The ATLAS first-level calorimeter trigger is a hardwarebased system designed to identify high-pT jets, electron/photon and tau candidates, and to measure total and missing ET. The trigger consists of a Preprocessor system which digitises 7200 analogue inputs, and two digital multicrate processor systems which find jets, measure energy sums, and identify localised energy deposits (electron/photon and tau candidates). In order to provide a trigger quickly enough, the hardware is parallel and pipelined. Experience so far of the Jet/Energy-sum and Cluster Processor system production, commissioning, and integration into ATLAS will be described
