28 September 2015 to 2 October 2015
Europe/Zurich timezone

Overview and Future Developments of the FPGA-based DAQ of COMPASS

1 Oct 2015, 14:50
Sala 02.1 (Lisbon)

Sala 02.1


IST (Instituto Superior Técnico ) Alameda Campus Av. Rovisco Pais, 1 1049-001 Lisboa Portugal


Dominik Steffen (Technische Universitaet Muenchen (DE))


COMPASS is a fixed-target experiment at the SPS at CERN dedicated to the study of hadron structure and spectroscopy. Since 2014, a hardware event builder consisting of nine custom designed FPGA-cards replaced the previous online computers increasing compactness and scalability of the DAQ. By buffering data, the system exploits the spill structure of the SPS averaging the maximum on-spill data rate over the whole SPS cycle. From 2016, a crosspoint switch connecting all involved high-speed links shall provide a fully programmable system topology and thus simplifies the compensation for hardware failure and improves load balancing.


COMPASS is a high-energy particle physics experiment at the Super Proton Synchrotron (SPS) at CERN. The purpose of the fixed target experiment is the study of hadron structure and hadron spectroscopy with high intensity muon and hadron beams.
In 2002, COMPASS started to take data using at first the ALICE data-acquisition software framework DATE. Since 2012, the COMPASS spectrometer has entered its second phase known as COMPASS-II with an increased number of detector channels of about 300,000. In 2014, the DAQ has been upgraded to a compact and more reliable system. The COMPASS experiment nowadays collects data using a novel DAQ architecture utilizing a hardware event builder and modern software tools. The hardware event builder is based on nine custom designed Data Handling Cards (DHC) which replace 30 distributed online computers, around 100 PCI cards, and the ethernet switch of the event building network of the previous system. As a result, the new DAQ is compact and scalable and provides higher bandwidth and better reliability.
The system makes use of the spill structure of the SPS beam by buffering data on different levels of the event builder and averaging the maximum on-spill data rate over the whole SPS cycle. As a result the online DAQ computers work independently from the initial detector rate of 1 GB/sec and deal only with a maximum aggregate rate of 400 MB/sec.
The system utilizes three independent interface networks for synchronization, event building, and data flow control. This functional division simplifies the software architecture, optimally synchronizes processes, and offers an efficient usage of the network bandwidth.

In 2015, it is planned to wire all point-to-point high speed links via a fully programmable crosspoint switch. The crosspoint switch will therefore provide a fully customizable DAQ network topology between front-end electronics, the event building hardware, and the online computers. The adaptability of the system topology allows to compensate for hardware failure in the event builder by activating spare resources replacing broken or malfunctioning modules. Algorithms shall identify hardware failure and synchronously reconfigure the DAQ topology to substitute the broken module by a spare one without human intervention.
In this way, the fully programmable crosspoint switch contributes substantially to an improved system reliability since every broken FPGA module of the event builder as well as the online computers can be exchanged on-the-fly and data loss is reduced. COMPASS DAQ with integrated crosspoint switch

Primary author

Dominik Steffen (Technische Universitaet Muenchen (DE))


Antonin Kveton (Czech Technical University (CZ)) Dmytro Levit (Technische Universitaet Muenchen (DE)) Igor Konorov (Technische Universitaet Muenchen (DE)) Jan Tomsa (Charles University (CZ)) Josef Novy (Czech Technical University (CZ)) Martin Bodlak (Charles University (CZ)) Miroslav Virius (Czech Technical University (CZ)) Stefan Huber (Technische Universitaet Muenchen (DE)) Vladimir Frolov (Joint Inst. for Nuclear Research (RU)) Vladimir Jary (Czech Technical University (CZ))

Presentation Materials