[Paper Review] Configuration of the ATLAS Trigger System

M. Elsing, T. Schoerner-Sadenius|ArXiv.org|Jun 5, 2003

Distributed and Parallel Computing Systems3 references6 citations

TL;DR

This paper presents a unified software configuration framework for the ATLAS trigger system, enabling consistent selection of physics signatures across the Level-1 (LVL1) hardware trigger and High-Level Trigger (HLT) software-based system. It uses recursive logic and XML-based configuration to map physics menus to trigger elements, with successful testing in offline and online test-beds, paving the way for integrated LVL1 and HLT configuration to ensure system-wide consistency.

ABSTRACT

In this paper a conceptual overview is given of the software foreseen to configure the ATLAS trigger system. Two functional software prototypes have been developed to configure the ATLAS Level-1 emulation and the High-Level Trigger software. Emphasis has been put so far on following a consistent approach between the two trigger systems and on addressing their requirements, taking into account the specific use-case of the `Region-of-Interest' mechanism for the ATLAS Level-2 trigger. In the future the configuration of the two systems will be combined to ensure a consistent selection configuration for the entire ATLAS trigger system.

Motivation & Objective

• To develop a unified configuration approach for the ATLAS trigger system that ensures consistency between the LVL1 hardware trigger and HLT software trigger.
• To define and implement a software-based configuration system for the HLT that supports complex, multi-step trigger sequences using trigger elements and algorithms.
• To enable the integration of LVL1 and HLT configurations by aligning their menu definitions and selection logic.
• To support efficient and selective event reduction from 40 MHz to 200 Hz through configurable, physics-driven trigger menus.
• To provide a testable, modular configuration system using XML and object-oriented design for both simulation and online use.

Proposed method

• The LVL1 configuration is implemented via a software prototype that translates trigger menus into hardware settings, focusing on algorithmic aspects rather than low-level hardware details.
• The HLT configuration uses two XML files: one for physics signatures (defined by required trigger elements), and one for sequences (defining input TEs, algorithms, and output TEs).
• A recursive algorithm derives all intermediate signatures and required sequences from the trigger menu, starting from basic trigger elements (e.g., 'EM20') and building up to complex physics signatures (e.g., '2e30i').
• The HLT configuration is parsed using the XERCES DOM API to build an object tree, which is then used to generate menu and sequence tables for event selection.
• The system supports a clear separation between LVL2 and EF by assigning the first set of sequences to LVL2 and the remainder to EF, based on timing and processing constraints.
• A UML class diagram models the configuration data structure, with pairs of MenuTable and SequenceTable objects storing signatures and algorithmic steps.

Experimental results

Research questions

• RQ1 How can a consistent configuration strategy be established across the LVL1 hardware trigger and HLT software trigger systems?
• RQ2 What software architecture enables the recursive derivation of complex trigger signatures from basic trigger elements?
• RQ3 How can XML-based configuration files be used to define both trigger menus and algorithmic sequences in a scalable and testable way?
• RQ4 What mechanisms ensure that the LVL1 and HLT systems make compatible decisions based on the same physics menu?
• RQ5 How can the configuration system support both offline simulation and online operation in a unified framework?

Key findings

• A functional prototype for LVL1 trigger configuration was developed and integrated into the ATLAS simulation chain, focusing on the algorithmic aspects of trigger menu translation.
• The HLT configuration system was successfully tested in both offline and dedicated online test-beds using XML-based configuration and object-oriented data structures.
• The recursive configuration logic correctly derived intermediate signatures such as '2e30' and '2ecand' from basic trigger elements like 'e30' and 'EM20'.
• The system enables a clear separation between LVL2 and EF processing by assigning sequences to each level based on timing and complexity.
• The configuration framework supports consistent trigger decisions across the entire system by aligning LVL1 and HLT logic on the same physics menu.
• Future integration of LVL1 and HLT configuration is planned, using the input menu table from the first HLT step to ensure end-to-end consistency in trigger selection.