基于嵌入式应用的Linux内核实时性改进研究

针对Linux内核存在的实时性问题,从实时操作系统的5个性能指标出发,分析了2.6内核实时性能的根本性制约因素为调度延迟和中断延迟。为了解决上述问题,设计并实现了新的任务模型和新的中断处理操作。着重介绍了新任务模型中的硬实时任务调度算法(优先级位图算法)以及新体系中断响应和中断处理操作流程,给出了关键代码,并进行了试验调试。经realfeel测试结果表明,新体系中实时任务的响应速度显著提高,达到了预期的研究目的。     

Real-time interrupt handling in Ada

The Ada? programming language defines the semantics of interrupt handling as part of the tasking mechanism, making it possible to construct implementation-independent interrupt handlers. However, for the Ada mechanism to be effective, an implementation must provide support not specified by the Ada standard, such as for initializing hardware interrupting devices, handling unexpected interrupts and optimizing for real-time performance constraints. This paper analyses some of the constraints that efficient interrupt support places on an implementation. It develops a model for the interaction between interrupt hardware and Ada tasks and describes optimizations for Ada interrupt handlers. Implementation issues, including task priorities and task termination for interrupt handlers, are discussed in detail.     

一种基于非抢占RM算法的可行性判决算法及应用

为中断服务例程建立了任务模型，在该模型的基础上给出了中断服务例程集使用非抢占RM调度的可行性的充分必要条件，并且基于该条件提出了一种新的非抢占RM算法的可行性判决算法。进一步地，给出了如何改进不可调度例程集的方法，并且将该方法应用到一个具体工程项目中，取得较好的效果。     

嵌入式微处理器NCS保护方式的异常与中断研究

保护方式下的异常与中断管理是微处理器设计的重要组成部分,文中探讨了异常与中断的数据结构、定义,表,给出了保护方式下的异常与中断管理算法;提出了异常／中断管理单元（ＥＩＭＵ）的细胞群结构,并指出细胞是异常／中断管理单元的基本测试单位;系统评价了任务门,中断门／陷阱门区别及优特点;最后用ＥＤＡ工具ＭＥＮＴＯＲ ＧＲＡＰＨＩＣＳ对异常与中断管理单元及其算法的ＲＴＬ级ＶＨＤＬ描述进行综合与仿真,验证了其正     

中断驱动控制系统的有界模型检验技术

针对一类中断驱动的航天控制系统,给出了有界模型检验的算法.这类系统由中断处理程序和操作系统调度的任务组成.当中断发生时,对应的中断处理程序响应中断事件,并可以修改控制变量值,以便在系统任务中完成后续工作.操作系统周期性地调度任务序列处理日常事务以及中断事件的后续工作.使用了带中断标记的时间自动机对中断事件和任务调度事件进行建模,并使用中断向量表和中断处理程序的伪代码模型共同描述中断的处理过程.控制变量将中断处理过程和系统任务相关联,中断处理程序可以设定某个控制变量,而系统任务则通过检查该控制变量来确定是否需要进行后续处理.对于这样的形式化模型,给出了检验关键时序性质的有界模型检验算法.该算法使用深度优先的方式遍历所有长度小于等于K的可行路径,并使用SMT Z3实现了对时间约束和规约的处理.     

嵌入式实时操作系统分析

实时多任务操作系统（RTOS）是嵌入式应用软件的基础和开发平台。在从功能、性能模型等角度对实时操作系统进行分析的基础上,描述了抢占式任务调度和中断禁止时间与中断延迟事件的实现。对Linux的系统调用功能的分析,是研究Linux内核源码几个很好的入口点之一。     

基于Lebesgue采样的动态反馈实时调度模型

提出一种基于Lebesgue采样方法和弹性调度算法的动态反馈实时调度模型。通过调整实时任务的执行速率,使软实时系统的系统负载始终保持在参考值以下。利用硬件看门狗技术在系统过载时产生中断,实现基于事件的Lebesgue采样。在实时操作系统RTAI中实现该调度模型,并对模型的暂态性能和稳态性能进行分析验证。实验结果表明,该模型不仅保持了系统的稳定性,还能显著降低调度算法的系统开销。     

SR-IOV密码设备中断传输过程建模

SR-IOV密码设备在虚拟化环境下执行运算时会产生大量I/O中断，导致CPU在Root模式与Non-Root模式之间频繁切换，带来巨大的系统性能开销，影响SR-IOV密码设备的运算性能。针对该问题，对SR-IOV密码设备I/O中断进行建模分析，根据密码任务先到先服务的规则构建了M/M/1排队模型，分析了影响系统性能的关键因素，并通过仿真和实验测试验证了模型的有效性，最后对系统性能进行了测试与分析。结果表明，该模型能够定量分析中断频率对中断响应时间和系统队长的影响。     

Recovering from interruptions: implications for driver distraction research

This research adopted a model of goal activation to study the mechanisms underlying interrupted task performance. The effects of interruption timing, type of interruption, and age on task time and primary task resumption time were explored under conditions in which attention was switched back and forth between two tasks, much as when drivers shift attention between attending to the road and to an in-vehicle task. The timing of interruptions had a significant impact on task resumption times, indicating that the most costly time to interrupt task performance is during the middle of a task. However, this effect was overshadowed by age-related performance decrements for older participants. Interruptions that prevented strategic rehearsal of goals resulted in longer resumption times as compared with interruptions that allowed rehearsal. Actual or potential applications of this research include the design of in-vehicle device user interfaces, the timing of in-vehicle messages, and current metrics for assessing driver distraction.     

Implementation and evaluation of global and partitioned scheduling in a real-time OS

In this work, we provide an experimental comparison between Global-EDF and Partitioned-EDF, considering the run-time overhead of a real-time operating system (RTOS). Recent works have confirmed that OS implementation aspects, such as the choice of scheduling data structures and interrupt handling mechanisms, impact real-time schedulability as much as scheduling theoretic aspects. However, these studies used real-time patches applied into a general-purpose OS. By measuring the run-time overhead of an RTOS designed from scratch, we show how close the schedulability ratio of task sets is to the theoretical hard real-time schedulability tests. Moreover, we show how a well-designed object-oriented RTOS allows code reuse of scheduling components (e.g., thread, scheduling criteria, and schedulers) and easy real-time scheduling extensions. We compare our RTOS to a real-time patch for Linux in terms of the task set schedulability ratio of several generated task sets. In some cases, Global-EDF considering the overhead of the RTOS is superior to Partitioned-EDF considering the overhead of the patched Linux, which clearly shows how different OSs impact hard real-time schedulers.     

基于VxWorks的多中断处理设计

考虑VxWorks的中断在具体实现上的特殊性,提出一个针对多块采集板系统的中断设计方案,把传统的中断服务程序分解为中断服务程序和中断服务任务,利用信号灯进行同步,通过在中断服务任务中引入用户定义的优先级,增强系统处理多中断时的可靠性和实时性。     

基于Xenomai的实时测控系统的研究与实现

介绍实时操作系统仿真框架Xenomai和操作系统自适应域环境Adeos(Adaptive Domain Environment for Operating System)的基本原理.分析带有中断屏蔽功能的Adeos中断管道机制,以及用户态下混合执行模式的实时任务被抢占和"优先级反转"问题.应用Xenomai的实时核构建了Xenomai/Linux双内核实时机制;通过Xenomai提供的可插式接口仿真模块实现了基于RTAI API的应用程序编程;结合IPC等具体硬件实现了一套模拟小型电站任务的实时测控系统.运行结果显示系统满足电力系统硬实时的时限要求且运行稳定.     

基于变量访问序模式的中断数据竞争检测方法

在航天嵌入式软件等中断驱动型软件中,中断数据竞争问题十分突出.然而中断在并发语义、同步机制、调度机制等方面与线程（任务）有诸多不同,具有Ad-hoc特征,难以统一刻画,因此主流的数据竞争检测方法并不适用.以航天嵌入式软件数据竞争案例库为基础进行了系统分析,提出刻画有害中断数据竞争的7种缺陷模式.针对其中最常见且最难解决的单变量访问序模式,基于抽象解释提出一种支持过程间分析、中断并发分析的高效检测方法.设计并实现了相应的检测工具SpaceDRC.实验表明,SpaceDRC能够在145毫秒内检测出约21400行程序中的真实数据竞争.SpaceDRC已经在多个航天重点型号中进行了应用,使得中断数据竞争专项分析的效率提高了至少5倍,并且降低了问题遗漏率.     

A framework for specifying and monitoring user tasks

Interrupting users engaged in tasks typically has negative effects on their task completion time, error rate, and affective state. Empirical research has shown that these negative effects can be mitigated by deferring interruptions until more opportune moments in a user’s task sequence. However, existing systems that reason about when to interrupt do not have access to models of user tasks that would allow for such finer-grained temporal reasoning. To enable this reasoning, we have developed an integrated framework for specifying and monitoring user tasks. For task specification, our framework provides a language that supports expressive specification of tasks using a concise notation. For task monitoring, our framework provides an event database and handler that manages events from any instrumented application and a task monitor that observes a user’s progress through specified tasks. We describe the design and implementation of our framework, showing how it can be used to specify and monitor practical, representative user tasks. We also report results from two user studies measuring the effectiveness of our existing implementation. The use of our framework will enable attention aware systems to consider a user’s position in a task when reasoning about when to interrupt.     

现代微处理器的中断处理技术

本文人中断的精确性，中断处理系统的实现方式，各类中断处理硬件等方面详细介绍现代微处理器中所采用的各种中断处理策略和硬件实现技术，并结合十种微处理器的中断处理实现，讨论中断处理的各个阶段中所能采用的策略与技术。     

一种嵌套中断系统的建模和分析方法

在嵌入式系统和各类操作系统中,中断机制是确保实时响应各类异步事件的重要方法.通常在处理一个中断事件的过程中,往往会有更紧迫的中断事件请求响应,因而发生中断嵌套.建模并验证嵌套中断系统是一个具有挑战性的工作.本文提出一种建模和验证嵌套中断系统的方法.首先,为中断系统提出了基于投影时序逻辑的定义,并将这种定义推广到包含任意多中断事件的中断系统上,从而得出嵌套中断系统基于投影时序逻辑的形式化模型.其次,使用投影时序逻辑定义的基本中断语句扩充建模仿真和验证语言（MSVL）并扩展MSVL语言的解释器使其可以对嵌套中断系统进行建模仿真和验证.最后通过一个实例展现本文所提出的方法的正确性和实用性.     

Deadline analysis of interrupt-driven software

Real-time, reactive, and embedded systems are increasingly used throughout society (e.g., flight control, railway signaling, vehicle management, medical devices, and many others). For real-time, interrupt-driven software, timely interrupt handling is part of correctness. It is vital for software verification in such systems to check that all specified deadlines for interrupt handling are met. Such verification is a daunting task because of the large number of different possible interrupt arrival scenarios. For example, for a Z86-based microcontroller, there can be up to six interrupt sources and each interrupt can arrive during any clock cycle. Verification of such systems has traditionally relied upon lengthy and tedious testing; even under the best of circumstances, testing is likely to cover only a fraction of the state space in interrupt-driven systems. This paper presents the Zilog architecture resource bounding infrastructure (ZARBI), a tool for deadline analysis of interrupt-driven Z86-based software. The main idea is to use static analysis to significantly decrease the required testing effort by automatically identifying and isolating the segments of code that need the most testing. Our tool combines multiresolution static analysis and testing oracles in such a way that only the oracles need to be verified by testing. Each oracle specifies the worst-case execution time from one program point to another, which is then used by the static analysis to improve precision. For six commercial microcontroller systems, our experiments show that a moderate number of testing oracles are sufficient to do precise deadline analysis.     

医疗外科机器人中面向任务对象的程序设计

本文介绍了一种用于实时控制系统的面向任务对象的程序设计方法。     

数据驱动的多星任务网络预测调度算法

多星任务调度是具有NP-hard特性的优化问题,随着卫星资源规模和任务需求规模的双重增长,传统调度方法求解效率不高.在轨卫星在常年运行过程中积累了丰富的调度数据.针对大规模多星任务调度场景,建立多星多波束任务调度模型,并提出数据驱动的多星任务网络预测调度算法对其求解.以分割的思想,实现多星场景下任务可调度性预测.从历史调度数据中,提取设定的3个静态特征和5个动态特征,构建并训练预测网络,预测任务被不同卫星完成的概率,并以冲突避免、负载均衡等为原则,得到初始任务和资源卫星的分配方案.进一步设计双链结构的进化算法,以双链编码形式表征上述关系,配合设计的交叉、修复等进化算子,优化初始方案中的任务序列与资源分配关系,输出最终任务调度方案.仿真结果表明,与改进蚁群算法、混合遗传算法和数据驱动并行调度算法相比,所提出算法在运行时间、方案收益和卫星负载均衡3方面均有较好的表现.     

Exploring the effects of trust,task interdependence and virtualness on knowledge sharing in teams

The sharing of knowledge within teams is critical to team functioning. However, working with team members who are in different locations (i.e. in virtual teams) may introduce communication challenges and reduce opportunities for rich interactions, potentially affecting knowledge sharing and its outcomes. Therefore, using questionnaire‐based data, this study examined the potential effects of different aspects of virtuality on a knowledge‐sharing model. Social exchange theory was used to develop a model relating trust to knowledge sharing and knowledge sharing to team effectiveness. The moderating effects of virtuality and task interdependence on these relationships were examined. A strong positive relationship was found between trust and knowledge sharing for all types of teams (local, hybrid and distributed), but the relationship was stronger when task interdependence was low, supporting the position that trust is more critical in weak structural situations. Knowledge sharing was positively associated with team effectiveness outcomes; however, this relationship was moderated by team imbalance and hybrid structures, such that the relationship between sharing and effectiveness was weaker. Organizations should therefore avoid creating unbalanced or hybrid virtual teams.