ZED-F9K - Integration manual
• Time mark on external input: reception time of time mark signal sent to external input
The latency of sensor data is the absolute difference between the time at which the sensor
measurement is taken and the time at which either the first byte of the UBX-ESF-MEAS message
or the pre-processor's time mark are detected at the receiver.
The latency for the wheel tick can be set with the
CFG-SFODO-LATENCY
key.
It is essential that the time tags used for all UBX-ESF-MEAS data have the same resolution.
ZED-F9K automatically generates UBX-ESF-MEAS messages containing measurements from the
internal IMU using the default time tag resolution of 1 millisecond. If the customer wants to input
odometer data with UBX-ESF-MEAS messages, it is essential that the odometer time tag has a
resolution of 1 millisecond.
3.2.4.2.1 First byte reception
The easiest way to determine the sensor measurement generation time is to have the GNSS receiver
assume the time of reception of the first byte of the UBX-ESF-MEAS message (minus the constant
configured latency in CFG-SFODO-LATENCY) to be the time of sensor measurement. This approach
is the simplest to implement, but Time mark on external input can yield better latency control and
compensation.
Figure 4: First byte reception
3.2.4.2.2 Time mark on external input
In this case, the preprocessor unit generating the measurements sends a signal to the EXTINT
input of the GNSS receiver, marking the moment of the measurement generation. The subsequent
UBX-ESF-MEAS message is then flagged accordingly, and the measurements in the message are
assumed to have been generated at the time of external signal reception (minus the constant
configured latency in CFG-SFODO-LATENCY). This approach is the preferred solution, but it can be
difficult to realize an exact analog time signal for the preprocessor unit.
Figure 5: Time mark on external input
UBX-20046189 - R01
3 Receiver functionality
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C1-Public
Early production information
