Found unsupported type in switch expression; switch expression must be of discrete type

Hello,

I use a Matlab Function block as state machine in my Simulink module. Everything works, except the RTL Code generation in the HDL Workflow Advisor. At this point I get the following error:

Found unsupported type in switch expression; switch expression must be of discrete type, Function 'MNIST_CNN/MAXPOOL_BANK_20/CONTROL/MATLAB Function' (#1650.355.365), line 13, column 9.

When writing the Matlab Code I reffered to this documentation: https://de.mathworks.com/help/hdlcoder/ug/model-a-state-machine-for-hdl-code-generation.html

My Matlab Code looks like this:

function [hStart,hEnd,valid,reset,enable] = maxpool_fsm(hStart_in,hEnd_in,valid_in)
%states:
ready = 0;
vector = 1;
matrix = 2;
wait_for_next_line=3;
% using persistent keyword to model state registers in hardware
persistent curr_state;
if isempty(curr_state)
    curr_state = ready;   
end
% switch to new state based on the value state register
switch (curr_state)
    case ready,        
        if (hStart_in==true && valid_in==true)
            curr_state=vector;
            valid=false;
            reset=true;
            enable=true;
            hEnd=false;
            hStart=true;
        else
            curr_state=ready;
            valid=false;
            reset=true;
            enable=true;
            hEnd=false;
            hStart=false;
        end
        
    case vector,        
        if (valid_in == true && hEnd_in==true)
            curr_state=wait_for_next_line;
            valid=true;
            reset=false;
            enable=true;
            hEnd=true;
            hStart=false;
        elseif (valid_in == true)
            curr_state=matrix;
            valid=true;
            reset=false;
            enable=true;
            hEnd=false;
            hStart=false;
        else
            curr_state=vector;
            valid=false;
            reset=true;
            enable=true;
            hEnd=false;
            hStart=false;
        end
        
    case matrix,       
        if (hEnd_in==true)
            curr_state=wait_for_next_line;
            valid = false;
            reset = false;
            enable = false;
            hEnd=true;
            hStart=false;
        elseif (valid_in==true)
            curr_state=vector;
            valid = false;
            reset = true;
            enable = true;
            hEnd=false;
            hStart=false;
        else
            curr_state=matrix;
            valid=false;
            reset=false;
            enable=false;
            hEnd=false;
            hStart=false;
        end
        
   
    case wait_for_next_line,
        if (hEnd_in==true)
            curr_state=ready;
            valid = false;
            reset=false;
            enable = false;
            hEnd=false;
            hStart=false;
        else
            curr_state=wait_for_next_line;
            valid = false;
            reset=false;
            enable = false;
            hEnd=false;
            hStart=false;
        end
    otherwise,
        valid = false;
        reset=false;
        enable = false;
        hEnd=false;
        hStart=false;
        
end

During compilation and simulation everything works. I have no clue, where the error is. In the Model Advisor the following error appeas:

Failed The model contains constructs that are unsupported for HDL code generation.

Error using hdlcoder.pirctx/invokeBackEnd

The model contains constructs that are unsupported for HDL code generation.

Error in slhdlcoder.HDLCoder/makehdl

Error in slhdlcoder.HDLCoder/makehdlturnkey

Error in downstream.DownstreamIntegrationDriver/runIPCoreCodeGen

Error in generateIPCore

Error in Simulink.ModelAdvisor/executeCheckCallbackFct

Error in Simulink.ModelAdvisor/run

Error in Simulink.ModelAdvisor/runCheck

Error in ModelAdvisor.Node/runTaskAdvisor

Error in ModelAdvisor.Node.runtohere>runToBreakpoint

Error in ModelAdvisor.Node.runtohere

A simple example where the control unit with the state machine is used is attached.

Thanks in advance!

Best Regards

[Kiran Kintali]

Can you share example types or sampel values used for hStart_in,hEnd_in,valid_in? It will help reproduce the issue. You provide this in a testbench file as well.

[Tobis Stelzer]

Thanks for your fast reply! These signals are all boolean and obtained via Pixel Control Bus Selector from the Pixel Control Bus Signal (ctrl) of a Line Buffer (Vision HDL Toolbox).

[Tobis Stelzer]

Here is a simple example/testbench, which uses the same control unit. It is designed for use with an 28x28x1 input image.

[Stefan Griebel]

I get the exact same error in R2020b when using a cut-and-paste of the Mathworks example code from Model a State Machine for HDL Code Generation - MATLAB & Simulink (mathworks.com)

The super simple Simulink Model is attached, and here is a copy of the .m code in the function block. The "Accepted Answer" in this thread is to NOT use a persisent variable, and add a delay outside the block, which is contrary to Mathworks own example! Am I missing something here?

%#codegen
function Z = mlhdlc_fsm_mealy(A)
% Mealy State Machine

% y = f(x,u) : 
% all actions are condition actions and 
% outputs are function of state and input 

% define states
S1 = 0;
S2 = 1;
S3 = 2;
S4 = 3;

persistent current_state;
if isempty(current_state)
    current_state = S1;   
end

% switch to new state based on the value state register
switch (current_state) 
    
    case S1,
        
        % value of output 'Z' depends both on state and inputs
        if (A)
            Z = true;
            current_state = S1;
        else
            Z = false;            
            current_state = S2;
        end
        
    case S2,
        
        if (A)
            Z = false;
            current_state = S3;
        else
            Z = true;
            current_state = S2;
        end
        
    case S3,
        
        if (A)
            Z = false;            
            current_state = S4;
        else
            Z = true;            
            current_state = S1;
        end
        
    case S4,
        
        if (A)
            Z = true;
            current_state = S1;
        else
            Z = false;            
            current_state = S3;
        end        
        
    otherwise,
        
        Z = false;
end

Answer 1

[Tobis Stelzer]

I solved the issue by not declaring the state variable as persistent, but instead using a delay outside the matlab function block:

function [hStart,hEnd,valid,reset,enable,curr_state_out] = maxpool_fsm(curr_state_in,hStart_in,hEnd_in,valid_in)

%states:

ready = uint8(0);

vctr = uint8(1);

mtrx = uint8(2);

wait_for_next_line=uint8(3);

% using persistent keyword to model state registers in hardware

%persistent curr_state;

curr_state_out=uint8(0);

if isempty(curr_state_out)

curr_state_out = ready;

end

% switch to new state based on the value state register

switch(curr_state_in)

case ready,

if (hStart_in==true && valid_in==true)

curr_state_out=vctr;

valid=false;

reset=true;

enable=true;

hEnd=false;

hStart=true;

else

curr_state_out=ready;

valid=false;

reset=true;

enable=true;

hEnd=false;

hStart=false;

end

case vctr,

if (valid_in == true && hEnd_in==true)

curr_state_out=wait_for_next_line;

valid=true;

reset=false;

enable=true;

hEnd=true;

hStart=false;

elseif (valid_in == true)

curr_state_out=mtrx;

valid=true;

reset=false;

enable=true;

hEnd=false;

hStart=false;

else

curr_state_out=vctr;

valid=false;

reset=true;

enable=true;

hEnd=false;

hStart=false;

end

case mtrx,

if (hEnd_in==true)

curr_state_out=wait_for_next_line;

valid = false;

reset = false;

enable = false;

hEnd=true;

hStart=false;

elseif (valid_in==true)

curr_state_out=vctr;

valid = false;

reset = true;

enable = true;

hEnd=false;

hStart=false;

else

curr_state_out=mtrx;

valid=false;

reset=false;

enable=false;

hEnd=false;

hStart=false;

end

case wait_for_next_line,

if (hEnd_in==true)

curr_state_out=ready;

valid = false;

reset=false;

enable = false;

hEnd=false;

hStart=false;

else

curr_state_out=wait_for_next_line;

valid = false;

reset=false;

enable = false;

hEnd=false;

hStart=false;

end

otherwise,

valid = false;

reset=false;

enable = false;

hEnd=false;

hStart=false;

end

Answer 2

[Robert Wittig]

Apparently state variable must be declared as fixed point as can be found here

https://de.mathworks.com/help/hdlcoder/ug/matlab-function-block-design-patterns-for-hdl.html

function Z = moore_fsm(A)

persistent moore_state_reg;

if isempty(moore_state_reg)

moore_state_reg = fi(0, 0, 2, 0);

end

S1 = 0;

S2 = 1;

S3 = 2;

S4 = 3;

switch uint8(moore_state_reg)

case S1,

Z = true;

if (~A)

moore_state_reg(1) = S1;

else

moore_state_reg(1) = S2;

end

case S2,

Z = false;

if (~A)

moore_state_reg(1) = S1;

else

moore_state_reg(1) = S2;

end

case S3,

Z = false;

if (~A)

moore_state_reg(1) = S2;

else

moore_state_reg(1) = S3;

end

case S4,

Z = true;

if (~A)

moore_state_reg(1) = S1;

else

moore_state_reg(1) = S3;

end

otherwise,

Z = false;

end