Developments Regarding the Integration of FPGA RDMA into the ATLAS Readout with FELIX in High Luminosity LHC

RDMA (Remote Direct Memory Access) is used by the ATLAS experiment at CERN in the new readout system based on FELIX (Front-End Link eXchange) for its networking layer. The FELIX system is used to interface the front-end electronics to commodity hardware in the server farm. In the current implementation of FELIX, RDMA communication is implemented using software on both ends of the RDMA links. FELIX is using RDMA through RoCE (RDMA over Converged Ethernet) to transmit data from its servers to the Software Readout Driver devices in the server farm using off-the-shelf networking equipment. As a consequence of the High Luminosity LHC upgrade, improvements in the data throughput will be needed. These improvements can be achieved by implementing RDMA support in the FELIX FPGA to simplify the path the data is taking through the readout system. This FPGA implementation of the RDMA protocol has been developed and tested. Now, a version of FELIX that uses this implementation is being proposed and demonstrated.