  For Run 3 (from 2021), the LHC will undergo a significant increase in
instantaneous luminosity to 1.5 times its current value which will lead to
larger collected statistics and an enhanced sensitivity to new physics. The
Phase-1 upgrade of the ATLAS Level-1 endcap muon trigger is essential to keep
the physics acceptance at Run 3. A new trigger logic to take coincidence with
detectors inside and outside the magnetic field is described and is shown to
reduce the trigger rate to lower than the required level in Run 3. A new
trigger board, NSL, to integrate all the information from various detectors,
has been developed, and the implementation of the new logic on the FPGA has
been successfully demonstrated.
