How to continuously read from the serial port in Matlab? - multithreading

Question

This is my code:
serialPort = 'COM3';
s = serial(serialPort,'BaudRate',9600);
if (s.Status == 'closed')
s.BytesAvailableFcnMode = 'byte';
s.BytesAvailableFcnCount = 200;
s.BytesAvailableFcn = #Serial_OnDataReceived;
fopen(s);
end
This is the CallBack function
function Serial_OnDataReceived(obj,event)
global s;
global i;
global endCheck;
global yVals;
global xVals;
if (s.Status == 'open')
while s.BytesAvailable > 0 && endCheck ~= '1',
data = str2num(fgetl(s));
dlmwrite ('SensorsReading.csv', data, '-append');
yVals = circshift(yVals,-1);
yVals(end) = data(3);
xVals = circshift(xVals,-1);
i = i + 0.0125;
xVals(end) = i;
end
figure(1);
plot(xVals,yVals);
end
end
Right after the FOPEN function, I get this Warning:
The BytesAvailableFcn is being disabled. To enable the callback property
either connect to the hardware with FOPEN or set the BytesAvailableFcn property.
Does the logic that happens in the callback function Serial_OnDataReceived run on a different thread?
Is there a way to pass parameters to the function? I want to modify an array in the main script from the callback function, which is in a different file. What's the best way to do so?
I am also trying to plot the values when they're updated to show some kind of dynamic animation.

Answer 1

I am not sure about what is generating the warning, but to answer your other question (how to pass parameter to the callback and how to update the plot), a better way to go would be to prepare your plot outside of the callback, then pass the handle to the callback for update only.
nPointsInFigure = 10 ; %// number of "sliding points" in your figure
step = 0.0125 ; %// X points spacing
xVals = linspace(-(nPointsInFigure-1)*step,0,nPointsInFigure) ; %// prepare empty data for the plot
yVals = NaN(nPointsInFigure,1) ;
figure(1) ;
hp = plot( xVals , yVals ) ; %// Generate the plot (with empty data) it will be passed to the callback.
serialPort = 'COM3';
s = serial(serialPort,'BaudRate',9600);
if (s.Status == 'closed')
s.BytesAvailableFcnMode = 'byte';
s.BytesAvailableFcnCount = 200;
s.BytesAvailableFcn = {#Serial_OnDataReceived,hp,step} ; %// note how the parameters are passed to the callback
fopen(s);
end
Your callback will become:
function Serial_OnDataReceived(obj,event,hp,step)
global endCheck; %// I don't know how you use that so I could not get rid of it.
xVals = get(hp,'XData') ; %// retrieve the X values from the plot
yVals = get(hp,'YData') ; %// retrieve the Y values from the plot
while obj.BytesAvailable > 0 && endCheck ~= '1',
data = str2num(fgetl(s));
dlmwrite ('SensorsReading.csv', data, '-append');
yVals = circshift(yVals,-1);
yVals(end) = data(3);
xVals = circshift(xVals,-1);
xVals(end) = xVals(end-1) + step ;
end
set( hp , 'XData',xVals , 'YData',yVals ) ; %// update the plot with the new values
Also note: (1) You don't need to check for the state open/close of the serial port within the callback function. If the event was triggered it means the port was open. (2) you don't need to declare s as global, the obj parameter is actually the serial object itself.

Answer 2

If the suggestion from Hoki does not work, try using a timer.
% The following line is useful for debugging
mytimerCallback = #(~, ~) disp('Caught error For Tenzo Timer');
if isempty(timerXbee)
timerXbee = timer('ExecutionMode','FixedRate','Period',0.1,...
'TimerFcn',{#storeDataFromSerial},'ErrorFcn', mytimerCallback);
try
start(timerXbee);
catch
disp('Timer Xbee');
disp '******** InstrumentSubscription ERROR *********'
disp (exception.message);
disp '***********************************************'
end
end
% If you are using a polling approach, request data
sendRequest(cmd);
connectionRequested = true;
Then implement the timer function that will be called every period
function storeDataFromSerial(~,~,~)
while (get(xbee, 'BytesAvailable')~=0)
serialProtocol();
end
end
When you want to disconnect the device and close the communication don't forget to stop the timer with
stop(timerXbee)