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
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