The UTC offset (TAI - UTC) is conveyed to PTP slave clocks from a PTP master clock within the Sync or FollowUp messages. The UTC valid flag (UTCV) indicates whether the UTC offset time is considered valid by a master device and therefore should be used by a PTP slave device.
In the sfptpd configuration file, the ptp_utc_valid_handling option identifies the action taken with the UTC offset value by sfptpd.
| Value | Description |
|---|---|
| default | If UTCV is set, use UTC, otherwise do not. |
| ignore | Ignore the UTC valid flag. Always apply the UTC offset. |
| prefer | Prefer master clocks that set the UTCV flag above those that do not. |
| require | Do not accept PTP messages from master clocks that do not set the UTCV flag. |
| override <seconds> | Ignore the UTC valid flag and UTC offset value set by the master clock. Use
only the value set by the override option. Important: You must ensure the
override <seconds> value is set to the
correct UTC offset. The UTC offset increments on the occasion of
each leap second. |