sfptpd will failover from PTP to NTP if there are active PTP alarms:
pps-no-signal pps-seq-num-error no-time-of-day pps-bad-signal no-sync-pkts no-follow-ups no-delay-resps no-pdelay-resps no-pdelay-resp-follow-ups no-tx-timestamps no-rx-timestamps no-interface clock-ctrl-failure
See PTP Alarms for a description of alarms.
If alarm conditions clear,
sfptpd will resume synchronization using PTP.
The selection_holdoff_interval (seconds) can be set to prevent immediate failover caused when only one or two PTP packets are not received.
sfptpd will NOT failover to NTP because of synchronization accuracy.