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External Time Reference

SentiBoard 2.0 supports external time references by synchronizing its Physical Hardware Clock (PHC) with an external 1 PPS signal.

Each (sensor) data message coming from SB2.0 will then have the UTC time field of the message set by the synchronized clock, effectively supplying all measurements in the reference time/clock given by the external unit.

Note that this functionality will depend on the PTP State of the SentiBoard 2.0 unit as described below:

PTP Grandmaster

While SB2.0 is acting as a PTP Grandmaster it can synchronize to an external time reference in two ways.

1 PPS Only

In this mode, a 1 PPS from an external unit is provided on one of the board's sensor ports (The Time-of-Validity pin). The SentiBoard will adjust the frequency of its PHC to align its internal timer to that of the external reference's 1 PPS signal. The SB2.0 clock will typically align within $100ns$ of the external reference clock.

1 PPS + Time Reference Message

If a time reference message is provided on the RX pin of the sensor port which is also receiving the 1 PPS signal on it's Time-of-Validity pin, all messages will be referenced in the time frame supplied by this time reference message.

As an example: if a GNSS receiver is connected to SB2.0 configured with a 1 PPS output together with an NMEA ZDA message string containing the exact timestamp of the most recent PPS, SentiBoard 2.0 will

  • Synchronize the PHC with the 1 PPS signal, meaning the clock of the GNSS receiver and the PHC of SB2.0 will have close to zero drift.
  • All data from SB2.0 will be timestamped in the GNSS receiver's time frame/format.

PTP Slave

While SB2.0 is acting as a PTP Slave, the external time reference is ignored and SB2.0 will only synchronize its understanding of time with the PTP Grandmaster Clock.

PTP Disabled

In this mode SB2.0 will synchronize with the External Time Reference signal in the same manner as in PTP Grandmaster mode. However, since PTP is disabled, the external time reference is not distributed to other network units as the time reference is not distributed through PTP.