
8
Synchronization
8021386/12G4 /2019-04-24 | SICK
OPERATING INSTRUCTIONS | NAV-LOC
50
Subject to change without notice
8.1.2
Synchronization via telegram request (polling) and HW port
The vehicle computer retrieves the internal time of the embedded application using the telegram
NAVGetTimestamp
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in the same way like used in option 1. Additionally, a hardware (HW) digital
output is set via
NAVSyncGetTimestampPort
. The hardware output provides a pulse of 128 ms
duration once the internal time stamp is written in the telegram.
Using the hardware port gives the option to calculate the delay for processing the request command
and the following response time.
An example could be to request the time stamp from NAV-LOC every 10 seconds.
NOTE
The vehicle computer is to be configured such that it responds to the risings edge of the output pulse.
After the vehicle computer has received the telegram, the AGV computer can correct the time difference
between the pulse and the reception of the time stamp included in the telegram.
As a result, the AGV computer can determine the actual time in NAV-LOC.
The following formula is used to calculate the resulting time offset after request of the sensor time
between the clock of the SIM and the clock of the vehicle computer:
Δt
offset
= TS
AGV
– t
transfer
– TS
NAV
Δt
offset
Resulting time difference (offset)
TS
AGV
Time stamp of the AGV computer
TS
NAV
Time stamp of NAV-LOC
t
transfer
Transfer time via the Ethernet interface
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See telegram listing in the Telegram Listing publication