Use Vehicle Network Toolbox with multiple CAN databases on a single CAN bus

I'm using Vehicle Network Toolbox (VNT) to itneract with a CAN bus using database files (.dbc files). I've got it working with the code below.

chanA = canChannel('Kvaser', 'Leaf Light v2 1', 1);

chanA.Database = canDatabase('OperatorControl.dbc');

That works fine, but now I want to interact with messages that are defined in different databases, but are on the same CAN bus. What is the best way to do that? Should I define a new CAN channel? I could do that, but it seems like it would become cumbersome if there are a lot of extra channels to deal with.

Can I combine multiple CAN databases into a single one before adding it to the CAN channel? Can I add more than one database to the CAN channel? I haven't been able to find a way to do that.

Thank you.

[Nishant Elkunchwar]

I second this question. The ability to add multiple dbc files to a channel is an essential functionality since the database files are usually defined per module.

[Nishant Elkunchwar]

Found a workaround here: https://www.mathworks.com/matlabcentral/answers/526383-can-i-attach-multiple-dbc-files-to-a-single-canchannel-object

Answer 1

[Daniel Bengtson]

There is a way to allow for an arbitraty number of databases to be applied to the same channel, but it is either rather involved or requires editing a core VNT class definition. I have only tested it with Vector hardware and the matlab virtual bus so far, so I cannot garantee that it works with Kvaser or with all VNT functions. I have confirmed that it allows for multiple databases to populate message names and signal data when reading from a live bus.

You can make an array of databases that retains the 'Database' class by doing something along these lines.

dbcDir = dir('databases\*.dbc'); % import DBC used for all processing

% read database files into dbc array
for i = 1:length(dbcDir)
    dbc(i) = canDatabase(strcat(dbcDir(i).folder,'\',dbcDir(i).name));
end

If you were to try take this array and set it as the database:

canch = canChannel('Vector','VN1610 1',2); % setup CAN channel
canch.Database = dbc; % set array of databases for channel

you will get an error like this:

Operands to the logical AND (&&) and OR (||) operators must be convertible to logical scalar values. Use the ANY or ALL functions to reduce operands to logical scalar values.
Error in can.Channel/set.Database (line 1315)
		if isa(newValue, 'can.Database') && isvalid(newValue) && newValue.Usable

This is the function that breaks when trying to apply an array of databases to a CAN channel. It is lines 1307-1322 of can.Channel.

    function set.Database(obj, newValue)
        % Validate the channel before using its functionality.
        assertValidity(obj);
        
        % Validate the new value. The value must be either a valid
        % can.Database type and a valid handle object or it must be
        % empty. Setting the property to empty is used to clear the
        % database from the channel.
        if isa(newValue, 'can.Database') && isvalid(newValue) && newValue.Usable
            obj.Database = newValue;
        elseif isempty(newValue)
            obj.Database = [];
        else
            error(message('vnt:Channel:InvalidDatabase'));
        end
    end

You can find the full path of this script by running:

which can.Channel

It breaks because of a simple dimension mismatch on line 1315 (the 'if'). The fix is also simple and is just to distill each of the three conditions down to a 1x1 logical value before &&ing them all together. The problem is that to implement the fix, we either have to edit a class definition in the VNT or (probably more safely) build a parallel set of functions that reference a new version of the Channel class definition. In this case that would likely require copying then modifying a substantial number of scripts within '\toolbox\vnt\vnt\+can'.

A modification such as shown below is all that is needed:

    function set.Database(obj, newValue)
        % Validate the channel before using its functionality.
        assertValidity(obj);
        
        % Validate the new value. The value must be either a valid
        % can.Database type and a valid handle object or it must be
        % empty. Setting the property to empty is used to clear the
        % database from the channel.
        
        % modified to use 'all' to essentially && each input along its own
        % vector before &&ing the results for the real logical check
        if isa(newValue, 'can.Database') && all(isvalid(newValue)) && all([newValue.Usable])
            obj.Database = newValue;
        elseif isempty(newValue)
            obj.Database = [];
        else
            error(message('vnt:Channel:InvalidDatabase'));
        end
    end

Now we can set the channel.Database with an array of databases, set baud rate, start the channel, and start recording by:

dbcDir = dir('databases\*.dbc'); % paths for all DBCs to be used for processing

% read database files into dbc array
for i = 1:length(dbcDir)
    dbc(i) = canDatabase(strcat(dbcDir(i).folder,'\',dbcDir(i).name));
end

canch = canChannel('Vector','VN1610 1',2); % setup CAN channel
canch.Database = dbc; % set array of databases for channel

tmp = get(canch); % init the channel so we can set baud rate
configBusSpeed(canch,250000); % set bus baud rate
start(canch); % start channel
msg = receive(canch,100000,OutputFormat="timetable"); % read next 100k messages on CAN bus

The 'Name' and 'Signals' fields in msg should have now populated referencing all databases provided by the array.