Matlab with external C function: coder.ceval pass a pointer to a structure (including arrays) to a external function

Hello,

I kinda want to do a similar thing as here , exept that the structure I want to pass includes vectors or arrays. Therefore the code is not working.

In general I try to write a driver block for Simulink for UART communication for a raspberry pi with a Matlab System. The UART code is working fine.

In my System code I create a struct and fill it with the inputs of the System. Now I want to pass a pointer to that struct to my extern send function (with some other arguments).

Here is the Code:

    toFluco_struct = struct('velocity',u1,'heading',u2);    

            coder.cinclude('piData.h');
            coder.cstructname(toFluco_struct, 'piData_toFluco_t', 'extern');

            coder.ceval('pidata_send', obj.fd, obj.packetID, coder.ref(piData_toFluco), obj.size);

piData.h

typedef struct { float velocity [3]; float heading [5]; } piData_toFluco_t;

void pidata_send(int uartsocket, uint8_t packet_id, piData_toFluco_t* packet_ptr, uint8_t size);

piData.c

    void pidata_send(int uartsocket, uint8_t packet_id, piData_toFluco_t* packet_ptr, uint8_t size){
uart_send(uartsocket, "\xff\xff\xff\xff", 4);       // Start-Byte
    uart_send(uartsocket, &packet_id, 1);               //Packet ID senden
uart_send(uartsocket, packet_ptr, size);            //Payload senden

I'm getting the following error message when compiling:

    Simulink detected an error 'coder.ref may only be applied to an expression of type V or V(E) where V is a variable and E is a numeric expression.'.

I would appreciate any help

Cheers Michael

Answer 1

[Akshat Dalal]

Hi Michael,

The error message you're encountering suggests that the coder.ref function is being used incorrectly. This function requires a variable, not an expression or a temporary value, as its argument. You will have to create a variable of the new struct type and then pass it as an argument to coder.ref. Here is how the updated code might look:

coder.cstructname(toFluco_struct, 'piData_toFluco_t', 'extern');

piData_toFluco = toFluco_struct; % Create a variable to hold the structure

coder.ceval('pidata_send', obj.fd, obj.packetID, coder.ref(piData_toFluco), obj.size); % Call the external C function

Hope this helps!