How to declare a struct in CCM

The warning clearly tells you what's the problem: you can use the section attribute only when you declare variables, not when you create types. In other words, declaring a type (a struct tag here) only tells the compiler, what the variable looks like, not where variables of that type are going to be located, nor how many of them will be defined. OTOH if you define variable of whatever type, you tell the compiler to allocate a space in memory for that variable, so that's the right time to tell the compiler where exactly to allocate that space (normally you tell nothing and the compiler allocates it into its default space).

Nor does a pointer - either a pointer variable or a pointer type - define, where is the pointed-to object allocated, so defining pointers is not a way to tell the allocation of the pointed-to objects (you can allocate a pointer variable itself, though)

Declare a variable of struct Assign_Pot type and give it a section attribute.

JW

Normally the default linker configuration file (say IAR) would put the stack in the CCM if available.

As such, all local variables (struct based) declared inside a function should end up in the CCM, so developers benefits from it right away.

The main difference between main RAM and CCM is when lots of DMA transfer is going on.

DMA will take CPU cycles to read/write the main RAM. If using USB HS, SPI DMA, ADC/DAC DMA, then frequently accessed variables (or pointers) might be worth going to the CCM memory. Naturally, DMA accessed variables shouldn't be moved in the CCM. The lower the core frequency (on battery budget?) the more of a difference it could make.

Hope this help!

Thanks a lot for all your tips!

type and give it a section attribute, for example:

Assign_Pot* Assign_Tab[100] __attribute__ ((section('.ccm')));

It will only declare the 100

pointer in the CCM, not all the variables inside the structure, isn't it?