Standby Master Clock

Enhanced PTP User Guide (UG1602)

Document ID
UG1602
Release Date
2022-10-18
Revision
1.0 English

It is quite common to deploy the network adapter in master clock mode as a secondary/backup master when the primary master is usually a dedicated PTP Grandmaster clock device having a time source reference such as. GPS.

The Best Master Clock Algorithm (BMC) uses a hierarchical selection algorithm to select the active master clock based on properties in the periodic Announce messages sent by all master clocks. Clock properties are considered in the following order:

  1. BMC priority 1.
  2. Class.
  3. Accuracy.
  4. Variance.
  5. BMC priority 2.
  6. Unique identifier (tie breaker).

In the ptp_master_freerun.cfg file the following clock properties are configurable (default values are shown):

# ptp_clock_priority1 128
# ptp_clock_priority2 128

Priority1 and priority2 values are in the range 0-255 (0 is the highest priority, 255 the lowest).

Important: When configured as a master clock the network adapter is using the UTC timescale. The UTC offset should be set to zero (0) in the sfptpd master config file.