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The VLTI Control System
General Description

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Scope

The VLTICS provides the functions to control all the heterogeneous devices belonging to the VLTI. The following table shows the VLTI main elements to be controlled, either directly or indirectly, and the external interfaces:

Direct Control Indirect Control External Interfaces
  • Auxiliary Telescopes
  • Delay Lines/LI>
  • VLTI Subsystems
    • VLTI UT Coude
    • Transfer Optics
    • Fringe Sensor Unit
    • Internal Alignment Unit
      • Image Alignment Unit
      • Pupil Alignment Unit
      • Fringe Phase Alignment Unit
  • Unit Telescope
    		•
  • Telescope Control Software
  • Data Flow System
  • Astronomical Site Monitor
  • Building Management System
  • VLTI Instrument Control Software
  • VLTI Human Operator
    		•

    The following figure shows the VLTICS inserted in its operational environment.

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    Control Hardware

    Because of the number, the heterogeneity and the locations of the Interferometer components, the VLTICS is based on a distributed, multi-platform, network-based architecture. Local Control Units (LCUs), composed by a VME backplane equipped with CPU boards and interface cards, perform real-time control of VLTI subsystems. Multi-user multi-tasking workstations (WSs) run high-level coordinating tasks and the graphical user interface software. Network links will provide the communication layer among all the computing nodes and a dedicated Time Bus will convey the time synchronization signal.

    The VLTI Control Hardware has an interface to the VLTI Instrumentation Control Hardware through the VLTI Backbone Network, and to the VLT Telescope Control System through a router connecting the VLTI and the VLT Backbone Networks.

    The system is designed to be highly modular, in the sense that the hardware and the software devoted to control a subsystem must have complete functionality by themselves, without any knowledge about other subsystems. Therefore direct links between LCUs are avoided, unless very special high bandwidth requirements necessitates dedicated point-to-point communication channels.

    The VLTI Control System uses VLT standard electronics. The workstations are equipped with X11 graphical terminals. The local area network employs Ethernet and ATM technology, using optical fibers.

    The following table provides the details about the VLTI control hardware.

    non-real-time real-time
  • HP or Sun Workstations
    		•
  • VMEbus
  • VLT Standard Boards:
    • CPU: MVME 167 (Motorola 68040)
    • Timing: ESO TIM Module
    • Digital I/O: Acromag AVME 9481
      • >
    • Analog I/O: VMIC VMIVME 3111
    • Motion Control: Maccon MAC4
    • Servo Amplifier: ESO VME4SA Module
    • CCD transputer interface: INMOS B016
    • Serial Interface: ESD ISER8
    • Encoder: Heidehain IK 320
    • VMEbus-VMEbus communication: VMIC VMIVME 5576

    The concept of the hardware architecture of the VLTI Control System is shown in the following figure.

    []

    Control Software

    The VLTI Control Software is essentially constituted by a set of running programs (processes), distributed on LCUs and WSs. They cooperate exchanging messages and sharing a common on-line database. The real-time control software of a subsystem run entirely at LCU level, while software of coordinating is implemented at the WS level. The software is built in functional layers; each layer provides all the required services to the next upper layer and hides the details of the lower layers.

    The VLTI Control Software is entirely based on the VLT common software (CCS/LCC).

    The following figure shows the VLTI Control Software within the global framework of the VLT Software.

    []

    The following table summarizes the services provided by CCS/LCC.

    WS platform (CCS) LCU platform (LCC)
  • on-line database
  • message system
  • command checking
  • event handling
  • scan system
  • time system
  • log system
  • error system
  • alarm system
  • booking system
  • engineering user interface
  • sampling utilities
  • graphical user interface toolkit (CCS/UIF)
  • object oriented interface (ECCS)
  • event-driven application toolkit (CCS/EVH)
  • on-line data base loader (CCS/DBL)
    		•
  • local database
  • message system
  • log system
  • error system
  • scan system
  • access control
  • sampling
  • I/O system
  • time services
  • start-up/shut-down procedures
  • command interpreter
  • simulation support
  • engineering user interface
  • device drivers for VLT standard boards
    		•

    The VLTICS is composed by a set a software packages and modules. Three main packages are defined and listed below.

    Interferometer Supervisor Software (ISS) provides the functions to operate the whole VLTI, like system start-up and shut-down, array configuration setting, observation preparation and run. It coordinates the high level tasks of all the main VLTI components.

    Auxiliary Telescope Control Software (ATCS) provides the functions to operate each AT, both at subsystem level (low level control of each device) and at coordination level (like during presetting, tracking, relocating to another station), and to command a group of ATs as a single entity.

    Delay Line Control Software (DLCS) provides the functions to operate the array of all DLs. It coordinates the operation of the DLs and provides control of each DL, both at subsystem level (low level control of each device) and at coordination level (like during presetting, searching for fringes, blind tracking, fringe tracking). The following diagram shows the software breakdown and the main interactions among VLTICS packages and external elements.

    []

    These packages are composed by several software modules, grouping set of logically and functionally related tasks. Each software module is designed as one or more cooperating processes. A module can run entirely on the WS platform, or in the LCU environment, or can also be split across both of them.

    The rest of the VLTI Control Software is arranged into the expression VLTI Subsystem Software, which refers to the programs needed to control those VLTI subsystems that are not already part of the Auxiliary Telescope System and of the Delay Line System. These control programs are, as usual, organized in modules, which have the features already explained in the previous paragraph. The subsystems are the following:

    The following scheme shows the module diagram.

    []
    Send comments to <mverola@eso.org>
    Last update: Apr 27, 1998
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