The phase-1 upgrade of the ATLAS level-1 calorimeter trigger

L1Calo is a hardware based pipelined system processing signals from the liquid- argon (LAr) and tile calorimeters and provides trigger signals to the Central Trigger Processor (CTP). It identifies events containing calorimeter-based physics objects, including electrons, pho- tons, taus, jets, and missing transverse momentum. In preparation for Run3, when the LHC is expected to run at higher energy and instantaneous luminosity, L1Calo and LAr are implementing a significant upgrade programme, in order to better perform in a challenging high-luminosity and high-pileup environment. The existing hardware will be replaced by a new system of feature extractor (FEX) modules, which will process finer LAr granularity information and execute more sophisticated algorithms to identify physics objects.