Embedded System Design

A unique feature of this open access textbook is to provide a comprehensive introduction to the fundamental knowledge in embedded systems, with applications in cyber-physical systems and the Internet of things. It starts with an introduction to the field and a survey of specification models and languages for embedded and cyber-physical systems. It provides a brief overview of hardware devices used for such systems and presents the essentials of system software for embedded systems, including real-time operating systems. The author also discusses evaluation and validation techniques for embedded systems and provides an overview of techniques for mapping applications to execution platforms, including multi-core platforms. Embedded systems have to operate under tight constraints and, hence, the book also contains a selected set of optimization techniques, including software optimization techniques. The book closes with a brief survey on testing. This fourth edition has been updated and revised to reflect new trends and technologies, such as the importance of cyber-physical systems (CPS) and the Internet of things (IoT), the evolution of single-core processors to multi-core processors, and the increased importance of energy efficiency and thermal issues

Embedded System Design

A unique feature of this open access textbook is to provide a comprehensive introduction to the fundamental knowledge in embedded systems, with applications in cyber-physical systems and the Internet of things. It starts with an introduction to the field and a survey of specification models and languages for embedded and cyber-physical systems. It provides a brief overview of hardware devices used for such systems and presents the essentials of system software for embedded systems, including real-time operating systems. The author also discusses evaluation and validation techniques for embedded systems and provides an overview of techniques for mapping applications to execution platforms, including multi-core platforms. Embedded systems have to operate under tight constraints and, hence, the book also contains a selected set of optimization techniques, including software optimization techniques. The book closes with a brief survey on testing. This fourth edition has been updated and revised to reflect new trends and technologies, such as the importance of cyber-physical systems (CPS) and the Internet of things (IoT), the evolution of single-core processors to multi-core processors, and the increased importance of energy efficiency and thermal issues

Influence of Memory Hierarchies on Predictability for Time Constrained Embedded Software

Safety-critical embedded systems having to meet real-time constraints are expected to be highly predictable in order to guarantee at design time that certain timing deadlines will always be met. This requirement usually prevents designers from utilizing caches due to their highly dynamic, thus hardly predictable behavior. The integration of scratchpad memories represents an alternative approach which allows the system to benefit from a performance gain comparable to that of caches while at the same time maintaining predictability. In this work, we compare the impact of scratchpad memories and caches on worst case execution time (WCET) analysis results. We show that caches, despite requiring complex techniques, can have a negative impact on the predicted WCET, while the estimated WCET for scratchpad memories scales with the achieved Performance gain at no extra analysis cost.Comment: Submitted on behalf of EDAA (http://www.edaa.com/

WCET-aware Software Based Cache Partitioning for Multi-Task Real-Time Systems

Caches are a source of unpredictability since it is very difficult to predict if a memory access results in a cache hit or miss. In systems running multiple tasks steered by a preempting scheduler, it is even impossible to determine the cache behavior since interrupt-driven schedulers lead to unknown points of time for context switches. Partitioned caches are already used in multi-task environments to increase the cache hit ratio by avoiding mutual eviction of tasks from the cache. For real-time systems, the upper bound of the execution time is one of the most important metrics, called the Worst-Case Execution Time (WCET). In this paper, we use partitioning of instruction caches as a technique to achieve tighter WCET estimations since tasks can not be evicted from their partition by other tasks. We propose a novel WCET-aware cache partitioning algorithm, which determines the optimal partition size for each task with focus on decreasing the system\u27s WCET for a given set of possible partition sizes. Employing this algorithm, we are able to decrease the WCET depending on the number of tasks in a set by up to 34%. On average, reductions between 12% and 19% can be achieved

A New Optimization Technique for Improving Resource Exploitation and Critical Path Minimization

This paper presents a novel approach to algebraic optimization of data-flow graphs in the domain of computationally intensive applications. The presented approach is based upon the paradigm of simulated evolution which has been proven to be a powerful method for solving large non-linear optimization problems. We introduce a genetic algorithm with a new chromosomal representation of data-flow graphs that serves as a basis for preserving the correctness of algebraic transformations and allows an efficient implementation of the genetic operators. Furthermore, we introduce a new class of hardware-related transformation rules which for the first time allow to take existing component libraries into account. The efficiency of our method is demonstrated by encouraging experimental results for several standard benchmarks

Interface Synthesis for Embedded Applications in a Codesign Environment

In embedded systems, programmable peripherals are often coupled with the main programmable processor to achieve desired functionality. Interfacing such peripherals with the processor qualifies as an important task of hardware software codesign. In this paper, three important aspects of such interfacing, namely the allocation of addresses to the devices, allocation of device drivers, and approaches to handle events and transitions have been discussed. The proposed approaches have been incorporated in a codesign system MICKEY. The paper includes a number of examples, taken from the results synthesized by MICKEY, to illustrate the ideas

Fast, predictable and low energy memory references through architecture-aware compilation

The design of future high-performance embedded systems is hampered by two problems: First, the required hardware needs more energy than is available from batteries. Second, current cache-based approaches for bridging the increasing speed gap between processors and memories cannot guarantee predictable real-time behavior. A contribution to solving both problems is made in this paper which describes a comprehensive set of algorithms that can be applied at design time in order to maximally exploit scratch pad memories (SPMs). We show that both the energy consumption as well as the computed worst case execution time (WCET) can be reduced by up to to 80% and 48%, respectively, by establishing a strong link between the memory architecture and the compiler

Computing Maximum Blocking Times with Explicit Path Analysis under Non-local Flow Bounds *

ABSTRACT Worst-case time (WCET) analyses for single tasks are well established and their results ultimately serve the purpose of providing execution time parameters for schedulability analyses. Besides WCET analysis, an important problem is maximum blocking time (MBT) analysis which is essential in deferred preemption schedules for the selection of preemption points. Among the most pressing problems in this context is the need for good path analyses, which are a fundamental bottleneck for selecting these points. Current state of the art relies on ILP-based or severely constrained explicit path analyses, both of which are unsatisfactory in general. In this paper, we propose a general explicit path analysis to compute maximum blocking times, specifically for scheduling policies with deferred preemption. The proposal improves the current state of the art significantly for both WCET and MBT analysis, as it is efficient, accurate, easily extensible and computes path lengths between all program points, without imposing any artificial constraints, and under a general flow bound model, unmatched by other existing explicit path analyses, while significantly outperforming the ILP-based approach. To the best of the authors' knowledge, no explicit path analysis for MBT has been proposed yet

Built-in Chaining: Introducing Complex Components into Architectural Synthesis

Abstract-In this paper, we extend the set of library components which are usually considered in architectural synthesis by components with built-in chaining. For such components, the result of some internally computed arithmetic function is made available as an argument to some other function through a local connection. These components can be used to implement chaining in a datapath in a single component. Components with built-in chaining are combinatorial circuits. They correspond to "complex gates" in logic synthesis. If compared to implementations with several components, components with built-in chaining usually provide a denser layout, reduced power consumption, and a shorter delay time. Multiplier/accumulators are the most prominent example of such components. Such components require new approaches for library mapping in architectural synthesis. In this paper, we describe an IP-based approach taken in our OSCAR synthesis system