Sonia R. Sachs

Taming heterogeneity - the Ptolemy approach

Modern embedded computing systems tend to be heterogeneous in the sense of being composed of subsystems with very different characteristics, which communicate and interact in a variety of ways-synchronous or asynchronous, buffered or unbuffered, etc. Obviously, when designing such systems, a modeling language needs to reflect this heterogeneity. Todays modeling environments usually offer a variant of what we call amorphous heterogeneity to address this problem. This paper argues that modeling systems in this manner leads to unexpected and hard-to-analyze interactions between the communication mechanisms and proposes a more structured approach to heterogeneity, called hierarchical heterogeneity, to solve this problem. It proposes a model structure and semantic framework that support this form of heterogeneity, and discusses the issues arising from heterogeneous component interaction and the desire for component reuse. It introduces the notion of domain polymorphism as a way to address these issues.

A Structural Linearization Principle for Processes

In [1], an induction principle for processes was given which allows one to apply model-checking techniques to parameterized families of processes. A limitation of the induction principle is that it does not apply to the case in which one process depends directly upon a parameterized number of processes, which number grows without bound. This would seem to preclude its application to families of N processes interconnected in a star topology. Nonetheless, we show that if the dependency can be computed incrementally, then the direct dependency upon the parameterized number of processes may be re-expressed recursively in terms of a linear cascade of processes, yielding in effect a “linearization” of the inter-process dependencies and allowing the induction principle to apply.

The Design of Platoon Maneuvers for IVHS

The use of control and communication technologies in vehicles and in the highway in the form of an Intelligent Vehicle/Highway System or IVHS is an approach that promises to increase capacity without building new roads. Our context is an IVHS system in which traffic is organized in platoons of very closely spaced cars under automatic control. We consider the design of three maneuvers that platoons must undertake: merging (of two platoons into one), splitting (of one platoon into two), and changing lanes. Because of space limitations, only merge is discussed in detail.

The programmable network prototyping system

The programmable network prototyping system (PNPS) uses a collection of reusable hardware modules that implement generic communications functions such as transmission, reception, signal propagation, and pattern matching. These modules are interconnected and configured to emulate a variety of communication networks whose behavior can be monitored under different load conditions. The user specifies a network as a set of interacting components using available software tools. These tools are accessible within a prototyping environment that includes a control system for configuring the hardware modules and interconnecting them according to the component specifications. Previously designed components are stored in a library and can be used to specify new networks. Although PNPS is designed to provide a prototyping environment for communication networks, some of the basic ideas can be useful in other contexts. >

Reprogrammable Platforms for High-Speed Data Acquisition

Complex embedded systems that do not target mass marketsoften have design and engineering costs that exceed production costs. Oneexample is the triggering and data acquisition system (DAQ) integrated intohigh-energy physics experiments. Parameterizable and reprogrammable architecturesare natural candidates as platforms for specialized embedded systems likehigh-speed data acquisition systems. In order to facilitate the design ofspecialized embedded systems, design strategies and tools are needed thatgreatly increase the efficiency of the design process. End-user programmabilityof reprogrammable platforms is essential, because system designers, withouttraining in low-level programming languages, are required to change the basedesign, compare designs, and generate configuration data for the reprogrammableplatforms. This paper presents a methodology for designing and evaluatinghigh-speed data acquisition systems using reprogrammable platforms.

A structural linearization principle for processes

In [11], an induction principle for processes was given which allows one to apply model-checking techniques to parameterized families of processes. A limitation of the induction principle is that it does not apply to the case in which one process depends directly upon a parameterized number of processes, which grows without bound. This would seem to preclude its application to families ofN processes interconnected in a star topology. Nonetheless, we show that if the dependency can be computed incrementally, then the direct dependency upon the parameterized number of processes may be re-expressed recursively in terms of a linear cascade of processes, yielding in effect a “linearization” of the inter-process dependencies and allowing the induction principle to apply.

Modelling Asynchrony with a Synchronous Model

The I/O Automaton paradigm of Lynch and Tuttle models asynchrony through an interleaving parallel composition and generalizes more common interleaving models based upon message-passing, such as Hoares CSP. It is not generally recognized that such interleaving models in fact can be viewed as a special cases of synchronous parallel composition, in which components all move in lock-step. Let A be any set of finite-state I/O Automata drawing actions from a fixed finite set containing a subset Δ, In this article we establish a translation T ∶ A → P to a class of ω-automata P closed under a synchronous parallel composition, for which T is monotonic with respect to implementation relative to Δ, and linear with respect to composition. Thus, for A1,..., A m , B1, ..., B n Σ A and A = A1∥ ⋯ ∥A m , B = B1∥ ⋯ ∥B N , if Δ is the set of actions common to both A and B, then A implements B (in the sense of I/O Automata) if and only if the ω-automaton language containment L(T(A1) ⊗ ⋯ ⊗ T(A m )) ⊂ L(T(B1) ⊗ ⋯ ⊗ T(B n )) obtains, where ∥ denotes the interleaving parallel composition on A and ⊗ denotes the synchronous parallel composition on P. For the class P, we use the L-process model of ω-automata. This result enables one to verify systems specified by I/O Automata through model-checkers such as COSPAN or SMV, that operate on models with synchronous parallel composition. The translation technique generalizes to other interleaving models, although in each case, the translation map must match the specific model. Proofs have been eliminated on account of space limitations. A full version (with all proofs) is available upon request.

Formal Verification of a Distributed Computer System

Modeling distributed computer systems is known to be a challenging enterprise. Typically, distributed systems are comprised of large numbers of components whose coordination may require complex interactions. Modeling such systems more often than not leads to the nominal intractability of the resulting state space. Various formal methods have been proposed to address the modeling of coordination among distributed systems components. For the most part, however, these methods do not support formal verification mechanisms. By way of contrast, the L-automata/L-processes model supports formal verification mechanisms which in many examples can successfully circumvent state space explosion problems, and allow verification proofs to be extended to an arbitrary number of components. After reviewing L-automata/L-processes formalisms, we present here the formal specification of a fault-tolerant algorithm for a distributed computer system. We also expose the L-automata/L-processes verification of the distributed system, demonstrating how various techniques such as homomorphic reduction, induction, and linearization, can be used to overcome various problems which surface as one models large, complex systems.

Multi-agent Model of Technological Shifts

We present a multi-agent simulation model of a concentrated industry undergoing technological change. The simulation consists of heterogeneous firm agents, heterogeneous consumer agents, and one intermediating agent, the auctioneer, who aggregates market information to transmit to agents and to arrive at prices. Firms seek to maximize profit by estimating market demand, entering and exiting product markets, and optimizing output based on strategic conjectures of competing firm behavior. Consumers maximize utility by optimizing consumption within their budget sets. The auctioneer matches firm research with shifting consumer preferences, diffuses product knowledge among firms and consumers, and sets prices. We study . technological shifts; the diffusion of new technologies that directly compete with and replace existing ones. Sensitivity analysis is discussed in terms of the effects that model parameters have on product adoption, demand, output, spending, price, and profits. We validate our model against actual industry data on film cameras versus digital cameras.

Reprogrammable platforms for high-speed data acquisition

Complex embedded systems that do not target mass markets often have design and engineering costs that exceed production costs. One example is the triggering and data acquisition system (DAQ) integrated into high-energy physics experiments. Parametrizable and reprogrammable architectures are natural candidates as platforms for specialized embedded systems like high-speed data acquisition systems. In order to facilitate the design of specialized embedded systems, design strategies and tools are needed that greatly increase the efficiency of the design process. End-user programmability of reprogrammable platforms is essential, because system designers, without training in low-level programming languages, are required to change the base design, compare designs, and generate configuration data for the reprogrammable platforms. This paper presents a methodology for designing and evaluating high-speed data acquisition systems using reprogrammable platforms.