Introduction

The Sequencer is a software component developed in the scope of the Instrument Control System Framework (ICS FW) as the generic tool for the execution of Observation Blocks (OB) and engineering scripts.

Scope

This document is the user manual for the ELT ICS Framework - Sequencer. The intended audience are ELT users, consortia developers or software quality assurance engineers.

Acronyms

DB	Database
CCS	Central Control System
ELT	Extremely Large Telescopen
FCF	Function Control Framework
GUI	Graphical User Interface
ICS	Instrument Control System
OB	Observation blocks
OHS	Observation Handling Software

Overview

The sequencer shall support the execution of OBs and engineering scripts to automatize maintenance and operational activities such as the daily startup/shutdown of the telescope.

The sequencer can be seen, broadly, as comprised of three main components.

Sequencer Engine

Allows to load and execute Sequencer scripts

Sequencer API

Allows to define Sequencer scripts

Sequencer GUI

Displays and interact graphically with Sequences

This documents shows how to use the Sequencer API in order to build Sequencer scripts. A basic tutorial is given in Tutorial. A more detailed look is shown in A Deeper Look. A work in progress is the Good Practices section that we plan to fill in with good advice.

The Sequencer package provides some command line tools, they are described in Sequencer Command Line Tools.

Naming Conventions

Observation Block

A high level view of telescope operations. An observation block is the smallest observational unit for a telescope. It is a rather complex entity, containing all information necessary to execute sequentially and without interruption a set of correlated exposures, involving a single target (i.e. a single telescope preset).

Sequencer Script

A sequencer script is a script that can be executed by the sequencer, i.e. a template or an engineering script. The sequencer script may have parameters whose values determine the exact execution behavior. The sequencer script defines the execution order and the sequencer steps.

Engineering Script

A high level procedure to carry out a specific engineering task. The engineering script is a sequencer script.

Sequencer Step

An entity containing executable code, defined within a sequencer script.

Template

An entity dealing with the setup and execution of an observation.