Periodic CAN Message Transmission

This example shows you how to use the automated CAN message transmit features of Vehicle Network Toolbox™ to send periodic messages. It uses Vector Virtual CAN channels connected in a loopback configuration. As this example is based on sending and receiving CAN messages on a virtual network, running Vehicle CAN Bus Monitor in conjunction may provide a more complete understanding of what the code is doing. To run Vehicle CAN Bus Monitor, open and configure it to use the same interface as the receiving channel of the example. Make sure to start Vehicle CAN Bus Monitor before beginning to run the example in order to see all of the messages as they occur.

Create the CAN Channels

Create CAN channels on which to use the automated message transmit commands.

txCh = canChannel('Vector', 'Virtual 1', 1);
rxCh = canChannel('Vector', 'Virtual 1', 2);

In this example, you will use a CAN database file to define and decode messages. Open the database and attach it to the CAN channels.

db = canDatabase('demoVNT_CANdbFiles.dbc');
txCh.Database = db;
rxCh.Database = db;

Create the CAN Messages

You can create CAN messages to register for periodic transmit using the database information.

msgFast = canMessage(db, 'EngineMsg');
msgSlow = canMessage(db, 'TransmissionMsg');

Configure Messages for Periodic Transmit

To configure a message for periodic transmit, use the transmitPeriodic command to specify the channel, the message to register on the channel, a mode value, and the periodic rate.

transmitPeriodic(txCh, msgFast, 'On', 0.100);
transmitPeriodic(txCh, msgSlow, 'On', 0.500);

Start the Periodic Message Transmit

When you start a channel which has periodic messages registered, transmit begins immediately. Allow the channels run for a short time.

start(rxCh);
start(txCh);
pause(2);

Modify Transmitted Data

To update the live message or signal data sent onto the CAN bus, write new values into the message you originally created using either the Data property or the signals interface.

msgFast.Signals.VehicleSpeed = 60;
pause(1);
msgFast.Signals.VehicleSpeed = 65;
pause(1);
msgFast.Signals.VehicleSpeed = 70;
pause(1);

Receive the Messages

Stop the CAN channels and receive all periodically transmitted messages for analysis.

stop(txCh);
stop(rxCh);
msgRx = receive(rxCh, Inf)
msgRx = 

  1x62 Message array with properties:

    ID
    Extended
    Name
    Database
    Error
    Remote
    Timestamp
    Data
    Signals
    UserData

Analyze the Periodic Transmit Behavior

You can analyze the distribution of messages by plotting the identifiers of each message against their timestamps. Notice the difference between how often the two messages appear according to their periodic rates.

plot([msgRx.Timestamp], [msgRx.ID], 'x')
ylim([0 2047])
title('Message Distribution', 'FontWeight', 'bold')
xlabel('Timestamp')
ylabel('CAN Identifier')

For further analysis, separate the two messages into individual arrays.

msgRxFast = extractAll(msgRx, 'EngineMsg')
msgRxSlow = extractAll(msgRx, 'TransmissionMsg')
msgRxFast = 

  1x51 Message array with properties:

    ID
    Extended
    Name
    Database
    Error
    Remote
    Timestamp
    Data
    Signals
    UserData


msgRxSlow = 

  1x11 Message array with properties:

    ID
    Extended
    Name
    Database
    Error
    Remote
    Timestamp
    Data
    Signals
    UserData

Analyze the timestamps of each set of messages to see how closely the average of the differences corresponds to the configured periodic rates.

avgPeriodFast = mean(diff([msgRxFast.Timestamp]))
avgPeriodSlow = mean(diff([msgRxSlow.Timestamp]))
avgPeriodFast =

    0.1000


avgPeriodSlow =

    0.5000

A plot of the received signal data reflects the updates in the message data sent on the CAN bus.

signals = [msgRxFast.Signals]
plot([msgRxFast.Timestamp], [signals.VehicleSpeed])
title('Vehicle Speed from EngineMsg', 'FontWeight', 'bold')
xlabel('Timestamp')
ylabel('Vehicle Speed')
axis([0 6 0 75])
signals = 

1x51 struct array with fields:

    VehicleSpeed
    EngineRPM

View Messages Configured for Periodic Transmit

To see messages configured on a channel for periodic transmit, use the transmitConfiguration command.

transmitConfiguration(txCh)
Periodic Messages

ID  Extended      Name             Data        Rate (seconds)
--- -------- --------------- ----------------- --------------
100 false    EngineMsg       0 0 0 0 70 0 0 0  0.100000
200 false    TransmissionMsg 0 0 0 0 0 0 0 0   0.500000


Event Messages

None

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