Cyber-Physical Systems (CPS) are integrations of computation and physical processes. Embedded computers and networks monitor and control the physical processes, usually with feedback loops where physical processes affect computations and vice versa. The economic and societal potential of such systems is vastly greater than what has been realized, and major investments are being made worldwide to develop the technology. There are considerable challenges, particularly because the physical components of such systems introduce safety and reliability requirements qualitatively different from those in general- purpose computing. Moreover, physical components are qualitatively different from object-oriented software components. Standard abstractions based on method calls and threads do not work. This paper examines the challenges in designing such systems, and in particular raises the question of whether today's computing and networking technologies provide an adequate foundation for CPS. It concludes that it will not be sufficient to improve design processes, raise the level of abstraction, or verify (formally or otherwise) designs that are built on today's abstractions. To realize the full potential of CPS, we will have to rebuild computing and networking abstractions. These abstractions will have to embrace physical dynamics and computation in a unified way.

/pdf/cyber-physical-systems-design-challenges-57gxu3wcxl.pdf

Cyber Physical Systems: Design Challenges

This review covers research on the topic of mixed criticality systems that has been published since Vestal’s 2007 paper. It covers the period up to and including December 2015. The review is organised into the following topics: introduction and motivation, models, single processor analysis (including job-based, hard and soft tasks, fixed priority and EDF scheduling, shared resources and static and synchronous scheduling), multiprocessor analysis, related topics, realistic models, formal treatments, and systems issues. An appendix lists funded projects in the area of mixed criticality.

/pdf/mixed-criticality-systems-a-review-3ftn7gd29e.pdf

Mixed Criticality Systems - A Review

Four relations are defined the use of which allow a reliability network to be expressed as a mathematical statement. Series and active and standby redundancy connections are allowed. The possibility of requiring more than one of the active branches to be operative is included. At the very least the result allows for typing in place of drawing a network description.

http://ieeexplore.ieee.org/iel5/24/5216426/05216446.pdf

Network Calculus

This paper argues that cyber-physical systems present a sub-stantial intellectual challenge that requires changes in both theories of computation and dynamical systems theory. The CPS problem is not the union of cyber and physical problems, but rather their intersection, and as such it demands models that embrace both. Two complementary approaches are identified: cyberizing the physical (CtP) means to endow physical subsystems with cyber-like abstractions and interfaces; and physicalizing the cyber (PtC) means to endow software and network components with abstractions and interfaces that represent their dynamics in time.

CPS foundations

Recently, contract-based design has been proposed as an “orthogonal” approach that complements system design methodologies proposed so far to cope with the complexity of system design. Contract-based design provides a rigorous scaffolding for verification, analysis, abstraction/refinement, and even synthesis. A number of results have been obtained in this domain but a unified treatment of the topic that can help put contract-based design in perspective was missing. This monograph intends to provide such a treatment where contracts are precisely defined and characterized so that they can be used in design methodologies with no ambiguity. In particular, this monograph identifies the essence of complex system design using contracts through a mathematical “meta-theory”, where all the properties of the methodology are derived from a very abstract and generic notion of contract. We show that the meta-theory provides deep and illuminating links with existing contract and interface theories, as well as guidelines for designing new theories. Our study encompasses contracts for both software and systems, with emphasis on the latter. We illustrate the use of contracts with two examples: requirement engineering for a parking garage management, and the development of contracts for timing and scheduling in the context of the AUTOSAR methodology in use in the automotive sector.

/pdf/contracts-for-system-design-4rnwl90agh.pdf

Contracts for System Design

A common trend in real-time safety-critical embedded systems is to integrate multiple applications on a single platform. Such systems are known as mixed-criticality (MC) systems as the applications are usually characterized by different criticality levels (CLs). Nowadays, multicore platforms are promoted due to cost and performance benefits. However, certification of multicore MC systems is challenging because concurrently executed applications with different CLs may block each other when accessing shared platform resources. Most of the existing research on multicore MC scheduling ignores the effects of resource sharing on the execution times of applications. This paper proposes a MC scheduling strategy which explicitly accounts for these effects. Applications are executed by a flexible time-triggered criticality-monotonic scheduling scheme. Schedulers on different cores are dynamically synchronized such that only a statically known subset of applications of the same CL can interfere on shared resources, e. g., memories, buses. Therefore, the timing effects of resource sharing are bounded and we quantify them at design time. We combine this scheduling strategy with a mapping optimization technique for achieving better resource utilization. The efficiency of the approach is demonstrated through extensive simulations as well as comparisons with traditional temporal partitioning and state-of-the-art scheduling algorithms. It is also validated on a real-world avionics system.

Scheduling of mixed-criticality applications on resource-sharing multicore systems

Recently, a number of frameworks were proposed to extend interface theory to the domains of single-processor and distributed real-time systems. This paper unifies some of these approaches and proves properties like refinement and independent implementability. We also explicitly state the requirements to a framework for these properties to be fulfilled. Further, a new notion of adaptive interfaces is introduced that supports the design by providing mechanisms for propagating system constraints, such as (end-to-end) delays, available computing and communication resources, buffer spaces, and energy. Guarantees and assumptions on interfaces are not any longer static but adapt according to the system environment. This can be used to answer synthesis questions at design time or to adapt system parameters to changing environment requirements at run-time. The applicability of the presented framework is proven by adapting it to a number of different real-time analysis models.

/pdf/real-time-interfaces-for-composing-real-time-systems-4ik0r6l6tm.pdf

Real-time interfaces for composing real-time systems

The embedded system industry is facing an increasing pressure for migrating from single-core to multi- and many-core platforms for size, performance and cost purposes. Real-time embedded system design follows this trend by integrating multiple applications with different safety criticality levels into a common platform. Scheduling mixed-criticality applications on today's multi/many-core platforms and providing safe worst-case response time bounds for the real-time applications is challenging given the shared platform resources. For instance, sharing of memory buses introduces delays due to contention, which are non-negligible. Bounding these delays is not trivial, as one needs to model all possible interference scenarios. In this work, we introduce a combined analysis of computing, memory and communication scheduling in a mixed-criticality setting. In particular, we propose: (1) a mixed-criticality scheduling policy for cluster-based many-core systems with two shared resource classes, i.e., a shared multi-bank memory within each cluster, and a network-on-chip for inter-cluster communication and access to external memories; (2) a response time analysis for the proposed scheduling policy, which takes into account the interferences from the two classes of shared resources; and (3) a design exploration framework and algorithms for optimizing the resource utilizations under mixed-criticality timing constraints. The considered cluster-based architecture model describes closely state-of-the-art many-core platforms, such as the Kalray MPPA®-256. The applicability of the approach is demonstrated with a real-world avionics application. Also, the scheduling policy is compared against state-of-the-art scheduling policies based on extensive simulations with synthetic task sets.

Mixed-criticality scheduling on cluster-based manycores with shared communication and storage resources

Many application domains require adaptive real-time embedded systems that can change their functionality over time. In such systems it is not only necessary to guarantee timing constraints in every operating mode, but also during the transition between different modes. Known approaches that address the problem of timing analysis over mode changes are restricted to fixed priority scheduling policies. In addition, most of them are also limited to simple periodic event stream models and therefore, they can not faithfully abstract the bursty timing behavior which can be observed in embedded systems. In this paper, we propose a new method for the design and analysis of adaptive multi-mode systems that supports any event stream model and can handle earliest deadline first (EDF) as well as fixed priority (FP) scheduling of tasks. We embed the analysis method into a well-established modular performance analysis framework based on Real-Time Calculus and prove its applicability by analyzing a case study.

Reliable mode changes in real-time systems with fixed priority or EDF scheduling

A common trend in real-time embedded systems is to integrate multiple applications on a single platform. Such systems are known as mixed-criticality (MC) systems when the applications are characterized by different criticality levels. Nowadays, multicore platforms are promoted due to cost and performance benefits. However, certification of multicore MC systems is challenging as concurrently executed applications of different criticalities may block each other when accessing shared platform resources. Most of the existing research on multicore MC scheduling ignores the effects of resource sharing on the response times of applications. Recently, a MC scheduling strategy was proposed, which explicitly accounts for these effects. This paper discusses how to combine this policy with an optimization method for the partitioning of tasks to cores as well as the static mapping of memory blocks, i.e., task data and communication buffers, to the banks of a shared memory architecture. Optimization is performed at design time targeting at minimizing the worst-case response times of tasks and achieving efficient resource utilization. The proposed optimization method is evaluated using an industrial application.

Mapping mixed-criticality applications on multi-core architectures

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