The preliminary design of the G-CLEF spectrograph instrument device control system

The Giant Magellan Telescope (GMT)-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, precision radial velocity optical echelle spectrograph. The preliminary software design incorporates a hierarchical, multi-level state machine. At the lowest level, the state machine utilizes GMT-provided frameworks to communicate with the hardware. At higher levels of abstraction, the design makes extensive use of State Chart Extensible Markup Language (SCXML) representations to define the operation of the instrument. The functionality of the design can be validated by executing these representations. The incorporation of an interpreter to directly execute the SCXML as a component of the control system is being investigated. The approaches used to develop the preliminary software design concept are described, the use and utility of SCXML for instrument control is discussed, and the application of the preliminary design to a subset of G-CLEF subsystems is demonstrated.