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EdgeSync Manual rev 1 | 51
EdgeSync Clock Sync States
EdgeSync clock at any instance of time can be in one of four following sync states:
•
FREE RUNNING
•
SYNTONIZING
•
SYNCHRONIZING
•
HOLDOVER
•
UNKNOWN/ERROR
FREE RUNNING State
The EdgeSync clock comes into this state upon initialization. The EdgeSync clock time is not set, the
clock class is DEFAULT (248), clock accuracy is UNKNOWN (0xFE).
The timescale is PTP, the UTC offset is initially set to 37 secs, leap flags are FALSE. In Free Running
state, the clock frequency comes from the on-board oscillator.
SYNTONIZING State
This state is only possible when the 1PPS-input signal from the GNSS interface is available, but not the
ToD-input signal and the clock become a PTP master.
When the EdgeSync engine is running in GNSS Only mode or PTP Only mode, the clock class is
automatically changed to either PRC_SYNC (6) or APP_SYNC (13) and the clock accuracy is set to
WITHIN_100_NS. In GNSS Primary, PTP Secondary mode, the clock class remains unchanged.
Note that the frequency can be traced, but not the time in this state. Once the ToD-input signal
becomes available the clock switches to SYNCHRONIZING state.
SYNCHRONIZING State
The EdgeSync clock enters this state when it starts to synchronize its time and frequency with either a
PTP or GNSS source. If the synchronization source is the GNSS, then both time and frequency are
present and traceable. The timescale is changed to PTP, the clock class is changed to PRC_SYNC (6)
and the clock accuracy is set to WITHIN_100_NS.
If the ToD-input signal becomes unavailable, while the 1PPS-input is still present, the EdgeSync clock
switches to SYNTONIZED state.
If the synchronization source is a PTP master, then the clock quality remains unchanged. The timescale
is set according to what is distributed by the PTP master. If the timescale distributed is PTP then the
UTC offset (if valid) and leap flags are also set to master’s values and the time source is set to PTP.
HOLDOVER State
The EdgeSync clock enters this state when the synchronization source is lost. If the clock was
synchronized with PTP master its clock class remains unchanged. Otherwise the clock class is modified
according the engine’s operational mode and the clock accuracy is changed based on the time spent in
the holdover state.
There is a static parameter which defines the clock stability. Currently it is fixed to 1 ns/s for a
temperature-stable environment. During the holdover state an estimated error value is calculated and
the clock accuracy is set according to that value.
