External Reference (GM)

Configuration

The Configuration of the GM is partially done by the Preset and then by the Configuration Tab under the Timing > External Reference (GM) section.

If the user selects the Custom Preset it might be able to configure the following parameters when expanding (+) to the Advanced View for the GM source type:

OID	Name	Value Type	Description
3.7110.x	gm/cfg/xxx		Configuration of the GM timing source (By Preset)..
3.7110.2	Align PPS	<Boolean>	Enable this to align the PPS output to the PPS input during the locking procedure. It should be enabled when using a GNSS receiver as external reference as PPS might be shifted from 10MHz after each GNSS relock.
3.7110.4	Source Type	• ATOMIC CLOCK • GNSS • PTP • OTHER	Type of timing source announced by the GM. It should correspond to the type of external reference that provides 10MHz/PPS to the front-panel of the device. (This field is informative and not used for decision making).
3.7110.7	PPS Mandatory	• YES • NO • STARTUP_ONLY	Controls whether an PPS input signal is needed to enter/stay active for the GM source.

The user can also configure the following parameters independently from the chosen preset:

OID	Name	Value Type	Description
3.7110.x	gm/cfg/xxx		Configuration of the GM timing source (By Preset)..
3.7110.1	GM Offset	<Integer> Default: 0	Offset to compensate user cable delay for PPS input (in picoseconds). When Align PPS is enabled the PPS output should be aligned to the PPS input but the user might want to compensate this delay.
3.7110.2	Priority1	<Integer> Default: 128	PTP Priority1 announced when the GM is active. It is mainly used by BMCA to force the best-clock selection using 1st priority (Lower values take precedence).
3.7110.3	Priority2	<Integer> Default: 128	PTP Priority2 announced when the GM is active. It is mainly used by BMCA to force the choice between two references when their clock qualities are the same (Lower values take precedence).
3.7110.11	Clock Accuracy	<Enum> Default: Unknown	It announces the expected accuracy provided by the external reference. It shall be conservatively estimated based on the type of time source (e.g., Atomic Clock <= 1ns, GNSS receiver <= 50ns).
3.7110.15	Leapsec file ignore	<Enum>Default: OFF	Leapsec_file_ignore disables the critical warning when the leap second file is expired.

Caution: If GM is used as a timing source, it should always be associated to the configuration of at least one NTP server to properly recover the time of day (ToD).

Info/Overview

The GM timing source provides its own overview panel under Overview > Timing General > External Reference (GM), where the user can easily audit the condition of its external reference (see figure below).

Overview tab for GM timing source.

It basically offers a readback of the configuration value (Source Type, Source Rank, Align PPS and PPS Mandatory) as detailed Configuration, along with an user friendly Message that summarize the state of the GM internal state machine and a Detected value that reports the situation with the external reference inputs signals. Finally, the validity of the leap second file needed to perform the conversion from UTC (NTP timescale) to TAI (PTP timescale) is detailed in the panel. A detailed explanation of the parameters is provided below:

OID	Name	Value Type	Description
3.7120.x	gm/info/xxx		Specific information about the state of GM timing source..
3.7120.0	Message	<String>	User friendly message that summarizes the current state of the GM timing source.
3.7120.2	PPS Detected	• NONE • PPS (Only) • CLK (Only) • PPS & CLK	Report the detection of external reference input on the front panel.
3.7120.4	Leap Second File Expiration Date	<String>	Expiration date of the leap seconds files. If there is more than one file, this will show the date that is further in the future. The date format is YYYY-MM-DD HH:MM:SS.
3.7120.5	Leap Second File Validity	<Bool> • No • Yes	“Yes” if the leap seconds file is valid. “No” if it is expired or missing. See Update Leap Seconds File for updating this file.