Comparing shared and distributed memory computers

There are two distinct types of MIMD (Multiple Instruction, Multiple Data) computers: the shared memory machine, e.g. Butterfly, and the distributed memory machine, e.g. Hypercubes, Transputer arrays. Typically these utilize different programming models: the shared memory machine has monitors, semaphores and fetch-and-add; whereas the distributed memory machine uses message passing. Moreover there are two popular types of operating systems: a multi-tasking, asynchronous operating system and a crystalline, loosely synchronous operating system.

In this paper I firstly describe the Butterfly, Hypercube and Transputer array MIMD computers, and review monitors, semaphores, fetch-and-add and message passing; then I explain the two types of operating systems and give examples of how they are implemented on these MIMD computers. Next I discuss the advantages and disadvantages of shared memory machines with monitors, semaphores and fetch-and-add, compared to distributed memory machines using message passing, answering questions such as “is one model ‘easier’ to program than the other?” and “which is ‘more efficient‘?”. One may think that a shared memory machine with monitors, semaphores and fetch-and-add is simpler to program and runs faster than a distributed memory machine using message passing but we shall see that this is not necessarily the case. Finally I briefly discuss which type of operating system to use and on which type of computer. This of course depends on the algorithm one wishes to compute.     

基于VxWorks的网络数据实时处理软件的设计与实现

机载实时数据处理可以大幅提高数据处理的效率。为满足机载网络化测试系统架构下的实时数据处理的需求,设计并实现了一种基于VxWorks的网络数据实时处理软件。该软件运行在多核嵌入式数据处理系统上,通过多任务并发执行的方法保证实时性。软件运行过程中利用零拷贝技术实时接收机载测试系统发送的网络包数据,然后按照自定义的文件格式存储原始数据,同时将需要处理的网络包存入数据处理缓存中,根据网络数据协议实时解析网络包数据,最后利用预留缓存的办法将处理结果写入结果文件。实践证明,该软件能快速接收并实时处理网络数据,同时将原始数据和结果数据进行存储,该方法有效提高了数据处理的效率,为飞行试验数据处理提供了新的途径。     

Generalized interface handler and multi-tasking operation in MS/DOS for PC-based SCADA system

This paper describes a generalized interface handler implemented on a PC-based SCADA system which can handle up to a total of 512 digital points and 512 analog points. It is aimed to provide a standard structure for SCADA application program to be independent from the interfacing hardware. Using the same data structure, a multi-tasking operation has also been implemented under the single-tasking operating system MS/DOS. The prototype SCADA system employing four different types of hardware interface is demonstrated.     

μC/OS-Ⅱ在嵌入式系统开发中的应用

通过对嵌入式系统软件开发中两种编程思路的分析，说明了采用实时多任务操作系统进行程序开发的优势。简略地分析了μC／OS-Ⅱ操作系统的特点．指出在嵌入式实时控制中应用该操作系统时，多任务的优先级设定是一个关键问题。最后．给出一个实例．论证了实时多任务操作系统μC／OS-Ⅱ在嵌入式系统开发中的应用。     

The role of reward and effort over time in task switching

When multitasking in a demanding environment, operators strategically switch between tasks. Two influences on this multi-task management behaviour are the perceived rewards gained from performing a task, and the perceived effort a task requires in order to be completed. Proportionally, reward over effort is ‘rate of return’, expressing that either reward or effort changing over time spent performing a task, may influence multitasking behaviour. In the current experiment, two of four tasks within a multitasking paradigm provided constant or diminishing reward and required either constant or increasing effort in their performance. For on-going tasks, decreasing reward and increasing effort required both increased the probability of a task switch. The theory contributed here supports the study of multi-task management, and task switching model development. We discuss each in the context of safety-critical applications.     

Webit四核处理器的性能分析

使用实时操作系统内核来进行多任务的管理,是目前嵌入式应用的一个趋势.面向设备的嵌入式应用由于其资源有限而受到严重的限制,单核处理器已经无法很好地满足一些实际应用.在8位AVR单片机基础上设计并实现了一个面向设备的抢占式实时多任务Webit四核处理器系统,它在总体上保留了Webit2.0内核的主要特性.webit四核处理器系统采用4个AT90S8515单片机,通过ISA总线相连,并行地处理多任务.实验结果表明其性能大大提高.     

Multi-tasking arbitration and behaviour design for human-interactive robots

Robots that interact with humans in household environments are required to handle multiple real-time tasks simultaneously, such as carrying objects, collision avoidance and conversation with human. This article presents a design framework for the control and recognition processes to meet these requirements taking into account stochastic human behaviour. The proposed design method first introduces a Petri net for synchronisation of multiple tasks. The Petri net formulation is converted to Markov decision processes and processed in an optimal control framework. Three tasks (safety confirmation, object conveyance and conversation) interact and are expressed by the Petri net. Using the proposed framework, tasks that normally tend to be designed by integrating many if–then rules can be designed in a systematic manner in a state estimation and optimisation framework from the viewpoint of the shortest time optimal control. The proposed arbitration method was verified by simulations and experiments using RI-MAN, which was developed for interactive tasks with humans.     

ARM嵌入式工控模块在电动汽车交流充电桩的应用

以ARM嵌入式工控模块T3871为硬件核心,结合嵌入式实时操作系统μC/OS-Ⅱ,完成了一种电动汽车交流充电桩的设计。通过分析交流充电桩的结构和工作过程,设计了控制系统的硬件电路。阐述了串口通信电路和CAN通信电路。介绍了在μC/OS-Ⅱ操作系统下多任务编程实现的方法,分析了多任务问消息传递实现的方式。试验测试表明,以ARM嵌入式工控模块为核心的交流充电桩具有良好的稳定性和扩展性。