Abstract
Recently, a stability of Data Acquisition System (DAQ) has become a vital precondition for a successful data taking in high energy physics experiments. The intelligent, FPGA-based Data Acquisition System (iFDAQ) of the COMPASS experiment at CERN is designed to be able to readout data at the maximum rate of the experiment and runsin a mode without any stops. DAQ systems fulfilling such requirements reach the efficiency up to 99%. The newly introduced continuously running mode enables to collect data without a necessity of any other user intervention.Such mode affects all processes of the iFDAQ with high emphasis on timing and precise synchronization. However, every undesirable interruption of data taking can potentially result in a possible loss of physics data. Running24/7 puts stress on reliability and robustness of the system. Therefore, the improvement of the iFDAQ stability had to come first. The continuously running mode and the improved iFDAQ stability helped to collect more physicsdata in the Run 2017. In the paper, we present the continuously running mode in more detail and discuss the overall iFDAQ stability.
Highlights
COMPASS (Common Muon and Proton Apparatus for Structure and Spectroscopy) [1, 2] is a fixed-target experiment at the Super Proton Synchrotron (SPS) accelerator at CERN near Geneva, Switzerland
In contrast to traditional event builders which are based on distributed online computers interconnected via an Ethernet Gigabit network, the event building task is completely executed in hardware
The software side of the iFDAQ [6, 12] is used for control and monitoring of the final three layers of the iFDAQ hardware (FPGA multiplexers, FPGA switch, and readout engines) and for read out of physics events from readout engines
Summary
COMPASS (Common Muon and Proton Apparatus for Structure and Spectroscopy) [1, 2] is a fixed-target experiment at the Super Proton Synchrotron (SPS) accelerator at CERN near Geneva, Switzerland. The software side of the iFDAQ [6, 12] is used for control and monitoring of the final three layers of the iFDAQ hardware (FPGA multiplexers, FPGA switch, and readout engines) and for read out of physics events from readout engines. The first source of instability is a memory access error (PCI/DMA) caused by scrambled data being transferred to the RAM of the readout engines It is the most time-consuming failure, since it requires to reboot all readout engine computers and the recovery procedure takes approximately 10 minutes on average. The increase of downtime in May of each year can be explained by the commissioning phase that takes place in the beginning of each year and in which all detectors, the frontend electronics and the iFDAQ do not operate in stable conditions
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