The Gemini Core Instrument Control System

S. M. Beard

Royal Observatory,¹ Blackford Hill, Edinburgh, EH9 3HJ, UK

¹The Royal Observatory Edinburgh is funded by the Particle Physics and Astronomy Research Council.

Abstract:

1. Introduction

1.1. Gemini Instruments

Gemini is an international project to build two 8m telescopes, at Mauna Kea in Hawaii and at Cerro Pachon in Chile. Several instruments are being developed for these telescopes by diverse groups in the USA, UK, Canada and Chile. All the instruments will share a common software platform, using VxWorks/VME hardware and EPICS, a real-time database control system (Dalesio 1995).

Table 1 shows the instruments which are currently planned for Gemini. The information is taken from Gillett (1995). The last three instruments in the table are shared with other telescopes. The others are facility instruments which are being built specifically for Gemini.

1.2. The Gemini Control System

The Gemini Control System (McGonegal 1996) consists of four principal systems: the Observatory Control System (Gillies 1996); the Telescope Control System (Mayer et al. 1996); the Data Handling System (Gaudet & Crabtree 1996); and the various Instrument Control Systems, as shown in Figure 1. The interfaces between these systems are described in Interface Control Documents (ICDs), as labelled on the diagram.

Figure 1: The four principal systems of the Gemini Control System.
Figure 1: PS 55 Kb

The Gemini Control System is designed to allow more than one instrument to be mounted and used simultaneously, so the operator will need to be able to switch between the different instruments easily. Besides this, the instruments will not necessarily be maintained and operated by the same people who built them. In order to save operational and maintenance costs it is important that there be as much commonality between the instruments as possible.

Each instrument (including the Acquisition Camera) is controlled by a separate Instrument Control System, which sits in the same operational environment governed by the same set of ICDs.

2. Structure of a Gemini Instrument Control System

A Gemini Instrument Control System consists of a Detector Controller, which sequences the detector and is responsible for reading and preprocessing the data from it, a Components Controller, which controls the instrument's mechanisms, and an Instrument Sequencer, which coordinates the other two subsystems, as shown in Figure 2.

Many of the Gemini instruments will use the same type of detector. The Detector Controllers are being developed separately from the instruments so that the instruments can share copies of the same Detector Controller. Instrument groups are responsible for the Instrument Sequencer and Components Controller parts of their system.

Figure 2: The Basic Structure of a Gemini Instrument Control System.
Figure 2: PS 33 Kb

3. The Core Instrument Control System

The Core Instrument Control System is a Gemini work package which helps to achieve the desired commonality between instruments. It builds on the earlier work of Johnson (1995), who developed a standard set of device drivers and compiled some excellent documentation describing how to set up a standard Gemini EPICS/VxWorks/VME system.

All the Gemini Instrument Control Systems have to: (i) respond to commands from the Observatory Control System (ICD/1); (ii) configure themselves and make observations in response to those commands; (iii) provide the Observatory Control System with a summary of their status (ICD/2); (iv) sample and store time-critical status items for inclusion in the data header; (v) communicate their data to the Data Handling System (ICD/3); (vi) communicate with the Telescope Control System (ICD/6)²; and (vii) interface to the standard Gemini buses (Time Bus, Synchro Bus, Event Bus and Interlock System).

The Core Instrument Control System provides an Instrument Control System template. The template includes an example of all the above operations and shows how to communicate with other Gemini systems, but it does not control any hardware. It can be compared with a LaTeX template which shows an author how to put together a paper adhering to the standards of the target publication without actually constraining the words that are written in the paper.

The goal of the project is to provide one solution to common problems, so instrument groups can concentrate on those operations which are unique to their instrument, avoid any duplication of effort and reduce their development costs.

The CICS passed its Preliminary Design Review in October 1995 and is scheduled for delivery in early 1997.

4. Further Information

Full details of the Core Instrument Control System may be found in the CICS documentation (Beard 1995) and my personal Gemini World Wide Web page. Details on the Gemini project and Gemini instruments may be found in the Gemini project home page.

Acknowledgments:

I am grateful to Rick McGonegal, Malcolm Stewart, Steve Wampler and Susan Wieland for providing comments on this paper.

References:

Dalesio, L. R. 1995, paper presented at ADASS V Conference in October 1995

Gaudet, S., & Crabtree, D. 1996, this volume

Gillett, F. 1995, Gemini 8-M Telescopes Project Newsletter, No. 10 (June 1995), 5

Gillies, K. 1996, this volume

Johnson, A. N. 1995, ``The Gemini Standard Controller Hardware Documentation'', Document SPE-C-G023, Gemini 8m Telescopes Project

Mayer, C. J., Laing, R., Taylor, P. B., & Wallace, P. T. 1996, this volume

McGonegal, R. J. 1996, this volume

²Note that the Telescope Control System is normally controlled by the Observatory Control System. Direct control by an instrument is reserved only for situations where there are unusual timing constraints.