System call from Simulink with external hardware (Raspberry PI)

I want to make a system call out of a Matlab Simulink model running on external hardware. In my case I want to switch the original Raspberry Pi Touch Display (7") off and an.

I tried using a Matlab function with a Matlab "system" command but it just doesn't have any affect on the display (the system calls itself works with the terminal).

    function display_backlight(old_status)
    coder.extrinsic('system')

    if old_status == 1
        system('echo 1 | sudo tee /sys/class/backlight/rpi_backlight/bl_power')
    else 
        system('echo 0 | sudo tee /sys/class/backlight/rpi_backlight/bl_power')
    end    
    end

Any ideas how to make this work or do I need to use another block like mentioned here https://stackoverflow.com/questions/4875981/system-call-from-simulink-possible (Link in the answer doesn't work)

Or do I even have to write this in C and integrate this to Simulink?

BTW: I asked the same question on stackoverflow but didn't get a response there (https://stackoverflow.com/questions/50024134/system-call-from-simulink-with-external-hardware-raspberry-pi)

Answer 1

[Uwe Lau]

This is my solution as it won't work directly from a matlab simulink block:

• 1. Add a "Matlab System" Block
• 2. Add an .m source file which runs .c/.h code.

display_backlight_on.m

classdef display_backlight_on < matlab.System ...
        & coder.ExternalDependency ...
        & matlab.system.mixin.Propagates ...
        & matlab.system.mixin.CustomIcon

      properties
          % Public, tunable properties.
      end

      properties (Nontunable)
          % Public, non-tunable properties.
      end

      properties (Access = private)
          % Pre-computed constants.
      end

      methods
          % Constructor
          function obj = display_backlight_on_trigger(varargin)
              % Support name-value pair arguments when constructing the object.
              setProperties(obj,nargin,varargin{:});
          end
      end

      methods (Access=protected)
          function setupImpl(obj) %#ok<MANU>

          end

          function stepImpl(obj,turn_on)  %#ok<INUSD>

              if isempty(coder.target)
                  % Place simulation output code here 
              else
                  % Call C-function implementing device output
                  coder.cinclude('display_backlight_on.h');
                  coder.ceval('display_backlight_on_command',turn_on);
              end
          end

          function releaseImpl(obj) %#ok<MANU>
              if isempty(coder.target)
                  % Place simulation termination code here
              else
                  % Call C-function implementing device termination
                  %coder.ceval('sink_terminate');
              end
          end
      end

      methods (Access=protected)
          %%Define input properties
          function num = getNumInputsImpl(~)
              num = 1;
          end

          function num = getNumOutputsImpl(~)
              num = 0;
          end

          function flag = isInputSizeLockedImpl(~,~)
              flag = true;
          end

          function varargout = isInputFixedSizeImpl(~,~)
              varargout{1} = true;
          end

          function flag = isInputComplexityLockedImpl(~,~)
              flag = true;
          end

          function icon = getIconImpl(~)
              % Define a string as the icon for the System block in Simulink.
              icon = 'display_backlight_on';
          end
      end

      methods (Static, Access=protected)
          function simMode = getSimulateUsingImpl(~)
              simMode = 'Interpreted execution';
          end

          function isVisible = showSimulateUsingImpl
              isVisible = false;
          end
      end

      methods (Static)
          function name = getDescriptiveName()
              name = 'display_backlight_on';
          end

          function b = isSupportedContext(context)
              b = context.isCodeGenTarget('rtw');
          end

          function updateBuildInfo(buildInfo, context)
              if context.isCodeGenTarget('rtw')
                 % Update buildInfo
                  srcDir = fullfile(fileparts(mfilename('fullpath')),'../src'); %#ok<NASGU>
                  includeDir = fullfile(fileparts(mfilename('fullpath')),'../include');
                  addIncludePaths(buildInfo,includeDir);    
                  addSourceFiles(buildInfo,'display_backlight_on.c',srcDir);        
              end
          end
      end
  end

• 3. Add a .c/.h file which runs the system command from c.

display_backlight_on.c

#include <display_backlight_on.h>

char command[50];        

void display_backlight_on_command(boolean_T turn_on)
{  
    if (turn_on == 1)
    {
        strcpy( command, "echo 0 | sudo tee /sys/class/backlight/rpi_backlight/bl_power" );
        system(command);
    }
}

display_backlight_on.h

#ifndef _DISPLAY_BACKLIGHT_ON_H_
#define _DISPLAY_BACKLIGHT_ON_H_

#include "rtwtypes.h"

void display_backlight_on_command(boolean_T turn_on);

#endif //_DISPLAY_BACKLIGHT_ON_H_