R31DS0087EU0101 Rev.1.01

Page 12

Sep.28.21

pcm4l Datasheet

reference tracker will stay in this stage until it is reset by the reference tracker supervisor, or a large frequency

or ToD offset is detected. If one of these events happens, the Assisted Time Reference Tracker will signal the

reference tracker supervisor that the lock state is lost and will then transfer to the “Stage 1: Idle Stage.”

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Stage 3: PTP Calibration Stage. In this stage, the Assisted Time Reference Tracker is in calibration mode, and

PTP corrections are disabled. The APTS supervisor is locked to the local time reference source and provides

phase and frequency corrections. A calibration engine collects information from the APTS supervisor to remove

any asymmetry to the PTP clock source.

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Stage 4: PTP Assisted Holdover Stage. In this stage, the Assisted Time Reference Tracker runs like an

adaptive PLL with asymmetry compensation enabled. It analyzes PDV statistics, compensates for asymmetry,

collects enough time stamps, makes a ToD offset estimation, and requests a frequency correction. The

reference tracker will stay in this stage until:

• The local time reference is re-qualified and locked. If this event happens, the Assisted Time Reference

Tracker will then return to the “Stage 3: PTP Calibration Stage” once lock is achieved.

• The calibration timer expires, or a reroute is detected. If one of these events happens, the Assisted Time

Reference Tracker will then transfer to “Stage 2: PTP Out of Specification Stage.”

• It is reset by reference tracker supervisor, or a large frequency or ToD offset is detected. If one of these

events happens, the Assisted Time Reference Tracker will signal the reference tracker supervisor that the

lock state is lost and will then transfer to “Stage 1 - Idle Stage.”

2.1.4

Adaptive Frequency Reference Tracker

The Adaptive Frequency Reference Tracker is designed to be used in networks where the PDV is large and the

main goal is to synchronize the frequency between the master and the slave. Similar to the Adaptive Time

Reference Tracker, it periodically analyzes the PDV statistics, and based on the PDV analysis results, the tracker

calculates the required time to collect the timestamps in order to achieve the target frequency synchronizing

accuracy. After collecting the timestamps, the Adaptive Frequency Reference Tracker selects a frequency

estimation algorithm based on the PDV analysis. The frequency offset is then estimated and the local oscillator

correction requests will be sent to the reference tracker supervisor to apply the frequency corrections.

The same outlier filter as Adaptive Time Reference Tracker is used.

The Adaptive Frequency Reference Tracker has three stages when it starts tracking a master clock or after it has

been reset by the RTS:

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Stage 1: Rough Time And Frequency Correction Stage. This stage takes 10 seconds or less depending on

the configuration setting. In this stage, the Adaptive Frequency reference Tracker makes a rough time

estimation and sends a phase correction request to the reference tracker supervisor. If a frequency correction is

configured, a rough frequency estimation is performed and a frequency correction request will be sent to the

supervisor as well. Then, the Adaptive Frequency Reference Tracker enters Stage 2.

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Stage 2: High Precision Frequency Correction Stage. This stage takes roughly one minute to several

minutes to do a frequency correction, depending on the PDV statistics. The maximum time spent in this stage is

determined by highPrecisionFrequencyCorrectionTimeMinutes. The tracker analyzes the PDV and determines

how long it needs to collect the time stamps. After collecting the required time stamps, the reference tracker will

perform a high precision frequency estimation. A frequency correction request will be sent to the reference

tracker supervisor. After this correction, the local clock should be synchronized in frequency with the master

clock. The Adaptive Frequency Reference Tracker then transfers to Stage 3.

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Stage 3: Frequency Correction Stage. In this stage, the Adaptive Frequency Reference Tracker continues

periodically analyzing PDV statistics, collects enough time stamps, makes a frequency offset estimation, and

requests a frequency correction to the reference tracker supervisor. The reference tracker will stay in this stage

until it is reset by the reference tracker supervisor, or a large frequency offset is detected. If one of these events

occurs, the Adaptive Frequency Reference Tracker will signal the reference tracker supervisor lost lock state

and will then transfer to the Stage 2 - High Precision Frequency Correction Stage.