  The Fred Young Submillimeter Telescope (FYST), on Cerro Chajnantor in the
Atacama desert of Chile, will conduct wide-field and small deep-field surveys
of the sky with more than 100,000 detectors on the Prime-Cam instrument.
Kinetic inductance detectors (KIDs) were chosen as the primary sensor
technology for their high density focal plane packing. Additionally, they
benefit from low cost, ease of fabrication, and simplified cryogenic readout,
which are all beneficial for successful deployment at scale. The cryogenic
multiplexing complexity is pulled out of the cryostat and is instead pushed
into the digital signal processing of the room temperature electronics. Using
the Xilinx Radio Frequency System on a Chip (RFSoC), a highly multiplexed KID
readout was developed for the first light Prime-Cam and commissioning Mod-Cam
instruments. We report on the performance of the RFSoC-based readout with
multiple detector arrays in various cryogenic setups. Specifically we
demonstrate detector noise limited performance of the RFSoC-based readout under
the expected optical loading conditions.
