Web Interface
In Depth
Before entering holdover:
n The Hardware Clock is synchronized to one of the Input References and reports Stratum
0 to the NTP daemon.
n The NTP daemon is synchronized to the Hardware Clock "reference clock" and reports
Stratum 1 to the network.
The Hardware Clock enters holdover when the Input Reference becomes unavailable and
no other Input References are available.
While in holdover:
n The Hardware Clock uses the internal oscillator to keep time (flywheeling).
n The NTP daemon (Stratum 1) remains synchronized to the Hardware Clock (Stratum 0,
Reference = the name of the last Input Reference).
n The SyncServer estimates the time error (difference) between the oscillator-based Hard-
ware Clock time and UTC.
n If two or more synchronizing NTP associations are available and the Hardware Clock
accumulates too much time error, the NTP daemon "drops" the Hardware Clock and syn-
chronizes with the best association, with a corresponding adjustment to its Stratum.
The Hardware Clock leaves holdover when one of the following occurs:
n An Input Reference becomes available again. (As a result, the NTP daemon returns to
Stratum 1 operation.)
n The estimated time error exceeds the user-configurable Time Error Limit.
If the estimated time error exceeds the user-configurable Time Error Limit:
n The Hardware Clock reports to the NTP daemon that it is unsynchronized (Stratum 16).
n If one or more synchronizing NTP associations are available, the NTP daemon syn-
chronizes with the best one, with a corresponding change to its stratum.
n If no synchronizing NTP associations are available, the NTP daemon's behavior is
determined by the settings on the NTP - Prefs page. See NTP - Prefs (on page 50).
n With the S300 and S350, the Hardware Clock synchronizes to the NTP daemon.
n With the S200, S250, and S250i, the Hardware Clock "flywheels" on the internal oscil-
lator until an Input Reference becomes available again.
TIMING - Sysplex
The Sysplex Timer port outputs serial time strings for IBM mainframe Sysplex systems. The
Sysplex Timer provides a common time reference across all the members of an IBM Sys-
plex. The Sysplex Timer is a key component when systems on multiple CPCs share access
to the same data.
See Sysplex Out (on page 116) for specifications and more information on the format of the
Sysplex output string.
Sysplex Output Configuration
The Sysplex Out port located on the rear panel outputs the time of day once per second.
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