R31DS0087EU0101 Rev.1.01

Page 16

Sep.28.21

pcm4l Datasheet

Figure 4. State Machine Diagram

2.4.1

Operational States

There are six states in the LOSM:

▪

Unqualified – Nothing is asserted about the quality of the Local PTP Clock in this state. The LOSM starts in the

state and enters on expiration of unqualified timer, unqualifiedTimeoutSeconds, when in the Holdover state.

▪

Lock Acquisition – At least one qualified reference is present prior to reaching the frequency locked state.

▪

Frequency Locked – The output clock is syntonized to an input reference within the user specified threshold,

frequencyLockThresholdPpb.

▪

Time Locked – The output clock is phase/time synchronized to an input reference within the user specified

threshold, timeLockThresholdNanoseconds.

▪

Holdover In-Specification – The RTS has lost its reference with no other qualified references available and

uses the stored data acquired in Locked mode to control its output clock. After entering holdover-in-spec, the

accuracy of its output depends on the Local PTP Clock (i.e., from physical layer assistance (SyncE traceable to

PRC) or local XO).

▪

Holdover Out-Of-Specification – The Holdover timer, holdoverTimeoutSeconds, has expired. After entering

holdover-out-of-spec, the accuracy of the PTP output depends on the Local PTP Clock and its time traceability

is lost.

2.4.2

Lock Acquisition Qualification Timeout

Once a best master is selected, the LOSM will enter the lock acquisition state, start the lock acquisition

qualification timer, and attempt to lock to the master. If the lock acquisition qualification timer expires before

frequency lock can be achieved then this master will be considered unusable and will be locked out.

Initial

FreeRun/

Unqualified

Initialization

Lock 

Acquisition

Holdover

Frequency 

Locked

Reference Acquired

Time Locked

Reference Lost 

(unqualified holdover)

Reference Lost 

(qualified holdover)

Holdover 

duration 

exceeded

Frequency Lock 

Succeeded

Reference Acquired 

(not locked)

Time Lock 

Succeeded

Reference Lost (qualified holdover)

PTP Reference Lost (unqualified holdover) 

and GNSS not Locked

Time Lock L ost

Reference Lost 

(qualified holdover)

Reference 

Acquired 

(locked)