Is there anyway to find a "lost" serialport?

I have made a matlab app which uses the new serialport comand. In some rare situations the serialport object can get "lost". This can happen if part of the program crashes and the serialport object gets written over before being closed. Or if the UIObject containing the serialport as a property gets deleted due to a crash. Once the serialport object is "lost" the port cannot be reconnected to without closing out of Matlab. This is a less than ideal solution because a lot of data is sometimes loaded by this program and it can take a while to restart. I have tried to remove all bugs from my program and make sure the serialport is always closed before being opened again but there are some fringe cases that have been hard to handel. As a last resort is it possible to either find open Matlab serialport objects, or "force close" a serialport Matlab is connected to (without restarting Matlab)?

Answer 1

[Pratyush Swain]

Hi James,

Yes, it is possible to find open MATLAB serialport objects and close them without restarting MATLAB.

Here's a method to find and close any open "serialport" objects:

% Clear any existing serial connections
if ~isempty(instrfind)
    fclose(instrfind);
    delete(instrfind);
end

But "instrfind" function will soon be removed in future releases.Another workaround is to simply clear the serialport object from the workspace which makes the port available again.Please follow the workflow below:

Starting by inspecting the serial ports conditions:

>> availableSerialObj = serialportlist("available");
>> disp(availableSerialObj);

Lets assume serial port COM6 is available. Initiate serial port COM6:

>> serialObj = serialport("COM6",11500,"Timeout",5);

To close and re-open the serial object you must clear the variable using the "clearvars" function.

>> clearvars('serialObj');

For more information on serial port connections, please refer to https://www.mathworks.com/help/matlab/ref/serialport.html

Hope these workarounds help resolve the issue.

[James London]

Thanks for the response. I have tried both of these solutions and they do not work in this situation.

As far as I can tell instrfind only works for serial, not serialport. It returns empty for me.

The problem I am having is the serialport object is no longer "in scope". So serialportlist returns all the ports. But serialportlist("available") returns all the ports except for the one that I "lost". This is of course becuase Matlab is still using that port, I just do not have the object "in scope". I put "in scope" in quotes becaues this can get a little complicated when talking about apps with a UI.

Here is an example of how the situation.

% Start a UI which contains a property called 'port'
Run MyUIApp

% Correct code
MyUIApp.port = serialport("COM3", 9600); % Connect to COM3
MyUIApp.port.writeline(" "); % Communicate
MyUIApp.port = []; % Disconnect
MyUIApp.port = serialport("COM3", 9600); % Reconnect to COM3

%%% MyUIAPP crashes for an unrealated reason.

% Restart the UI
Run MyUIApp

% This throws an error "Dot indexing is not supported ..." because this is
% no longer a serialport object. It is currently empty after MyUIApp ran.
MyUIApp.port.writeline(" ");

% This throws an error "Error using serialport" because when an app crashes
% the properties of that app are not cleared or set to empty. They are now
% just "out of scope". 
MyUIApp.port = serialport("COM3", 9600);

[Daniel]

Any luck finding a solution? I am having the same issue.

[James London]

No luck so far.