Early prototyping and testing of CERN LHC CMS high-granularity calorimeter slow-control system

The Compact Muon Solenoid (CMS) high-granularity calorimeter (HGCAL) upgrade for CERN's Large Hadron Collider (LHC) high-luminosity phase is a detector with more than 6 million channels that will provide precise sensing and measurement of position, timing, and energy of the particles produced in the collisions of the beams. The HGCAL electronics are a large and complex set of processing systems split into front-end and back-end. The front-end, located in the experimental cavern, consists of $\boldsymbol{\approx 150}$ thousand radiation tolerant ASICs. The high-density FPGA-based back-end is housed away from the radiation area in a set of Advanced Telecommunications Computing Architecture (ATCA) boards and crates hosting $\boldsymbol{\approx 100}$ FPGAs. Each ATCA back-end board will comprise one (or two) FPGAs, managing up to $\boldsymbol{\approx 120}$ optical links, each providing a transmission rate of 10.24 Gb/s between the back-end and the front-end electronics. Each back-end FPGA is responsible for configuring and monitoring up to $\boldsymbol{\approx 3500}$ front-end ASICs and will be controlled by software running on a back-end MPSoC that provides the entry point for the whole control procedure. This paper presents the design and implementation of the prototyping infrastructure deployed to test and validate the slow-control block of the HGCAL back-end electronics, together with the related interfaces with the controller MPSoC and the front-end transceiver ASICs. The required functionalities have been validated with a ZCU102 Xilinx Ultrascale+ development board, which emulated the back-end elements that are still under development and not yet available for this comprehensive test. This development board was connected to other custom ASIC development boards via optical links, emulating the front-end side of the system, also still under development. Besides providing reliable testing and validation of the operation of the whole infrastructure, the prototyping platform also allowed to attain the required software/hardware portability that ensures easy integration/replacement of all the (still) emulated components with their final implementations.