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Net Slope Scaling Code Replacement

You can define code replacement entries for multiplication and division operations on fixed-point data types such that they match the net slope between operator inputs and output. The net slope entries can map a range of slope and bias values to a replacement function for multiplication or division.

This example shows how to develop a code replacement library to optimize the performance of fixed point net slope operations by providing information on how to define code replacement for a divide operation. To develop a code replacement library use either the interactive or programmatic approach. For more information, see Develop a Code Replacement Library.

Interactively Develop a Code Replacement Library

  1. Open the Code Replacement Tool (crtool), from the MATLAB command line with the following command:

    >>crtool

  2. Create a table.

    1. From the crtool context menu, select File > New Table.

    2. In the right pane, name the table crl_table_netslopeScaling. Click Apply.

  3. Create an entry. From the crtool context menu, select File > New entry > Fixed Point Net Slope Operation.

  4. Create entry parameters. In the Operation drop-down list, select Divide.

  5. Create the conceptual representation. The conceptual representation describes the signature of the function that you want to replace. In the Conceptual function subsection of the crtool, specify the return argument, y1, and the input argument, u1 and u2 with the Data Type of fixdt(true,16,*,*) and the Argument Type of Scalar.

  6. Create the implementation representation. The implementation representation describes the signature of the optimization function. In the Function arguments subsection of the crtool, specify the return argument, y1, and the input argument, u1 and u2 with the Data Type of int 16. Also set the Net slope Adjustment Factor as 1 and Net Fixed Exponent as 0.

    Specify a Name for the replacement function under Function prototype.

  7. Specify build information. Click the Build Information tab to open the build requirements pane. Specify the files (source, header, object) that the code generator requires for code replacement. For this example, you do not need to specify build information.

  8. Validate and save the table. In the Mapping Information tab, click Validate entry. In the crtool context menu, select File > Save table > Save.

  9. Register a code replacement library. Registration creates a library composed of the tables that you specify. Select File > Generate registration file. In the Generate registration file dialog box, fill out these fields:

    To use your code replacement library, refresh your current MATLAB session with the command:

    >>sl_refresh_customizations

  10. Verify the code replacement library. From the MATLAB command line, open the library by using the Code Replacement Viewer and verify that the table and entry are correctly specified. For more information, see Verify Code Replacement Library. Configure your model to use the code replacement library, generate code, and verify that replacement occurs as expected. If unexpected behavior occurs, examine the hit and miss logs to troubleshoot the issues.

Programmatically Develop a Code Replacement Library

  1. Open the programmatic interface from the MATLAB menu by selecting New > Function.

  2. Create a table.

    1. Create a function with the name of your code replacement library table that does not have arguments and returns a table object. You can use this function to call your code replacement library table.

    2. Create a table object by calling RTW.TflTable.

    function hTable = crl_table_netslopeScaling
% Create a function to call the code replacement library table 

%% Create a table object
hTable = RTW.TflTable;

  3. Create an entry. Because this example replaces a function, create a code replacement entry in your table by calling the entry function RTW.TflCOperationEntryGenerator_NetSlope.

    function hTable = crl_table_netslopeScaling
% Create a function to call the code replacement library table 

%% Create a table object
hTable = RTW.TflTable;

%% Create an entry
hEntry = RTW.TflCOperationEntryGenerator_NetSlope;

  4. Set operator entry parameters with a call to the setTflCOperationEntryParameters function. The parameters specify the type of operation as division, the saturation mode as wrap on overflow, rounding modes as unspecified, and the name of the replacement function as user_div_*. NetSlopeAdjustmentFactor and NetFixedExponent specify the F and E parts of the net slope F2E.

    function hTable = crl_table_netslopeScaling
% Create a function to call the code replacement library table 

%% Create a table object
hTable = RTW.TflTable;

%% Create an entry
hEntry = RTW.TflCOperationEntryGenerator_NetSlope;

%% Create entry parameters
hEntry.setTflCOperationEntryParameters(...
   'Key',                      'RTW_OP_DIV', ...
   'Priority',                 90, ...
   'SaturationMode',           'RTW_WRAP_ON_OVERFLOW', ...
   'RoundingModes',            {'RTW_ROUND_CEILING'}, ...
   'NetSlopeAdjustmentFactor',   1.0, ...
   'NetFixedExponent',           0.0, ...
   'ImplementationName',       's16_div_s16_s16', ...
   'ImplementationHeaderFile', 's16_div_s16_s16.h', ...
   'ImplementationSourceFile', 's16_div_s16_s16.c');

  5. Create conceptual arguments y1, u1, and u2. This example uses calls to the createAndAddConceptualArg function to create and add an argument with one function call. Specify each argument as fixed-point, 16 bits, and signed. Also, for each argument, specify that code replacement request processing does not check for an exact match to the call-site slope and bias values.

    function hTable = crl_table_netslopeScaling
% Create a function to call the code replacement library table 

%% Create a table object
hTable = RTW.TflTable;

%% Create an entry
hEntry = RTW.TflCOperationEntryGenerator_NetSlope;

%% Create entry parameters
hEntry.setTflCOperationEntryParameters(...
   'Key',                      'RTW_OP_DIV', ...
   'Priority',                 90, ...
   'SaturationMode',           'RTW_WRAP_ON_OVERFLOW', ...
   'RoundingModes',            {'RTW_ROUND_CEILING'}, ...
   'NetSlopeAdjustmentFactor',   1.0, ...
   'NetFixedExponent',           0.0, ...
   'ImplementationName',       's16_div_s16_s16', ...
   'ImplementationHeaderFile', 's16_div_s16_s16.h', ...
   'ImplementationSourceFile', 's16_div_s16_s16.c');

%% Create the conceptual representation
createAndAddConceptualArg(hEntry, 'RTW.TflArgNumeric', ...
   'Name',           'y1', ...
   'IOType',         'RTW_IO_OUTPUT', ...
   'CheckSlope',     false, ...
   'CheckBias',      false, ...
   'DataType',       'Fixed', ...
   'IsSigned',       true, ...
   'WordLength',     16);

createAndAddConceptualArg(hEntry, 'RTW.TflArgNumeric', ...
   'Name',           'u1', ...
   'IOType',         'RTW_IO_INPUT', ...
   'CheckSlope',     false, ...
   'CheckBias',      false, ...
   'DataType',       'Fixed', ...
   'IsSigned',       true, ...
   'WordLength',     16);

createAndAddConceptualArg(hEntry, 'RTW.TflArgNumeric', ...
   'Name',           'u2', ...
   'IOType',         'RTW_IO_INPUT', ...
   'CheckSlope',     false, ...
   'CheckBias',      false, ...
   'DataType',       'Fixed', ...
   'IsSigned',       true, ...
   'WordLength',     16);

  6. Create the implementation representation. The implementation representation describes the signature of the optimization function. This example uses calls to the createAndSetCImplementationReturn and createAndAddImplementationArg functions to create and add implementation arguments to the entry. Implementation arguments must describe fundamental numeric data types (not fixed-point data types). In this case, the output and input arguments are 16 bits and signed (int16).

    function hTable = crl_table_netslopeScaling
% Create a function to call the code replacement library table 

%% Create a table object
hTable = RTW.TflTable;

%% Create an entry
hEntry = RTW.TflCOperationEntryGenerator_NetSlope;

%% Create entry parameters
hEntry.setTflCOperationEntryParameters(...
   'Key',                      'RTW_OP_DIV', ...
   'Priority',                 90, ...
   'SaturationMode',           'RTW_WRAP_ON_OVERFLOW', ...
   'RoundingModes',            {'RTW_ROUND_CEILING'}, ...
   'NetSlopeAdjustmentFactor',   1.0, ...
   'NetFixedExponent',           0.0, ...
   'ImplementationName',       's16_div_s16_s16', ...
   'ImplementationHeaderFile', 's16_div_s16_s16.h', ...
   'ImplementationSourceFile', 's16_div_s16_s16.c');

%% Create the conceptual representation
createAndAddConceptualArg(hEntry, 'RTW.TflArgNumeric', ...
   'Name',           'y1', ...
   'IOType',         'RTW_IO_OUTPUT', ...
   'CheckSlope',     false, ...
   'CheckBias',      false, ...
   'DataType',       'Fixed', ...
   'IsSigned',       true, ...
   'WordLength',     16);

createAndAddConceptualArg(hEntry, 'RTW.TflArgNumeric', ...
   'Name',           'u1', ...
   'IOType',         'RTW_IO_INPUT', ...
   'CheckSlope',     false, ...
   'CheckBias',      false, ...
   'DataType',       'Fixed', ...
   'IsSigned',       true, ...
   'WordLength',     16);

createAndAddConceptualArg(hEntry, 'RTW.TflArgNumeric', ...
   'Name',           'u2', ...
   'IOType',         'RTW_IO_INPUT', ...
   'CheckSlope',     false, ...
   'CheckBias',      false, ...
   'DataType',       'Fixed', ...
   'IsSigned',       true, ...
   'WordLength',     16);

%% Create the Implementation Representation
createAndSetCImplementationReturn(hEntry, 'RTW.TflArgNumeric', ...
                              'Name',           'y1', ...
                              'IOType',         'RTW_IO_OUTPUT', ...
                              'IsSigned',       true, ...
                              'WordLength',     16, ...
                              'FractionLength', 0);

createAndAddImplementationArg(hEntry, 'RTW.TflArgNumeric',...
                              'Name',           'u1', ...
                              'IOType',         'RTW_IO_INPUT', ...
                              'IsSigned',       true, ...
                              'WordLength',     16, ...
                              'FractionLength', 0);

createAndAddImplementationArg(hEntry, 'RTW.TflArgNumeric',...
                              'Name',           'u2', ...
                              'IOType',         'RTW_IO_INPUT', ...
                              'IsSigned',       true, ...
                              'WordLength',     16, ...
                              'FractionLength', 0);

%% Add the entry to the table
addEntry(hTable, hEntry);

  7. Specify build information. In the entry parameters, specify files (header, source, object) that the code generator needs for code replacement. For this example, build information is not required.

  8. Validate and save the customization file. From the MATLAB menu, save this customization file by selecting File > Save. From the command line, validate the code replacement library table by calling it:

    >> hTable = crl_table_netslopeScaling

  9. Register the code replacement library. Registration creates a code replacement library by defining the library name, code replacement tables, and other information. Create a registration file by using these specifications:

    function rtwTargetInfo(cm)
 
cm.registerTargetInfo(@loc_register_crl);
end
 
function this = loc_register_crl 
 
this(1) = RTW.TflRegistry; 
this(1).Name = 'CRL for net slope scaling’;
this(1).TableList = {'crl_table_netslopeScaling.m'}; % table created in this example
this(1).TargetHWDeviceType = {'*'};
this(1).Description = 'Example code replacement library';

end

    To use your code replacement library, refresh your current MATLAB session with the command:

    >>sl_refresh_customizations

  10. Verify the code replacement library. From the MATLAB command line, open the library by using the Code Replacement Viewer and verify that the table and entry are correctly specified. For more information, see Verify Code Replacement Library. Configure your model to use the code replacement library, generate code, and verify that replacement occurs as expected. If unexpected behavior occurs, examine the hit and miss logs to troubleshoot the issues.

Limitations

  • For the conceptual arguments of a net slope operation replacement entry, you must set these parameters:

    • CheckSlope — false

    • CheckBias — false

  • For net slope operation replacement entries, you must set MustHaveZeroNetBias to true.

  • You must set SlopesMustBeTheSame depending on the operation type:

    • Add/Minus — true

    • Cast/Shift — true

    • Mul/Div/MulDiv — false

  • For non-trivial net slope or bias cases, use RTW.TflCOperationEntryML instead.

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