R31DS0087EU0101 Rev.1.01

Page 14

Sep.28.21

pcm4l Datasheet

2.2.2

Phase Slope Limit and Instant Reference Switching

The phase slope limiting feature can be configured to limit the rate of output phase movement when the servo

switches from one RT to another. The following parameters in “ptpPacketReferenceSwitch” configuration are used

for phase slope limiting:

▪ “referenceSwitchType” – Set type to “PhaseSlopeLimit” to select reference switch type as phase slope limited

switch.

▪ “phaseSlopeLimit” – The limit of output phase movement rate in the unit of nanosecond per second.

If “referenceSwitchType” is set to “PhaseSlopLimit” and the slave is time locked to the target master, the value of

“phaseSlopeLimit” will be applied when there is a switch between RTs. If “referenceSwitchType” is set to

“PhaseSlopeLimit” and the slave is frequency locked to the target master, the frequency lock threshold will be

applied when the reference switch occurs.

If “referenceSwitchType” is set to “Instant”, no phase slope limit will be applied if the slave ToD offset to the target

master is larger than 10 microseconds, or 1 ppm per second phase slope limit will be applied if the offset is less

than 10 microseconds.

2.2.3

Reference Switching Thresholds

These thresholds take effect only if the reference switch type is hitless or phase slope limited. If the reference

switch type is hitless and the absolute value of the ToD offset is within the thresholds, then apply a hitless switch;

otherwise, apply a phase slope limit. If the reference switch type is phase slope limited and the absolute value of

the ToD offset is within the thresholds, then apply PSL; otherwise, apply a hitless switch.

The reference switch thresholds are configured by the JSON parameters lowerTodThresholdNanoseconds and

upperTodThresholdNanoseconds.

2.2.4

Revertive/Non-revertive Switching (G.8265)

Revertive switching is the default behavior for switching between masters. When the best master, as selected by

the telecom master selection algorithm, is registered or restored due to loss of signal, etc, the servo will switch

from the master it is currently tracking to the new best master.

When revertive switching is disabled, master switching is non-revertive (i.e., servo will only switch to different

master if the current master is disqualified due to loss of signal, etc.). One exception is when the new master that

comes up is a better master than the current master the servo is tracking and the servo has not achieved

frequency lock with the current master yet; in this case, the servo will switch to the new master.

2.2.5

Wait-to-Restore (G.8265)

When configured, wait-to-restore ensures the previously disqualified RT (due to signal failure, etc.) is only again

considered for the best master selection when it is fault-free for the time period specified by the wait to restore

time.

The wait to restore time can be configured globally for all masters using the configuration parameter

“masterWaitToRestoreTimeoutValue”, or individually using the management API function

mngApi_SetWaitToRestoreTimeout().

The following management API functions can be used to monitor/query wait to restore time for each individual

master:

▪ mngApi_GetWaitToRestoreTimeout – Returns the current value of wait to restore time

▪ mngApi_IsWaitToRestoreTimerRunning – Checks whether wait to restore timer is running

▪ mngApi_ClearWaitToRestoreTimer – Clears the running wait to restore timer

The unit for wait to restore time is in seconds to allow for configuration flexibility.