs can occur if programmers do not adhere to a carefully worked out discipline of coding when they use such features, but there is very little that the underlying type system or semantics can do to help in detecting these problems.This project is working to bridge the gap between these two important fields, and to demonstrate how embedded systems development can benefit from and inform programming language research. In particular, the project is focusing on the ongoing development and use of a high-level language called Timber that supports an implicit notion of concurrency, asynchronous communication, and non-blocking, reactive programming. All of these features are directly relevant in the context of embedded systems design. In addition, the project is developing new analysis and compilation techniques that enable non-functional aspects of behavior to be specified using high-level constraints and policies for graceful degradation. Because they are specified at a high level, these constraints can continue to serve as meaningful descriptions of requiredbehavior, even as programs evolve to accommodate new functionality or to support new platforms. The key to success is a declarative approach in which programmers focus on what is required, while compilers determine how it should be accomplished, using the results of analysis to guide the selection of an appropriate, low-level implementation strategy.With the transition from research to industry in mind, the project is focusing on tools for PC/104 systems, which is an industry standard and an important sector in today's embedded systems market. In the longer term, the project is contributing to shifts in attitude and beneficial changes in the role that programming language technology can plays in the delivery of more widespread, more flexible, more reliable, and more secure embedded systems.