FELIX: first operational experience with the new ATLAS readout system and perspectives for HL-LHC

Over the next decade, the ATLAS detector will be required to operate in an increasingly harsh collision environment. To maintain physics performance, the detector will undergo a series of upgrades during major shutdowns. A key goal of these upgrades is to improve the capacity and flexibility of the detector readout system. To this end, the Front-End Link eXchange (FELIX) system was developed as the new interface between the data acquisition; detector control and TTC (Timing, Trigger and Control) systems; and new or updated trigger and detector front-end electronics. FELIX functions as a router between custom serial links from front end ASICs and FPGAs to data collection and processing components via a commodity switched network. The serial links may aggregate many slower links or be a single high bandwidth link. FELIX also forwards the LHC bunch-crossing clock, fixed latency trigger accepts and resets received from the TTC system to front-end electronics. FELIX uses commodity server technology in combination with FPGA-based PCIe I/O cards. FELIX servers run a software routing platform serving data to network clients performing a number of data preparation, monitoring and control functions. This presentation covers the design of FELIX as well as the first operational experience gained during the Run 3 starting, including the challenges faced commissioning the system for each ATLAS sub-detector. Finally, the planned evolution of FELIX for High-Luminosity LHC will be described, including architectural changes and status of early integration with detector development projects.