Detecting a serial port valid after disconnect/reconnect

I asked before with a long question and got no answers, so let's keep it simpler.

Serial port is connected to Arduino

Arduino resets, so I need to:

1. Detect that it's gone without throwing an error

2. Reconnect

Results:

Connected and callback set

K>> app.Pico

ans =

Serialport with properties:

Port: "COM16"

BaudRate: 57600

NumBytesAvailable: 0

Hit reset on Pico get following error message ( but it doesn't stop my program from running)

Unable to detect connection to the serialport device. Ensure that the device is plugged in and create a new serialport object.

If there is no "keep alive" function for serial ports ( Walter Roberson in https://www.mathworks.com/matlabcentral/answers/1722140-cant-read-the-serial-port) then what is generating this error? How can I catch it without constantly checking the connection myself?

If I could trap the error here that would be a great start.

So let's look at where we are:

K>> app.PicoCom

ans =

Serialport with properties:

In 'testmeaslib:CustomDisplay:PropertyWarning',

data type supplied is incorrect for parameter {0}.

Not useful, but I can check it right?

K>> isvalid(app.PicoCom)

ans =

logical

1

Really? It's still valid? Let's try

K>> serialportlist("available")

ans =

1×2 string array

"COM1" "COM16"

OK, at least I can see it's back in the list of available ports. Is this the best (fastest) way to find out?

Also I can't check in the input call back because then it's too late. Error thrown already.

K>> delete(app.PicoCom)

K>> app.PicoCom

ans =

handle to deleted Serialport

K>> isvalid(app.PicoCom)

ans =

logical

0

At least once deleted it's not valid. Let's reconnect:

K>> app.PicoCom = serialport()

K>> app.PicoCom

ans =

Serialport with properties:

Port: "COM16"

BaudRate: 57600

NumBytesAvailable: 0

ByteOrder: "little-endian"

DataBits: 8

StopBits: 1

Parity: "none"

FlowControl: "none"

Timeout: 10

Terminator: "CR/LF"

Back to normal as soon as I add

K>> configureCallback(app.PicoCom,"terminator",@app.PicoInput);

So I think I've got recovery OK. How about detecting when coms are lost?

BTW serialportfind is only useful when teh prot is there. If it's missing then looking throws an error...

K>> serialportfind

ans =

Serialport with properties:

In 'testmeaslib:CustomDisplay:PropertyWarning',

data type supplied is incorrect for parameter {0}.

Apparently it's a valid question to ask, just not a useful answer.

K>> isvalid(serialportfind)'

ans =

logical

1

[Walter Roberson]

Note: the lack of keep-alives for serialport() does not necessarily imply that there are no keep-alives for ports opened with arduino(), even if arduino() uses serialport() internally.

[Gavin]

I'm using an Arduino, but NOT Matlab's Arduino module. Just the serial port. I don't want any ML hand holding or interference in my Arduino code.

[Gavin]

Now I'm really confused. I've been using my workaround to check if the port is connected and now...

K>> serialportlist

ans =

1×2 string array

"COM1" "COM16"

So the device is there, but

K>> serialportlist("available")

ans =

"COM1"

But either Windows or Matlab won't let me have it back!

Other than rebooting the computer is there a way to fix this trap?

I've limited the computer to only be alloweed to have 2 COM ports, the built in COM1 and my USB port to simplify things. Here's the code I'm using to check what's up and I'm getting code 3 returned. There but not there.

function b = CheckAvailPort(app)     % v61 depends on 2 serial ports on system
    % returns 0 if properly connected
    ports = serialportlist("available");
    portCT = size(ports,2);
    if  portCT == 2           % Not connected
        delete(app.PicoCom);    % Leaves a "valid" dead deleted port!
        app.PicoCom = [];       % Clean it up
        app.RebootPicoButton.BackgroundColor = 'yellow';
        b = 1;                  % one port to connect, Init will work
    else
% Make sure we have a COM port if it seems to be connected
        if portCT == 1
            try     % If PicoComm isn't a valid port this will fail
                if  regexp(app.PicoCom.Port, regexptranslate('wildcard', 'COM*'))        
                    b = 0;      % all good
                    app.RebootPicoButton.BackgroundColor = 'white';
                else
                    app.RebootPicoButton.BackgroundColor = 'red';
                    b = 2;  % Something strange, haven't seen this problem yet
                end
            catch
                app.RebootPicoButton.BackgroundColor = 'red';
        warningMessage = sprintf(...
'No Pico USB device. Check connection and that Pico LED is flashing.');
uialert(app.MouseOdor,warningMessage,"No Pico found", "Icon","error"); 
                b = 3;  % Maybe Arduino has the port, or Pico locked up and not seen by Windoze
            end
        else
             warningMessage = sprintf(...
'Too many USB devices. This program will not work.');
uialert(app.MouseOdor,warningMessage,"Extra USB devices found.", "Icon","error"); 
            b = 4;
        end
    end
end

Answer 1

[埃博拉酱]

You may want to set the ErrorOccurredFcn property of serialport:

S=serialport('COM4',9600);
S.ErrorOccurredFcn=@(varargin)disp(varargin);

[Gavin]

Thanks that shoud help with part 1

[Gavin]

I tried it but I guess I don't have the syntax right I did this:

function PicoError(app)     % more to add?
AddDebugText(app,"!!! Pico Error trapped");
app.RebootPicoButton.BackgroundColor = 'red';
end

and set it up like this:

ports = serialportlist("available");
app.PicoCom = serialport(ports(1,2),57600); % attach 2nd port
configureTerminator(app.PicoCom,"CR/LF"); % What Pico returns to trigger callback
app.PicoCom.ErrorOccurredFcn=@app.PicoError;
%-------------- later when INIT is done I add
configureCallback(app.PicoCom,"terminator",@app.PicoInput);
% to capture the async input, and that works

I don't understand what is the simplest form of (varargin)disp(varargin) that I can use to just let me know there is an error.

What I get is:

Warning: Error while executing listener

callback for Custom event. Source has been deleted:

Error using MouseOdor62/PicoError

Too many input arguments.

Error in

MouseOdor62>@(varargin)app.PicoError(varargin{:})

(line 460)

app.PicoCom.ErrorOccurredFcn=@app.PicoError;

^^^^^^^^^^^^^

Error in

matlabshared.transportlib.internal.client.GenericClient/errorCallbackFunction

(line 953)

obj.ErrorOccurredFcn(ex);

^^^^^^^^^^^^^^^^^^^^^^^^

And so on for a few pages...

Getting it to work in AD is not so easy as the M example given I suspect.

[埃博拉酱]

The official documentation doesn't give a function signature for ErrorOccurredFcn, so you'll have to try it yourself. I don't know how many input arguments I need, too, so I used varargin to accept any number of arguments. You can also use varargin, or disp varargin like I did and see how many inputs there are.

[Gavin]

Thanks for the help. I hadn't understood if varargin was literal or something I have to substitute for. After experimenting it turns out this works:

app.PicoCom.ErrorOccurredFcn=@(~)app.PicoError

So it wants one to start but doesn't care about it. A little doc could go a long way.

So now that I trap the error when it occurs I can deal with it.