Demonstration of the Dynamic Flowgraph Methodology using the Titan II Space Launch Vehicle Digital Flight Control System

The Dynamic Flowgraph Methodology (DFM) is a new approach for embedded system safety analysis. This methodology integrates the modeling and analysis of the hardware and software components of an embedded system. The objective is to complement the traditional approaches which generally follow the philosophy of separating out the hardware and software portions of the assurance analysis. In this paper, the DFM approach is demonstrated using the Titan II Space Launch Vehicle Digital Flight Control System. The hardware and software portions of this embedded system are modeled in an integrated framework. In addition, the time dependent behavior and the switching logic can be captured by this DFM model. In the modeling process, the dimensionality of the decision tables for software subroutines creates a problem. A possible solution for solving the software portion of the DFM model is suggested. This approach makes use of a well-known numerical method, the Newton-Raphson method, to solve the equations implemented in the subroutines in reverse. Convergence can be achieved in a few steps.