Posted by MSchultz on 2017-06-15 02:43

Before I go on to give advice here, let me state for the record that i’ve never tried to do with an ARM core device and GCC what you’re describing here, but I’m familiar in a general sense with the concept of placing a section of code that is “loaded” in ROM/FLASH and then copied/relocated to RAM, and have done this with different toolchains and MCUs other than the STM32.

I think you have the linker script syntax correct - in particular, the bit at the end of the .itcm_text section declaration (>ITCM_RAM AT >FLASH) is critical. You want to make sure that your itcm-destined code is loaded into ROM (flash), but is located in ITCM_RAM.

I think what you’re looking for is the appropriate attribute syntax that you add to all functions that you want placed in a non-standard section. Here’s what it would look like:

int foo(int bar) __attribute__((section(".itcm_text")))
{
    // Code
}

You’ll need to add the attribute directive shown in the example above to each function or variable declaration that you want to have placed in the .itcm_text section.

You might want to modify your linker command file to add some symbol definitions that will make it easier for your code to find (and copy) the .itcm_text section to ITCM_RAM

.itcm_text :
{
. = ALIGN(4);
itcm_text_start = .;
*(.itcm_text) /* Fast-executing code */
*(.itcm_text*) /* Fast-executing code */
. = ALIGN(4);
itcm_text_end = .;
} >ITCM_RAM AT >FLASH

When it comes time to copy the ITCM code in ROM to ITCM_RAM, you should be able to do something like this:

// The "variables" referenced here don't actually contain anything meaningful - they are defined as symbols
// within the linker script. To extract the value assigned to each of these symbols, you need to take the
// address-of them (use the & address-of operator); e.g.:
// unsigned int section_start = (unsigned int) &itcm_text_start;

extern const unsigned char itcm_text_start;	// Make these uint8_t/char so they are treated as byte pointers when address-of'ed
extern const unsigned char itcm_text_end;

unsigned int itcm_text_size = (unsigned int) (&itcm_text_end - &itcm_text_start); // Pointer math should will work if these are declared as a char/byte type
unsigned char *itcm_ram_addr = ??? // Fill this in - could also get it from linker symbol if you add one
memcpy(itcm_ram_addr, &itcm_text_start, itcm_text_size);

Caveat: I’ve written the above “off the cuff” after doing a little research - I’ve not actually tried or tested any of it. I’ve probably got one or more of the details wrong. I may need to do something like this in one of my own projects I’ll be working on soon so I figured I’d start to research it now and possibly answer laltmann’s question at the same time.