C. Jacobs

CMS DAQ Event Builder Based on Gigabit Ethernet

The CMS Data Acquisition System is designed to build and Alter events originating from 476 detector data sources at a maximum trigger rate of 100 KHz. Different architectures and switch technologies have been evaluated to accomplish this purpose. Events will be built in two stages: the first stage will be a set of event builders called FED Builders. These will be based on Myrinet technology and will pre-assemble groups of about 8 data sources. The second stage will be a set of event builders called Readout Builders. These will perform the building of full events. A single Readout Builder will build events from 72 sources of 16 KB fragments at a rate of 12.5 KHz. In this paper we present the design of a Readout Builder based on TCP/IP over Gigabit Ethernet and the optimization that was required to achieve the design throughput. This optimization includes architecture of the Readout Builder, the setup of TCP/IP, and hardware selection.

Trigger using track search and kinematical analysis for rare decay channels at high rates

Abstract We report on the definition and construction of the trigger system for the CP violation experiment with tagged K 0 (PS195) at LEAR, the low energy antiproton machine at CERN. The beam is assumed to have a continuous intensity of 2 × 10 6 antiprotons per second. The requirements for fast and efficient rejection are stringent.

The CMS event builder demonstrator and results with Myrinet

Abstract The data acquisition system for the CMS experiment at the Large Hadron Collider (LHC) will require a large and high performance event building network. Several switch technologies are currently being evaluated in order to compare different architectures for the event builder. One candidate is Myrinet. This paper describes the demonstrator which has been setup to study a small-scale (16×16) event builder based on PCs running Linux connected to Myrinet and Ethernet switches. A detailed study of the Myrinet switch performance has been performed for various traffic conditions, including the behaviour of composite switches. Results from event building studies are presented, including measurements on throughput, overhead and scaling. Traffic shaping techniques have been implemented and the effect on the event building performance has been investigated. The paper reports on performances and maximum event rate obtainable using custom software, not described, for the Myrinet control program and the low-level communication layer, implemented in a driver for Linux. A high performance sender is emulated by creating a dummy buffer that remains resident in the network interface and moving from the host only the first 64 bytes used by the event building protocol. An approximate scaling in N is presented assuming a balanced system where each source sends on average data to all destinations with the same rate.

The CMS event builder demonstrator based on Myrinet

The data acquisition system for the CMS experiment at the Large Hadron Collider (LHC) will require a large and high performance event building network. Several switch technologies are currently being evaluated in order to compare different architectures for the event builder. One candidate is Myrinet. This paper describes the demonstrator which has been set up to study a small-scale (8/spl times/8) event builder based on a Myrinet switch. Measurements are presented on throughput, overhead and scaling for various traffic conditions. Results are shown on event building with a push architecture.

FEDkit: a design reference for CMS data acquisition inputs

CMS has adopted S-LINK64 [1] as the standard interface between the detector front end readout and the central Data Acquisition (DAQ) system. The S-LINK64 is a specification of a FIFO-like interface. This includes mechanical descriptions of connector and daughter board format and electrical signal definition. The hardware/software package described in this paper (FEDkit) emulates the central DAQ side of this interface at the data rate required by the final DAQ system. The performance, integration with the CMS DAQ software framework, and plans for future developments for the DAQ input interface are also presented.

The Terabit/s Super-Fragment Builder and Trigger Throttling System for the Compact Muon Solenoid Experiment at CERN

The Data Acquisition System of the Compact Muon Solenoid experiment at the Large Hadron Collider reads out event fragments of an average size of 2 kB from around 650 detector front-ends at a rate of up to 100 kHz. The first stage of event-building is performed by the Super-Fragment Builder employing custom-built electronics and a Myrinet optical network. It reduces the number of fragments by one order of magnitude, thereby greatly decreasing the requirements for the subsequent event-assembly stage. Back-pressure from the down-stream event-processing or variations in the size and rate of events may give rise to buffer overflows in the subdetectors front-end electronics, which would result in data corruption and would require a time-consuming re-sync procedure to recover. The Trigger-Throttling System protects against these buffer overflows. It provides fast feedback from any of the subdetector front-ends to the trigger so that the trigger can be throttled before buffers overflow. This paper reports on new performance measurements and on the recent successful integration of a scaled-down setup of the described system with the trigger and with front-ends of all major subdetectors. The on-going commissioning of the full-scale system is discussed.

The Final prototype of the Fast Merging Module (FMM) for readout status processing in CMS DAQ

The Trigger Throttling System (TTS) adapts the trigger frequency to the DAQ readout capacity in order to avoid buffer overflows and data corruption. The states of all ~640 readout units in the CMS DAQ are read out and merged by hardware modules (FMMs) to obtain the status of each detector partition. The functionality and the design of the second and final prototype of the FMM are presented in this paper.

The 2 Tbps "data to surface" system of the CMS data acquisition

The data acquisition system of the CMS experiment, at the CERN LHC collider, is designed to build 1 MB events at a sustained rate of 100 kHz and to provide sufficient computing power to filter the events by a factor of 1000. The data to surface (D2S) system is the first layer of the data acquisition interfacing the underground subdetector readout electronics to the surface event builder. It collects the 100 GB/s input data from a large number of front-end cards (650), implements a first stage event building by combining multiple sources into larger-size data fragments, and transports them to the surface for the full event building. The data to surface system can operate at the maximum rate of 2 Tbps. This paper describes the layout, reconfigurability and production validation of the D2S system which is to be installed by December 2005

A uniform XML-based approach to manage data acquisition hardware devices

A comprehensive model based on XML technologies to interface data acquisition hardware devices for configuration and control purposes is presented. The model builds upon the use of a unified syntax for describing hardware devices, configuration data, test results as well as control sequences. The integration of the model with the online software framework of the CMS experiment is under evaluation.

The CMS High Level Trigger System

The CMS data acquisition (DAQ) system relies on a purely software driven high level trigger (HLT) to reduce the full Level 1 accept rate of 100 kHz to approximately 100 Hz for archiving and later offline analysis. The HLT operates on the full information of events assembled by an event builder collecting detector data from the CMS front-end systems. The HLT software consists of a sequence of reconstruction and filtering modules executed on a farm of O(1000) CPUs built from commodity hardware. This paper presents the architecture of the CMS HLT, which integrates the CMS reconstruction framework in the online environment. The mechanisms to configure, control, and monitor the filter farm and the procedures to validate the filtering code within the DAQ environment are described.