How can S-function builder work with fixed point inputs and outputs?

Hi,

I'm using MATLAB R2017a with Windows 10 64 bits. The compiler installed in the computer is MinGW64 Compiler. Then, my objective is to use S-function builder with inputs and outputs as fixed point variables. I want to use the different functions compiled in the libfixedpoint.lib library as, for example, trigonometric functions.

The data type of input u0 and output y0 are defined as fixed-point binary point scaling with the word length as 32 bits and the fraction length as 21 bits. The output code is very simple: y0[0] = u0[0]. When I click the Build bottom the next message appears: "gcc:error:libfixedpoint.lib: No such file or directory"

In the Libraries pane I have wrotten the next command (inside the Library/Object/Source files (one per line) window): LIB_PATH C:\Program Files\MATLAB\R2017a\extern\lib\win64\microsoft\libfixedpoint.lib. But I look for this file in the computer and the path it is correct.

Finally, which is the procedure to configure the S-function builder block working with Fixed-Point Variables?

Answer 1

[Gillian Rosen]

Hi Carlos,

  I understand that you are creating an S-Function using the S-Function Builder block with fixed-point inputs and outputs. You are getting an error when you try to build that the 'libfixedpoint.lib' library cannot be found, and you would like to know what you need for configuring the S-function builder to use fixed-point variables. 

For the build error, the following troubleshooting questions may help narrow down the issue: 

1. Are you able to include other libraries from this folder?

2. Are you able to include libraries from other locations, such as your current folder?  

3. Are you able to include source/object files without error? 

When you set the data types of the input and output to a fixed-point type, the S-Function builder will automatically add the appropriate #include directories for working with fixed-point variables to the generated S-Function. You can open the generated S-Function file and see that they have been added as indicated in the following documentation page: 

https://www.mathworks.com/help/fixedpoint/ug/structure-of-the-s-function.html

[Carlos Miguel Espinar]

Hi Gillian,

I have solved the problem changing the MATLAB version. Initially, I was using MATLAB 2017a for 64-bits Windows version. Now, I have updated to MATLAB 2017b for 64-bits Windows. Then, I can declare fixed-point inputs and outputs variables in the S-function builder and the block compiles correctly.

Then, the next step is to use math functions as sin, cos, etc., with fixed-point variables inside the S-functions builder block and, also, declaring in the Outputs tab a new local variable as fixed-point type.

Which is the language I should use to do it? My purpose is to emulate control algorithms that I will, posteriorly, implement in a DSP with fixed-point variables,

[Gillian Rosen]

The S-Function Builder block is only able to create C-MEX S-Functions, so you will need to use C code inside this block.