Softtide: A Deterministic Middleware for Real-Time Systems

Correct synchronisation in a distributed system is a difficult. One effective approach to the problem is to employ a logical clock on the high-level design, which ensures deterministic concurrency. However, most real-time network protocols only provide the means for physical time synchronisation. Therefore, in the end, the inherent logical clock has to be compiled away and mapped to physical time, losing many of its benefits. We propose a new middleware called softtide, which aims to facilitate the implementation and deployment of systems with an inherent logical clock. The idea is to provide a global logical clock through API, as the basis for scheduling task executions and message transmissions. At the same time, maintain a relatively stable relation between the logical clock and physical time, to limit the jitters between devices. The synchronisation mechanism is inspired by a recent protocol called bittide, which features a decentralised architecture. Softtide has the following mathematical properties: (1) Logical synchrony, where the transmission delays between devices are constant in logical time. (2) Its behaviour is deterministic even in the presence of network delays, differing clock frequencies, and faults. (3) Finally, softtide is decentralised in nature, where devices can dynamically join and leave. The synchronised logical clock provided by softtide simplifies the design, compilation, and validation of real-time distributed systems. Empirically we show the real-world performance of softtide to always produce deterministic results.