Customize Match and Replacement Process

During the build process, the code generator uses:

  • Preset match criteria to identify functions and operators for which application-specific implementations replace default implementations.

  • Preset replacement function signatures.

It is possible that preset match criteria and preset replacement function signatures do not completely meet your function and operator replacement needs. For example:

  • You want to replace an operator with a particular fixed-point implementation function only when fraction lengths are within a particular range.

  • When a match occurs, you want to modify your replacement function signature based on compile-time information, such as passing fraction-length values into the function.

To add extra logic into the code replacement match and replacement process, create custom code replacement table entries. With custom entries, you can specify additional match criteria and modify the replacement function signature to meet application needs.

To create a custom code replacement entry:

  1. Create a custom code replacement entry class, derived from RTW.TflCFunctionEntryML (for function replacement) or RTW.TflCOperationEntryML (for operator replacement).

  2. In your derived class, implement a do_match method with a fixed preset signature as a MATLAB® function. In your do_match method, provide either or both of the following customizations that instantiate the class:

    • Add match criteria that the base class does not provide. The base class provides a match based on:

      • Argument number

      • Argument name

      • Signedness

      • Word size

      • Slope (if not specified with wildcards)

      • Bias (if not specified with wildcards)

      • Math modes, such as saturation and rounding

      • Operator or function key

    • Modify the implementation signature by adding additional arguments or setting constant input argument values. You can inject a constant value, such as an input scaling value, as an additional argument to the replacement function.

  3. Create code replacement entries that instantiate the custom entry class.

  4. Register a library containing the code replacement table that includes your entries.

During code generation, the code replacement match process tries to match function or operator call sites with the base class of your derived entry class. If the process finds a match, the software calls your do_match method to execute your additional match logic (if any) and your replacement function customizations (if any).

Customize Code Match and Replacement for Functions

This example shows how to use custom code replacement table entries to refine the match and replacement logic for functions. The example shows how to:

  • Modify a sine function replacement only if the integer size on the current target platform is 32 bits.

  • Change the replacement such that the implementation function passes in a degrees-versus-radians flag as an input argument.

  1. To exercise the table entries that you create in this example, create an ERT-based model with a sine function block. For example:

    In the Inport block parameters, set the signal Data type to double. If the value selected for Configuration Parameters > Hardware Implementation > Device type supports an integer size other than 32, do one of the following:

    • Select a temporary target platform with a 32-bit integer size.

    • Modify the code to match the integer size of your target platform.

  2. Create a class, for example TflCustomFunctionEntry, that is derived from the base class RTW.TflCFunctionEntryML. The derived class defines a do_match method with the signature:

    function ent = do_match(hThis, ...
        hCSO, ...
        targetBitPerChar, ...
        targetBitPerShort, ...
        targetBitPerInt, ...
        targetBitPerLong, ...
        targetBitPerLongLong)

    In the do_match signature:

    • ent is the return handle, which is returned either as empty (indicating that the match failed) or as a TflCFunctionEntry handle.

    • hThis is a handle to the class instance.

    • hCSO is a handle to an object that the code generator creates for querying the library for a replacement.

    • Remaining arguments are the number of bits for various data types of the current target.

    The do_match method:

    • Adds required additional match criteria that the base class does not provide.

    • Makes required modifications to the implementation signature.

    In this case, the do_match method must match only targetBitPerInt, representing the number of bits in the C int data type for the current target, to the value 32. If the code generator finds a match, the method sets the return handle and creates and adds an input argument. The input argument represents whether units are expressed as degrees or radians, to the replacement function signature.

    Alternatively, create and add the additional implementation function argument for passing a units flag in each code replacement table definition file that instantiates this class. In that case, this class definition code does not create the argument. That code sets only the argument value. For an example of creating and adding additional implementation function arguments in a table definition file, see Customize Code Match and Replacement for Scalar Operations.

    classdef TflCustomFunctionEntry < RTW.TflCFunctionEntryML
  methods
    function ent = do_match(hThis, ...
        hCSO, ... %#ok
        targetBitPerChar, ... %#ok
        targetBitPerShort, ... %#ok
        targetBitPerInt, ... %#ok
        targetBitPerLong, ... %#ok
        targetBitPerLongLong) %#ok
      % DO_MATCH - Create a custom match function. The base class
      % checks the types of the arguments prior to calling this
      % method. This will check additional data and perhaps modify
      % the implementation function.

      ent = []; % default the return to empty, indicating the match failed.

      % Match sine function only if the target int size is 32 bits
      if targetBitPerInt == 32
        % Need to modify the default implementation, starting from a copy
        % of the standard TflCFunctionEntry.
        ent = RTW.TflCFunctionEntry(hThis);

        % If the target int size is 32 bits, the implementation function
        % takes an additional input flag argument indicating degress vs.
        % radians. The additional argument can be created and added either
        % in the CRL table definition file that instantiates this class, or
        % here in the class definition, as follows:
        createAndAddImplementationArg(ent, 'RTW.TflArgNumericConstant', ...
                                      'Name',           'u2', ...
                                      'IsSigned',       true, ...
                                      'WordLength',     32, ...
                                      'FractionLength', 0, ...
                                      'Value',          1);
      end
    end
  end
end

    Exit the class folder and return to the previous working folder.

  3. Create and save the following code replacement table definition file, crl_table_custom_sinfcn_double.m. This file defines a code replacement table that contains a function table entry for sine with double input and output. This entry instantiates the derived class from the previous step, TflCustomFunctionEntry.

    function hTable = crl_table_custom_sinfcn_double

hTable = RTW.TflTable;

%% Add TflCustomFunctionEntry
fcn_entry = TflCustomFunctionEntry;
setTflCFunctionEntryParameters(fcn_entry, ...
    'Key',                      'sin', ...
    'Priority',                 30, ...
    'ImplementationName',       'mySin', ...
    'ImplementationHeaderFile', 'mySin.h', ...
    'ImplementationSourceFile', 'mySin.c');

createAndAddConceptualArg(fcn_entry, 'RTW.TflArgNumeric', ...
     'Name',         'y1', ...
     'IOType',       'RTW_IO_OUTPUT', ...
     'DataTypeMode', 'double');

createAndAddConceptualArg(fcn_entry, 'RTW.TflArgNumeric', ...
     'Name',         'u1', ...
     'IOType',       'RTW_IO_INPUT', ...
     'DataTypeMode', 'double');

% TflCustomFunctionEntry class do_match method will create and add
% an implementation function argument during code generation if
% the supported integer size on the current target is 32 bits.
copyConceptualArgsToImplementation(fcn_entry);

addEntry(hTable, fcn_entry);

  4. Check the validity of the code replacement table entry.

    • At the command prompt, invoke the table definition file.

      tbl = crl_table_custom_sinfcn_double

    • In the Code Replacement Viewer, view the table definition file.

      crviewer(crl_table_custom_sinfcn_double)

Customize Code Match and Replacement for Nonscalar Operations

This example shows how to create custom code replacement entries that add logic to the code match and replacement process for a nonscalar operation. Custom entries specify additional match criteria or modify the replacement function signature to meet application needs.

This example restricts the match criteria for an element-wise multiplication replacement to entries with a specific dimension range. When a match occurs, the custom do_match method modifies the replacement signature to pass the number of elements into the function.

Files for developing and testing this code replacement library example are available in matlab/help/toolbox/ecoder/examples/code_replacement/custom_elemmult:

  • do_match method — @MyElemMultEntry/MyElemMultEntry.m

  • Replacement function source and header files — src/myMulImplLib.c and src/myMulImplLib.h

  • Model — myElemMul.slx

  • Code replacement table definition — myElemMultCrlTable.m

  • Registration file — rtwTargetInfo.m

To create custom code replacement entries that add logic to the code replacement match and replacement process:

  1. Create a class, for example MyElemMultEntry, which is derived from the base class RTW.TflCOperationEntryML. The derived class defines a do_match method with the following signature:

    function ent = do_match(hThis, ...
    hCSO, ... 
    targetBitPerChar, ...
    targetBitPerShort, ...
    targetBitPerInt, ...
    targetBitPerLong, ...
    targetBitPerLongLong)

    In the do_match signature:

    • ent is the return handle, which is returned as empty (indicating that the match failed) or as a TflCOperationEntry handle.

    • hThis is the handle to the derived instance.

    • hCSO is a handle to an object that the code generator creates for querying the library for a replacement.

    • Remaining arguments are the number of bits for various data types of the current target.

    The do_match method:

    • Adds match criteria that the base class does not provide.

    • Makes changes to the implementation signature.

    The do_match method relies on the base class for checking data types and dimension ranges. If the code generator finds a match, do_match:

    • Sets the return handle.

    • Uses the conceptual arguments to compute the number of elements in the array. In the replacement entry returned, sets the value of the constant implementation argument as the number of elements of the array.

    • Updates the code replacement entry such that it matches CSOs that have the same argument dimensions.

    classdef MyElemMultEntry < RTW.TflCOperationEntryML
    methods
        function obj = MyElemMultEntry(varargin)
            mlock;
            obj@RTW.TflCOperationEntryML(varargin{:});
        end
        
        function ent = do_match(hThis, ...
            hCSO, ... %#ok
            targetBitPerChar, ... %#ok
            targetBitPerShort, ... %#ok
            targetBitPerInt, ... %#ok
            targetBitPerLong, ... %#ok
            targetBitPerLongLong ) %#ok
            
            %  Fourth implementation arg represents number of elements for producing matches.
            assert(strcmp(hThis.Implementation.Arguments(4).Name,'numElements'));
            
            ent = RTW.TflCOperationEntry(hThis);
            
            % Calculate number of elements and set value of injected constant.
            ent.Implementation.Arguments(4).Value = prod(hCSO.ConceptualArgs(1).DimRange(1,:));
            
            % Since implementation has been modified for specific DimRange, update 
            % returned entry to match similar CSOs only.
            for idx =1:3
                ent.ConceptualArgs(idx).DimRange = hCSO.ConceptualArgs(idx).DimRange;
            end
        end
    end
end

  2. Create and save the following code replacement table definition file, myElemMultCrlTable.m. This file defines a code replacement table that contains an operator entry generator for element-wise multiplication. The table entry:

    • Instantiates the derived class myElemMultEntry from the previous step.

    • Sets operator entry parameters with the call to the setTflCOperationEntryParameters function.

    • Creates conceptual arguments y1, u1, and u2. The argument class RTW.TflArgMatrix specifies matrix arguments to match. The three arguments are set up to match 2-dimensional matrices with at least two elements in each dimension.

    • Calls the getTflArgFromString function to create a return value and four implementation arguments. Arguments u1 and u2 are the operands, y1 is the product, and the fourth argument is the number of elements.

      Alternatively, the do_match method of the derived class myElemMultEntry can create and add the implementation arguments. When the number of additional implementation arguments required can vary based on compile-time information, use the alternative approach.

    • Calls addEntry to add the entry to a code replacement table.

    function hLib = myElemMultCrlTable

libPath = fullfile(fileparts(which(mfilename)),'src');

hLib = RTW.TflTable;
%---------- entry: RTW_OP_ELEM_MUL ----------- 
hEnt = MyElemMultEntry;
hEnt.setTflCOperationEntryParameters( ...
          'Key', 'RTW_OP_ELEM_MUL', ...
          'Priority', 100, ...
          'SaturationMode', 'RTW_WRAP_ON_OVERFLOW', ...
          'ImplementationName', 'myElemMul_s32', ...
          'ImplementationSourceFile', 'myMulImplLib.c', ...
          'ImplementationSourcePath', libPath, ...
          'ImplementationHeaderFile', 'myMulImplLib.h', ...
          'ImplementationHeaderPath', libPath, ...
          'SideEffects', true, ...
          'GenCallback','RTW.copyFileToBuildDir');

% Conceptual Args

arg = RTW.TflArgMatrix('y1', 'RTW_IO_OUTPUT',  'int32');
arg.DimRange = [2 2; Inf Inf];
hEnt.addConceptualArg(arg);

arg = RTW.TflArgMatrix('u1', 'RTW_IO_INPUT',  'int32');
arg.DimRange = [2 2; Inf Inf];
hEnt.addConceptualArg(arg);

arg = RTW.TflArgMatrix('u2', 'RTW_IO_INPUT',  'int32');
arg.DimRange = [2 2; Inf Inf];
hEnt.addConceptualArg(arg);

% Implementation Args 

arg = hEnt.getTflArgFromString('unused','void');
arg.IOType = 'RTW_IO_OUTPUT';
hEnt.Implementation.setReturn(arg); 

arg = hEnt.getTflArgFromString('u1','int32*');
hEnt.Implementation.addArgument(arg);

arg = hEnt.getTflArgFromString('u2','int32*');
hEnt.Implementation.addArgument(arg);

arg = hEnt.getTflArgFromString('y1','int32*');
arg.IOType = 'RTW_IO_OUTPUT';
hEnt.Implementation.addArgument(arg);

arg = hEnt.getTflArgFromString('numElements','uint32',0);
hEnt.Implementation.addArgument(arg);

hLib.addEntry( hEnt );

  3. Check the validity of the code replacement table entry.

    • At the command prompt, invoke the table definition file.

      tbl = myElemMultCrlTable

    • In the Code Replacement Viewer, view the table definition file.

      crviewer(myElemMultCrlTable)

Customize Code Match and Replacement for Scalar Operations

This example shows how to create custom code replacement entries that add logic to the code match and replacement process for a scalar operation. Custom entries specify additional match criteria or modify the replacement function signature to meet application needs.

For example:

  • When fraction lengths are within a specific range, replace an operator with a fixed-point implementation function.

  • When a match occurs, modify the replacement function signature based on compile-time information, such as passing fraction-length values into the function.

This example modifies a fixed-point addition replacement such that the implementation function passes in the fraction lengths of the input and output data types as arguments.

To create custom code replacement entries that add logic to the code replacement match and replacement process:

  1. Create a class, for example TflCustomOperationEntry, that is derived from the base class RTW.TflCOperationEntryML. The derived class defines a do_match method with the following signature:

    function ent = do_match(hThis, ...
        hCSO, ...
        targetBitPerChar, ...
        targetBitPerShort, ...
        targetBitPerInt, ...
        targetBitPerLong, ...
        targetBitPerLongLong)

    In the do_match signature:

    • ent is the return handle, which is returned as empty (indicating that the match failed) or as a TflCOperationEntry handle.

    • hThis is the handle to the class instance.

    • hCSO is a handle to an object that the code generator creates for querying the library for a replacement.

    • Remaining arguments are the number of bits for various data types of the current target.

    The do_match method adds match criteria that the base class does not provide. The method makes modifications to the implementation signature. In this case, the do_match method relies on the base class for checking word size and signedness. do_match must match only the number of conceptual arguments to the value 3 (two inputs and one output) and the bias for each argument to value 0. If the code generator finds a match, do_match:

    • Sets the return handle.

    • Removes slope and bias wild cards from the conceptual arguments (the match is for specific slope and bias values).

    • Writes fraction-length values for the inputs and output into replacement function arguments 3, 4, and 5.

    You can create and add three additional implementation function arguments for passing fraction lengths in the class definition or in each code replacement entry definition that instantiates this class. This example creates the arguments, adds them to a code replacement table definition file, and sets them to specific values in the class definition code.

    classdef TflCustomOperationEntry < RTW.TflCOperationEntryML
  methods
    function ent = do_match(hThis, ...
        hCSO, ... %#ok
        targetBitPerChar, ... %#ok
        targetBitPerShort, ... %#ok
        targetBitPerInt, ... %#ok
        targetBitPerLong, ... %#ok
        targetBitPerLongLong) %#ok

      % DO_MATCH - Create a custom match function. The base class
      % checks the types of the arguments prior to calling this
      % method. This class will check additional data and can
      % modify the implementation function.

      % The base class checks word size and signedness. Slopes and biases
      % have been wildcarded, so the only additional checking to do is
      % to check that the biases are zero and that there are only three
      % conceptual arguments (one output, two inputs)

      ent = []; % default the return to empty, indicating the match failed

      if length(hCSO.ConceptualArgs) == 3 && ...
          hCSO.ConceptualArgs(1).Type.Bias == 0 && ...
          hCSO.ConceptualArgs(2).Type.Bias == 0 && ...
          hCSO.ConceptualArgs(3).Type.Bias == 0

        % Modify the default implementation. Since this is a
        % generator entry, a concrete entry is created using this entry
        % as a template. The type of entry being created is a standard
        % TflCOperationEntry. Using the standard operation entry
        % provides required information, and you do not need
        % a custom match function.
        ent = RTW.TflCOperationEntry(hThis);

        % Since this entry is modifying the implementation for specific
        % fraction-length values (arguments 3, 4, and 5), the conceptual argument
        % wild cards must be removed (the wildcards were inherited from the
        % generator when it was used as a template for the concrete entry).
        % This concrete entry is now for a specific slope and bias. 
        % hCSO holds the slope and bias values (created by the code generator).
        for idx=1:3
          ent.ConceptualArgs(idx).CheckSlope = true;
          ent.ConceptualArgs(idx).CheckBias = true;

          % Set the specific Slope and Biases
          ent.ConceptualArgs(idx).Type.Slope = hCSO.ConceptualArgs(idx).Type.Slope;
          ent.ConceptualArgs(idx).Type.Bias = 0;
        end

        % Set the fraction-length values in the implementation function.
        ent.Implementation.Arguments(3).Value = ...
           -1.0*hCSO.ConceptualArgs(2).Type.FixedExponent;
        ent.Implementation.Arguments(4).Value = ...
           -1.0*hCSO.ConceptualArgs(3).Type.FixedExponent;
        ent.Implementation.Arguments(5).Value = ...
           -1.0*hCSO.ConceptualArgs(1).Type.FixedExponent;
      end
    end
  end
end

    Exit the class folder and return to the previous working folder.

  2. Create and save the following code replacement table definition file, crl_table_custom_add_ufix32.m. This file defines a code replacement table that contains a single operator entry, an entry generator for unsigned 32-bit fixed-point addition operations, with arbitrary fraction-length values on the inputs and the output. The table entry:

    • Instantiates the derived class TflCustomOperationEntry from the previous step. If you want to replace word sizes and signedness attributes, you can use the same derived class, but not the same entry, because you cannot use a wild card with the WordLength and IsSigned arguments. For example, to support uint8, int8, uint16, int16, and int32, add five other distinct entries. To use different implementation functions for saturation and rounding modes other than overflow and round to floor, add entries for those match permutations.

    • Sets operator entry parameters with the call to the setTflCOperationEntryParameters function.

    • Calls the createAndAddConceptualArg function to create conceptual arguments y1, u1, and u2.

    • Calls createAndSetCImplementationReturn and createAndAddImplementationArg to define the signature for the replacement function. Three of the calls to createAndAddImplementationArg create implementation arguments to hold the fraction-length values for the inputs and output. Alternatively, the entry can omit those argument definitions. Instead, the do_match method of the derived class TflCustomOperationEntry can create and add the three implementation arguments. When the number of additional implementation arguments required can vary based on compile-time information, use the alternative approach.

    • Calls addEntry to add the entry to a code replacement table.

    function hTable = crl_table_custom_add_ufix32

hTable = RTW.TflTable;

% Add TflCustomOperationEntry
op_entry = TflCustomOperationEntry;

setTflCOperationEntryParameters(op_entry, ...
    'Key',                      'RTW_OP_ADD', ...
    'Priority',                 30, ...
    'SaturationMode',           'RTW_SATURATE_ON_OVERFLOW', ...
    'RoundingModes',            {'RTW_ROUND_FLOOR'}, ...
    'ImplementationName',       'myFixptAdd', ...
    'ImplementationHeaderFile', 'myFixptAdd.h', ...
    'ImplementationSourceFile', 'myFixptAdd.c');

createAndAddConceptualArg(op_entry, 'RTW.TflArgNumeric', ...
     'Name',       'y1', ...
     'IOType',     'RTW_IO_OUTPUT', ...
     'CheckSlope', false, ...
     'CheckBias',  false, ...
     'DataType',   'Fixed', ...
     'Scaling',    'BinaryPoint', ...
     'IsSigned',   false, ...
     'WordLength', 32);

createAndAddConceptualArg(op_entry, 'RTW.TflArgNumeric', ...
      'Name',       'u1', ...
      'IOType',     'RTW_IO_INPUT', ...
      'CheckSlope', false, ...
      'CheckBias',  false, ...
      'DataType',   'Fixed', ...
      'Scaling',    'BinaryPoint', ...
      'IsSigned',   false, ...
      'WordLength', 32);

createAndAddConceptualArg(op_entry, 'RTW.TflArgNumeric', ...
       'Name',       'u2', ...
       'IOType',     'RTW_IO_INPUT', ...
       'CheckSlope', false, ...
       'CheckBias',  false, ...
       'DataType',   'Fixed', ...
       'Scaling',    'BinaryPoint', ...
       'IsSigned',   false, ...
       'WordLength', 32);

% Specify replacement function signature
createAndSetCImplementationReturn(op_entry, 'RTW.TflArgNumeric', ...
    'Name',       'y1', ...
    'IOType',     'RTW_IO_OUTPUT', ...
    'IsSigned',   false, ...
    'WordLength', 32, ...
    'FractionLength', 0);

createAndAddImplementationArg(op_entry, 'RTW.TflArgNumeric', ...
    'Name',       'u1', ...
    'IOType',     'RTW_IO_INPUT', ...
    'IsSigned',   false, ...
    'WordLength', 32, ...
    'FractionLength', 0);

createAndAddImplementationArg(op_entry, 'RTW.TflArgNumeric', ...
    'Name',       'u2', ...
    'IOType',     'RTW_IO_INPUT', ...
    'IsSigned',   false, ...
    'WordLength', 32, ...
    'FractionLength', 0);

% Add 3 fraction-length args. Actual values are set during code generation.
createAndAddImplementationArg(op_entry, 'RTW.TflArgNumericConstant', ...
    'Name',       'fl_in1', ...
    'IOType',     'RTW_IO_INPUT', ...
    'IsSigned',   false, ...
    'WordLength', 32, ...
    'FractionLength', 0, ...
    'Value',       0);

createAndAddImplementationArg(op_entry, 'RTW.TflArgNumericConstant', ...
    'Name',       'fl_in2', ...
    'IOType',     'RTW_IO_INPUT', ...
    'IsSigned',   false, ...
    'WordLength', 32, ...
    'FractionLength', 0, ...
    'Value',       0);

createAndAddImplementationArg(op_entry, 'RTW.TflArgNumericConstant', ...
    'Name',       'fl_out', ...
    'IOType',     'RTW_IO_INPUT', ...
    'IsSigned',   false, ...
    'WordLength', 32, ...
    'FractionLength', 0, ...
    'Value',       0);

addEntry(hTable, op_entry);

  3. Check the validity of the operator entry.

    • At the command prompt, invoke the table definition file.

      tbl = crl_table_custom_add_ufix32

    • In the Code Replacement Viewer, view the table definition file.

      crviewer(crl_table_custom_add_ufix32)

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