SOFTWARE INTERFACE

The ATCS Interface

The tif module is responsible for providing the central and only command interface between external users and the TCS. The VLTI Interferometer Supervisor Software is the most typical high level user for the VLTI Auxiliary Telescopes.

The VLTI Supervisor Software user processes communicate with the ATCS by sending commands to and receiving replies from the tif. The tif internally dispatches the commands to the responsible TCS processes, receives their replies and passes them back to the caller.

To enable multiple read access to TCS public data, a Data Query Library is provided which is linked to the user process and thus is not subject to the booking system. Also a public Event Configuration Library is provided to attach events to TCS data items. These libraries are described in section Application Programming Interface.

Commands

The following table alphabetically lists the telescope control commands. On top of these TCS commands, the tif control process accepts all the usual VLT standard commands and a small set of specific commands used for maintenance purposes.

The complete set of commands accepted by an AT tif control process is described in the CDT in appendix

Units and coordinate systems for command parameters follow VLT conventions.

These are perhaps not the ones some users would expect, or might be different to what is used in other contexts (like FITS Headers). Please, make sure that you always check units and conventions in the Command Definition Table.

This document describes the interface between AT and ISS, i.e all the interfaces needed to control the ATs for VLTI observations. TIF in itself will probably also have more commands, used to control the telescope not for pure VLTI coordinating purposes. This anyway does not include operations performeds by the operators on control panels. For example operating the enclosure is done via a dedicated AT control panel, that uses internal AT commands, not defined in tif. This is because we do not want enclosure commands to be public for other applications than the operator control panels and AT internal procedures.

Telescope Commands

Sending commands to TIF processes

• To have ATCS or ATCS Simulation Package installed and configured (see VLT TCS User Manual [AD10])
• Environment variables properly set (see VLT TCS User Manual [AD10])
• A running environment with ATCS or ATCS Simulation database branch (see in particular section Using the TCS Database and Event Interface Library )
• A running ATCS or ATCS Simulation software.

Application Programming Interface

The data access libraries are not subject to booking constraints, allowing multiple read access to the ATCS data. 

• The Data Query Library retrieves ATCS data items. This includes functions to retrieve FITS header keywords.
• The Event Configuration Library attaches events to ATCS data items
• The two data libraries are combined in the tifLibs library files (both static and shared versions) under $VLTROOT/lib and can be linked to an application in the usual way (see man-page of the vltMakefile). The sources need to include the tif.h header file to access library functions. See VLT TCS User Manual [AD10] for man-pages of the libraries and for a sample program.

Data Query Library

The list of supported data items (configured by tif in the database) is loaded at startup or init of any tif application.

The set of functions that return groups of related data items in structures:

• tifGetPosition(): the telescope position in various coordinates.
• tifGetStates(): the states of ATCS modules.
• tifGetStatus(): the status of the ATCS (returned data still to be defined).
  The information returned by the Data Query Library always reflects the state of the ATCS correctly even after ATCS shut-down or when a process crashes.

• tifGetByName()
  is provided to query single data items by name. The routine takes a symbolic name, as a string or by using provided defines, as input parameter and returns the data associated with that name in a user buffer, and also information about the data type.

• HMS: hours, minutes, seconds and fractions of seconds
• DMS: degrees, arcminutes, arcseconds and fractions of arcseconds
• MJD: modified julian date
• BOOL: boolean (TRUE or FALSE)

Named Data Items

FITS header data

• tifGetFitsStart(): Generate the TCS FITS keywords at start of exposure
• tifGetFitsEnd(): Generate the TCS FITS keyword at end of exposure and dump in file

TCS FITS Header Keywords

Event Configuration Library

The supported event items (configured by tif in the database) are read only once at startup of any tif application.

The routines

• tifAttachEvent()
• tifDetachEvent()

The following table presents a list of all currently supported named events.

The actual name for the enum to be used in the call to tifAttachEvent()is obtained adding the prefix tifEVENT to the name in the first column of the table.

This list will be extended in subsequent releases of this document and software.

Database Events

Using the ATCS Database and Event Interface Library

• To have ATCS or ATCS Simulation Package installed and configured (see VLT TCS User Manual [AD10])
• Environment variables properly set (see VLT TCS User Manual [AD10])
• A running environment with ATCS or ATCS Simulation database.
• The code should be written in C++ or at least compiled with the C++ compiler, i.e. the files should have the .C (capital C) filename extension. For more details on how C and C++ code interact, refer to the eccs [AD 07] and evh [AD 09] user manuals.
• The Makefile must contain proper definitions for the TARGET_TCS to be built.
• The library tifLibs must be linked with the code. A typical VLT C++ application requires also the following set of libraries: evh eccs fnd C++ CCS.
• If tifGetFitsStart() and tifGetFitsEnd() are used also the following libraries must be linked with the code; oslx slx misc tcsVcc msw .
• The include file tif.h contains all the necessary definitions and function prototypes. VLT TCS User Manual [AD10]
  contains three complete and working sample programs, two using the Data Query Library and the other one using the Event Configuration Library.

Online Database Access Classes

The class tifTCS_PUBLIC can be instantiated in any user database to provide a local image of the ATCS public data items. This class is used when the TCS database, real or simulated, is NOT in the same environment as the user database. In this case, the scan system is used to update the user database with values from the ATCS environment (real or simulated).

The class tifTCS_LOCAL has the same structure as tifTCS_PUBLIC (it is a subclass) and provides the same items, but can be instantiated in the same environment where TCS itself is running, i.e. when simulated TCS data are a part of the user database. In this case, the items are updated using the calculation engine, instead of the scan system.

These classes have been implemented to provide access to ATCS data for UIF instrument panels and Sequencer scripts, while C and C++ applications should use the tif Query Library.

For performance reasons, not more than one instance of the classes should be used in each environment.

Structure of the tifTCS_XXX public on-line database classes

This has been done in order to allow a more structured access to the items themselves and to optimize performance on the update of the items, that is based on the RTAP calculation engine.

What follows is the structure of the class:

tifATCS_PUBLIC