15.2.1 Resource Synchronization / Real-Time Concepts for Embedded Systems / Библиотека (книги, учебники и журналы) / В помощь Веб-Мастеру

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Master the fundamental concepts of real-time embedded system programming and jumpstart your embedded projects with effective design and implementation practices. This book bridges the gap between higher abstract modeling concepts and the lower-level programming aspects of embedded systems development. You gain a solid understanding of real-time embedded systems with detailed practical examples and industry wisdom on key concepts, design processes, and the available tools and methods.

Delve into the details of real-time programming so you can develop a working knowledge of the common design patterns and program structures of real-time operating systems (RTOS). The objects and services that are a part of most RTOS kernels are described and real-time system design is explored in detail. You learn how to decompose an application into units and how to combine these units with other objects and services to create standard building blocks. A rich set of ready-to-use, embedded design “building blocks” is also supplied to accelerate your development efforts and increase your productivity.

Experienced developers new to embedded systems and engineering or computer science students will both appreciate the careful balance between theory, illustrations, and practical discussions. Hard-won insights and experiences shed new light on application development, common design problems, and solutions in the embedded space. Technical managers active in software design reviews of real-time embedded systems will find this a valuable reference to the design and implementation phases.

Qing Li is a senior architect at Wind River Systems, Inc., and the lead architect of the company’s embedded IPv6 products. Qing holds four patents pending in the embedded kernel and networking protocol design areas. His 12+ years in engineering include expertise as a principal engineer designing and developing protocol stacks and embedded applications for the telecommunications and networks arena. Qing was one of a four-member Silicon Valley startup that designed and developed proprietary algorithms and applications for embedded biometric devices in the security industry.

Caroline Yao has more than 15 years of high tech experience ranging from development, project and product management, product marketing, business development, and strategic alliances. She is co-inventor of a pending patent and recently served as the director of partner solutions for Wind River Systems, Inc.

About the Authors

Qing Li i

Книги автора: Маркетинг для государственных и общественных организаций Real-Time Concepts for Embedded Systems

/ Carolyn Yao i

Книги автора: Real-Time Concepts for Embedded Systems

Книга: Real-Time Concepts for Embedded Systems

15.2.1 Resource Synchronization

Access by multiple tasks must be synchronized to maintain the integrity of a shared resource. This process is called resource synchronization, a term closely associated with critical sections and mutual exclusions.

Mutual exclusion is a provision by which only one task at a time can access a shared resource. A critical section is the section of code from which the shared resource is accessed.

As an example, consider two tasks trying to access shared memory. One task (the sensor task) periodically receives data from a sensor and writes the data to shared memory. Meanwhile, a second task (the display task) periodically reads from shared memory and sends the data to a display. The common design pattern of using shared memory is illustrated in Figure 15.1.

Figure 15.1: Multiple tasks accessing shared memory.

Problems arise if access to the shared memory is not exclusive, and multiple tasks can simultaneously access it. For example, if the sensor task has not completed writing data to the shared memory area before the display task tries to display the data, the display would contain a mixture of data extracted at different times, leading to erroneous data interpretation.

The section of code in the sensor task that writes input data to the shared memory is a critical section of the sensor task. The section of code in the display task that reads data from the shared memory is a critical section of the display task. These two critical sections are called competing critical sections because they access the same shared resource.

A mutual exclusion algorithm ensures that one task's execution of a critical section is not interrupted by the competing critical sections of other concurrently executing tasks.

One way to synchronize access to shared resources is to use a client-server model, in which a central entity called a resource server is responsible for synchronization. Access requests are made to the resource server, which must grant permission to the requestor before the requestor can access the shared resource. The resource server determines the eligibility of the requestor based on pre-assigned rules or run-time heuristics.

While this model simplifies resource synchronization, the resource server is a bottleneck. Synchronization primitives, such as semaphores and mutexes, and other methods introduced in a later section of this chapter, allow developers to implement complex mutual exclusion algorithms. These algorithms in turn allow dynamic coordination among competing tasks without intervention from a third party.

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