Initial upgrade of the ATLAS Level-1 Calorimeter Trigger

The Level-1 calorimeter trigger~(L1Calo) of the ATLAS experiment has been operating well since the start of Large Hadron Collider~(LHC) data taking, and played a major role in the Higgs boson discovery. To face the new challenges posed by the upcoming increases of the LHC proton beam energy and luminosity, a series of upgrades is planned for the L1Calo. This paper presents the first L1Calo upgrade program for the initial upgrade phase in 2013-14. The program includes substantial improvements to the analogue and digital signal processing. Two existing digital algorithm processor subsystems will receive substantial hardware and firmware upgrades, allowing topological information to be transmitted and processed. An entirely new subsystem, the L1 topological processor, will receive real-time data from both the upgraded L1Calo and L1 muon trigger to perform trigger algorithms based on entire event topologies. The expected performance improvements are described together with the upgraded hardware and firmware implementations. The status of the prototypes, integration and commissioning efforts at the time of writing are also reviewed.