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LSST Interface Definitions


  • CSC - Commandable SAL Component
  • DDS - Data Distribution Services
  • LSST - Large Synoptic Survey Telescope
  • SAL - Service Abstraction Layer
  • TSSW - LSST Telescope & Site Software
  • XML - eXtensible Markup Language


This repository contains all the interface definition files for all the CSCs of the LSST. All of the CSCs communicate using the DDS protocol. TSSW provides a wrapper utility around DDS, called the Service Abstraction Layer or SAL.

The SAL produces libraries in C++, LabVIEW, and Java for each CSC. These libraries are then used by all the CSCs that need to publish or subscribe to any message topic. The Python interface to DDS is handled by ts_salobj

Installation and Usage

This repo is primarily a single location for all the definition files. This repo in conjuction with the SAL are used to produce the code libraries. Please refer to the documentation in the ts_sal project for instructions on manually producing those libraries.

Build Documentation

To build the documentation::

cd doc
package-docs clean
package-docs build


To ensure the successful build of your libraries, there are unit tests contained in the tests/ directory. To run them, first setup the test environment

pip install .[test]

This will install the pytest, astropy, lxml and numpy dependency modules used to verify the XML files are correct.

Then to run the unit tests, simply execute:

pytest -ra

from anywhere in the repository. This will run the tests and print out a short summary of the results, including tests that are skipped for known reasons. The messages associated with the skipped tests include Jira ticket numbers to track the issues. Please navigate to

to find the specific ticket.

XML formatting, XML linting

Linting is enforced on GitHub through GitHub Actions (.github/workflows/xml-format.yaml).

lxml ( is used in unit tests to verify files conform to the XML format standards. Additionally, pre-commit has been setup on this repo, so various linting checks are done with each push to GitHub. If you wish to have these checks run locally with each commit, please follow the instructions in the TSSW Developer Guide

Test Utilities

The file, located in python/lsst/ts/xml, contains functions and variables used throughout the testing. The lists of generic Commands and Events, as well as Reserved Words, imposed by third party tools, are all defined in Most importantly, the independent list of expected CSCs is also defined here. If these lists change, the corresponding list in must also be updated. For example, if a CSC is added, removed or renamed, the tests will produce the following error:

AssertionError: There is an unexpected number of CSCs.

In case this error occurs, the subsystems list in should be updated accordingly.

Add, Rename or Delete a CSC

Please follow the process defined the TSSW Developer Guide to add or remove CSC.

NOTE: Any changes to the list of CSCs must be approved at the CAP meeting BEFORE the changes are made. Please add an agenda item to the appropriate weekly meeting.

Adding, renaming or deleting a CSC, involve operations on files and directories within python/lsst/ts/xml.

To add a CSC:

  • Add an entry in data/sal_interfaces/SALSubsystems.xml
  • Add directory in data/sal_interfaces for the CSC
  • Add necessary topic type XML files in the new CSC directory
  • Add entry in CSC list in

To rename a CSC:

  • Rename the entry in data/sal_interfaces/SALSubsystems.xml
  • Rename CSC in dependency entries if applicable
  • Rename directory in data/sal_interfaces
  • Rename files in CSC directory making sure to update the contents too
  • Rename CSC entry in list

To delete a CSC:

  • Delete entry in data/sal_interfaces/SALSubsystems.xml
  • Delete CSC in dependency entries if applicable
  • Delete directory and files in data/sal_interfaces corresponding to CSC
  • Delete CSC entry from list

Enums and other constants

This repository contains the enumeration values and tables used by other projects. Those are stored in ( and (


We use SemVer for versioning. For the versions available, see the tags on this repository.

Contact Information

Please contact with any questions or concerns.