Control and monitoring software for the Greenland Telescope

We describe the latest development of the control and monitoring system of the Greenland Telescope (GLT). The GLT is a 12-m radio telescope aiming to carry out the sub-millimeter Very Long Baseline Interferometry (VLBI) observations through the Event Horizon Telescope (EHT) and the Global Millimeter VLBI Array (GMVA), to image the shadows of super massive black holes. The telescope is currently located at the Thule Air Base for commissioning before deployed to the Summit Station. The GLT participated in the VLBI observing campaigns in 2018 and 2019 and fringes were successfully detected at 86 and 230 GHz. Our antenna control software was adapted from the Submillimeter Array (SMA), and as a result for single-dish observations we added new routines to coordinate it with other instruments. We are exploring new communication interfaces; we utilized both in-memory and on-disk databases to be part of the interfaces not only for hardware monitoring but also for engineering event logging. We plan to incorporate the system of the James Clerk Maxwell Telescope for the full Linux-based receiver control. The current progress of integrating our receivers, spectrometers, sub-reflector, and continuum detector into control is presented, together with the implementation of the commissioning software for spectral line pointing. We also describe how we built the anti-collision protection and the recovery mechanism for the sub-reflector hexapod.