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Integrate External C Functions That Pass Input and Output Arguments as Parameters with a Fixed-Point Data Type

This example shows how to use the Legacy Code Tool to integrate legacy C functions that pass their inputs and outputs by using parameters of fixed-point data type.

The Legacy Code Tool allows you to:

  • Provide the legacy function specification.

  • Generate a C-MEX S-function that is used during simulation to call the legacy code.

  • Compile and build the generated S-function for simulation.

  • Generate a block TLC file and optional rtwmakecfg.m file that is used during code generation to call the legacy code.

Provide the Legacy Function Specification

Functions provided with the Legacy Code Tool take a specific data structure or array of structures as the argument. The data structure is initialized by calling the function legacy_code() using 'initialize' as the first input. After initializing the structure, assign its properties to values corresponding to the legacy code being integrated. For detailed help on the properties, call legacy_code('help'). The prototype of the legacy functions being called in this example is:

myFixpt timesS16(const myFixpt in1, const myFixpt in2, const uint8_T fracLength)

where myFixpt is logically a fixed point data type which is physically a typedef to a 16-bit integer:

myFixpt = Simulink.NumericType;
myFixpt.DataTypeMode = 'Fixed-point: binary point scaling';
myFixpt.Signed = true;
myFixpt.WordLength = 16;
myFixpt.FractionLength = 10;
myFixpt.IsAlias = true;
myFixpt.HeaderFile = 'timesFixpt.h';

The legacy source code is in the files timesFixpt.h, and timesS16.c.

% rtwdemo_sfun_gain_fixpt
def = legacy_code('initialize');
def.SFunctionName = 'rtwdemo_sfun_gain_fixpt';
def.OutputFcnSpec = 'myFixpt y1 = timesS16(myFixpt u1, myFixpt p1, uint8 p2)';
def.HeaderFiles   = {'timesFixpt.h'};
def.SourceFiles   = {'timesS16.c'};
def.IncPaths      = {'rtwdemo_lct_src'};
def.SrcPaths      = {'rtwdemo_lct_src'};

Generate an S-Function for Simulation

To generate a C-MEX S-function according to the description provided by the input argument 'def', call the function legacy_code() again with the first input set to 'sfcn_cmex_generate'. The S-function calls the legacy functions in simulation. The source code for the S-function is in the file rtwdemo_sfun_gain_fixpt.c.

legacy_code('sfcn_cmex_generate', def);

Compile the Generated S-Function for Simulation

After you generate the C-MEX S-function source file, to compile the S-function for simulation with Simulink®, call the function legacy_code() again with the first input set to 'compile'.

legacy_code('compile', def);
### Start Compiling rtwdemo_sfun_gain_fixpt
    mex('-compatibleArrayDims', '-I/mathworks/devel/bat/Bdoc16a/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/tmp/Bdoc16a_342494_6186/tpb227ff9c_7457_42c7_ad22_0e13480900da', '-c', '-outdir', '/tmp/Bdoc16a_342494_6186/tp68579236_3fc0_45ed_9891_10e3c291ec29', '/mathworks/devel/bat/Bdoc16a/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src/timesS16.c')
Building with 'gcc'.
MEX completed successfully.
    mex('rtwdemo_sfun_gain_fixpt.c', '-compatibleArrayDims', '-I/mathworks/devel/bat/Bdoc16a/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/tmp/Bdoc16a_342494_6186/tpb227ff9c_7457_42c7_ad22_0e13480900da', '/tmp/Bdoc16a_342494_6186/tp68579236_3fc0_45ed_9891_10e3c291ec29/timesS16.o')
Building with 'gcc'.
MEX completed successfully.
### Finish Compiling rtwdemo_sfun_gain_fixpt
### Exit

Generate a TLC Block File for Code Generation

After you compile the S-function and use it in simulation, you can call the function legacy_code() again with the first input set to 'sfcn_tlc_generate' in order to generate a TLC block file to support code generation through Simulink® Coder™. If the TLC block file is not created and you try to generate code for a model that includes the S-function, code generation fails. The TLC block file for the S-function is: rtwdemo_sfun_gain_fixpt.tlc.

legacy_code('sfcn_tlc_generate', def);

Generate an rtwmakecfg.m File for Code Generation

After you create the TLC block file, you can call the function legacy_code() again with the first input set to 'rtwmakecfg_generate' to generate an rtwmakecfg.m file to support code generation through Simulink® Coder™. If the required source and header files for the S-function are not in the same folder as the S-function, and you want to add these dependencies in the makefile produced during code generation, generate the rtwmakecfg.m file.

legacy_code('rtwmakecfg_generate', def);

Generate a Masked S-Function Block for Calling the Generated S-Function

After you compile the C-MEX S-function source, you can call the function legacy_code() again with the first input set to 'slblock_generate' to generate a masked S-function block that is configured to call that S-function. The software places the block in a new model and it can be copied to an existing model.

% legacy_code('slblock_generate', def);

Show the Generated Integration with Legacy Code

The model rtwdemo_lct_fixpt_params shows integration with the legacy code. The subsystem TestFixpt serves as a harness for the call to the legacy C function via the generated S-function.

open_system('rtwdemo_lct_fixpt_params')
open_system('rtwdemo_lct_fixpt_params/TestFixpt')
sim('rtwdemo_lct_fixpt_params')
Min, max and overflow logging is active on the model <a href="matlab:open_system('rtwdemo_lct_fixpt_params')">rtwdemo_lct_fixpt_params</a>. To see the simulation data that was collected, open <a href="matlab:fxptdlg('rtwdemo_lct_fixpt_params')">Fixed-Point Tool</a>. To learn how to control this setting, refer to the <a href="matlab:helpview(fullfile(docroot,'fixedpoint','fixedpoint.map'), 'minMaxOverflow')">documentation</a>.

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