FPGA Stream-Monitoring of Real-time Properties

An essential part of cyber-physical systems is the online evaluation of real-time data streams. Especially in systems that are intrinsically safety-critical, a dedicated monitoring component inspecting data streams to detect problems at runtime greatly increases the confidence in a safe execution. Such a monitor needs to be based on a specification language capable of expressing complex, high-level properties using only the accessible low-level signals. Moreover, tight constraints on computational resources exacerbate the requirements on the monitor. Thus, several existing approaches to monitoring are not applicable due to their dependence on an operating system. We present an FPGA-based monitoring approach by compiling an RTLola specification into synthesizable VHDL code. RTLola is a stream-based specification language capable of expressing complex real-time properties while providing an upper bound on the execution time and memory requirements. The statically determined memory bound allows for a compilation to an FPGA with a fixed size. An advantage of FPGAs is a simple integration process in existing systems and superb executing time. The compilation results in a highly parallel implementation thanks to the modular nature of RTLola specifications. This further increases the maximal event rate the monitor can handle.