Hi Adrian,
To transmit messages with precise timing, you need a real-time system or hardware support for buffering and scheduling messages. The "NI-9860" module in a "cDAQ" chassis does have some capabilities for deterministic timing, but this usually requires using NI's software tools, like LabVIEW with the NI-XNET driver, which is designed for real-time applications.
The timing of your MATLAB script by using a more precise timer object or by adjusting the priorities of MATLAB's execution, but this will not guarantee real-time performance.
Here's an example MATLAB script of how to use a timer object to transmit CAN messages at a more consistent interval:
% Load the DBC file
candb = canDatabase("example_dbcfile.dbc");
message = canMessage(candb, 'example_message');
canch = canChannel('NI','CAN3');
start(canch)
t = linspace(0, 5, 5000); % 5 seconds at 1000 Samples/s
f = 0.5; % Sine frequency Hz
sine = 0.7 * sin(2 * pi * f * t); % Create sine
% Start transmitting the sine wave
transmitSineWave(canch, message, sine, 1000); % 1000 Hz transmission rate
function transmitSineWave(canch, message, sine, frequency)
% Create a timer object
t = timer;
t.ExecutionMode = 'fixedRate'; % Execute the timer repeatedly at a fixed rate
t.Period = 1 / frequency; % Set the period of the timer based on the desired frequency
t.TasksToExecute = length(sine); % Set the number of times to execute the timer
t.TimerFcn = @(~, ~) transmitOneSample(canch, message, sine); % Timer function to call
t.StopFcn = @(~, ~) delete(t); % Clean up the timer after execution
% Start the timer
start(t);
end
function transmitOneSample(canch, message, sine)
persistent index;
if isempty(index)
index = 1;
end
% Update the signal value
message.Signals.example_signal = sine(index);
% Transmit the CAN message
transmit(canch, message);
% Update the index or reset if it reaches the end of the sine array
index = index + 1;
if index > length(sine)
index = 1;
end
end
