using C code for serial port communication in matlab via mex file

Hi,

I have implemented a C code for the serial port Communication. I want to use this function in matlab. I read the documentation about mex file (mex function) and i made the changes which i need for mexFunction. When i write mex serial_port.c to the command line everything is fine and matlab generates serial_port.mexa64. But when i want to use it and write serial_port() to the command line the serial port is not opening. what could be the problem?

here is my code:

#include "mex.h"
#include <stdio.h>
#include <fcntl.h>  
#include <termios.h>
#include <errno.h>  

    void mexFunction (int nlhs, mxArray *plhs[], int nrhs, 
      const mxArray *prhs[])

    {
        if(nrhs != 0) {
        mexErrMsgIdAndTxt("MyToolbox:arrayProduct:nrhs",
                          "zero inputs required.");
        }

        if(nlhs != 0) {
        mexErrMsgIdAndTxt("MyToolbox:arrayProduct:nlhs",
                          "Two output required.");
         }

      char serial;
      struct termios SerialPortSettings;

      serial= open("/dev/ttyACM1", O_RDWR | O_NOCTTY);
      printf("%i \n",serial);

      tcgetattr(serial, &SerialPortSettings);

      cfsetispeed(&SerialPortSettings,B9600);  
      cfsetospeed(&SerialPortSettings,B9600);

      SerialPortSettings.c_cflag &= ~PARENB;
      SerialPortSettings.c_cflag &= ~CSTOPB;
      SerialPortSettings.c_cflag &= ~CSIZE;  
      SerialPortSettings.c_cflag &= ~CS8;

      SerialPortSettings.c_cflag &= ~CRTSCTS;
      SerialPortSettings.c_cflag |= CREAD | CLOCAL ;
      
      SerialPortSettings.c_cc[VMIN] = 9;  
      SerialPortSettings.c_cc[VTIME] = 0; 
      
      SerialPortSettings.c_iflag &= ~(IXON | IXOFF | IXANY);
      SerialPortSettings.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG);
      
      tcsetattr(serial,TCSANOW,&SerialPortSettings);

      char writeb[9];
      writeb[0]=1;
      writeb[1]=2;
      writeb[2]=0;
      writeb[3]=0;
      writeb[4]=0;
      writeb[5]=0;
      writeb[6]=0;
      writeb[7]=200;
      writeb[8]=writeb[0]+writeb[1]+writeb[2]+writeb[3]+writeb[4]+writeb[5]+writeb[6]+writeb[7];
      
      int bytes_written=0;

      bytes_written=write(serial,writeb,sizeof(writeb));

      char readb[9];
      int bytes_read;
      int a;
      bytes_read=read(serial,&readb,9);

      a=readb[2];
      printf("%i \n",a);
      close(serial);
    }

best regards

[Walter Roberson]

In most Unix derived operating systems for a number of years now, by default users do not have read/write access to serial ports, which is implemented as the user not being the owner of /dev/tty* and the device not having o+rw permissions. Also some of the common model control programs set the "other" permissions back to --- after use, so you might not be able to just chmod once and hope it sticks (though it might, if you are not using any of those programs.) Also beware that tty* devices can end up getting re-created pr have permissions changed at boot time (as the system dynamically repopulates the device table) so you might need to edit a kernel table to get the permissions to be applied automatically at boot.

[Ahmet Tuna]

Hi Walter,

thank you for the answer. if i open a serial port on matlab without c-code it is working. so i think access to serial port is not the problem. But i found another solution. I can use the c- code on Simulink with a matlab function block an coder.ceval. Know i want to use c++ class but it is not working. Can you help me?

best regards

[Walter Roberson]

There is no direct access from MATLAB or Simulink to C++ classes, unless perhaps there is something that can be done with custom code generation.

See however, the discussion at https://www.mathworks.com/matlabcentral/answers/783-i-have-a-c-class-how-can-i-interface-to-it-through-a-matlab-class

[Ahmet Tuna]

thank you. i have read this article. I also read another article https://www.mathworks.com/examples/simulink-coder/mw/simulinkcoder-ex06428671-integrate-external-c-object-methods. Do you know something about this legacy code. I don't understand how i have to use it.

cheers