Sep 25 – 29, 2006
Valencia, Spain
Europe/Zurich timezone

ATLAS TDAQ RoI Builder and the Level 2 Supervisor system

Sep 26, 2006, 5:35 PM
Valencia, Spain

Valencia, Spain

IFIC – Instituto de Fisica Corpuscular Edificio Institutos de Investgación Apartado de Correos 22085 E-46071 València SPAIN




The ATLAS High Level Trigger (HLT) uses information from the hardware based Level 1 Trigger system to guide the retrieval of information from the readout system. The Level 1 Trigger elements (jet, electromagnetic, muon candidate, etc.) determine Regions of Interest (RoIs) that seed further trigger decisions. This paper describes the device - the RoI Builder - that collects these data from the Level 1 Trigger and the Level 2 Supervisors (L2SV) Farm that makes these data available to the HLT. The status of the system design and the results of the tests and integration into ATLAS TDAQ system are presented.


The Region of Interest Builder (RoIB) is intended to build RoI records from data
received from the Level 1 Trigger system and distribute the records at high input
rate to a number of Level 2 Supervisors (L2SV) in a farm. From there the RoI
records will be distributed to the High Level Trigger (HLT) processors that require
it for further event selection and disposition.
The RoIB, located in the underground counting room, takes raw event fragments from
various Level 1 Trigger sources, assembles all the fragments of a given event into
an RoI record, selects a target L2SV processor, and then sends the RoI record to
this processor. The ROIB is implemented as a number of VME boards in a 9U VME crate
with a custom built backplane.
The Level 2 Supervisor farm, located in the surface TDAQ computing farm barracks,
is composed of commercial rack mounted PCs. They are connected to the RoIB via
ATLAS standard SLINKs and to the High Level Trigger – via Ethernet. A single Level
2 Supervisor processor never sees the full Level 1 rate and it can manage the
required input/output event rate.
The RoIB and L2SV system has undergone a number of prototypes, a series of design
reviews and several tests, and integration with individual parts of the Level 1
Trigger system and the HLT. Now it enters the commissioning stage via incremental
installation of individual RoIB components and connection of the Level 1 Trigger
system up to the fully populated RoIB crate. The size of the L2SV farm will be
supplemented according to need determined by the increasing event rate during

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