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Fixed Point Parameters

This example shows you how to use the Legacy Code Tool to integrate legacy C functions that pass their inputs and outputs 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, and

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

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. For detailed help on the properties, call legacy_code('help')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 found in the files timesFixpt.htimesFixpt.h, and timesS16.ctimesS16.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'};

Generating an S-Function for Use During Simulation

The function legacy_code() is called again with the first input set to 'sfcn_cmex_generate' in order to automatically generate a C-MEX S-function according to the description provided by the input argument 'def'. This S-function is used to call the legacy functions in simulation. The source code for the S-function is found in the file rtwdemo_sfun_gain_fixpt.crtwdemo_sfun_gain_fixpt.c.

legacy_code('sfcn_cmex_generate', def);

Compiling the Generated S-Function for Simulation

After the C-MEX S-function source file is generated, the function legacy_code() is called again with the first input set to 'compile' in order to compile the S-function for simulation with Simulink®.

legacy_code('compile', def);
### Start Compiling rtwdemo_sfun_gain_fixpt
    mex('-I/mathworks/devel/bat/BR2014bd/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/tmp/BR2014bd_145981_71764/tp4158f466_f880_4d13_8860_84bec2a1c213', '-c', '-outdir', '/tmp/BR2014bd_145981_71764/tpeb3c4214_3fa6_4d48_8179_556cc60d476a', '/mathworks/devel/bat/BR2014bd/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/BR2014bd/build/matlab/toolbox/rtw/rtwdemos/rtwdemo_lct_src', '-I/tmp/BR2014bd_145981_71764/tp4158f466_f880_4d13_8860_84bec2a1c213', '/tmp/BR2014bd_145981_71764/tpeb3c4214_3fa6_4d48_8179_556cc60d476a/timesS16.o')
Building with 'gcc'.
MEX completed successfully.
### Finish Compiling rtwdemo_sfun_gain_fixpt
### Exit

Generating a TLC Block File for Code Generation

After the S-function is compiled and used in simulation, the function legacy_code() can be called 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™. Code generation will fail if the TLC block file is not created and you try to generate code for a model that includes the S-function. The TLC block file for the S-function is: rtwdemo_sfun_gain_fixpt.tlcrtwdemo_sfun_gain_fixpt.tlc.

legacy_code('sfcn_tlc_generate', def);

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.

legacy_code('rtwmakecfg_generate', def);

Generating a masked S-Function block for calling the generated S-Function

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 a masked S-function block that is configured to call that S-function. The block is placed in a new model and can be copied to an existing model.

% legacy_code('slblock_generate', def);

Showing the Generated Integration with Legacy Code

The model rtwdemo_lct_fixpt_paramsrtwdemo_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')

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