Takashi Tomita

Daisuke Ishii, Takashi Tomita, Toshiaki Aoki et al.

MATLAB/Simulink provides a practical modeling language and a simulation engine for the development of cyber-physical systems. To ensure the quality of the developed models, there are formal verification tools available, such as Simulink Design Verifier (SLDV) and third-party SMT-based model checkers (SmtMC). However, due to the absence of a semantics of Simulink that covers every element of models and the details of its numerical behavior, the reliability of the model checkers themselves is often doubtful, potentially analyzing models differently from the simulator. This work aims to verify the quality of the Simulink model checkers by addressing the following items. 1) Formalization of the basic block types of Simulink. It involves defining block type feature sets and the bit-precise behavior of the blocks. 2) A method for testing bit-precise conformance relations among the tools for each block type. The pass rate of our test suites measures (i) conformance of model checking results with simulation results by Simulink and (ii) conformance between the results of SmtMC and SLDV. 3) Experiment to perform tests on 10 block types. We confirmed that SmtMC efficiently passed all test cases, while SLDV achieved pass rates of only 94-96% and 80-90% for conformance (i) and (ii), respectively. We analyzed the causes of failed tests, such as errors, corner cases, and timeouts.

Daisuke Ishii, Takashi Tomita, Kenji Onishi et al.

Synchronous systems provide a basic model of embedded systems and industrial systems are modeled as Simulink diagrams and/or Lustre programs. Although the test generation problem is critical in the development of safe systems, it often fails because of the spatial and temporal complexity of the system descriptions. This paper presents a compositional test generation method to address the complexity issue. We regard a test case as a counterexample in safety verification, and represent a test generation process as a deductive proof tree built with dedicated inference rules; we conduct both spatial- and temporal-compositional reasoning along with a modular system structure. A proof tree is generated using our semi-automated scheme involving manual effort on contract generation and automatic processes for counterexample search with SMT solvers. As case studies, the proposed method is applied to four industrial examples involving such features as enabled/triggered subsystems, multiple execution rates, filter components, and nested counters. In the experiments, we successfully generated test cases for target systems that were difficult to deal with using the existing tools.