Overview and Future Developments of the intelligent, FPGA-based DAQ (iFDAQ) of COMPASS

Modern experiments in high energy physics impose great demands on reliability, efficiency, and data rate of Data Acquisition Systems (DAQ). In order to address these needs, we present a versa- tile and scalable DAQ which executes the event building task entirely in FPGA modules. In 2014, the intelligent FPGA-based DAQ (iFDAQ) was deployed at the COMPASS experiment located at the Super Proton Synchrotron (SPS) at CERN. The core of the iFDAQ is its hardware Event Builder (EB), which consists of up to nine custom designed FPGA modules complying with the μ TCA/AMC standard. The EB replaced 30 distributed online computers and around 100 PCI cards increasing compactness, scalability, reliability, and bandwidth compared to the previous system. The iFDAQ in the configuration of COMPASS provides a bandwidth of up to 500 MB/s of sustained rate. By buffering data on different levels, the system exploits the spill structure of the SPS beam and averages the maximum on-spill data rate of 1.5 GB/s over the whole SPS duty cycle. It can even handle peak data rates of 8 GB/s. Its Run Control Configuration and Readout (RCCAR) software offers native user-friendly control and monitoring tools and together with the firmware of the modules provides built-in intelligence like self-diagnostics, data consis- tency checks, and front-end error handling. From 2017, all involved point-to-point high-speed links between front-end electronics, the hardware EB, and the readout computers will be wired via a passive programmable crosspoint switch. Thus, multiple event building topologies can be configured to adapt to different system sizes and communication patterns.