Speaker
Description
The CMS Phase-2 upgrade introduces a new high-granularity calorimeter (HGCAL). The HGCAL back-end will use about 300 Serenity-S1 FPGA boards using Samtec FireFly electro-optical modules with a link speed of up to 25 Gb/s. Existing production tests only validate the high-speed links via copper loopback cables. We present an Optical Acceptance Test (OAT) framework providing comprehensive link and slow-control validation with installed FireFly modules under realistic conditions. The OAT combines loopback and board-to-board testing, extended Bit Error Rate (BER) measurements, and continuous module health monitoring within an automated workflow, delivering structured diagnostics and ensuring reliable large-scale system deployment.
Summary (500 words)
During the CMS Phase-2 Upgrade the current endcap calorimeter will be replaced with the high granularity calorimeter (HGCAL). The HGCAL trigger and data acquisition (TDAQ) back-end will use about 300 Serenity-S1 ATCA FPGA boards. These boards employ Samtec electro-optical FireFly modules for both front-end readout and inter-board communication. Depending on their functional role (trigger stage-1, trigger stage-2, DAQ, or non-zero suppression) the board is populated with different numbers and "flavours" of FireFly modules supporting data rates of 10, 16, and 25 Gb/s.
The Serenity-S1 board, developed by the central Serenity group, is based on the Advanced Telecommunications Computing Architecture (ATCA) standard and serves as a generic high-performance readout board across multiple CMS subdetectors with a total production of more than 700 boards. To ensure all installed boards are functional, a multi-stage quality is used. Initial Factory Acceptance Tests (FAT) and User Acceptance Tests (UAT), performed by the Serenity group, verify board functionality and basic high-speed link performance before the boards are passed to the sub-detector groups for testing to their specific needs. FAT and UAT are limited by only validating the high-speed links with copper loopback cables and short-duration Bit Error Rate (BER) measurements. Consequently, neither the optical transmission paths nor the I2C-based slow-control interfaces to the FireFly modules are fully validated at this stage.
To address these limitations, we present a dedicated Optical Acceptance Test (OAT) framework developed within the HGCAL collaboration. The OAT provides comprehensive validation of all optical links and associated control interfaces under realistic operating conditions. The testing procedure includes systematic link verification using both optical loopback and board-to-board topologies, enabling end-to-end characterization of transmission paths. Automated I2C communication tests are implemented to validate module configuration, monitoring, and control functionality across all installed FireFly modules.
In addition, the framework performs extended BER measurements over longer time intervals to assess link stability and identify marginal channels that may not be detected in short tests. Health metrics of the FireFly modules, such as power consumption and temperature are continuously monitored and logged. The entire process is automated, enabling high-throughput testing suitable for batch production while minimizing operator intervention.
The OAT framework generates structured pass/fail reports and detailed diagnostics for each board, providing traceability and facilitating rapid identification of faulty components or marginal performance. This systematic approach ensures that all Serenity-S1 boards meet the reliability and performance requirements of the HGCAL back-end system prior to installation.