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

Integrate legacy C functions that pass their inputs and outputs by using parameters of a fixed-point data type with the Legacy Code Tool.

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.

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 prototype of the legacy functions being called in this example is:

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

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 during 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('-I/mathworks/devel/bat/Bdoc17a/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/tmp/Bdoc17a_538369_144755/publish_examples2/tp336cbbfe/ex05928773', '-c', '-outdir', '/tmp/Bdoc17a_538369_144755/publish_examples2/tp489e90fb_3aa3_4270_9db5_fd18ec1f7f58', '/mathworks/devel/bat/Bdoc17a/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src/timesS16.c')
Building with 'gcc'.
MEX completed successfully.
    mex('rtwdemo_sfun_gain_fixpt.c', '-I/mathworks/devel/bat/Bdoc17a/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/tmp/Bdoc17a_538369_144755/publish_examples2/tp336cbbfe/ex05928773', '/tmp/Bdoc17a_538369_144755/publish_examples2/tp489e90fb_3aa3_4270_9db5_fd18ec1f7f58/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. Set the first input to 'sfcn_tlc_generate' to generate a TLC block file. The block file specifies how the generated code for a model calls the legacy code. If you do not generate a TLC block file 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. Set the first input to 'rtwmakecfg_generate' to generate an rtwmakecfg.m file that supports code generation. 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. Set the first input to 'slblock_generate' to generate a masked S-function block that calls that S-function. The software places the block in a new model. You can copy the block to an existing model.

legacy_code('slblock_generate', def);

Show the Generated Integration with Legacy Code

The model rtwdemo_lct_fixpt_params shows integration of the model 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')

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