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Growth in the number of transistors per die of an integrated circuit has provided impetus to the development of system-on-chip microprocessors (SoCs). They are becoming ubiquitous and appear in home appliances, cell phones, tablet, laptop, and desk-top computers, and lately even as building blocks in high-end computer systems. As the semiconductor manufacturing technology progresses in concert with Moore’s law, SoCs clearly represent the trend of the future of microprocessor design. SoCs vary widely in composition, complexity and sophistication depending on the computing applications for which they are intended: some are simple single-processor systems, while others range from a few to a few tens of processor cores and contain other hardware functional blocks, storage elements, memory controllers and interfaces to external high-speed interconnections such as PCI Express, SRIO, and others. In any such SoC, the on-chip interconnections play a central role in its operation and contribute vitally to the performance of the applications running in it. This chapter explores the choices of interconnections that may be employed and discusses the criteria for their selection. The chapter illustrates the interconnection selection process by describing an example SoC and examining the interconnections it contains.
Synchronization is the key mechanism used within software applications to safely and efficiently leverage today’s multicore hardware architectures. This chapter aims to build your expertise and knowledge in software synchronization, from the needs behind synchronization to the possible solutions to implement synchronization. The target reader of this chapter is the embedded multicore software developer, along with the tester, project manager, and customer, in order to educate the entire software development team about the technology and the issues. Problems that occur when synchronization is not used, or when it is used badly, are considered. An in-depth look at how to achieve synchronization and also specific conditions that require synchronization are the primary focus of this chapter. Specific synchronization support for different languages, along with design patterns useful for architecting of a synchronized system, are discussed. The chapter wraps up looking at side-effects (good and bad) and problems encountered when writing synchronization code, as well as hardware and operating system effects on synchronization.
Unlike general-purpose computing systems, multicore embedded systems are designed with a specific application in mind. The memory access patterns for the application can be used to customize the memory architecture of the device. This chapter presents a synopsis of memory types and architecture commonly used in multicore embedded systems. It examines the many trade-offs that can be considered when designing the memory architecture. It considers factors such as whether the memory should be shared or distributed among the multiple cores; will the cores benefit from memory cache and what should the cache configuration be; is there a cache coherency protocol used; should there be other memory types on the device such as scratch pad SRAMs and eDRAMs; does the device use a DMA for memory transfers, and other factors. It provides guidance to the embedded system designers to tailor the memory architecture to their needs.
Synchronization hardware is a fundamental requirement for concurrent software. Ultimately, software depends upon strong guarantees for atomicity, which can only be provided by hardware. Fortunately, hardware can provide a simple but powerful programming interface to higher-level software using only a few synchronization primitives. These few primitives can support a surprisingly broad range of capabilities in software. Yet, even with hardware support to ensure functional correctness, there is an unavoidable performance overhead to pay for synchronization. In recent years, hardware designed to replace precise locking with speculative lock avoidance (e.g., lock-free programming) has begun to emerge. This chapter provides an in-depth look at the lowest level hardware/software interface for synchronization, along with explanations of how the underlying hardware ensures atomicity, and considerations related to weakly consistent memory models. This is complemented with a discussion of various lock avoidance techniques.
This chapter discusses the potential of and role of system virtualization in meeting the flexibility, scalability, portability, and robustness demands of next-generation multicore embedded systems. Common architectural approaches to hypervisors are compared, including a strong focus on effective sharing and management of I/O peripherals across virtual machines. The chapter also describes and contrasts the virtualization hardware assistance features available in common multicore processors. Finally, emerging applications and use cases enabled by system virtualization are provided.
This chapter discusses communication and synchronization libraries which can be used to implement parallelism in your embedded application. Details will be shared on several common libaries including Windows Threads, POSIX Threads, Threading Building Blocks, OpenMP, and MCAPI.
As in any complex architecture, debug and instrumentation resources are critical for multicore design. Debug instrumentation provides information for post-silicon debug analysis, software optimization, and performance monitoring. In this chapter, we introduce debug concepts useful for multicore; we deconstruct and discuss different debug instrumentation blocks and interfaces, including typical operations and system integration; and we discuss differences, considerations, and approaches more appropriate to multicore debug. This is followed by multicore debug examples, some of which are based on open standards and some on commercially-available blocks from processor IP providers.
Efficient software development requires adequate toolsets to assist the developer in analyzing and optimizing a software application’s performance. With the relatively recent advent of multicore embedded hardware platforms, toolsets for supporting multicore development have appeared, although, in some cases, capabilities may be missing or immature, leaving software developers to manually massage outputs from one tool into inputs for the next tool or struggling to investigate unexpected multicore behaviors. This section reviews those multicore tools currently available for software developers as well as those that are still needed for adequate support.
Some embedded systems require so much performance that they cannot tolerate the overhead imposed by an operating system. Such systems can be built with little to no operating system services, and are often referred to as “bare-metal” systems. Because most programming techniques rely on system services, bare-metal programming requires a different way of implementing code on a multicore platform. This chapter describes where bare-metal systems are used, those aspects that differentiate them from more standard systems, and how they can be designed and programmed.