How to Share Buffer Between C Function Code (C Caller, C Function, S Functions)?

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Hi, a little bit of context about what I'm trying to achieve.
I have a shared list of objects that needs to be accessed by multiple C functions (for example Insert, Remove, Get at X index, etc). I tried to make this work using C Caller blocks, but the behaviour I am observing is that each C Caller block has its own list even though it is static and declared globally in a shared header.
So I am trying to share the state of some variables between multiple C functions. I read about S Functions, C Functions block and C Caller block, but I haven't found a clear way to do it. Work vectors look interesting, but they don't seem to be supporting complex types like structures.
Thank you very much for your time.

Respuestas (2)

Pratyush
Pratyush el 31 de Jul. de 2023
I understand that you are looking to share the state of variables between multiple C functions in MATLAB, one possible solution is to use the S-Function block.
To share complex types like structures between multiple C functions, you can use pointers. Here's a general outline of how you can achieve this:
1. Create a structure that represents your list of objects in MATLAB. For example:
% MATLAB code
list = struct('objects', cell(1, N));
2. Write a C function that takes a pointer to the list structure as an argument and performs the desired operations (insert, remove, etc.). This function should be declared as an external function in MATLAB.
/* C code */
void modifyList(struct List* list) {
// Perform operations on the list
}
3. Create an S-Function block in Simulink and write the C code that implements the desired functionality. You can use the S-Function template provided by MATLAB as a starting point.
4. In the S-Function code, include the header file that defines the structure and the C function. Then, declare a pointer to the list structure and pass it to the C function.
/* S-Function code */
#include "list.h"
void mdlInitializeSizes(SimStruct *S) {
// ...
}
void mdlStart(SimStruct *S) {
// Allocate memory for the list structure
struct List* list = malloc(sizeof(struct List));
// Pass the pointer to the C function
modifyList(list);
// ...
}
void mdlOutputs(SimStruct *S, int_T tid) {
// ...
}
void mdlTerminate(SimStruct *S) {
// Free the memory allocated for the list structure
free(list);
}
5. Build the S-Function and use it in your Simulink model. The S-Function block will have access to the shared list structure, and you can perform operations on it using the C functions.
Note that this approach requires you to manually manage memory allocation and deallocation for the list structure.

Roy Mathew
Roy Mathew el 3 de Ag. de 2023
For the C caller block, if you are using a shared header to specify static globals, the objects would be shared by all C Callers and C Function blocks in the same model.
If you are using C Caller blocks in multiple models and would like to share the same headers, you can use a Simulink Library model and specify the Headers/Sources in Modeling->Simulation Custom Code setting. All the C callers can be defined in the library model. The C caller blocks in the library can then be used across multiple models by creating links and the global data would be shared.
This page has an example that uses C Caller blocks from a library model.
https://www.mathworks.com/help/simulink/slref/bring-custom-image-filter-algorithms-as-reusable-blocks-in-simulink.html

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