Equal Slope and Zero Net Bias Code Replacement

You can define code replacement entries for addition or subtraction of fixed-point data types such that they match the relative slope and bias values (equal slope and zero net bias) across operator inputs and output. These entries allow you to disregard slope and bias values when mapping relative slope and bias values to a replacement function for addition or subtraction.

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 an addition 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

Open the Code Replacement Tool (crtool), from the MATLAB command line with the following command:
```
>>crtool
```
Create a table.
1. From the crtool context menu, select File > New Table.
2. In the right pane, name the table crl_table_equal_slope_netbias_add. Click Apply.
Create an entry. From the crtool context menu, select File > New entry > Fixed Point Net Slope Operation.
Create entry parameters. In the Operation drop-down list, select Addition.
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.
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.
Specify a Name for the replacement function under Function prototype.
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.
Validate and save the table. In the Mapping Information tab, click Validate entry. In the crtool context menu, select File > Save table > Save.
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
```
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

Open the programmatic interface from the MATLAB menu by selecting New > Function.
Create a table.
1. Create a function to call your code replacement library table. The function should not have arguments and return a table object.
2. Create a table object by calling RTW.TflTable.
```
function hTable = crl_table_equal_slope_netbias_add
% Create a function to call the code replacement library table 

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

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_equal_slope_netbias_add
% 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. Because this examples replaces a function, create entry parameters by calling the function setTflCOperationEntryParameters.

function hTable = crl_table_equal_slope_netbias_add
% 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_ADD', ...
    'Priority',                 90, ...
    'SaturationMode',           'RTW_WRAP_ON_OVERFLOW', ...
    'RoundingModes',            {'RTW_ROUND_UNSPECIFIED'}, ...
    'SlopesMustBeTheSame',      true, ...
    'MustHaveZeroNetBias',      true, ...
    'ImplementationName',       'u16_add_SameSlopeZeroBias', ...
    'ImplementationHeaderFile', 'u16_add_SameSlopeZeroBias.h', ...
    'ImplementationSourceFile', 'u16_add_SameSlopeZeroBias.c');

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_equal_slope_netbias_add
% 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_ADD', ...
    'Priority',                 90, ...
    'SaturationMode',           'RTW_WRAP_ON_OVERFLOW', ...
    'RoundingModes',            {'RTW_ROUND_UNSPECIFIED'}, ...
    'SlopesMustBeTheSame',      true, ...
    'MustHaveZeroNetBias',      true, ...
    'ImplementationName',       'u16_add_SameSlopeZeroBias', ...
    'ImplementationHeaderFile', 'u16_add_SameSlopeZeroBias.h', ...
    'ImplementationSourceFile', 'u16_add_SameSlopeZeroBias.c');

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

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

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

Create the implementation representation. The implementation representation describes the signature of the optimization function. This example uses calls to the createAndSetCImplementationReturn function 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_equal_slope_netbias_add
% 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_ADD', ...
    'Priority',                 90, ...
    'SaturationMode',           'RTW_WRAP_ON_OVERFLOW', ...
    'RoundingModes',            {'RTW_ROUND_UNSPECIFIED'}, ...
    'SlopesMustBeTheSame',      true, ...
    'MustHaveZeroNetBias',      true, ...
    'ImplementationName',       'u16_add_SameSlopeZeroBias', ...
    'ImplementationHeaderFile', 'u16_add_SameSlopeZeroBias.h', ...
    'ImplementationSourceFile', 'u16_add_SameSlopeZeroBias.c');

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

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

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


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

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

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


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

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.
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_equal_slope_netbias_add
```

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 with 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 equal slope and zero net bias code replacement’;
this(1).TableList = {'crl_table_equal_slope_netbias_add.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

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.