Arduino SPI writeRead function unavailable in Simulink

I am trying to execute multiple SPI writes in one solver step of a simulink program. So I enclosed all of my SPI write calls in one functions and I initialize the relevant objects before running the simulink code. However, at execution simulink complains about 'writeRead' function being undefined when it tries to execute the transfers. I have included the two program segments that I am using.

% init.m
global arduinodev; global extdac;
arduinodev = arduino('COM4', 'Due', 'Libraries', 'SPI');
extdac = device(arduinodev, 'SPIChipSelectPin', 'D52', 'SPIMode', 1, 'bitorder', 'msbfirst') ;

% MATLAB Function
function dacWrite(extdac, values)
    %DACWRITE Writes the 6 values received to the Helmholtz Cage Controller
    %DAC
    %
    l = length(values);
    if ( l ~= 6 ) 
        return
    end
    % code n
    coden = 0b10000000 ;
    for dac = 1:6
        cmd = bitor(coden, dac) ;
        val = uint16(values(dac));
        if ( val > 0x0fff )
            val = 0x0fff ;
        end
        low = bitshift(uint8(bitand(val,0x00ff)),4);
        high = uint8(bitshift(uint16(val),-4,'uint16'));
        %fprintf("0x%x 0x%x 0x%x\n", cmd, high, low);
        dacout = [cmd, high, low];
        writeRead(extdac, dacout);
    end %for
    dacout = [ 0b11000001 0x00 0x00 ] ; % loadn
    writeRead(extdac, dacout);
end

Here is the image of the Simulink Code Block that I am using:

And here is the error I am getting:

Undefined function or variable 'writeRead'.

Function 'MATLAB Function' (#23.590.615), line 21, column 9:
"writeRead(extdac, dacout)"

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/fixedpoint/ref/coder.extrinsic.html

In the case where you are using either no acceleration or else only the first step of acceleration, then you can use coder.extrinsic() to have Simulink talk to the MATLAB engine to run the function.

However, there is currently no way to generate deployable code for the writeRead() call. Notice that https://www.mathworks.com/help/supportpkg/arduinoio/ref/writeread.html does not have any section for "extended capabilities", so there is no code generation available for it.

[Sunip Mukherjee]

Thanks! I ended up writing my own Arduino server code that reads 12 bytes over serial and programs the DAC with those, while the Simulink code uses generic serial communication to send the 12 bytes to the Arduino at each cycle.