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PS reprint
B. Marshall, K. Gillies, J. Lewis
National Optical Astronomy Observatories, Tucson, AZ 85726
The six telescopes at Kitt Peak operated by NOAO for KPNO and WIYN use a variety of methods for control of the telescopes, sub-systems, and instruments. There is also a variety of user interfaces used with these systems. We first give an overview of these methods and then describe the integration of these systems. The KPNO telescopes discussed are: Mayall 4 meter, 2.1 meter, Coude Feed, 0.9 meter, and the Burrell-Schmidt. The WIYN telescope is a 3.5 meter telescope operated by NOAO for the WIYN Consortium (University of Wisconsin, Indiana University, Yale University, and NOAO).
The Burrell Schmidt telescope is the simpliest in terms of the control system and interfaces. The telescope is operated by manual control. The only computer control is for the filter wheel, which is operated by a VL188 STDbus processor programmed in FORTH. Commands are sent via a RS-232 serial line from a Sun workstation. The data acquisition system is based on the AMD 2901, programmed with microcode. As with the other KPNO telescopes, the Sun workstation-based data acquisition user interface is an IRAF task, ICE (Schaller 1992). ICE operates the detector controller and the filter wheel and builds an IRAF data file for further processing within IRAF.
The telescope control computer for the 0.9 meter is a PDP-11/23 based FORTH system. The subsystems and instruments are controlled via custom hardware based on CAMAC and programmed in FORTH. At the 0.9 meter, ICE communicates with the PDP-11 via FORTH commands over an RS-232 interface, both for simple control and for status information for the FITS headers. Other telescope control and setup commands are entered by the astronomer via FORTH commands in a terminal window.
The other three KPNO telescopes: The 4 meter, 2.1 meter, and Coude Feed have very similar control systems. The computers are VxWorks based 68030 systems, and most of the control hardware is custom built with CAMAC interfaces. There are also embedded STDbus controllers using VL188 processors programmed in FORTH at the 4 meter and the 2.1 meter for the drive servos and the operator console. At the 4 meter there is a PLC system which is controlled via vendor supplied software and is not yet integrated with the other software. The VxWorks based TCS (Thompson 1992) provides a FORTH-like serial line interface similar to the one at the 0.9 meter (for compatibility) which is used by ICE. This same interface is used by Wildfire (Heim, Buchholz, & Luce 1994), which is a transputer based system for the control of the infrared detectors at the 4 meter and 2.1 meter. Both ICE and WILDFIRE are command-line systems. The TCS also provides a Tcl based RPC protocol for sending commands and receiving status via the ethernet. Graphical user interfaces written in XView and Tk (Ousterhout 1994) provide operator interfaces to the telescopes and instruments.
At WIYN there are a number of control systems. There are 3 VxWorks based 68030 systems, one for telescope control and another one for active control of the primary mirror. The third system includes image processing hardware and is used to control guiding. The other subsystems at WIYN are controlled via serial lines, some of these systems include STDbus based 80C88 processors (programmed in `C').
The WIYN Message System protocol interconnects all these systems (with both ethernet and serial implementations). Command interpretors are used to provide an ASCII command interface to the WIYN Message System. An extensive operator user interface (Mills 1995) which is written in Tk provides control of all the WIYN systems and displays the telemetry from those systems. The WIYN instruments are controlled via serial lines from a Sun workstation either directly or with STDbus based 80C88 controllers. They are integrated using the GWC protocol, which is based on the WIYN message system.
The CCD controllers at WIYN are transputer based ARCON systems, using an IRAF based interface (similar to ICE) developed at CTIO and extended by NOAO in order to interface to the WIYN systems. The ARCON interface uses GWC to connect to the telescope and instruments.
We use 3 main methods for the integration of telescopes, instruments, and user interfaces.
The serial line commands consist of both the FORTH TCS commands and commands provided by low-level instrument controllers. The FORTH commands provided by the TCS (native FORTH at the 0.9m, and emulated FORTH commands at 3 other telescopes) provide some simple control functions (e.g., telescope focus) and access to telescope information for FITS headers. Some of this communication is in binary form. There is limited error handling ability with these systems, and no alarms or unsolicited messages from the low level systems. The commands sets provided by the instruments use ASCII. The data acquisition systems (for all telescopes other than WIYN) use these serial line commands.
The operator interfaces (for control of the telescopes and instruments) use ethernet based RPC protocols. These are all point-to-point protocols. The full command set of the VxWorks-based telescope control systems is available via Sun RPC. A command shell built with Tcl is provided (tcpShell) for command line control. The graphical user interfaces use Tcl-rpc to communicate using the same command set. For each command, a current value and the current status are returned. The status values are: DONE, BUSY, and FAILED. The GUI must poll the system at regular intervals to get the status of a command. For inter-GUI communication, the main protocol is Tcl-dp. There are also servers for guide stars and user coordinates which provide access via Tcl-rpc and Sun RPC.
At WIYN a message bus is used for integration. The base protocol is the WIYN Message System. Routers are used to connect the various distributed processes. Some of these processes are connected via serial interfaces, and use a serialized version of the WIYN Message System. The rest of the telescope and subsystem control uses the ethernet version of the WIYN Message System and the WIYN router. The messages are in binary form, and a telemetry system called the Engineering Data Stream (EDS) is built from these messages. A command line interface built with Tcl is provided which converts ASCII commands into WIYN messages.
For instrument integration at WIYN we use the Generic WIYN Client (GWC) protocol, which is layered on the WIYN message system. A new router (mpg_router) was written to provide connections between GWC processes (clients) and also a connection to the WIYN router. The GWC protocol was modeled after EPICS Channel Access, with the addition of command processing. The GWC library is built with Tcl and is also compatible with Tk, Motif, and XView for event processing.
The clients define streams which consist of related typed attributes (similar to EPICS process variables). Other clients can subscribe to these attributes such that they get notified whenever these values change. A sample data stream (part of the TCS Dome stream) is shown in Table 1. The following data types are supported: strings, integers, shorts, longs, enumerated types, floats, and doubles. These values are sent in the platform independent XDR format. The ``mpg_router'' converts the WIYN telemetry into GWC streams.
The command mechanism for these clients is built using the attributes. One or more attributes define a command, which is registered with the router. Other clients can then send these commands and/or can subscribe to the results of the command, which includes the current state of the attributes and the current status (BUSY, DONE, ERROR, or ALERT). The system is event driven; no polling is necessary.
Future plans include phasing out the FORTH systems, implementing GWC at the other telescopes, and incorporating EPICS in the VxWorks systems.
Mills, D. 1995, The WIYN Telescope Graphical User Interface, SPIE, Vol. 2479
Ousterhout, J. 1994, Tcl and the Tk Toolkit, (Addison-Wesley)
Percival, J. 1995, Remote Observing from the Bottom Up: The Architecture of the WIYN Control System, SPIE, Vol. 2479
Schaller, S. 1992, in Astronomical Data Analysis Software and Systems I, ASP Conf. Ser., Vol. 25, eds. D. M. Worrall, C. Biemesderfer, & J. Barnes (San Francisco, ASP), p. 482
Thompson, D. 1992, Remote Telescope Control at Kitt Peak, Observing at a Distance: Proceedings of a Workshop on Remote Observing, eds. D. Emerson & R. Clowes, 115