Simulink coder packed structs

Hello, is there a way to have the Simulink autocoder turn bus objects into packed structs (byte alignment=1)? E.g., the struct definition might look like:

struct __attribute__((__packed__)) mystruct_A {
    char a;
    int b;
    char c;
};

Thanks!

[John]

@David Did you ever figure out how to do this?

Answer 1

[Mark McBroom]

See the "Alignment" property for Simulink.Bus elements defined here: https://www.mathworks.com/help/simulink/slref/simulink.bus.html

Thanks.

Mark.

[Amin]

The Alignment property of Simulink.Bus does not make the generated C struct packed (byte-aligned). It only controls the alignment of the bus as a whole in memory, not the internal layout of its elements.

For example, even with Alignment = 1, the generated code is still of the form:

typedef struct {
real32_T a;
uint16_T b;
uint8_T  c;
} MyStruct;

and the compiler may still insert padding between fields.

So this does not produce:

typedef struct __attribute__((__packed__)) {
...
    } MyStruct;

As far as I understand, to achieve a truly packed layout with Simulink Coder, the only robust approaches are:

1. Define the struct manually in a header with __attribute__((__packed__)) and set the bus to Imported, or
2. Accept the generated struct layout and design the binary data to match the compiler’s padding.

If there is a way to force packed structs directly from Simulink Coder (e.g., via configuration or TLC), I would be very interested to know.