Safety-Critical Java (SCJ) is a version of Java for real-time, embedded, safety-critical applications. It supports certification via abstractions that enforce a particular program architecture, with controlled concurrency and memory models. SCJ is an Open Group standard, with a reference implementation, but little support for reasoning. Here, we present SCJ-Circus, a refinement notation for specification and verification of low-level models of SCJ programs. SCJ-Circus is part of the Circus family of state-rich process algebras: it includes the Circus constructs for modelling of sequential and concurrent behaviour based on Z and CSP, and the real-time and object-oriented extensions of Circus, in addition to the SCJ abstractions. We present the syntax of SCJ-Circus and its semantics, defined by mapping SCJ-Circus constructs to those of Circus. We also detail a refinement strategy that takes a Circus design that adheres to a multiprocessor cyclic executive pattern and produces an SCJ program design, described in SCJ-Circus. Finally, we show how this refinement strategy can be extended for more complex program architectures
