Memory allocation Issue

Hi

When using the Arm Compiler for Embedded 6 toolchain, you can place a heap in the memory map using a ARM_LIB_HEAP or ARM_LIB_STACKHEAP region in a scatter-file at link-time.  Please see:

https://developer.arm.com/documentation/100073/0623/The-Arm-C-and-C---Libraries/Stack-and-heap-memory-allocation-and-the-Arm-C-and-C---libraries/Stack-pointer-initialization-and-heap-bounds

The heap may be in a separate region from the stack (the "two region memory model"), or the stack & heap may be in a single region ("one region memory model"), for example:

#ifdef TWO_REGION
  ARM_LIB_STACK 0x20006000 EMPTY 0x0800
  {
  }
  ARM_LIB_HEAP  0x20006800 EMPTY 0x0800
  {
  }
#else
  ARM_LIB_STACKHEAP 0x20006000 EMPTY 0x1000
  {
  }
#endif

Note that the heap grows up in memory from its base, and the stack grows down in memory from the initial stack pointer.

Please take a look at the ready-made "startup_Cortex-M7_AC6" example that is provided in Arm DS.  Many of the other examples also show placement of stack & heap in the scatter-file.

Hope this helps

Stephen

Thanks Stephen
It was so helpful.
I will test it and get back to you soon!

Hi again!

I Went through the description and wrote this scatter file

/* Define the entire 256 kB DTCM region */
LR_DTCM 0x20000000 0x00040000 {

/* Execution region for code and read-only data.
Here we reserve 128 kB from 0x20000000 to 0x2001FFFF. */
ER_DTCM 0x20000000 0x00020000 {
*(InRoot$$Sections)
*(.text*)
*(.rodata*)
*(.constdata*)
*(.ARM.Collect*)
*(+RO)
}

/* Execution region for read-write data.
Here we reserve 32 kB from 0x20020000 to 0x20027FFF. */
RW_DTCM 0x20020000 0x00008000 {
*(.data*)
*(.bss*)
*(+RW)
}

/* Define the heap region for dynamic allocations.
This reserve is 64 kB from 0x20028000 to 0x20037FFF. */
ARM_LIB_HEAP 0x20028000 EMPTY 0x00010000 {
/* Heap region: 64 kB available for malloc() */
}

/* Define the stack region.
Here we reserve 32 kB from 0x20038000 to 0x2003FFFF. */
ARM_LIB_STACK 0x20038000 EMPTY 0x00008000 {
/* Stack region: 32 kB */
}
}

Any suggestions if it is the right one to dedicate 64kB of 256kB from DTCM?

Warm regards

Hi again

As a quick test, I added your scatter file above into the "startup_Cortex-M7_AC6" example.  With some tweaks, I was able to get the example basically working.

Note that the default C library itself uses some heap space for things like printf, so your full "samples_size = 1 << 15" didn't quite fit in the heap space, but "samples_size = 1 << 14" did.

I could see a malloc call executing & returning correctly, with "out" being 0x20028060, which looks correct.  
That's 0x20028000 (your heap base) plus 0x60 bytes of C library private workspace.

Stephen

Thank you Stephen
It was a great help!
The issue is resolved.

Hi again!

I have sort of a small question.
I have created this scatter file in my C project in ARM DS.

The question is when I go to my CMSIS project, can I use the same scatter file, or any changes and modifications should be made on that?

And in my file, both stack and heap are created in DTCM. Shall I define ITCM statically in the same scatter file as well?

regards

CMSIS Packs typically provide referenc scatter files for the device used, but you can of course edit as appropriate, for example to locate the stack/heap in the DTCM rather than general memory.

Hi

Thank you Ronan and Stephen for providing me the insights, now I changed the scatter file in a way that my code can use the resources in an optimized way!

Warm regards
Mehran