The Input Output Timed Automaton a Model for Real-time Parallel Computation

In this paper, we present the Input Output Timed Automaton (IOTA) model for the speciica-tion and veriication of parallel real-time digital systems. Our model extends Nancy Lynch's IOA model Lynch:88a] to allow for the inclusion of timing properties. We have used the IOTA model to study a range of real-time digital systems. In particular, we used it to specify and verify asynchronous circuit designs Bestavros:89a] and to specify, analyze and simulate behaviors of autonomous creatures Bestavros:90b]. In Bestavros:90a], we developed a language and environment for the executable speciication of parallel real-time interactive tasks based on the IOTA model. A IOTA is an abstraction that encapsulates a real-time task. A system is modeled as a network of such IOTAs communicating with each other over channels. A IOTA might be the speciication or the actual implementation of a software/hardware module. This allows the representation of both the external environment and the programmed system along with the available computational resources in a unique framework. IOTAs can be composed together to form higher level IOTAs. A IOTA implements another, if all external behaviors of the rst (the implementation) are also external behaviors of the second (the speciication.) We use timed possibility mappings to test for the implementation relationship. This is the primary tool that is used to verify that an implementation meets the required speciication.