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Growing software complexity is an increasing challenge for the software development of modern cyber-physical systems. A classical strategy for taming this complexity is to partition system behaviors into different operational modes specified at design time. Such a multi-mode system can change behavior by switching between modes at run-time. A complementary approach for reducing software complexity is provided by component-based software engineering (CBSE), which reduces complexity by building systems from composable, reusable and independently developed software components. CBSE and the multi-mode approach are fundamentally conflicting in that component-based development conceptually is a bottom-up approach, whereas partitioning systems into operational modes is a top-down approach with its starting point from a system-wide perspective. In this article, we show that it is possible to combine and integrate these two fundamentally conflicting approaches. The key to simultaneously benefiting from the advantages of both approaches lies in the introduction of a hierarchical mode concept that provides a conceptual linkage between the bottom-up component-based approach and system level modes. As a result, systems including modes can be developed from reusable mode-aware components. The conceptual drawback of the approach—the need for extensive message exchange between components to coordinate mode-switches—is eliminated by an algorithm that collapses the component hierarchy and thereby eliminates the need for inter-component coordination. As this algorithm is used from the design to implementation level (“compilation”), the CBSE design flexibility can be combined with efficiently implemented mode handling, thereby providing the complexity reduction of both approaches, without inducing any additional design or run-time costs. At the more specific level, this article presents (1) a mode mapping mechanism that formally specifies the mode relation between composable multi-mode components and (2) a mode transformation technique that transforms component modes to system-wide modes to achieve efficient implementation

Growing software complexity is an increasing challenge for the software development of modern embedded systems. A classical strategy for taming the software complexity is to partition system behaviors into different operational modes specified at design time. Such a multi-mode system can change behavior by switching between modes at runtime. Component-Based Software Engineering (CBSE) is a complementary approach to the software development of complex systems that fosters reuse of independently developed software components. CBSE and the multi-mode approach are fundamentally conflicting in that component-based development conceptually is a bottom-up approach, whereas partitioning systems into operational modes is a topdown approach. In this report we show that it is possible to combine and integrate these two fundamentally conflicting approaches. The key to simultaneously benefitting from the advantages of both approaches lies in the introduction of a hierarchical mode concept that provides a conceptual linkage between the bottom-up component-based approach and system level modes. As a result, systems including modes can be developed from reusable mode-aware components in the modeling phase. The conceptual drawback of the approach—the need for extensive message exchange between components to coordinate mode switches—is eliminated by an algorithm that collapses the component hierarchy and thereby eliminates the need for inter-component coordination. As this algorithm is used from the design to implementation level (“compilation”), the CBSE design flexibility can be combined with efficiently implemented mode handling. At the more specific level, this report presents (1) a mode mapping mechanism which formally specifies the mode relation between composable multi-mode components, (2) a mode transformation technique that transforms component modes to system-wide modes to achieve efficient implementation, and (3) a prototype tool that implements the mode mapping mechanism and mode transformation technique.

Self-adaptivity, characterized by the ability to dynamically adjust behavior at runtime, is a growing trend in the evolution of modern embedded systems. While self-adaptive systems tend to be flexible and autonomous, self-adaptivity may inevitably complicate software design, test and analysis. A strategy for taming the growing software complexity of self-adaptive systems is to partition system behaviors into different operational modes specified at design time. Such a multi-mode system can change behavior by switching between modes at runtime under certain circumstances. Multi-mode systems can benefit from a complementary approach to the software development of complex systems: Component-Based Software Engineering (CBSE), which fosters reuse of independently developed software components. However, the state-of-the-art component-based development of multi-mode systems does not take full advantage of CBSE, as reuse of modes at component level is barely addressed. Modes are often treated as system properties, while mode switches are handled by a global mode manager. This centralized mode management entails global information of all components, whereas the global information may be inaccessible in component-based systems. Another potential problem is that a single mode manager does not scale well, particularly at design time,  for a large number of components and modes.

In this thesis we propose a distributed solution to the component-based development of multi-mode systems, aiming for a more efficient and scalable mode management. Our goal is to fully incorporate modes in software component reuse, supporting reuse of multi-mode components, i.e., components able to run in multiple modes. We have developed a generic framework, the Mode-Switch Logic (MSL), which not only supports reuse of multi-mode components but also provides runtime mechanisms for handling mode switch. MSL includes three fundamental elements: (1) a mode-aware component model with the formal specification of reusable multi-mode software components; (2) a mode mapping mechanism for the seamless composition of multi-mode components; and (3) a mode-switch runtime mechanism which is executed by each component in isolation from its functional execution and coordinates the mode switches of different components without the need of global mode information. The mode-switch runtime mechanism has been verified by model checking in conjunction with mathematical proofs. We also provide a mode-switch timing analysis for the runtime mechanism to respect real-time requirements.

MSL is dedicated to the mode aspect of a system irrespective of component execution semantics, thus independent of the choice of component models. We have integrated MSL in the ProCom component model with the extension of support for reuse of multi-mode components and distributed mode-switch handling. Although the distributed mode-switch handling of MSL is more flexible and scalable than the conventional centralized approach, when components are deployed on a single hardware platform and global mode information is available, centralized mode-switch handling is more efficient in terms of runtime overhead and mode-switch time. Hence, MSL is supplemented with a mode transformation technique to enhance runtime mode-switch efficiency by converting the distributed mechanism to a centralized mechanism. MSL together with the mode transformation technique has been implemented in a prototype tool where one can build multi-mode systems by reusing multi-mode components. The applicability of MSL is demonstrated in two proof-of-concept case studies.

Component-Based Software Engineering (CBSE) is by the reuse of software components an effective approach to managing the growing software complexity of embedded systems. Another technique for reducing software complexity is to partition the system behavior into different operational modes, with each mode being associated with a unique behavior. Such a multi-mode system can change behavior by switching between modes under certain circumstances. Integrating CBSE and the multi-mode approach, we have developed the Mode Switch Logic (MSL), a framework dedicated to the development of multi-mode systems composed by reusable multi-mode components, i.e. components which can run in different modes. The mode switch handling of MSL is based on a fully distributed architecture in the sense that a system mode switch is achieved by the joint mode switches of different independently developed components. Algorithms that by inter-component communication guarantee the correctness of the mode switch have been developed. In this paper, we propose a mode transformation technique as a supplement to MSL for converting the distributed mode switch handling of MSL to a centralized mode switch handling. The goal is to enhance the run-time mode switch efficiency when components are deployed on a single hardware platform and global mode information is available. We demonstrate this technique by an example and reveal its potential industrial value.

Component-Based Software Engineering (CBSE) is by the reuse of software components an effective approach to managing the growing software complexity of embedded systems. Another technique for reducing software complexity is to partition the system behavior into different operational modes, with each mode being associated with a unique behavior. Such a multi-mode system can change behavior by switching between modes under certain circumstances. Integrating CBSE and the multi-mode approach, we have developed the Mode Switch Logic (MSL), a framework dedicated to the development of multi-mode systems composed by reusable multi-mode components, i.e. components which can run in different modes. The mode switch handling of MSL is based on a fully distributed architecture in the sense that a system mode switch is achieved by the joint mode switches of different independently developed components. Algorithms that by inter-component communication guarantee the correctness of the mode switch have been developed. In this report, we propose a mode transformation technique as a supplement to MSL for converting the distributed mode switch handling of MSL to a centralized mode switch handling. The goal is to enhance the run-time mode switch efficiency when components are deployed on a single hardware platform and global mode information is available. We demonstrate this technique by an example and reveal its potential industrial value.

Hierarchical scheduling frameworks (HSFs) are a means for composing complex real-time embedded systems from independently developed and analyzed applications. To support multiple modes in a two-level HSF, the multi-mode adaptive hierarchical scheduling framework MMAHSF has recently been presented supporting different mode-change mechanisms. Currently, we provide a formalization and verification of mode changes in MMAHSF using the UPPAAL model checker for certain mode-change mechanisms. The verification indicates that MMAHSF and the proposed mode-change mechanisms are deadlock-free and guarantee mode changes in bounded time.

Hierarchical scheduling frameworks (HSFs) are a means for composing complex real-time embedded systems from independently developed and analyzed applications. To support multiple modes in a two-level HSF, the multi-mode adaptive hierarchical scheduling framework MMAHSF has recently been presented supporting different mode-change mechanisms. Currently, we provide a formalization and verification of mode changes in MMAHSF using the UPPAAL model checker for certain mode-change mechanisms. The verification indicates that MMAHSF and the proposed mode-change mechanisms are deadlock-free and guarantee correct mode changes in bounded time.

Software reuse is deemed as an effective technique for managing the growing software complexity of large systems. Software complexity can also be reduced by partitioning the system behavior into different modes. Such a multi-mode system is able to dynamically change its behavior by switching between different modes. When a multi-mode system is developed by reusable software components, a crucial issue is how to achieve a seamless composition of multi-mode components and handle mode switch properly. This is the motivation for the Mode Switch Logic (MSL), supporting the development of component-based multi-mode systems by providing mechanisms for mode switch handling. In this paper, MSL is extended and adapted to systems with emergency triggering of mode switches that must be handled with minimal delay. We propose an Immediate Handling with Buffering (IHB) approach to enable the responsive handling of such an emergency event in the presence of other concurrent non-emergency mode switch events. We present a model checking based verification of IHB and illustrate its benefits by an example.

Component-Based Software Engineering has been introduced as a technique for the development of complex systems. Software complexity can also be reduced by partitioning the system behavior into different modes. Such a multi-mode system is able to change its behavior at runtime by switching between different operational modes. When a multimode system is developed by reusable software components, a crucial issue is how to achieve a seamless composition of multi-mode components and also how to handle mode switch properly. This is the motivation for the Mode Switch Logic (MSL), supporting the development of component-based multi-mode systems by providing mechanisms for mode switch handling. In this report, MSL is extended and adapted to systems with emergency triggering of mode switches that must be handled with minimal delay. We propose an approach, called Immediate Handling with Buffering (IHB), to enable the responsive handling of such an emergency event in the presence of other concurrent non-emergency mode switch events. We present a model checking based verification of the IHB approach, and illustrate its benefits by a small example.

The growing complexity of embedded systems software entails new development techniques. Component-Based Software Engineering is undoubtedly suitable for the development of complex systems thanks to its inherent component reuse. Another approach to reduce software complexity is by partitioning the system behavior into different operational modes. Each mode is associated with a unique behavior and the system can change behavior by switching between modes. When such a multi-mode system is developed by reusable software components, a crucial issue is how to achieve a seamless composition of multi-mode components and also how to handle mode switch properly. As an integrated solution to the challenges of multi-mode component-based software system development we have proposed the Mode Switch Logic (MSL). The current version of MSL assumes independent handling of a single mode switch scenario, i.e. that no other mode switch is triggered until an ongoing mode switch is completed. For a wide class of systems, this is an unrealistic assumption. In this paper we lift this assumption by proposing an extension of MSL to handle multiple mode switch scenarios concurrently triggered by different components.