Spectracom TSync-PCIe, User Manual

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Enable Priority Time Ref 1PPS Ref
en 1 gps0 gps0
en 2 ird0 ird0
en 3 ira0 ira0
en 4 hst0 epp0
en 5 hst0 self
dis 6 self self
dis 0
dis 0
Table 6-2:
Example default table
Legend:
gps = GPS Reference, ird = IRIG DCLS Reference, ira = IRIG AM Reference, epp = External 1PPS
Reference, hst0 = Host Reference, self = Self Reference
Entries can be added to and deleted from the working table. In addition, individual entries can
be enabled or disabled. Their priorities can be changed at any time. Any changes to the table
will cause the reference monitor to reevaluate the best reference to use for synchronization.
The working table can be saved to the user table and persisted, or it can be reset to the default
table or an already existing user table at any time.
At any given time, the highest priority enabled entry in the table that has both a valid time and
a valid 1PPS reference will be used as the best reference for synchronization. The power of the
reference monitor is in its ability to generate any combination of time and 1PPS references in
any priority. For example, if a user has a high precision 1PPS source, this can serve as the
provided external 1PPS reference and can be paired with a GNSS time reference.
The reference tables, the currently selected best reference, and the current validity states of all
input references can be requested from the board.
6.3 Clock Subsystem
The clock subsystem is the heart of the TSync-PCIe timing architecture. Time is maintained in the
board’s hardware and incremented in 5- nsec units, while sub- second information is
tracked. Time, from seconds through years, is incremented based on the internal 1PPS derived
from the selected input reference.
By default, system time is maintained in UTC, but this can be set to TAI, GPS, or a local times
cale (with DST rules). Offsets between timescales are maintained on the board to facilitate con
versions between the timescales. The offsets can be set by the user or, depending on the
references available, may be automatically determined. Users who wish to use a specific times
cale must provide the timescale offset from an input reference or by setting it manually.
The clock subsystem can handle several types of time discontinuities, including leap years, leap
seconds, DST transitions, and a user-settable discontinuity. Leap years are automatically detec
ted and handled by the system. Leap seconds, if set from the user or received from an input
6.3 Clock Subsystem
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Instruction Manual XYZ Rev. R
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