Responsible Frameworks for Heterogeneous Modeling and Design of Embedded Systems

Jie Liu

Ph.D. thesis, Technical Memorandum UCB/ERL M01/41
Electronics Research Laboratory, University of California, Berkeley, December 20th, 2001.



This dissertation studies modelling and design frameworks for heterogeneous embedded systems. Heterogeneity, in the sense that components in a system have diverse interaction styles, complicates embedded system design and challenges understandability, composability, and scalability of models. Hierarchical heterogeneous modeling approaches tame the design complexity by hierarchically composing semantically different modeling frameworks. Frameworks are software architectures that define component ontology and interaction styles. Formal frameworks for embedded software make programming models and software architectures reusable.

Embedded systems that engage the real world need to be reactive. This dissertation focuses on studying reactivity and its composition in different frameworks. It introduces the reactor model as an abstract operational semantics to capture interactions among components and frameworks. Within a framework, a component execution is a precise reaction if all the prerequisites for the reaction are satisfied before it is being triggered. A framework that only triggers precise reactions is a responsible framework. Precise reactions and responsible frameworks allow us to capture compositionality of reactions, answering questions such as how a composition of a framework and components can treated as an atomic component at a higher level. This compositionality is key for hierarchically composing heterogeneous models.

Precise reactions and responsible frameworks are discussed for timed models. Having a notion of time helps designers define timely reactions. But it also brings challenges to timed frameworks to precisely determine the triggering time. In terms of modeling mixed-signal and hybrid systems, the challenge is how to precisely control the progression of modeling time. We present techniques for a responsible continuous-time framework to have compositional precise reactivity. These techniques involve optimistic look-ahead execution and possible rollback.

We further study precise reaction and responsible frameworks for priority-based run-time embedded software. A timed multitasking (TM) model of computation is proposed for programming reactive real-time embedded software. This model brings time determinism to the programming model level. We sketch a responsible run-time system that preserves the timing semantics of TM models.