A DSP based Calorimeter Trigger for the DØ experiment

We describe the goals, design, implementation, and performance of the DØ Level 1.5 Calorimeter Trigger. This system has been added to the DØ hardware trigger and is based on Digital Signal Processors (DSP´s). The Level 1.5 Calorimeter Trigger is a combined hardware and software system which can identify objects (e.g. isolated electrons), or combinations of objects in the calorimeter. The system uses the Level 1 Calorimeter Trigger Tower data and applies filtering algorithms based on neighbor sums of the electromagnetic (EM) and total (EM+hadronic) transverse Energies. Eleven Local DSP´s, operating in parallel, process data from overlapping sections of the calorimeter and transfer their results to a Global DSP where the Level 1.5 Calorimeter Trigger decision is made. This decision is then sent to the Level 1.5 Trigger Framework as one of the inputs to the final trigger decision. The average processing time is measured at 136 μs, which implies a maximum input rate of 370 Hz for a 5% deadtime. More than most hardware trigger processors built for High Energy Physics experiments so far, this project relies on commercial products, and uses them in an application for which they were designed and optimized. The resulting system offers advantages in terms of flexibility and upward migration as improved products become available