A Distributed Virtual Time System on Embedded Linux for Evaluating Cyber-Physical Systems

Cyber-physical systems have a cyber presence, collecting and transmitting data, while also collecting information and modifying the physical surrounding world. In order to evaluate the cyber-security of cyber-physical systems, simulation and modeling is a tool often used. In this work, we develop a distributed virtual time system that enables the synchronization of virtual clocks between physical machines enabling a high fidelity simulation based testing platform. The platform combines physical computing and networking hardware for the cyber presence, while allowing for offline simulation and computation of the physical world. By incorporating virtual clocks into distributed embedded Linux devices, the testbed creates the opportunity to interrupt real and emulated cyber-physical applications to inject offline simulated data values. The ability to run real applications and being able to inject simulated data temporally transparent to the running process allows for high fidelity experimentation. Distributed virtual time enables processes and their clocks to be paused, resumed, and dilated across embedded Linux devices through the use of hardware interrupts and a common kernel module. By interconnecting the embedded devices' general purpose IO pins, they can coordinate and synchronize through a distributed virtual time kernel module with low overhead, under 50 microseconds for 8 processes across 4 embedded Linux devices.