Electronic – How to validate that a function is executing from RAM

functionram

I'm trying to execute a control function as quickly as possible from SRAM on an STM32F3xx using GCC (System Workbench toolchain).

__attribute__((ramfunc)) f1(void) {
  // Set GPIO pin
  // Do something that is faster from RAM
  // Clear GPIO pin
}

void f2(void) {
  // Set GPIO pin
  // Do something that is faster from RAM
  // Clear GPIO pin
}

How can I check to make sure that it is actually executing from RAM? Will printing its address tell me the flash location or the RAM location?

printf("f1 address = 0x%p\n", f1);
printf("f2 address = 0x%p\n", f2);

Is there an operation that will have an extremely different timing behavior if I measure it with an oscilloscope that I can compare?

f1();
f2();

From the output.map file:

.text.f1       0x0000000008007470       0x18 src/controller.o
.text.f2       0x0000000008007488       0x18 src/controller.o

From the log:

f1 address = 0x0x8007471
f2 address = 0x0x8007489

Relevant links:

http://www.openstm32.org/forumthread5894

https://www.silabs.com/community/mcu/32-bit/forum.topic.html/how_can_i_executeco-6Zv7

Excerpt from LinkerScript.ld file showing my added ramfunc section that doesn't seem to be enough:

/* Initialized data sections goes into RAM, load LMA copy after code */
  .data : 
  {
    . = ALIGN(4);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */
    *(.ramfunc)        /* .ramfunc sections */
    . = ALIGN(4);
    _edata = .;        /* define a global symbol at data end */
  } >RAM AT> FLASH

Best Answer

Wow, OK, thanks for clarifying where RAM starts on this device, Chris Stratton.

It looks like I finally proved that it can work on a more isolated project.

Control experiment:

f1 address = 0x0x8003161
f2 address = 0x0x8003179

After qualifying the function signature:

__attribute__ ((section (".ramfunc"))) void f1(void) {
...
}

I get log line:

f1 address = 0x0x200009b9
f2 address = 0x0x8003161

Note that this required adding the .ramfunc line to the linker script:

/* Initialized data sections goes into RAM, load LMA copy after code */
  .data : 
  {
    . = ALIGN(4);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */
    *(.ramfunc)        /* .ramfunc sections */
    . = ALIGN(4);
    _edata = .;        /* define a global symbol at data end */
  } >RAM AT> FLASH

To directly answer the original question, yes, you should be able to print the address of the function and see that it is in a different region OR check the .map file OR use the debugger to check this address.

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