5 Modeling and Simulation of TDL Applications

Most of the existing modeling tools and frameworks for embedded applications use levels of abstraction where execution and communication times of computational tasks are not captured. Thus, properties such as time and value determinism can be lost when refining the model closer to a target platform. The Logical Execution Time (LET) paradigm has been proposed to deal with this issue, by enabling specification of platform-independent execution times of periodic time-triggered computational tasks at higher levels of abstraction.

This chapter deals with modeling and simulation of embedded applications where LET requirements are specified by using the Timing Definition Language (TDL). TDL provides a programming model for time- and event-triggered components suitable for large distributed systems. We present specific TDL extensions that increase the expressiveness of the language, accommodating the needs of control applications such as minimum sensor-actuator delays. We describe simulation of TDL programs in dataflow models (using Simulink) and discrete event (DE) models (using Ptolemy II). We show how the Ptolemy II based simulation can be used to validate preservation of timing and value behaviors when mapping a DE model of an application with concurrent components into a sequential implementation platform with fixed priority preemptive scheduling.