We present the Sparse Synchronous model (SSM) of computation, which allows a programmer to specify software timing more precisely than the traditional “heartbeat” of mainstream operating systems or the synchronous languages. SSM is a mix of semantics inspired by discrete event simulators and the synchronous languages designed to operate in resource-constrained environments such as microcontrollers. SSM provides precise timing prescriptions, concurrency, and determinism. We present SSM, its motivations, and details of a lightweight runtime system upon which a future language will be built.