Antenna Computer

Antenna ComputerA new antenna computer consists of a 21-slot VMEbus backplane, Motorola PowerPC 604 CPU module, Bancomm IRIG-B decoder and SBS GreenSpring IndustrialPack modular I/Os (analog inputs/outputs, TTL inputs/outputs, optocoupled digital inputs/outputs, IEEE-488 interface, serial interface). The computer chassis is mounted on the left-most 19" rack in the AOS room. I/O signals are routed from the Sidecab receiver room via SCSI-like shielded cables. It controls the telescope axes, secondary mirror focus and beam switch, Sidecab receiver optics and local phase locks, and Cassegrain instrument rotators. It also drives the status display monitors. In addition, it serves as a NTP server for the observatory, using a local GPS clock as reference.

The important difference from the old antenna computer is that this new computer runs UN*X-like hard real-time operating system LynxOS 3.0.1 from Lynx RTS. Also, it is a standalone system with local storage devices (hard disk and CD-ROM drives), unlike the old one which was a diskless, (sort of) bootp system.

Software for Telescope Control

First things first. Credits and acknowledgements go to the following products, organizations and individuals:

A new telescope control software for the CSO is based on the AT & T Bell Laboratories' OBS. For the top half part of the software, which is responsible for user interface, astrometry, non-RT device control, etc., the COMB (1997-beta) is used as a code base, the original OBS (1994) is merged, then it is almost completely rewritten using ANSI/ISO C instead of K&R C, extensively modified and numerous CSO-specific functions are added. The USNO's NOVAS C library and Dr. P.T. Wallace's SLALIB (C version) are used to handle B1950.0 coordinates. The bottom half part, which does all the RT jobs including telescope and dome feedback control, is derived from the Bell Labs' TRACKER (part of the OBS system), then multi-threaded and fitted to the CSO telescope. The telescope & dome feedback control code is originally taken from the OVRO's C code. The CSO's original FORTH code, which is based on the OVRO's FORTH code, is reverse engineered to create some low level device control codes in C. A telescope status display program, UIP interface program and all the device drivers are written at the CSO.