INS401 User’s Manual
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Doc# 7430-3305-08
Page 24
Payload
RTCM 3.2 protocol messages
Input GNSS RTK correction data is in RTCM format based on the version 3.x protocol,
including a series of RTCM messages, e.g. GPS observation (type ID 1077), GLONASS
observation (type ID 1087), GPS ephemeris (type ID 1019), and so on. The different type of
RTCM messages can be accommodated in one Aceinna binary packet. If the length of a full
epoch of RTCM messages is less than 1490 (1500-10) bytes, they can fit in one ethernet data
frame. Note that the 10 bytes are the overhead of one Aceinna binary packet.
EXAMPLE
Assuming that the length of an epoch of RTCM messages is 1024 bytes, the ethernet data frame
is described as below:
Destination
Address
6 bytes
INS401 MAC address, 0x02 0x00 0x00 0x00 0x00 0x02
Source
Address
6 bytes
User controller board MAC address, 0x04 0x00 0x00 0x00 0x00 0x04
Length
2 bytes
1024+10=1034
User Data
Base RTCM
packet length
Header
2 bytes
0x5555
Message ID
2 bytes
0x0b02
Length
4 bytes
1024
Payload
1024 bytes
base RTCM data (1077, 1087,
1019, …)
Checksum
2 bytes
crc16 check sum
Checksum
bytes
4 bytes
Data frame checksum
In addition, another user input of the INS401 is defined as below, in order to enhance the dead
reckoning (DR) performance of the IMU based INS solution. The accurate vehicle speed from
the vehicle reference point provides accurate speed constraint to the along-track direction. This
speed is decoded from CAN odometer messages, and usually is the average of the two rear
wheels odometer speed. In such case, the vehicle reference point (VRP) is the middle point of the
two rear wheels in the vehicle frame.
Table 8 Vehicle Speed Data
Message
Vehicle speed from vehicle reference point, provided by vehicle
manufacturer*
Message ID
0x0b01
Length
4
Payload Description
：
Byte Offset Type
Name
Unit
Description
0
float
speed
km/h Positive if forward driving,
negative if backward moving,
zero if stationary.
*Odometer speed resolution: 0.1 m/s or equivalent to odometer accuracy achievable
User Commands
Several user commands are defined on the ethernet interface for the user system (e.g. a vehicle)
to poll information from INS401 and to set user parameters in INS401. The user request
