  Cyber-Physical Systems (CPS) consist of software interacting with the
physical world, such as robots, vehicles, and industrial processes. CPS are
frequently responsible for the safety of lives, property, or the environment,
and so software correctness must be determined with a high degree of certainty.
To that end, simply testing a CPS is insufficient, as its interactions with the
physical world may be difficult to predict, and unsafe conditions may not be
immediately obvious. Formal verification can provide stronger safety guarantees
but relies on the accuracy of the verified system in representing the real
system. Bringing together verification and implementation can be challenging,
as languages that are typically used to implement CPS are not easy to formally
verify, and languages that lend themselves well to verification often abstract
away low-level implementation details. Translation between verification and
implementation languages is possible, but requires additional assurances in the
translation process and increases software complexity; having both in a single
language is desirable. This paper presents a formalization of MARVeLus, a CPS
language which combines verification and implementation. We develop a
metatheory for its synchronous refinement type system and demonstrate verified
synchronous programs executing on real systems.
