Technical Support Center

Determination of the CAN Latency


ADMA Delay – Sample Time to CAN Bus#

The mean delay of the first ADMA_3.0 CAN Message can be calculated as followed:

With:

tCalc,Mean= 1136 µs
txmit_FPGA_Msg= 9 µs
nMsg= Number of selected CAN Messages in the Web interface

ADMA CAN Message Delay#

There is a fixed delay for each CAN message, that depends on the CAN messages sent before. These delays can be calculated as followed:

With:

Baudrate= Configured Baudrate in baud
MPCD_Msg= Number of preceding CAN messages (Activated ADMA CAN messages with a lower CAN ID Offset than the CAN Message to be calculated)
tDelay_Calc= ADMA Delay – Sample Time to CAN Bus

Example – CAN Delay of data packet “Accelerations (horizontal)”#

Number of selected CAN Messages in the Web interfacenMsg15
CAN-Message Accel_Horizontal_X CAN-ID OffsetnByteoffsetB+9

Now there are two ways to calculate the MPCD_MSG value:

Preceding Messages#

Count the activated messages sent before the message to be calculated (check data packet table of used data format). In our case these are the following data packets:
• Status
• Error_Warning
• Rates (horizontal)

Result:
MPCDMsg = 3

Note: The CAN messages Status and Error Warning are activated permanently!

Byte Offset#

Count the deactivated messages
• INS-Sensors Body-X
• INS-Sensors Body-Y
• INS-Sensors Body-Z
• Rates (Body)
• Accelerations (Body)

Result:
Deactivated Messages nDeactivated = 5

Result:
MPCD_Msg = (9 – 1) – 5 = 3

Final calculation:

tCalc,Mean= 1136 µs
txmit_FPGA_Msg= 9 µs
nMsg= 15
nByteoffsetB+9
MPCD_Msg3
Configured Baud rate1000 kbaud

Results:
tDelay_Calc = 1136 µs + (9 µs * (2+15)
tDelay_Calc = 1289 µs
tDelayMsg = 1289 µs + (3 * (111bit / 1000k + 9 µs))
tDelayMsg = 1289 µs + (3 * 120 µs)
tDelayMsg = 1649 µs

Note: CAN-Message = CAN Data block with 8 Byte

Applikationsingenieur | bei GeneSys seit 2014

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