ATLAS Data Acquisition

ATLAS is a general purpose High Energy Physics experiment at the Large Hadron Collider. The trigger and data acquisition (DAQ) system is designed to handle the extremely high data rates. The three level ATLAS trigger system (Level 1, Level 2 and Event Filter) reduces the data rate from 40 MHz bunch crossing down to ~200 Hz. The DAQ system is designed to transport data at different trigger levels to the mass storage, with main subsystems including the dataflow, a combination of custom designed components and commodity processors running multithread software applications and connected by Gigabit Ethernet, the online software responsible for the configuration, control and information sharing of the system, and the monitoring software responsible for the data quality assurance. The system is being continuously commissioned in situ with detectors, to take cosmic data and the LHC beam data in 2008

The use of Ethernet in the DataFlow of the ATLAS Trigger & DAQ

The article analyzes a proposed network topology for the ATLAS DAQ DataFlow, and identifies the Ethernet features required for a proper operation of the network: MAC address table size, switch performance in terms of throughput and latency, the use of Flow Control, Virtual LANs and Quality of Service. We investigate these features on some Ethernet switches, and conclude on their usefulness for the ATLAS DataFlow network.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, March 2003, 10 pages, LaTeX, 10 eps figures. PSN MOGT01

The ROD crate DAQ software framework of the ATLAS data acquisition system

In the ATLAS experiment at the LHC, the ROD Crate DAQ provides a complete software framework to implement data acquisition functionality at the boundary between the detector specific electronics and the common part of the data acquisition system. Based on a plugin mechanism, it allows selecting and using common services (like data output and data monitoring channels) and developing software to control and acquire data from detector specific modules providing the infrastructure for control, monitoring and calibration. Including also event building functionality, the ROD Crate DAQ is intended to be the main data acquisition tool for the first phase of detector commissioning. This paper presents the design, functionality and performance of the ROD Crate DAQ and its usage in the ATLAS data acquisition system and during detector tests

Design and Prototyping of the ATLAS High Level Trigger

This paper outlines the design and prototyping of the ATLAS High Level Trigger (HLT) which is a combined effort of the Data Collection, HLT and PESA (Physics and Event Selection Architecture) subgroups within the ATLAS TDAQ collaboration. Two important issues, already outlined in the ATLAS HLT, DAQ and DCS Technical Proposal [1] will be highlighted: the treatment of the LVL2 Trigger and Event Filter as aspects of a general HLT with a view to easier migration of algorithms between the two levels; unification of the selective data collection for LVL2 and Event Building