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Astronomical Data Analysis Software and Systems VI ASP Conference Series, Vol. 125, 1997 Gareth Hunt and H. E. Payne, eds.

The ESO VLT CCD Detectors Software
Antonio Longinotti European Southern Observatory, Garching bei Munchen, D-85748 Ё Germany, E-mail: alongino@eso.org Abstract. Charge Coupled Devices (CCD) are currently by far the most widely used typ e of detector in astronomy. At the ESO Very Large Telescop e (VLT), on mount Paranal in Chile, ab out 40 technical CCD cameras will b e in op eration for auto-guiding, field viewing, and wavefront sensing, as well as more than ten scientific CCD cameras for instruments working at optical wavelengths. After a brief introduction to the VLT Control System, the VLT CCD Detectors Control Software is presented.

1.

Introduction

The VLT Control System is a distributed system consisting of a set of UNIX Workstations, dedicated to high level op erations, such as coordination of subsystem activities and interface to the users, and VME-based Local Control Units (LCU), dedicated to the control of sub-systems hardware. The op erating system used on the LCUs is VxWorks. All computing units--Workstations and LCUs-- are connected through LANs. The CCD Software Package (Longinotti et al. 1995) is built on top of the VLT common software, which is a layer of services (drivers, libraries, utilities) used by all VLT applications (Raffi 1995). It has b een designed as one package to control all CCD cameras, b oth scientific (SCCD) and technical (TCCD). In this way, costs for software maintenance are reduced and the interface to applications is standardized, in that instrumentation and telescop e software interface to all cameras in one and the same way (§4). It b ecame available as part of the VLT Software in Octob er 1995, and four releases have b een issued since then. It is currently used at the ESO New Technology Telescop e for auto-guiding (two TCCDs), image analysis for active optics (two TCCDs), image quality assessment (two TCCDs), the EMMI instrument (two SCCDs and one TCCD for slit viewing), and the SUSI instrument (one SCCD). It is also used by the VLT FORS instrument (one SCCD), and in ESO labs for SCCD and TCCD new chip and camera tests and verification.

2.

System Architecture (Workstation and LCU) describ ed onics (ACE), and based on a transthe CCD camera head. has the following characteristics:

In addition to the two standard platforms ab ove, a third--called Array Control Electr puter network and DSP--is used to control The software running on each platform 418

© Copyright 1997 Astronomical Society of the Pacific. All rights reserved.


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Figure 1.

VLT CCD and Real-Time Display.

· Workstation. It includes programmatic and interactive user interface. The language used is C, with Tcl/Tk used for GUIs. · LCU. The core of the camera system control runs here. Performance is optimized in that op erations such as read-out from ACE and image transfer to the Workstation, are p erformed in parallel whenever p ossible. Image data are temp orarily saved in the LCU memory (e.g., for image re-transmission in case of a network failure). The language used is C. · ACE. The transputer and DSP based emb edded software runs here. It provides the direct interface to the camera electronics. The languages used are Occam (transputers) and C (DSP).

3.

Functionality

Compared to the previous generation of ESO CCD systems, in addition to the standard functionality (different readout modes and sp eeds provided, binning, windowing, execution and control of an exp osure, p ossibly rep eated n times, storage of data in FITS files, telemetry, and temp erature control), it implements:


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Figure 2.

VLT CCD stand-alone control panel.

· Real-time image pro cessing on LCU for TCCDs (image quality improvement, centroiding calculation, hook for user function implementing sp ecial algorithms). · Gain setting as part of the user setup. · Parallel readout from up to four outputs. The physical image is reconstructed within the LCU. · Display of images while they are b eing read-out, on any X-11 terminal through the VLT Real-Time Display facility (see Figure 1). · A Graphical User Interface (GUI), to control and monitor the status of a CCD camera as a simple stand-alone instrument--extremely useful for lab oratory and field testing (see Figure 2 and §5). · Supp ort for sp ecial control hardware on LCU, such as the high precision shutter for the FORS instrument.


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· Supp ort for new generation controllers. Ab out 80% of the LCU software is indep endent from the particular controller connected to the LCU VME crate, and can therefore b e re-used with other controllers. 4. Interface to External Software Packages

The interface to external software is well defined and consists of standard comp onents within the VLT software: · Command/Replies, based on the VLT Message System. · Setup files, containing exp osure setup definitions. · FITS files, containing the images produced as the result of exp osures. 5. Usage as Stand-alone Instrument

The CCD Software is able to work as a simple stand-alone instrument through a control panel, built using the VLT panel editor, which is based on Tcl/Tk (see Figure 2). Among others, it allows the following actions: · Define a single exp osure setup and save it in a setup file, or retrieve already defined setup files. · Define a sequence of exp osures (e.g., for standard calibration op erations). · Start exp osures, monitor their status, and p ossibly stop, pause, or ab ort them. · Display images with the VLT Real-time Image Display. · Interface to VLT data flow. Acknowledgments. I would like to thank here the p eople who contributed to the development of the VLT CCD software, in particular, C. Cumani and P. Duhoux. For more information or questions, please contact A. Longinotti (e-mail to alongino@eso.org). Information can also b e retrieved through anonymous ftp.1 References Raffi, G. 1995, The Messenger, 81 , 5 Herlin, T., Brighton, A., & Biereichel, P. 1995, The Messenger, 81, 6 Longinotti, A., Cumani C., & Duhoux, P. 1995, The Messenger, 82, 7

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ftp://te1.hq.eso.org/vlt/pub/do c, files ccd*