Inputs Passed by Value or Address to Legacy Functions

Open Model

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

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

Providing 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, you have to assign its properties to values corresponding to the legacy code being integrated. 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)

where FLT is a typedef to float. The legacy source code is found 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 = [];

% sldemo_sfun_filterV1
def = legacy_code('initialize');
def.SFunctionName = 'sldemo_sfun_filterV1';
def.OutputFcnSpec = 'single y1 = filterV1(single u1, single u2, single p1)';
def.HeaderFiles   = {'myfilter.h'};
def.SourceFiles   = {'filterV1.c'};
def.IncPaths      = {'sldemo_lct_src'};
def.SrcPaths      = {'sldemo_lct_src'};
defs = [defs; def];

% sldemo_sfun_filterV2
def = legacy_code('initialize');
def.SFunctionName = 'sldemo_sfun_filterV2';
def.OutputFcnSpec = 'single y1 = filterV2(single u1[1], single u2, single p1)';
def.HeaderFiles   = {'myfilter.h'};
def.SourceFiles   = {'filterV2.c'};
def.IncPaths      = {'sldemo_lct_src'};
def.SrcPaths      = {'sldemo_lct_src'};
defs = [defs; def];

Generating and Compiling an S-Function for Use During Simulation

The function legacy_code() is called again with the first input set to generate_for_sim in order to automatically generate and compile the C-MEX S-function according to the description provided by the input argument defs. This S-function is used to call the legacy functions in simulation. The source code for the S-function is found in the files sldemo_sfun_filterV1.c and sldemo_sfun_filterV2.c.

legacy_code('generate_for_sim', defs);

### Start Compiling sldemo_sfun_filterV1
    mex('-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368/sldemo_lct_src', '-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368', '-c', '-outdir', '/tmp/Bdoc24a_2528353_1244492/tp0a45c7d9_1390_49e4_8b04_8ab6373adcbf', '/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368/sldemo_lct_src/filterV1.c')
Building with 'gcc'.
MEX completed successfully.
    mex('sldemo_sfun_filterV1.c', '-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368/sldemo_lct_src', '-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368', '/tmp/Bdoc24a_2528353_1244492/tp0a45c7d9_1390_49e4_8b04_8ab6373adcbf/filterV1.o')
Building with 'gcc'.
MEX completed successfully.
### Finish Compiling sldemo_sfun_filterV1
### Exit

### Start Compiling sldemo_sfun_filterV2
    mex('-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368/sldemo_lct_src', '-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368', '-c', '-outdir', '/tmp/Bdoc24a_2528353_1244492/tp4b25f2e9_ce70_4e78_911a_3a5680f2b021', '/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368/sldemo_lct_src/filterV2.c')
Building with 'gcc'.
MEX completed successfully.
    mex('sldemo_sfun_filterV2.c', '-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368/sldemo_lct_src', '-I/tmp/Bdoc24a_2528353_1244492/tp39b65575/simulink_features-ex08075368', '/tmp/Bdoc24a_2528353_1244492/tp4b25f2e9_ce70_4e78_911a_3a5680f2b021/filterV2.o')
Building with 'gcc'.
MEX completed successfully.
### Finish Compiling sldemo_sfun_filterV2
### Exit

Generating an `rtwmakecfg.m` File for Code Generation

After the TLC block file is created, the function legacy_code() can be called again with the first input set to rtwmakecfg_generate in order to generate an rtwmakecfg.m file to support code generation through Simulink® Coder™. Generate the rtwmakecfg.m file if the required source and header files for the S-functions are not in the same directory as the S-functions, and you want to add these dependencies in the makefile produced during code generation.

Note: Complete this step only if you are going to simulate the model in accelerated mode.

legacy_code('rtwmakecfg_generate', def);

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

After the C-MEX S-function source is compiled, the function legacy_code() can be called again with the first input set to slblock_generate in order to generate masked S-function blocks which are configured to call those S-functions. The blocks are placed in a new model and can be copied to an existing model.

legacy_code('slblock_generate', defs);

Integrate the Legacy Code

The model sldemo_lct_filter shows integration 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('sldemo_lct_filter')
open_system('sldemo_lct_filter/TestFilter')
sim('sldemo_lct_filter');