The National Bureau of Standards Center for Manufacturing Engineering is currently conducting research to help define interface and data format standards necessary to support the factory of the future. In support of this goal, NBS has implemented an experimental factory, called the Automated Manufacturing Research Facility (AMRF). The evolution of the AMRF has included the development of a Real-Time Control System (RCS) to direct robot motions according to high-level commands received from a supervisory workstation controller and environmental data obtained by local sensors. During the development of RCS, it became clear that large-scale software for real-time control is fundamentally different, and in some aspects, more complex than that intended for scientific or business applications. Specifically, software designed for control purposes must contend with a large number of non-deterministic states which complicates program synthesis and makes testing and debugging extremely difficult. This paper discusses these problems, and how they are addressed by RCS.