How can I get an output to Matlab command from generated code (Matlab system object)

I have created a matlab system object that is called in a simulink program. I am trying to debug it by getting values in the Matlab command window or the simulink diagnostic window.

I am trying to get "obj.device" values to see if the call to my C code function "i2c_setup" works.

I have tried to do with coder.extrinsic('sprintf') and sprintf('The device ID is: %d ', obj.device);

but without success.

Do you have any suggestion ?

 classdef I2C_read_custom < realtime.internal.SourceSampleTime & ...
        coder.ExternalDependency
    %#codegen
    %#ok<*EMCA>
    
    properties
        % Public, tunable properties.
        device = 0;
    end
...
...    
    methods (Access=protected)
        function setupImpl(obj) %#ok<MANU>
            coder.extrinsic('sprintf')
            if isempty(coder.target)
                % Place simulation setup code here
            else
                % Call C-function implementing device initialization: int8_T i2c_setup(const uint8_T devId);
                coder.cinclude('I2C_read2.h');
                obj.device =  coder.ceval('i2c_setup', uint8(hex2dec("0x34")));   % Slave address is hardcoded
%                 obj.device =  coder.ceval('i2c_setup_V2');   % Slave address is hardcoded

                
                sprintf('The device ID is: %d ', obj.device);
            end
        end
 ...
 ...

[Jonas]

why do u use a system object for that?

if you create the obejct using

myObj=I2C_read_custom();

you shoud be able to access the property device by

myObj.device

[Sylvain]

the system object is used in a simulink program that is then deployed on a Raspberry Pi. The myObj.device will be called in the stepImpl(obj), see below. I want to access myObj.device value for debugging:

                ...
                ...
                sprintf('The device ID is: %d ', obj.device);
            end
        end
        
        function y = stepImpl(obj)   %#ok<MANU>
            y = uint8(zeros(32,1));
            if isempty(coder.target)
                % Place simulation output code here
                y = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]';
            else
                % Call C-function implementing device output: uint8_T readBytes(uint8_T file,uint8_T *buffer,uint8_T buffer_length);
                coder.ceval('readBytes',obj.device,coder.ref(y),32);
            end
        end

below the C code that return negative values if error occurs

int8_T i2c_setup(const uint8_T devId){
    uint8_T fd=0 ;
    if ((fd = open ("/dev/i2c-1", O_RDWR)) < 0)
        return -1;
     if (ioctl (fd, I2C_SLAVE, devId) < 0)
        return -2;
    return fd ;
}

Answer 1

[Dinesh]

Hi Sylvian,

To display values in the MATLAB command window or the Simulink diagnostic window during simulation, you can use the "disp" function with the "coder.extrinsic" command. Here's how you can modify your code to display the device ID:

1. Inside the "setupImpl" method, add "coder.extrinsic('disp')" to declare "disp" as an extrinsic function. This allows you to call the "disp" function from within the generated code.
2. Replace the "sprintf" line with the following code to display the device ID:

deviceIDStr = sprintf('The device ID is: %d', obj.device);
coder.extrinsic('disp');
disp(deviceIDStr);

Here's the modified "setupImpl" function with the changes:

methods (Access=protected)
    function setupImpl(obj) %#ok<MANU>
        coder.extrinsic('sprintf')
        coder.extrinsic('disp')
        if isempty(coder.target)
            % Place simulation setup code here
        else
            % Call C-function implementing device initialization: int8_T i2c_setup(const uint8_T devId);
            coder.cinclude('I2C_read2.h');
            obj.device =  coder.ceval('i2c_setup', uint8(hex2dec("0x34")));   % Slave address is hardcoded
            % obj.device =  coder.ceval('i2c_setup_V2');   % Slave address is hardcoded
                
            deviceIDStr = sprintf('The device ID is: %d', obj.device);
            disp(deviceIDStr);
        end
    end
end

I believe that this will resolve your issue. Let me know if you have questions.

[Walter Roberson]

Note that this has to do with deployment to Raspberry Pi, so the debugging has to be a the Raspberry Pi level, if I understand correctly. However my understanding is that coder.extrinsic cannot be used with deployed code -- not unless the user supplies their own replacement code with the same name (which is a supported workflow if I understand correctly.)

[Sylvain]

ok, I will have a try, when I have some time in my hands.

I am not sure what @Walter Roberson's comment mean for me. I am intending to use this functionality with the tune and monitor mode.

[Walter Roberson]

https://www.mathworks.com/help/simulink/slref/coder.extrinsic.html?s_tid=doc_ta

During standalone code generation, the code generator attempts to determine whether an extrinsic function only has a side effect (for example, by displaying a plot) or whether it affects the output of the function in which it is called (for example, by returning a value to an output variable). If there is no change to the output, the code generator proceeds with code generation, but excludes the extrinsic function from the generated code. Otherwise, the code generator produces a compilation error.

Your sprintf and disp would potentially be discovered as only being for side effects (display on the screen) and if so the call to them would simply be omitted during code generation, without error. If Coder cannot figure out that it is only for side effect then Coder will error.

Answer 2

[Walter Roberson]

If want to emit debugging messages in a deployed executable, you have three choices:

• you can make them into signals that are logged; Or
• you can make them into signals that are transmitted to a device; Or
• you can use coder.ceval() or similar to call outside routines to do the output. Hardware specific routines, or at the very least printf() to standard output and hope standard output is connected to an accessible console. With Raspberry chances are good that you could fopen() and fprintf(), maybe even to a serial port; with Arduino I don't believe fopen is available (no file system) but perhaps fopen of a device is possible.