R31DS0087EU0101 Rev.1.01

Page 15

Sep.28.21

pcm4l Datasheet

2.2.6

Master Lock-out (G.8265)

The user has the option to lock out certain masters. By locking out the master, it will be excluded from the master

selection consideration. The following management APIs are used for master lock-out:

▪

mngApi_SetG82651MasterLockoutEnable – Enable/disable master lock out

▪

mngApi_GetG82651MasterLockoutEnable – Query whether master is locked out

2.3 APTS Supervisor

The APTS Supervisor is a state machine implemented in the device adaptor that monitors the GNSS DPLL

channel and periodically sends time and frequency information to the reference trackers. The APTS Supervisor

provides a high-level indication of the operational status of the GNSS clock. There are four states in the APTS

Supervisor:

▪

Unqualified – Nothing is asserted about the quality of the GNSS clock in this state. The APTS Supervisor starts

in the state.

▪

Wait First TOD Read – The GNSS DPLL channel is locked and qualified. In this state it will attempt to get a

PTP ToD from the PTP channel. Once the initial ToD is retrieved, it will enter the Locked state.

▪

GNSS Locked – The GNSS DPLL channel is locked and qualified. The GNSS and PTP output clocks are

phase/time synchronized to the local time reference.

▪

GNSS Holdover – The APTS Supervisor has lost its local time reference with no other qualified references

available and it uses the stored data acquired in Locked mode to control its output clock. After entering

holdover, the accuracy of the GNSS outputs depends on its local clock (i.e., from physical layer assistance

[SyncE traceable to PRC] or local XO). If the holdover timer expires, the APTS Supervisor will return to the

Unqualified state.

2.4 Local Oscillator State Machine (LOSM)

The LOSM is a core component of the PCM and is the main part of the RTS. The states may be interpreted as

signaling the quality of the Local PTP Clock in relation to its active input reference, if such a reference exists. Input

references may take the form of a remote GM or BC, electrical references such as SyncE, or local GNSS

reference.

The LOSM follows the PTP clock modes as described in ITU-T G.8275.1 Appendix V and G.8275.2 Appendix IV.

The LOSM provides a high-level indication of the operational status of the entire clock. This can then be used to

map to PTP port states as defined in IEEE 1588 and provide a mapping to content of the Announce message

fields. The following table provides a mapping of the LOSM state and the ITU-T clock mode.

Table 1. ITU-T Clock Mode Mapping

ITU-T

Clock Mode

pcm4l

LOSM Clock State

ptp4l

Clock Servo State

Free-Run

Unqualified

S0

Acquiring

Lock Acquisition

S1

Locked

Frequency Locked /

Time Locked

S2 (/ S3)

Holdover-In-Specification

Holdover-In-Specification

N/A

Holdover-Out-Of-Specification

Holdover-Out-Of-Specification

N/A