MATLAB Examples

Integrate External C Functions That Pass Input Arguments By Value Versus Address

This example shows how to use the Legacy Code Tool to integrate legacy C functions that pass their input arguments by value versus address.

With the Legacy Code Tool, you can:

  • Provide the legacy function specification.
  • Generate a C-MEX S-function that calls the legacy code during simulation.
  • Compile and build the generated S-function for simulation.
  • Generate a TLC block file and optional rtwmakecfg.m file that specifies how the generated code for a model calls the legacy code.

Contents

Provide the Legacy Function Specification

Legacy Code Tool functions take a specific data structure or array of structures as the argument. You can initialize the data structure 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 prototypes of the legacy functions being called in this example are:

  • FLT filterV1(const FLT signal, const FLT prevSignal, const FLT gain)
  • FLT filterV2(const FLT* signal, const FLT prevSignal, const FLT gain)

FLT is a typedef to float. The legacy source code is in the files your_types.h, myfilter.h, filterV1.c, and filterV2.c.

Note the difference in the OutputFcnSpec defined in the two structures; the first case specifies that the first input argument is passed by value, while the second case specifies pass by pointer.

defs = [];

% rtwdemo_sfun_filterV1
def = legacy_code('initialize');
def.SFunctionName = 'rtwdemo_sfun_filterV1';
def.OutputFcnSpec = 'single y1 = filterV1(single u1, single u2, single p1)';
def.HeaderFiles   = {'myfilter.h'};
def.SourceFiles   = {'filterV1.c'};
def.IncPaths      = {'rtwdemo_lct_src'};
def.SrcPaths      = {'rtwdemo_lct_src'};
defs = [defs; def];

% rtwdemo_sfun_filterV2
def = legacy_code('initialize');
def.SFunctionName = 'rtwdemo_sfun_filterV2';
def.OutputFcnSpec = 'single y1 = filterV2(single u1[1], single u2, single p1)';
def.HeaderFiles   = {'myfilter.h'};
def.SourceFiles   = {'filterV2.c'};
def.IncPaths      = {'rtwdemo_lct_src'};
def.SrcPaths      = {'rtwdemo_lct_src'};
defs = [defs; def];

Generate S-Functions for Simulation

To generate C-MEX S-functions according to the description provided by the input argument 'defs', call the function legacy_code() again with the first input set to 'sfcn_cmex_generate'. The S-functions call the legacy functions in simulation. The source code for the S-functions is in the files rtwdemo_sfun_filterV1.c and rtwdemo_sfun_filterV2.c.

legacy_code('sfcn_cmex_generate', defs);

Compile the Generated S-Functions for Simulation

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

legacy_code('compile', defs);
### Start Compiling rtwdemo_sfun_filterV1
    mex('-I/mathworks/devel/bat/Bdoc17b/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/private/tmp/Bdoc17b_685977_71560/publish_examples7/tp77ae8b45/ex19632214', '-c', '-outdir', '/private/tmp/Bdoc17b_685977_71560/publish_examples7/tp6288f0f0_72a8_4caf_98d5_1a462d3f3170', '/mathworks/devel/bat/Bdoc17b/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src/filterV1.c')
Building with 'Xcode with Clang'.
MEX completed successfully.
    mex('rtwdemo_sfun_filterV1.c', '-I/mathworks/devel/bat/Bdoc17b/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/private/tmp/Bdoc17b_685977_71560/publish_examples7/tp77ae8b45/ex19632214', '/private/tmp/Bdoc17b_685977_71560/publish_examples7/tp6288f0f0_72a8_4caf_98d5_1a462d3f3170/filterV1.o')
Building with 'Xcode with Clang'.
MEX completed successfully.
### Finish Compiling rtwdemo_sfun_filterV1
### Exit

### Start Compiling rtwdemo_sfun_filterV2
    mex('-I/mathworks/devel/bat/Bdoc17b/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/private/tmp/Bdoc17b_685977_71560/publish_examples7/tp77ae8b45/ex19632214', '-c', '-outdir', '/private/tmp/Bdoc17b_685977_71560/publish_examples7/tpa2040570_7ccd_4f14_8f6c_f5e8cb023666', '/mathworks/devel/bat/Bdoc17b/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src/filterV2.c')
Building with 'Xcode with Clang'.
MEX completed successfully.
    mex('rtwdemo_sfun_filterV2.c', '-I/mathworks/devel/bat/Bdoc17b/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/private/tmp/Bdoc17b_685977_71560/publish_examples7/tp77ae8b45/ex19632214', '/private/tmp/Bdoc17b_685977_71560/publish_examples7/tpa2040570_7ccd_4f14_8f6c_f5e8cb023666/filterV2.o')
Building with 'Xcode with Clang'.
MEX completed successfully.
### Finish Compiling rtwdemo_sfun_filterV2
### Exit

Generate TLC Block Files for Code Generation

After you compile the S-functions and use them in simulation, you can call the function legacy_code() again with the first input set to 'sfcn_tlc_generate' to generate TLC block files. Block files specify how the generated code for a model calls the legacy code. If you do not generate TLC block files and you try to generate code for a model that includes the S-functions, code generation fails. The TLC block files for the S-functions are rtwdemo_sfun_filterV1.tlc and rtwdemo_sfun_filterV2.tlc.

legacy_code('sfcn_tlc_generate', defs);

Generate an rtwmakecfg.m File for Code Generation

After you create the TLC block files, 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. If the required source and header files for the S-functions are not in the same folder as the S-functions, and you want to add these dependencies in the makefile produced during code generation, generate the rtwmakecfg.m file.

legacy_code('rtwmakecfg_generate', defs);

Generate Masked S-Function Blocks for Calling the Generated S-Functions

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 masked S-function blocks that call the S-functions. The software places the blocks in a new model. From there you can copy them to an existing model.

legacy_code('slblock_generate', defs);

Show the Generated Integration with Legacy Code

The model rtwdemo_lct_filter shows integration of the model with the legacy code. The subsystem TestFilter serves as a harness for the calls to the legacy C functions via the generate S-functions, with unit delays serving to store the previous output values.

open_system('rtwdemo_lct_filter')
open_system('rtwdemo_lct_filter/TestFilter')
sim('rtwdemo_lct_filter')