ZED-F9K - Integration manual
If both the network latency and the client latency can safely be assumed to be very low (or are
known), the client can choose to set the accuracy of the time message (tacc) to a much smaller value
(e.g. 0.5 s). This will result in a faster TTFF. The latency can also be adjusted as needed. However,
these fields should be used with caution: if the time accuracy is not correct when the time data
reaches the receiver, the receiver may experience prolonged or even failed startups.
For optimal results, the client should establish an accurate sense of time itself (e.g. by calibrating
its system clock using a local NTP service) and then modify the time data received from the service
as appropriate.
3.8 Save-on-shutdown feature
The save-on-shutdown feature (SOS) enables the u-blox receiver to store the contents of the
battery-backed RAM to an external flash memory and restore it upon startup. This allows the u-
blox receiver to preserve some of the features available only with a battery backup (preserving
configuration, IMU calibration, and satellite orbit knowledge) without having a battery backup
supply present. It does not, however, preserve any kind of time knowledge. Save-on-shutdown
must be commanded by the host. The restoring of data on startup is automatically done if the
corresponding data is present in the flash. Data expiration is not checked.
The following outlines the suggested shutdown procedure when using the save-on-shutdown
feature:
• With the UBX-CFG-RST message, the host commands the u-blox receiver to stop, specifying
reset mode 0x08 ("Controlled GNSS stop") and a BBR mask of 0 ("Hotstart").
• The host commands the saving of the contents of BBR to the flash memory using the UBX-
UPD-SOS-BACKUP message.
• For a valid request the u-blox receiver reports on the success of the backup operation with a
UBX-UPD-SOS-ACK message.
• The host powers off the u-blox receiver.
The startup procedure is as follows:
• The host powers on the u-blox receiver.
• The u-blox receiver detects the previously stored data in the flash. It restores the corresponding
memory and reports the success of the operation with a UBX-UPD-SOS-RESTORED message
on the port on which it had received the save command message (if the output protocol filter on
that port allows it). It does not report anything if no stored data has been detected.
• Additionally the u-blox receiver outputs a UBX-INF-NOTICE and/or a NMEA-TXT message
with the contents
RESTORED
in the boot screen (depends on the configuration of the port and
information messages) upon success.
• Optionally the host can deliver coarse time assistance using UBX-MGA-INI-TIME_UTC for
better startup performance.
Once the u-blox receiver has started up it is recommended to delete the stored data using a UBX-
UPD-SOS-CLEAR message. The u-blox receiver responds with a UBX-ACK-ACK / UBX-ACK-NAK
message.
UBX-20046189 - R01
3 Receiver functionality
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C1-Public
Early production information
