ZED-F9R-Integration manual
GNSS Signal gnssId sigId numWords period
GLONASS L2OF 6 2 3 2s
Table 29: Data message formats reported by UBX-RXM-SFRBX
3.13 Forcing a receiver reset
Typically, in GNSS receivers, a distinction is made between cold, warm, and hot start, depending on
the type of valid information the receiver has at the time of the restart.
• Cold start: In cold start mode, the receiver has no information from the last position (e.g.
time, velocity, frequency etc.) at startup. Therefore, the receiver must search the full time and
frequency space, and all possible satellite numbers. If a satellite signal is found, it is tracked
to decode the ephemeris (18-36 seconds under strong signal conditions), whereas the other
channels continue to search satellites. Once there is a sufficient number of satellites with
valid ephemeris, the receiver can calculate position and velocity data. Other GNSS receiver
manufacturers call this startup mode Factory startup.
• Warm start: In warm start mode, the receiver has approximate information for time, position,
and coarse satellite position data (Almanac). In this mode, after power-up, the receiver
normally needs to download ephemeris before it can calculate position and velocity data.
As the ephemeris data usually is outdated after 4 hours, the receiver will typically start with
a warm start if it has been powered down for more than 4 hours. In this scenario, several
augmentations are possible. See Multiple GNSS assistance.
• Hot start: In hot start mode, the receiver was powered down only for a short time (4 hours
or less), so that its ephemeris is still valid. Since the receiver does not need to download
ephemeris again, this is the fastest startup method.
Using the UBX-CFG-RST message, you can force the receiver to reset and clear data, in order to see
the effects of maintaining/losing such data between restarts. For this, the UBX-CFG-RST message
offers the navBbrMask field, where hot, warm and cold starts can be initiated, and also other
combinations thereof.
The reset type can also be specified. This is not related to GNSS, but to the way the software restarts
the system.
• Hardware reset uses the on-chip watchdog, in order to electrically reset the chip. This is an
immediate, asynchronous reset. No Stop events are generated.
• Controlled software reset terminates all running processes in an orderly manner and, once
the system is idle, restarts operation, reloads its configuration and starts to acquire and track
GNSS satellites.
• Controlled software reset (GNSS only) only restarts the GNSS tasks, without reinitializing the
full system or reloading any stored configuration.
• Hardware reset (after shutdown) uses the on-chip watchdog. This is a reset after shutdown.
• Controlled GNSS stop stops all GNSS tasks. The receiver will not be restarted, but will stop any
GNSS-related processing.
• Controlled GNSS start starts all GNSS tasks.
3.14 Firmware upload
ZED-F9R is supplied with firmware. u-blox may release updated images containing, for example,
security fixes, enhancements, bug fixes, etc. Therefore it is important that customers implement a
firmware update mechanism in their system.
A firmware image is a binary file containing the software to be run by the GNSS receiver. A firmware
update is the process of transferring a firmware image to the receiver and storing it in non-volatile
flash memory.
UBX-20039643 - R06
3 Receiver functionality Page 84 of 119
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