ATLAS TDAQ Glossary

Aims and Procedures

Aim: Establish a set of acronyms and expressions for the ATLAS Trigger DAQ community which can be referenced in any document. This is being developed to avoid multiple conflicting definitions and therefore unify the understanding throughout the trigger DAQ community.

Procedure: The definitions have been collected from various documents and from the various communities inside Trigger DAQ. A number of these expressions and acronyms have been adjusted to their current use and very often the old definition is given with the comment that it is obsolete or only valid for a certain context. Please participate by sending comments or new definitions to Marc Dobson and Fred Wickens.

Acronyms

BC

Front-End    Bunch Crossing
 

BCID

Front-End    Bunch Crossing Identifier
 

BCR

Front-End    Bunch Counter Reset
 

CERN

General    European Laboratory for Particle Physics
 

CF

General    Connect Forum
 

Cid

General   Obsolete?    Crate identifier
 

CMT

General    Configuration Management Tool
 

ConfDB

Online Software    Configuration Database
 

CORBA

Online Software    Common Object Request Broker Architecture
 

CTP

General    Central Trigger Processor
 

CVS

General    Concurrent Versions System
 

DAL

General    Data Access Library
 

DAQ

General    Data Acquisition System
 

DC

General    Data Collection
 

DCS

General    Detector Control System
 

DDC

Online Software    DAQ-DCS Communication
 

DF

General    Data Flow System
 

DFM

General    Data Flow Manager
 

Did

General    Destination identifier
 

DIG

General    Detector Interface Group
 

DMA

General    Direct Memory Access
 

DSA

Online Software    Diagniostics Supervision Agent
 

DVS

1. DCS   Obsolete ???    Data Viewing System
    
2. Online Software    Diagnostics and Verification System
    

EB

General    Event Builder
 

EBIF

General    Event Builder InterFace
 

ECR

Front-End    Event Counter Reset
 

ED

Online Software    Event Dump
 

EF

General    Event Filter
 

EFD

General    Event Filter Dataflow
 

EH

General    Event Handler
 

EL1ID

General    Extended Level-1 ID
 

ELMB

DCS    Embedded Local Monitor Board
 

ESA

General    European Space Agency
 

EVS

Online Software    Event Viewing System
 

FE

General    Front End
 

Gid

General    Global event identifier
 

HLT

General    High Level Triggers
 

IGUI

Online Software    Integrated Graphical User Interface
 

ILU

General    Inter-Language Unification System
 

IOM

General    I/O Module
 

IPC

General    Inter-Process Communication
 

IPC_REF_FILE

Online Software    IPC Reference File
 

IS

Online Software    Information System
 

L1A

Front-End    LVL1 accept
 

L1ID

Front-End    LVL1 Trigger Accept Identifier
 

L2IF

General    Level-2 Interface (Obsolete)
 

L2PU

General    Level-2 Processing Unit
 

L2SV

General    Level-2 Supervisor
 

LDAQ

General    Local DAQ
 

LHC

General    Large Hadron Collider
 

LVL1

General    Level-1 trigger system
 

LVL2

General    Level-2 trigger system
 

MRS

Online Software    Message Reporting System
 

OBK

Online Software    Online BookKeeper
 

OH

Online Software    Online Histograming
 

OKS

General    Object Kernel Support
 

PCI

General    Peripheral Component Interconnect
 

PESA

General    Physics and Event Selection Architecture
 

PID

General    Partition Identifier
 

PMG

Online Software    Process Manager
 

pROS

General    pseudo-ROS
 

PT

General    Processing Task
 

RC

Online Software    Run Control System
 

RDB

Online Software    Remote Database
 

RM

Online Software    Resource Manager
 

ROB(in)

General    Read-Out Buffer (input stage)
 

ROC

General    Read-Out Crate (Specific implementation of a ROS)
 

ROD

General    Read-Out Driver
 

RoI

General    Region of Interest
 

RoIB

General    Region of Interest Builder
 

ROL

General    Read-Out Link
 

ROS

General    Read-Out Subsystem
 

SFC

General   Obsolete, except test beam    Sub-Farm Crate
 

SFI

1. General    Sub-Farm Input
    
2. General   Obsolete    Switch to Farm Interface
    

SFO

General    Sub-Farm Output
 

Sid

General    Source identifier
 

SRT

General    Software Release Tools
 

StP

General    Software through Pictures
 

TDAQ

General    ATLAS Trigger/DAQ/DCS
 

TM

Online Software    Test Manager (also TMGR)
 

TMGR

Online Software    Test Manager
 

TRG

General    Trigger Module (function inside present implementation of ROS)
 

TTC

Front-End    Timing, Trigger and Control (TTC)
 

TTCrx

Front-End    TTC Receiver
 

TTCvi

Front-End    TTC VME Interface
 

Expressions

Back-end system

General   Obsolete, see Online System    All the software for configuring, controlling and monitoring of the DAQ prototype -1. It excludes: the management, processing and transportation of physics data.
 

Bunch Counter Reset (BCR)

Front-End    Signal broadcast by the TTC system once per LHC orbit (89 µs) to control the phase of the local bunch counters.
 

Bunch Crossing (BC)

Front-End    Bunch Crossing.
 

Bunch Crossing Identifier (BCID)

Front-End    Number that defines the bunch crossing at which an event occurred. Potential bunch crossings are numbered 0 to 3563 per LHC orbit, starting with the first following the LHC extractor gap.
 

Central Trigger Processor (CTP)

General    The place where the LVL1 trigger is generated.
 

Collector

General    An element of an EF sub-farm which obtains events from the processing elements of the sub-farm and provides them to the SFO.
 

Component

Online Software    An internal part of the online software sub-system (e.g run-control, message reporting system etc.)
 

Concurrent Versions System (CVS)

General    The software version control system provides the possibility to record the history of file modifications and retrieve previous versions [2].
 

Conditions database

General    The conditions database contains the record of the detector confitions for all data taking. This includes calibration and geometry constants and any other parameters required for the data analysis.
 

Configuration databases (ConfDB)

Online Software    The configuration databases store the parameters necessary to describe the TDAQ system's architecture, hardware and software components, and running modes (and status?).
 

Configuration Management Tool (CMT)

General    This is the configuration management tool which has been adopted by ATLAS and which helps build and run the ATLAS software.
 

Crate control

DAQ-1    A high-level DAQ function of the LDAQ which allows an operator to coordinate the activities of IOMs within a DAQ-unit. A more detailed definition is given in [1].
 

Crate fragment

General   Obsolete, see ROS fragment    The set of ROB fragments, within a ROC, with the same Gid and buffered within the L3IF.
 

Crate identifier (Cid)

DAQ-1   Obsolete    The unique system wide identifier of a ROC.
 

DAQ configuration

DAQ-1   Replaced by TDAQ configuration    Source: ATLAS Prototype DAQ Back-End Software User Requirements Document
A set of hardware pieces and software objects used to take data from the detectors.
 

DAQ partition

DAQ-1   Replaced by TDAQ partition    Source: ATLAS Prototype DAQ Back-End Software User Requirements Document
A configuration that involves the DAQ and one or more sub-detectors and represents an independent entity that can be used to take data or perform tests.
 

DAQ Run

DAQ-1   Needs Revising    Source: ATLAS Prototype DAQ Back-End Software User Requirements Document
A continuous period in time of data taking using a given hardware and software configuration and a defined set of run parameters. It is identified by a unique run number. The run begins when the DAQ, detectors and other sub-systems are correctly configured and the machine conditions are acceptable. A run terminates either cleanly when the pre-defined goals of the run are met (e.g. a certain number of events have been taken) or aborts when a serious unexpected problem occurs (e.g. loose the beam or the machine conditions are unacceptable etc.) or when the configuration of the partition changes.
 

DAQ-unit

DAQ-1   Obsolete    The functionality of the read-out crate or the sub-farm crate concerned with the management and transportation of physics data.
 

Data Collection (DC)

1. General    DataCollection is a subsystem of the Atlas TDAQ DataFlow system responsible for the movement of event data from the ROS to the LVL2 Processing and to the EventFilter and also to MassStorage. DataCollection is not responsible for initializing and formatting (or preprocessing) of event fragments inside the ROS, neither is it responsible for preprocessing or performing trigger decisions in the LVL2 Processing Unit or in the EF SubFarm.
    
2. DAQ-1   Obsolete    The collecting and possible ordering of a set of ROB fragments into a crate fragment.
    

Data Collection Framework

General    A set of services used by all LVL2 and EB applications, which provides a unified program structure and common interfaces to Configuration Database, Run Control and other Online Software services.
 

Data control messages

DAQ-1   Obsolete    The data, excluding ROB or crate fragments, exchanged between IOMs. They cause the receiving IOM to perform a specific action.
 

Data Flow Manager (DFM)

1. General    The DFM orchestrates the correct flow of data fragments between ROSs and SFIs. It is triggered by the L2SV, load balances the event building tasks on the SFIs and ensures that the ROSs do not overflow their internal memory buffers.
    
2. DAQ-1    An element of the event building sub-system which ensures the correct flow of data between event builder sources and destinations.
    

Data Flow system (DF)

1. General    System comprising the ROS and DC HLT subsystems (previously also included HLT but this is now a separate system).
    
2. DAQ-1    All software and hardware required for the management, transportation and monitoring of physics data.
    

Data Taking Period (Obsolete?)

General    Source: ATLAS Prototype DAQ Back-End Software User Requirements Document
A succession of DAQ runs in which no major changes are made to the detector and DAQ configurations.
 

Data Viewing System (DVS)

DCS    Allows users to have access to aggregate displays, such as histograms and trace plots, representing the performance of sub-systems of the data acquisition system [3].
 

Derandomizer

General    Place where the data corresponding to a LVL1 trigger accept are stored before being read out.
 

Destination identifier (Did)

General   Where is this used?    The unique system wide identifier of a destination. This is a high-level identifier, independent of technology.
 

Detector Control System (DCS)

General    It comprises the control of the subdetectors and of the common infrastructure of the experiment and the communication with the services of CERN (cooling, ventilation, electricity distribution, safety etc.) and the LHC accelerator.
 

Detector event type

General   Provisional    An identifier, unique within a sub-detector, which identifies the data within a ROB fragment, e.g. a ROB fragment may contain calibration or monitoring data.
 

Diagnostic package (DVS)

Online System    This element uses the test manager to diagnose problems with the TDAQ system and confirm its functionality.
 

Distributor

General    An element of an EF sub-farm which obtains events from the SFI and distributes them to the processing elements within it's sub-farm.
 

Event

General    All ROB fragments with the same Gid.
 

Event Builder (EB)

General    Part of the Data Collection sub-system, it merges all the fragments belonging to a unique L1ID into a full event at a single destination.
 

Event Builder Destination

General    See SFI.
 

Event Builder Interface (EBIF)

General    Part of the current ROS implementation (eg as used in the test beam) responsible for collecting ROB fragments within the ROS and forwarding them to the event builder.
 

Event Builder Source

General    A element of the event building sub-system which puts ROS fragments into the event building network.
 

Event Counter Reset (ECR)

Front-End    Signal broadcast by the TTC system to reset the local event counters.
 

Event Filter (EF)

General    The hardware and software required for the final stage of the on-line event selection, data monitoring and calibration using offline style algorithms operating on complete events accepted by LVL2.
 

Event Filter Dataflow (EFD)

General    Part of the event filter system.???
 

Event Filter Farm

General    The farm of processors in which the Event Filter runs. The same farm may also be used for different purposes, e.g. calibration, by running different software on the farm.
 

Event Filter Interface (EFIF)

DAQ-1   Obsolete, still used in testbeam DAQ    An instance of an IOM. It receives data control messages from the trigger module and collects ROB fragments, from the ROBs within its ROC, to form a crate fragment. The crate or ROB fragments are subsequently input into the Event building sub-system.
 

Event Filter Sub-Farm

General    A sub-set of the Event Filter Farm. Input and output are provided, respectively, by the Sub Farm Input and Output elements.
 

Event filter supervisor

General    The hardware and software required to globally control the Event Filter. It is also responsible for the configuration, initialisation and overall error handling of the Event Filter.
 

Event fragment

General    A generic term for a sub-set of event data. Specific instances of an event fragment are ROD, ROB, ROS and sub-detector fragments.
 

Event Handler (EH)

General    The logical object within the EF consisting of an event distributor, an event collector, one or more processing elements, an event handler supervisor and an appropriate communication layer.
 

Event Handler Supervisor

General    Part of the EF system. The object in charge of the control of the event handler. It provides initialization, configuration and run control functionalities. It also provides monitoring information to the Event Filter supervisor.
 

Event sampling

DAQ-1   Obsolete?    A high-level DAQ function of the LDAQ which provides crate or ROB fragments to applications mounted in the back-end. A more detailed definition is given in [1].
 

Event type

General    A unique ATLAS TDAQ wide identifier which classifies an event, e.g. physics, calibration, monitoring. Within the current event format this is implemented as a sequence of words from the LVL1/LVL2 triggers.
 

Event Viewing System (EVS)

General   Obsolete?    Provides the facility for viewing event data in all detectors, together with a description of the event classification [1].
 

Extended Level-1 ID (EL1ID)

General    The L1ID extended to 32 bits by concatenating an 8 bit ECR counter in the high end bits.
 

Fast Controls

General    Control signals broadcast by the TTC system in synchronism with the LHC clock and orbit signals, such as BCR, ECR, Clear, Run, Pause, Restart, Abort, Stop, selective Resets and synchronous Test commands.
 

Front End Data Stream

General    Virtual or real link between the derandomizer and the ROD, through which the FE data are transmitted.
 

Generic I/O module

DAQ-1, ROS    An element, incorporating both software and hardware, which encapsulates the common core functionality of the I/O modules.
 

Global event Identifier (Gid)

General    For a given run, the unique TDAQ wide identifier of an event added to the event during event building.
 

High Level Triggers (HLT)

General    Comprised of both the LVL2 and EF, the two ATLAS trigger levels that are implemented primarily in software.
 

I/O module (IOM)

DAQ-1, ROS    An element, incorporating both software and hardware, within a DAQ-unit which receives, buffers and outputs: ROB fragments and or crate fragments and or data control messages. More specifically it is a ROB or TRG or L3IF or SFI.
 

Level three interface (L3IF)

General   Obsolete, see Event builder interface   
 

Level-1 Buffer

General    Buffer (analogue or digital) included in the FE electronics which retains the data until the L1A is received.
 

Level-1 trigger (LVL1)

General    The ATLAS First Level Trigger system provides a hardware based first trigger decision using only a sub-set of an event's data (Calorimeter and Muon only). Normaly only the events accepted by LVL1 are transferred from the detectors into the HLT/DAQ system.
 

Level-1 Trigger Type

General    An 8-bit word transmitted with the L1A and giving information about the type of event.
 

Level-2 Farm

General    The farm of processors in which the LVL2 software runs.
 

Level-2 Sub-Farm

General    A sub-set of the LVL2 farm.
 

Level-2 trigger (LVL2)

General    The ATLAS Second Level Trigger system provides a software based second stage trigger decision, to reduce the rate of triggers from LVL1 by about a factor of 100. It uses 'Regions of Interest' (RoI) as given by the LVL1 trigger to selectively read out only certain parts of the ATLAS detector hardware and computes a LVL2 trigger decision.
 

Local DAQ (LDAQ)

DAQ-1, ROS    The element which provides the high-level DAQ functions, not related to the main flow of data, within the Dataflow. It also provides the interface to the back-end. A more detailed definition is given in [1].
 

LVL1 Accept (L1A)

Front-End    LVL1 trigger Accept signal produced by the Central Trigger Processor(CTP) when an event has met the LVL1 trigger criteria.
 

LVL1 Trigger Accept Identifier (L1ID)

Front-End    A L1ID is built at different levels of the read-out system. The TTCrx provides a 24 bit L1ID with each L1A signal. In conjunction with the BCID, it defines uniquely an event.
 

LVL2 Processing Unit (L2PU)

General    The L2PU is the application running on one of the Level-2 processors, hosting the HLT processing algorithms and also incorporating the calculations from which the LVL2 trigger decision is derived.
 

LVL2 Supervisor (L2SV)

General    The L2SV is the interface to the LVL1 system via the RoI Builder. It is responsible for distributing events to the LVL2 farm/subfarms and manages the computing resources by means of load balancing algorithms. L2SV receives(computes??) the final LVL2 decision on an event based the result from the LVL2 Processing Unit. The decision results are communicated to the DataFlow Manager (DFM) so that accepted events can be further analyzed, and rejected events can be flushed from the Read Out System memory.
 

Message Reporting System (MRS)

Online Software    A facility which allows all software components in the ATLAS TDAQ system to report error messages to other components.
 

Network controller

DAQ-1   Obsolete, need new definition for DC    The technology specific hardware and software which initialises, configures, controls and monitors the event building network.
 

Network interface

General   Obsolete    The technology specific hardware and software which connects modules to the event building network.
 

Object Kernel Support (OKS)

General    This is a package which provides a simple active persistent in-memory object manager which is used to implement run-time configuration databases.
 

Objectivity/DB

General    A fully distributed object orientated database previously used for the configuration, versions and backup databases. No longer used in ATLAS TDAQ.
 

Online system

General    All the software for configuring, controlling and monitoring of the TDAQ system. It excludes the management, processing and transportation of physics data.
 

Partition

General    The physical and or logical separation of one or more elements of the experiment into mutually exclusive sub-sets. An example is DAQ partition.
 

Partition Identifier (PID)

General    The unique identifier of a partition. This is a high-level identifier, independent of technology.
 

Partition manager

General    Formalises the allocation of hardware and software elements, allowing people to work in parallel without interference.
 

Physics Data

General    Source: ATLAS Prototype DAQ Back-End Software User Requirements Document
Data taken from detector equipment representing physics events.
 

Process manager (PMG)

Online Software    This element performs basic job control of software components of the TDAQ (starting, stopping and monitoring basic status).
 

Processing Element

General    A logical object consisting of one or more processing tasks and the processing node on which they are running.
 

Processing Node

General    The hardware on which run one or more EF processing tasks or LVL2 Processing Units.
 

Processing Task (PT)

General    The software running on an EF processing node in charge of transforming the event data. The transformation may be filtering, reformatting, monitoring or calibration. Several processing tasks can be running concurrently on the same processing node.
 

pseudo-ROS (pROS)

General    The pROS is the application which receives the detailed LVL2 result from the LVL2 Processing Units for each event to be passed to event building. At event building time the pROS is treated just like a ROS, thus including the detailed LVL2 result into the full event.
 

Raw Data

General    Data provided by the front-end electronics to the read-out buffer.
 

Read-Out Buffer (ROB)

1. General    Standard module which receives data from on or more RODs, stores them and makes them available to the LVL2 trigger processors and, for LVL2-selected events, to the EB. Data are stored during the LVL2 build time and for selected events until the Event is built inthe EB.
    
2. DAQ-1   Obsolete    An instance of an IOM. It receives and buffers ROB fragments from a ROD via a ROL and provides the data to the level two trigger system and Event Filter. It also receives data control messages from other IOMs within its ROC.
    

Read-Out Crate (ROC)

DAQ-1    The combined functionality of the LDAQ, TRG, EBIF and one or more ROBs.
 

Read-Out Driver (ROD)

General    The detector specific Front-End Functional element which gathers data from the derandomizers over one or more data streams and builds ROD fragments of events to be sent to the ROS or RoIB.
 

Read-Out Link (ROL)

General    The physical link between ROD and ROS through which the data are sent at the event rate of the LVL1 trigger.
 

Read-Out System (ROS)

General    A sub-system of the ATLAS TDAQ responsible for reading out the ATLAS RODs and for supplying event fragments to the LVL2 and EB sub-systems.
 

Region of Interest (RoI)

General    A region limited in eta and phi, indicated by the LVL1 trigger to contain candidates for objects requiring further computation. In the case of B-physics triggers at low luminosity, some ROI's may be defined internally within the level-2 trigger system.
 

Region of Interest Builder (RoIB)

General    The element which combines RoI information from different parts of LVL1 and forwards it to a LVL2 supervisor.
 

ROB fragment

General    Set of ROD fragments within one ROB with the same GID.
 

ROD fragment

General    Data provided by the front-end electronics to the ReadOut System (ROS).
 

ROS fragment

General    The set of ROB fragments, within a ROS Modular Unit, with the same Gid and to be sent to LVL2 or EB.
 

ROS Modular Unit

General    A sub-division of the ROS used for the readout of part of the ATLAS detector.
 

Run bookkeeper

General    An element which archives information about the data recorded to permanent storage by the TDAQ system.
 

Run Control

General    Controls the data taking activities by coordinating the operating of the TDAQ sub-systems, online software components and external systems
 

S-LINK

General    The S-LINK Interface specification defines the signals and protocol that are presented to the user at each end of the ReadOut Link. It also recommends the format of the link boards.
 

Software Release Tools (SRT)

General    These tools are used to manage the development of multiple concurrent versions of software packages. Replaced by CMT in the TDAQ system.
 

Software through Pictures (StP)

General    This is the Software through Pictures for the Object Modelling Technique. It is a graphical, object-oriented modelling environment that helps people work together to analyse and design critical systems. No longer used in the TDAQ system.
 

Source identifier (Sid)

General    The unique system wide identifier of a source. This is a high-level identifier, independent of technology.
 

Status display

General    An element which presents the status of the current data taking run to the user in terms of its main run parameters, detector configuration, trigger rate and state of run controller.
 

Sub-detector

General    Physical grouping of the system that corresponds to a whole element of the detector using the same FE electronics (ex: calorimeter, TRT...).
 

Sub-Farm

General   Needs refining to include LVL2    The basic component of the Event Filter. It comprises the Event Handler and the Sub-Farm DAQ.
 

Sub-Farm Crate (SFC)

DAQ-1    The combined functionality of the LDAQ, the switch to farm interface and Sub-farm output.
 

Sub-Farm Input (SFI)

General    Part of the data collection sub-system. The location where full event are built by the EB.
 

Sub-Farm Output (SFO)

1. General    Part of the data collection which outputs to mass storage the complete events received from the EF.
    
2. DAQ-1   Obsolete    An instance of an IOM. It receives (and possibly buffers) events from the Event Filter and sends them to one or more storage systems.
    

Sub-system

General    Source: ATLAS Prototype DAQ Back-End Software User Requirements Document
A major part of the TDAQ not covered by the online software sub-system (e.g. front-end DAQ, event builder etc.) Other sub-systems are not defined in this document.
 

Switch to farm interface (SFI)

General   Replaced by Sub-Farm Input    Part of the datacollection subsystem.
 

TDAQ configuration

General    A set of hardware pieces and software objects used to take data from the detectors.
 

TDAQ partition

General    A configuration that involves the DAQ and one or more sub-detectors and represents an independent entity that can be used to take data or perform tests.
 

Test manager

General    Provides a means of organising individual tests for hardware and software components.
 

Timing, Trigger and Control (TTC)

General    Standard system which allows the distribution of timing, trigger and control signals. The system delivers the standard TTC signals such as the LHC clock, L1A and Fast Controls, and provides for the distribution of other detector-specific commands and data.
 

Tools.h++

Online Software    The Rogue Wave Tools.h++ is an internationalised C++ foundation class library which contains basic data types and container classes, includes support for exception and multi-threaded programs, allows to use Endian streams for exchanging binary data among Windows, OS/2 and Unix environments, and provides non-intrusive persistence for objects.
 

Trigger module (TRG)

DAQ-1, ROS    An instance of an IOM. It receives data control messages from the system and sends them to other IOMs within its ROC.
 

TTC Receiver (TTCrx)

??    TTC receiver ASIC which delivers the decoded and deskewed TTC signals, bunch and event counters required by FE electronics controllers.
 

TTC VME Interface (TTCvi)

??    The TTCvi is a VME module which delivers the A-channel and B-channel signals to the TTC transmitter crate. These two signals carry timing, trigger and control information. The TTC A-channel is used only to transmit the L1A signal, the TTC B-channel is used to transmit framed and formatted commands and data.
 

XOFF

General    An S-LINK signal that causes the link to suspend transfers. It allows the ROS to apply back-pressure to the ROD. De-assertion of this signal allows transfers to continue.
 

XON

General    An S-LINK signal that causes the link to resume transfers. It allows the ROS to cancel back-pressure to the ROD.
 

References

[1]

ATLAS Technical Proposal, CERN/LHCC/94-43, 15 December 1994, (ISBN 92-9083-067-0)
 

[2]

PSS-05 Software Engineering Standards defined by ESA Board for Software Standardisation and Control, BSSC (ISBN 0-13-106568-8)
 

[3]

ATLAS Detector Control System User Requirements Document PSS05-ATLAS-DCS-URD
 

[4]

The raw event format in the ATLAS Trigger & DAQ, ATL-DAQ-98-129