The Compact Processing Module for the Upgrade of the ATLAS Tile Calorimeter Towards the High-Luminosity LHC

The Tile Calorimeter (TileCal) is the central hadronic calorimeter of the ATLAS experiment at the Large Hadron Collider (LHC). In 2026, the LHC will undergo a series of upgrades leading to the High-Luminosity LHC (HL-LHC), which will provide an instantaneous luminosity 5 to 7 times larger than the nominal LHC design value. The ATLAS Tile Calorimeter Phase-II Upgrade will completely replace the readout electronics with a new clock distribution and readout architecture with a fully digital trigger system to process more complex physics events while maintaining the trigger selection efficiency. The upgraded on-detector electronics will transmit detector data every 25 ns to the Compact Processing Modules (CPMs) in the counting rooms, which handle real-time energy reconstruction, trigger data transmission, and clock distribution. A total of 128 CPMs hosted in 32 ATCA carriers will read out the entire detector with a total data bandwidth of 40 Tbps. Each CPM, equipped with a Xilinx Kintex UltraScale KU115 FPGA and six FireFly modules, processes data from two TileCal modules, transmitting both reconstructed and raw data to TDAQi and FELIX systems. In addition, the CPM distributes the accelerator clock and configuration commands to the DaughterBoards in the on-detector. This work presents the current status of the CPM developments for the HL-LHC and the roadmap towards its installation in the ATLAS experiment.