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Create and Process Messages Using Database Definitions

This example shows you how to create, receive and process messages using information stored in CAN database files. This example uses the CAN database file, demoVNT_CANdbFiles.dbc.

Open the Database File

Open the database file and examine the Messages property to see the names of all message defined in this database.

db = canDatabase('demoVNT_CANdbFiles.dbc')
db.Messages
db = 

  Database with properties:

             Name: 'demoVNT_CANdbFiles'
             Path: '/tmp/Bdoc21a_1606923_186538/tp6e149c41/ex80654288/demoVNT_CANdbFiles.dbc'
            Nodes: {}
         NodeInfo: [0x0 struct]
         Messages: {5x1 cell}
      MessageInfo: [5x1 struct]
       Attributes: {}
    AttributeInfo: [0x0 struct]
         UserData: []


ans =

  5x1 cell array

    {'DoorControlMsg'   }
    {'EngineMsg'        }
    {'SunroofControlMsg'}
    {'TransmissionMsg'  }
    {'WindowControlMsg' }

View Message Information

Use messageInfo to view message information, including the identifier, data length, and a signal list.

messageInfo(db, 'EngineMsg')
ans = 

  struct with fields:

             Name: 'EngineMsg'
     ProtocolMode: 'CAN'
          Comment: ''
               ID: 100
         Extended: 0
            J1939: []
           Length: 8
              DLC: 8
              BRS: 0
          Signals: {2x1 cell}
       SignalInfo: [2x1 struct]
          TxNodes: {0x1 cell}
       Attributes: {}
    AttributeInfo: [0x0 struct]

You can also query for information on all messages at once.

messageInfo(db)
ans = 

  5x1 struct array with fields:

    Name
    ProtocolMode
    Comment
    ID
    Extended
    J1939
    Length
    DLC
    BRS
    Signals
    SignalInfo
    TxNodes
    Attributes
    AttributeInfo

View Signal Information

Use signalInfo to view signal definition information, including type, byte ordering, size, and scaling values that translate raw signals to physical values.

signalInfo(db, 'EngineMsg', 'EngineRPM')
ans = 

  struct with fields:

             Name: 'EngineRPM'
          Comment: ''
         StartBit: 0
       SignalSize: 32
        ByteOrder: 'LittleEndian'
           Signed: 0
        ValueType: 'Integer'
            Class: 'uint32'
           Factor: 0.1000
           Offset: 250
          Minimum: 250
          Maximum: 9500
            Units: 'rpm'
       ValueTable: [0x1 struct]
      Multiplexor: 0
      Multiplexed: 0
    MultiplexMode: 0
          RxNodes: {0x1 cell}
       Attributes: {}
    AttributeInfo: [0x0 struct]

You can also query for information on all signals in the message at once.

signalInfo(db, 'EngineMsg')
ans = 

  2x1 struct array with fields:

    Name
    Comment
    StartBit
    SignalSize
    ByteOrder
    Signed
    ValueType
    Class
    Factor
    Offset
    Minimum
    Maximum
    Units
    ValueTable
    Multiplexor
    Multiplexed
    MultiplexMode
    RxNodes
    Attributes
    AttributeInfo

Create a Message Using Database Definitions

Specify the name of the message when you create a new message to have the database definition applied. CAN signals in this messages are represented in engineering units in addition to the raw data bytes.

msgEngineInfo = canMessage(db, 'EngineMsg')
msgEngineInfo = 

  Message with properties:

   Message Identification
    ProtocolMode: 'CAN'
              ID: 100
        Extended: 0
            Name: 'EngineMsg'

   Data Details
       Timestamp: 0
            Data: [0 0 0 0 0 0 0 0]
         Signals: [1x1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

   Other Information
        Database: [1x1 can.Database]
        UserData: []

View Signal Information

Use the Signals property to see signal values for this message. You can directly write to and read from these signals to pack or unpack data from the message.

msgEngineInfo.Signals
ans = 

  struct with fields:

    VehicleSpeed: 0
       EngineRPM: 250

Change Signal Information

Write directly to the signal to change a value and read its current value back.

msgEngineInfo.Signals.EngineRPM = 5500.25
msgEngineInfo.Signals
msgEngineInfo = 

  Message with properties:

   Message Identification
    ProtocolMode: 'CAN'
              ID: 100
        Extended: 0
            Name: 'EngineMsg'

   Data Details
       Timestamp: 0
            Data: [23 205 0 0 0 0 0 0]
         Signals: [1x1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

   Other Information
        Database: [1x1 can.Database]
        UserData: []


ans = 

  struct with fields:

    VehicleSpeed: 0
       EngineRPM: 5.5003e+03

When you write directly to the signal, the value is translated, scaled, and packed into the message data using the database definition.

msgEngineInfo.Signals.VehicleSpeed = 70.81
msgEngineInfo.Signals
msgEngineInfo = 

  Message with properties:

   Message Identification
    ProtocolMode: 'CAN'
              ID: 100
        Extended: 0
            Name: 'EngineMsg'

   Data Details
       Timestamp: 0
            Data: [23 205 0 0 71 0 0 0]
         Signals: [1x1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

   Other Information
        Database: [1x1 can.Database]
        UserData: []


ans = 

  struct with fields:

    VehicleSpeed: 71
       EngineRPM: 5.5003e+03

Receive Messages with Database Information

Attach a database to a CAN channel that receives messages to apply database definitions to incoming messages automatically. The database decodes only messages that are defined. All other messages are received in their raw form.

rxCh = canChannel('MathWorks', 'Virtual 1', 2);
rxCh.Database = db
rxCh = 

  Channel with properties:

   Device Information
            DeviceVendor: 'MathWorks'
                  Device: 'Virtual 1'
      DeviceChannelIndex: 2
      DeviceSerialNumber: 0
            ProtocolMode: 'CAN'

   Status Information
                 Running: 0
       MessagesAvailable: 0
        MessagesReceived: 0
     MessagesTransmitted: 0
    InitializationAccess: 1
        InitialTimestamp: [0x0 datetime]
           FilterHistory: 'Standard ID Filter: Allow All | Extended ID Filter: Allow All'

   Channel Information
               BusStatus: 'N/A'
              SilentMode: 0
         TransceiverName: 'N/A'
        TransceiverState: 'N/A'
       ReceiveErrorCount: 0
      TransmitErrorCount: 0
                BusSpeed: 500000
                     SJW: []
                   TSEG1: []
                   TSEG2: []
            NumOfSamples: []

   Other Information
                Database: [1x1 can.Database]
                UserData: []

Receive Messages

Start the channel, generate some message traffic and receive messages with physical message decoding.

start(rxCh);
generateMsgsDb();
rxMsg = receive(rxCh, Inf, 'OutputFormat', 'timetable');
rxMsg(1:15, :)
ans =

  15x8 timetable

        Time        ID     Extended            Name                       Data              Length      Signals       Error    Remote
    ____________    ___    ________    _____________________    ________________________    ______    ____________    _____    ______

    0.039786 sec    100     false      {'EngineMsg'        }    {[     0 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 
    0.039803 sec    200     false      {'TransmissionMsg'  }    {[     0 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 
    0.039828 sec    400     false      {'DoorControlMsg'   }    {[     0 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 
    0.039832 sec    600     false      {'WindowControlMsg' }    {[             0 0 0 0]}      4       {1x1 struct}    false    false 
    0.039834 sec    800     false      {'SunroofControlMsg'}    {[                 0 0]}      2       {1x1 struct}    false    false 
    0.064773 sec    100     false      {'EngineMsg'        }    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.089761 sec    100     false      {'EngineMsg'        }    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.089764 sec    200     false      {'TransmissionMsg'  }    {[     4 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 
    0.11485 sec     100     false      {'EngineMsg'        }    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.1398 sec      100     false      {'EngineMsg'        }    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.1398 sec      200     false      {'TransmissionMsg'  }    {[     4 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 
    0.16479 sec     100     false      {'EngineMsg'        }    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.16479 sec     400     false      {'DoorControlMsg'   }    {[     1 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 
    0.18982 sec     100     false      {'EngineMsg'        }    {[177 131 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.18983 sec     200     false      {'TransmissionMsg'  }    {[     4 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 

Stop the channel and clear it from the workspace.

stop(rxCh);
clear rxCh

Examine a Received Message

Inspect a received message to see the applied database decoding.

rxMsg(10, :)
rxMsg.Signals{10}
ans =

  1x8 timetable

       Time       ID     Extended        Name                   Data              Length      Signals       Error    Remote
    __________    ___    ________    _____________    ________________________    ______    ____________    _____    ______

    0.1398 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 


ans = 

  struct with fields:

    VehicleSpeed: 50
       EngineRPM: 3.5696e+03

Extract All Instances of a Specified Message

Use MATLAB notation to extract all instances of a specified message by name.

allMsgEngine = rxMsg(strcmpi('EngineMsg', rxMsg.Name), :);
allMsgEngine(1:15, :)
ans =

  15x8 timetable

        Time        ID     Extended        Name                   Data              Length      Signals       Error    Remote
    ____________    ___    ________    _____________    ________________________    ______    ____________    _____    ______

    0.039786 sec    100     false      {'EngineMsg'}    {[     0 0 0 0 0 0 0 0]}      8       {1x1 struct}    false    false 
    0.064773 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.089761 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.11485 sec     100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.1398 sec      100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.16479 sec     100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1x1 struct}    false    false 
    0.18982 sec     100     false      {'EngineMsg'}    {[177 131 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.21485 sec     100     false      {'EngineMsg'}    {[177 131 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.23975 sec     100     false      {'EngineMsg'}    {[177 131 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.26478 sec     100     false      {'EngineMsg'}    {[177 131 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.28982 sec     100     false      {'EngineMsg'}    {[ 91 133 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.31478 sec     100     false      {'EngineMsg'}    {[ 91 133 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.33981 sec     100     false      {'EngineMsg'}    {[ 91 133 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.36479 sec     100     false      {'EngineMsg'}    {[ 91 133 0 0 55 0 0 0]}      8       {1x1 struct}    false    false 
    0.38981 sec     100     false      {'EngineMsg'}    {[201 130 0 0 54 0 0 0]}      8       {1x1 struct}    false    false 

Plot Physical Signal Values

Plot the values of database decoded signals over time. Reference the message timestamps and the signal values in variables.

signalTimetable = canSignalTimetable(rxMsg, 'EngineMsg');
signalTimetable(1:15, :)
plot(signalTimetable.Time, signalTimetable.VehicleSpeed)
title('Vehicle Speed from EngineMsg', 'FontWeight', 'bold')
xlabel('Timestamp')
ylabel('Vehicle Speed')
ans =

  15x2 timetable

        Time        VehicleSpeed    EngineRPM
    ____________    ____________    _________

    0.039786 sec          0             250  
    0.064773 sec         50          3569.6  
    0.089761 sec         50          3569.6  
    0.11485 sec          50          3569.6  
    0.1398 sec           50          3569.6  
    0.16479 sec          50          3569.6  
    0.18982 sec          55          3621.3  
    0.21485 sec          55          3621.3  
    0.23975 sec          55          3621.3  
    0.26478 sec          55          3621.3  
    0.28982 sec          55          3663.9  
    0.31478 sec          55          3663.9  
    0.33981 sec          55          3663.9  
    0.36479 sec          55          3663.9  
    0.38981 sec          54          3598.1