  With the planned addition of tracking information to the Compact Muon
Solenoid (CMS) Level-1 trigger for the High-Luminosity Large Hadron Collider
(HL-LHC), the trigger algorithms can be completely reconceptualized. We explore
the feasibility of using particle flow-like reconstruction and pileup per
particle identification (PUPPI) pileup mitigation at the hardware trigger
level. This represents a new type of multi-subdetector pattern recognition
challenge for the HL-LHC. We present proof-of-principle studies on both physics
and hardware-resource performance of a prototype algorithm for use by CMS in
the HL-LHC era.
