Implementation of the Global Physical Time for the Domain Model of The Virtual Path of the DLR Hand-Arm System

Kurzfassung

Global physical time notion plays a fundamental role in many distributed applications. Much research has been made in the development of algorithms for time synchronization of drifting distributed clocks, as well as dissemination of global physical time reference. The aim of this work is to find a high-precision lightweight fault-tolerant solution with short convergence time for the SpaceWireinterconnected FPGAs of the DLR Hand-Arm system under using two different time distribution strategies: global clock dissemination and local (loop) synchronization. SpaceWire allows for (at least) two methods for physical time synchronization. The tightness of achievable synchronization is strongly dependent on the communication jitter and oscillator instabilities, as well as other user-defined constraints. In this thesis, a detailed quantitative analysis of the system’s architecture, oscillators, and corresponding achievable precision has been made. Furthermore, other user constraints, such as utilization of communication channels, have been taken into account. The resulting formulas have been applied to calculate practical values for the DLR Hand-Arm system. Also, the choice of the solution has been made according to the taxonomy of clock synchronization methods which was also developed within the scope of this thesis. The extended classification and the results of quantitative analysis can potentially be integrated into the domain model of the Virtual Path of the Hand-Arm System and may be used in the future for automatic generation of synchronization modules for diverse hardware elements, such as FPGAs or CPLDs, depending on user-defined optimality constraints. A constructive approach, starting with pinpointing the underlying system’s properties and the non-functional characteristics of the algorithm, to modular construction of the algorithm and the necessary functional properties has been used. The resulting solution can guarantee high-precision synchrony with some nonzero probability which can be made considerably high, depending on the resulting resource demands. Modules of the algorithm, including the clock controller and communication jitter compensation have been simulated under extreme values of system parameters. Stability and precision have been also demonstrated by means of numerous simulations. Furthermore, the global convergence of the algorithm has been briefly discussed.