Time and synchronization

Correct time is part of the scientific data model. EDD uses several related but distinct quantities:

Reference time

The observatory standard, normally distributed from a maser or GNSS-disciplined source through 1-PPS and frequency references.

sync_time

UTC Unix epoch associated with a digitizer sample counter. Pipelines combine it with sample rate and packet indices to reconstruct sample timestamps.

Host time

System time used for control actions, logs, filenames, and metadata queries. It must be synchronized, but it is not a substitute for the digitizer sample clock.

EDD identifier and transition times

Provenance values generated by the Master Controller for a provision, configure cycle, and measurement.

Site commissioning must verify 1-PPS polarity, reference-frequency lock, digitizer synchronization, leap-second handling, sample-rate accuracy, packet timestamp rollover, host NTP/PTP state, and the time convention used by every output format. Store timestamps as UTC. A local timezone setting may be used only for display or directory naming.

Before an observation, compare the digitizer’s reported sync epoch with a decoded downstream packet and a written data header. After firmware, clock, packetizer, or format changes, repeat an independent absolute-timing test.