SMT32CubeIDE - How to store a const struct at a specific flash memory address?

[ERODR.1]

I'm trying to store a const struct at a specific flash memory location using the STM32CubeIDE. I tried appending the __attribute__((at(address))) to the struct initialization, but the compiler ignores it: "warning: 'at' attribute directive ignored [-Wattributes]"

const runtimeParams params __attribute__((at(0x0801F800))) = {
  // ... initialization values
};

What would be the correct way to accomplish this?

[TDK · Accepted solution]

There's not an easy way to do this in GCC. You either need to create a separate section in the linker to place the code, or use a pointer to store it somewhere directly while ensuring nothing else lives in that space.

[ERODR.1]

Thanks for your input. I created a new section in the linker as suggested.

[ERODR.1]

For anybody else wondering how to do it. I edited the STM32F072CBTX_FLASH.ld to add a new section as below:

  /* Runtime parameters section in FLASH */
  _params_start_address = 0x0801F800;
  
  .params _params_start_address :
  {
    . = ALIGN(4);
    KEEP (*(.params))
  } >FLASH

And then specified the section attribute in the const initialization as follows:

const runtimeParams __attribute__((section (".params"))) params = {
  // ... Initialization values
};

[rohittheozzy]

This creates an overlap with the .rodata for stm32f030, how do you get around this?

MEMORY
{
  RAM    (xrw)    : ORIGIN = 0x20000000,   LENGTH = 8K
  FLASH    (rx)    : ORIGIN = 0x8000000,   LENGTH = 64K
}

[gbm]

MEMORY
{
  RAM    (xrw)    : ORIGIN = 0x20000000,   LENGTH = 8K
  FLASH    (rx)    : ORIGIN = 0x8000000,   LENGTH = 64K
  PARAMFLASH (rx) : ORIGIN = 0x801F800,   LENGTH = 2K
}

.params _params_start_address :
  {
    . = ALIGN(4);
    KEEP (*(.params))
  } >PARAMFLASH

This should be one step closer to what you want to achieve.

I assume however, that you want to keep the config data when flashing a new program. If this is the case, don't declare the structure as const, just make sure that the address is unused (outside of MEMORY ranges), then do this:

#define cfg_in_Flash (*(const struct cfgdata_ *)(CFG_ADDRESS))

[rohittheozzy]

Thank you, actually my flash is only 64K and the setting area that I want to allocate is 1K. Now this setting area needs to be at a perticular location in the flash. I am able to compile the whole thing now with at attribute. But it doesn't place the setting block in the correct location. I just need to keep the block in correct position. Is it possible to do it without changing the code area?

[gbm]

Use the 2nd solution above, just make sure that your code ends before CFG_ADDRESS.

If you use real STM32F103C8T6, you may store the data at 0x801f800 - end of 128 KiB Flash.