Errors using codegen when using structure as return values of function

Hi folks,

I'm with Northrop Grumman.

Here's a function with a structure for input values (PhyInit), and a return value that I intend to be a structure:

I have a Test Bench that calls this code and it runs successfully. But when I compile with codegen, I get an error:

This structure does not have a field 'Waveform'; new fields cannot be added when structure has been read or used.

This structure does not have a field 'decDelay'; new fields cannot be added when structure has been read or used.

function [TxReturn] = PhyTxMlx(PhyInit)        %#codegen
dataIn = PhyInit.data;
    % Initialization variables are in PhyInit structure
    % tPoly = poly2trellis(PhyInit.constrlen,PhyInit.genpoly); % codegen
    tPoly = poly2trellis([5 4],[23 35 0; 0 5 13]);
    dataEnc = convenc(dataIn,tPoly);
    dataSymbolsIn = bit2int(dataEnc,PhyInit.BitsPerSymbol);
    IQMod = qammod(dataSymbolsIn,PhyInit.M);
    % TxReturn.rrcFilter =
    % rcosdesign(PhyInit.rolloff,PhyInit.filtlen,PhyInit.sps); codegen
    % constants
    TxReturn.rrcFilter = rcosdesign(0.25,10,4); % codegen needs constants
    txSignal = upfirdn(IQMod,TxReturn.rrcFilter,4,1);
    %
    % Return Values from this function
    %
    % TxReturn = struct;              % create structure for return values
    TxReturn.Waveform = txSignal;   % return IQ complex waveform
    TxReturn.decDelay = 10;         % return filter delay for BER report
end

[Bill Chou]

Hello Dr. Kurt,

I'm with Product Marketing for Coder products including MATLAB Coder. I'd like to make sure we're able to help answer your questions in this thread and the other one you recently posted.

Could you reach out to me via [e-mail]? I can check with our Northrop Grumman account team to make sure we're able to help you along.

Thanks!

Bill Chou

Product Marketing, Code Generation

Answer 1

[Ryan Livingston]

The issue that Coder is flagging is that you have something like

someStruct.field1 = value;
use(someStruct.field1);

% This line is what Coder is complaining about because someStruct was used
% above
someStruct.field2 = value;

In particular, for your code I'd suggest rewriting to

function [TxReturn] = PhyTxMlx(PhyInit)        %#codegen
dataIn = PhyInit.data;
    % Initialization variables are in PhyInit structure
    % tPoly = poly2trellis(PhyInit.constrlen,PhyInit.genpoly); % codegen
    tPoly = poly2trellis([5 4],[23 35 0; 0 5 13]);
    dataEnc = convenc(dataIn,tPoly);
    dataSymbolsIn = bit2int(dataEnc,PhyInit.BitsPerSymbol);
    IQMod = qammod(dataSymbolsIn,PhyInit.M);
    % TxReturn.rrcFilter =
    % rcosdesign(PhyInit.rolloff,PhyInit.filtlen,PhyInit.sps); codegen
    % constants
    % Ryan: Don't write into the struct and then read it here to avoid
    % Coder limitations. Use a temporary rrcFilter in the interim.
    rrcFilter = rcosdesign(0.25,10,4); % codegen needs constants
    txSignal = upfirdn(IQMod,rrcFilter,4,1);
    %
    % Return Values from this function
    %
    % TxReturn = struct;              % create structure for return values
    % Ryan: Now write the values into the output struct
    TxReturn.rrcFilter = rrcFilter;
    TxReturn.Waveform = txSignal;   % return IQ complex waveform
    TxReturn.decDelay = 10;         % return filter delay for BER report
end

[Dr W Kurt]

Ryan,

Thank you so much. What I did was set it up such that the structure is created all at once:

f1 = 'EIRP'; v1 = EIRP;

f2 = 'decDelay'; v2 = decDelay;

f3 = 'dataOut'; v3 = dataOut;

f4 = 'traceBack'; v4 = traceBack;

TxAntennaReturn = struct(f1,v1,f2,v2,f3,v3,f4,v4);

This works, and it also makes the code much easier to read/interpret

[Ryan Livingston]

Great!