Clear a persistent variable in a MATLAB Fcn block as serial object

Hello! I am using following code for read data from serial port:

function y = fcn(u)
coder.extrinsic('only3')
coder.extrinsic('strncmp')
coder.extrinsic('serial', 'fopen','fread')
coder.extrinsic('get')
persistent s a b
y = uint8(zeros(2,1));  %signal is an uint8

   if isempty(s)
     % only do this the first time
      s = serial('COM12','Terminator','', 'InputBufferSize', 1024);
      a = '000';
      b = false;
      a = only3(get(s,'status'));
  b = strncmp(a,'clo',3);

      switch double(b)
      case 1
          fopen(s);
      otherwise
          fclose(s);
      end
  end

     y = uint8(fread(s,[2 1],'uint8'));

Where 'only3' is my function that takes only the first 3 chars from a string. The problem is that communication does not terminate with simulation stopping. Switch case has no effect (I thought that it shuts down reading after an other run). How can I clear persistent variable 's' and reset the block after stopping?

Answer 1

[Paul]

clear fcn

[Marco]

I tried that but it returns an error:

Open failed: Port: COM12 is not available. No ports are available. Use INSTRFIND to determine if other instrument objects are connected to the requested device. Block Gyro/Serial Read (#59) While executing: State During Action

where #59 points to 'fopen(s)' command

Answer 2

[Friedrich]

Hi,

A MATLAB FCN Block is a bad idea here. Better would be a MATLAB LVL 2 S-function because you can better control your serial port. In the mdlStart you create your serial object and later in the mdlTerminate you close it propperly. In the mdlOutputs you calculate the signal as usual.

[Marco]

I tried with S-Function level 2 but it was very slow or however it had not same performances like MATLAB Fcn.

[Friedrich]

But at least it works ;)

Can you post your S-function here? Maybe something wasn't implemented efficiently.

[Marco]

Of course, I used this content http://www.mathworks.it/matlabcentral/fileexchange/25478-serialio-mex

but I edited that because it did not work: (sorry for file instead code but question editor does not allow me to write a so long code); where before execution I must run this script to load configurations:

clear all ;

%For write operation

serobjw = serial('COM12') ;           % Creating serial port object now its connected to COM12

%Set connection properties
serobjw.Baudrate = 9600;      % Set the baud rate at the specific value
set(serobjw, 'Parity', 'none') ;     % Set parity as none
set(serobjw, 'Databits', 8) ;        % set the number of data bits
set(serobjw, 'StopBits', 1) ;        % set number of stop bits as 1
set(serobjw, 'Terminator', '') ; % set the terminator value to newline

set(serobjw, 'OutputBufferSize', 16) ;   % Buffer for write operation, default it is 512
set(serobjw,'InputBufferSize',16);

get(serobjw) ;       

fopen(serobjw) ;
get(serobjw, 'Status')                 % Gets the status of connection if 'open' connection was established

Data arrives after some lag. I do not know if it is a "packing problem" (the sender have a int16 data and I convert/re-convert it using byte-pack/unpack block, fut with a MATLAB Fcn it works in real time.

[Friedrich]

So you create the serial object on the ML side and then pass it in to the S-Fcn at each call. This sounds like overhead to me. What happens if you create the serial object in the mdlInitializeSizes and make it a global variable? In that way you don't need to pass it in every time the S-Fcn is called. Does the performance get better?

In addition you are currently using a LVL 1 S-Fcn. I don't know if there might be a performance difference between LVL 1 and LVL 2 S-fcn.

[Marco]

Are you saying that I have to modify mdlInitializeSizes section as:

    function [sys,x0,str,ts]=mdlInitializeSizes(stime)
global s
  s = serial('COM12');
  fopen(s)
    sizes = simsizes;
    sizes.NumContStates  = 0;
  sizes.NumDiscStates  = 0;
  sizes.NumOutputs     = 2;
  sizes.NumInputs      = 0;
  sizes.DirFeedthrough = 1;
  sizes.NumSampleTimes = 1;   % at least one sample time is needed

sys = simsizes(sizes);
x0  = [];
str = [];
ts  = [stime 0];

   end

??? In this way it should call object creation and opening only one time, is it?

[Friedrich]

Yes. You open the serial port in the mdlInitializeSizes and close it in the mdlTerminate.

Answer 3

[Ryan Livingston]

Another thought could be to use the serial port I/O blocks directly in Simulink. See the Blocks heading here:

http://www.mathworks.com/help/instrument/direct-interface-communication-in-simulink.html

I am not too familiar with them, but they may facilitate a simpler interface to your hardware.

These could perform the I/O and then you could process the data using the method of your choosing.