Global Trigger (uGT)

The Global Trigger is the final step of the CMS Level-1 Trigger and therefore a very important part of the data taking process for the CMS experiment. It is responsible for generating the so called "finalOR" signal which triggers the readout of the detector and serves as basis for further calculations by the High Level Trigger.the data taking.

The next generation of the Global Trigger for the CMS will be designed based on FPGAs of the powerful Xilinx Virtex-7 family, which combines unsurpassed flexibility with regard to reconfiguration and high robustness, with benefits concerning the testability aspect. The Global Trigger is going to be designed for high-performance, high-bandwidth processing applications. It targets the MP7 board as it offers 72 input/output links. The upgraded system is based on uTCA technology and 10Gbps optical links. The GT implements the "menu" of triggers, which is a set of selection requirements applied to the final list of objects (i.e. electrons/photons, muons, jets, taus, etc.), required by the algorithms of the High Level Trigger to meet the physics data-taking objectives. This menu will include triggers ranging from simple single object selections with Et above a set threshold to selections requiring coincidences of several objects with topological conditions amongst them. Trigger conditions will be defined by using the "L1-Trigger Menu Editor" (L1TME) software. This software interface facilitates reprogramming the FPGA logic by translating human-readable physics algorithms into the VHDL code required for firmware creation. The GT is designed to synchronize all trigger candidates at the same time at the logic chip, and making any correlation between them, implement prescaler and counter for each algorithm then perform a final OR of all algorithm bits.