New Software-Based Readout Driver for the ATLAS Experiment

To maintain sensitivity to new physics in the coming years of Large Hadron Collider (LHC) operations, A Toroidal LHC ApparatuS (ATLAS) collaboration has been working on upgrading a portion of the front-end (FE) electronics and replacing some parts of the detector with new devices that can operate under the much harsher background conditions of future LHC runs. The legacy FE of the ATLAS detector sent data to the data acquisition (DAQ) system via the so-called Read Out Drivers (RODs) custom-made VMEbus boards devoted to data processing, configuration, and control. The data were then received by the Read Out System (ROS), which was responsible for buffering them during the High-Level Trigger (HLT) processing. From Run 3 onward, all new trigger and detector systems will be read out using new components, replacing the combination of the ROD and the ROS. This new path will feature an application called the Software Read Out Driver (SW ROD), which will run on a commodity server receiving FE data via the Front-End Link eXchange (FELIX) system. The SW ROD will perform event fragment building and buffering as well as serving the data on request to the HLT. The SW ROD application has been designed as a highly customizable high-performance framework providing support for detector-specific event building and data processing algorithms. The implementation that will be used for Run 3 of the LHC is capable of building event fragments at a rate of 100 kHz from an input stream consisting of up to 120 MHz of individual data packets. This document will cover the design and the implementation of the SW ROD application and will present the results of performance measurements executed on the server models selected to host SW ROD applications during Run 3.