Joseph Porter

Foundation for Model Integration: Semantic Backplane

One of the primary goals of the Adaptive Vehicle Make (AVM) program of DARPA is the construction of a model-based design flow and tool chain, META, that will provide significant productivity increase in the development of complex cyber-physical systems. In model-based design, modeling languages and their underlying semantics play fundamental role in achieving compositionality. A significant challenge in the META design flow is the heterogeneity of the design space. This challenge is compounded by the need for rapidly evolving the design flow and the suite of modeling languages supporting it. Heterogeneity of models and modeling languages is addressed by the development of a model integration language – CyPhy – supporting constructs needed for modeling the interactions among different modeling domains. CyPhy targets simplicity: only those abstractions are imported from the individual modeling domains to CyPhy that are required for expressing relationships across sub-domains. This “semantic interface” between CyPhy and the modeling domains is formally defined, evolved as needed and verified for essential properties (such as well-formedness and invariance). Due to the need for rapid evolvability, defining semantics for CyPhy is not a “one-shot” activity; updates, revisions and extensions are ongoing and their correctness has significant implications on the overall consistency of the META tool chain. The focus of this paper is the methods and tools used for this purpose: the META Semantic Backplane. The Semantic Backplane is based on a mathematical framework provided by term algebra and logics, incorporates a tool suite for specifying, validating and using formal structural and behavioral semantics of modeling languages, and includes a library of metamodels and specifications of model transformations.Copyright

Model-based control design and integration of cyberphysical systems: an adaptive cruise control case study

The systematic design of automotive control applications is a challenging problem due to lack of understanding of the complex and tight interactions that often manifest during the integration of components from the control design phase with the components from software generation and deployment on actual platform/network. In order to address this challenge, we present a systematic methodology and a toolchain using well-defined models to integrate components from various design phases with specific emphasis on restricting the complex interactions that manifest during integration such as timing, deployment, and quantization. We present an experimental platform for the evaluation and testing of the design process. The approach is applied to the development of an adaptive cruise control, and we present experimental results that demonstrate the efficacy of the approach.

Digital passive attitude and altitude control schemes for quadrotor aircraft

This paper presents a formal method to design a digital inertial control system for quad-rotor aircraft. In particular, it formalizes how to use approximate passive models in order to justify the initial design of passive controllers. Fundamental limits are discussed with this approach — in particular, how it relates to the control of systems consisting of cascades of three or more integrators in which input actuator saturation is present. Ultimately, two linear proportional derivative (PD) passive controllers are proposed to be combined with a nonlinear saturation element. It is also shown that yaw control can be performed independently of the inertial controller, providing a great deal of maneuverability for quad-rotor aircraft. A corollary, based on the sector stability theorem provided by Zames and later generalized for the multiple-input-output case by Willems, provides the allowable range of k for the linear negative feedback controller KI in which the dynamic system H1 : x1 → y1 is inside the sector [a1, b1], in which −∞ < a1, 0 < b1 ≤ ∞, and b1 > a1. This corollary provides a formal method to verify stability, both in simulation and in operation for a given family of inertial set-points given to the quad-rotor inertial controller. The controller is shown to perform exceptionally well when simulated with a detailed model of the STARMAC, which includes blade flapping dynamics.

TOWARDS AUTOMATED EVALUATION OF VEHICLE DYNAMICS IN SYSTEM-LEVEL DESIGNS

We describe the use of the Cyber-Physical Modeling Language (CyPhyML) to support trade studies and integration activities in system-level vehicle designs. CyPhyML captures parameterized component behavior using acausal models (i.e. hybrid bond graphs and Modelica) to enable automatic composition and synthesis of simulation models for significant vehicle subsystems. Generated simulations allow us to compare performance between different design alternatives. System behavior and evaluation are specified independently from specifications for design-space alternatives. Test bench models in CyPhyML are given in terms of generic assemblies over the entire design space, so performance can be evaluated for any selected design instance once automated design space exploration is complete. Generated Simulink models are also integrated into a mobility model for interactive 3-D simulation.Copyright

Co-simulation framework for design of time-triggered cyber physical systems

Designing cyber-physical systems (CPS) is challenging due to the tight interactions between software, network/platform, and physical components. A co-simulation method is valuable to enable early system evaluation. In this paper, a cosimulation framework that considers interacting CPS components for design of time-triggered (TT) CPS is proposed. Virtual prototyping of CPS is the core of the proposed frame-work. A network/platform model in SystemC forms the backbone of the virtual prototyping, which bridges control software and physical environment. The network/platform model consists of processing elements abstracted by real-time operating systems, communication systems, sensors, and actuators. The framework is also integrated with a model-based design tool to enable rapid prototyping. The framework is validated by comparing simulation results with the results from a hardware-in-the-loop automotive simulator.

A co-simulation framework for design of time-triggered automotive cyber physical systems

Abstract Designing cyber-physical systems (CPS) is challenging due to the tight interactions between software, network/platform, and physical components. Automotive control system is a typical CPS example and often designed based on a time-triggered paradigm. In this paper, a co-simulation framework that considers interacting CPS components for assisting time-triggered automotive CPS design is proposed. Virtual prototyping of automotive vehicles is the core of this framework, which uses SystemC to model the cyber components and integrates CarSim to model the vehicle dynamics. A network/platform model in SystemC forms the backbone of the virtual prototyping. The network/platform model consists of processing elements abstracted by real-time operating systems, communication systems, sensors, and actuators. The framework is also integrated with a model-based design tool to enable rapid prototyping. The framework is validated by comparing simulation results with the results from a hardware-in-the-loop automotive simulator. The framework is also used for design space exploration (DSE).

An Experimental Model-Based Rapid Prototyping Environment for High-Confidence Embedded Software

The development of embedded software for high confidencesystems is a challenging task that must be supportedby a deep integration of control theoretical and computational aspects. Model-based development of embeddedsoftware has been practiced for more than a decade now,but very few integrated approaches have emerged to provideend-to-end support for the process, and integrate platformaspects as well as verification. The paper describes anearly version of a model-based prototyping toolchain thatprovides such support and covers most engineering steps.The toolchain is coupled with a hardware-in-the-loop simulation system, allowing quick experimental evaluation ofdesigns.

Towards a time-triggered schedule calculation tool to support model-based embedded software design

Time-triggered architectures (TTA) provide replica determinism in safety-critical distributed embedded software designs. TTA has become a crucial part of many high-confidence embedded paradigms, as it decouples functional concerns from platform timing concerns in system designs. Complex embedded software development workflows for safety-critical applications are increasingly managed by model-based design tools, in order to support automated verification and reconcile conflicts between functional and non-functional concerns in designs. We present a prototype scheduling tool (ESched) which calculates cyclic schedules for time-triggered networks. ESched supports the model-based workflow of the ESMoL modeling language and tool suite. Using ESMoL, designers can rapidly iterate through simulating a control design, capturing platform effects in models, generating a schedule (if feasible), and re-simulating the control design subject to the platform model and the computed schedule. ESched specifications include a number of useful platform parameters, and it supports troubleshooting of infeasible schedules by allowing the user to specify partial platform models to solve.

Automated synthesis of Time-Triggered Architecture-based TrueTime models for platform effects simulation and analysis

The TrueTime toolbox simulates real-time control systems, including platform-specific details like process scheduling, task execution and network communications. Analysis using these models provides insight into platform-induced timing effects, such as jitter and delay. For safety-critical applications, the Time-Triggered Architecture (TTA) has been shown to provide the necessary services to create robust, fault-tolerant control systems. Communication induced timing effects still need to be simulated and analyzed even for TTA-compliant models. The process of adapting time-invariant control system models, through the inclusion of platform specifics, into TTA-based TrueTime models requires significant manual effort and detailed knowledge of the desired platforms execution semantics. In this paper, we present an extension of the Embedded Systems Modeling Language (ESMoL) tool chain that automatically synthesizes TTA-based TrueTime models. In our tools, timeinvariant Simulink models are imported into the ESMoL modeling environment where they are annotated with details of the desired deployment platforms. A constraint-based offline scheduler then generates the static TTA execution schedules. Finally, we synthesize new TrueTime models that encapsulate all of the TTA execution semantics. Using this approach it is possible to rapidly prototype, evaluate, and modify controller designs and their hardware platforms to better understand deployment induced performance and timing effects.

Towards Automated Exploration and Assembly of Vehicle Design Models

We describe the use of the Cyber-Physical Modeling Language (CyPhyML) to support trade studies and integration activities in system-level vehicle designs. CyPhyML captures integration interfaces across multiple design domains for system components, and generic design assembly rules given in terms of architecture alternatives. The CyPhyML tools support automated exploration of system-level architectural and parametric tradeoffs using a suite of design exploration tools that can be applied to models at different levels of fidelity and scale. Our overall approach includes exploration over the space of potential designs by evaluating structural combinations and then comparison of designs by simulating the dynamics of systems and subsystems with varying degrees of detail. In that flow, we use the DESERT toolkit for design tradeoffs that can be evaluated from the structure of the design model (i.e. interconnections of components and their parameters). DESERT extends a graphical modeling language with concepts and relations to define structural alternatives and constraints on system properties. Alternatives are given in an abstract way, decoupled from the details of the encoding of the combinatorial design space problem for the underlying binary decision diagram (BDD) solver. For desirable design instance models, the tools automatically assemble complete vehicle or subsystem computer-aided design (CAD) models from the associated component CAD models, and likewise create detailed finite-element structural analysis (FEA) models for selected component assemblies. Evaluation results are presented in a dashboard display which provides comparisons between different valid designs over all specified design metrics.Copyright