__user_initial_stackheap()

Define one special execution region in your scatter‑loading description file, ARM_LIB_STACKHEAP. This region has the EMPTY attribute.

This causes the library to select an implementation of __user_initial_stackheap() that uses this as the combined heap/stack region. This uses the value of the symbols Image$$ARM_LIB_STACKHEAP$$Base and Image$$ARM_LIB_STACKHEAP$$ZI$$Limit.

Define two special execution regions in your scatter‑loading description file, ARM_LIB_HEAP and ARM_LIB_STACK. Both regions have the EMPTY attribute.

This causes the library to select an implementation of __user_initial_stackheap() that uses the value of the symbols Image$$ARM_LIB_HEAP$$Base, Image$$ARM_LIB_HEAP$$ZI$$Limit, Image$$ARM_LIB_STACK$$Base, and Image$$ARM_LIB_STACK$$ZI$$Limit.

An example scatter‑loading description file to define both ARM_LIB_HEAP and ARM_LIB_STACK is shown in Example 2.23.

FLASH_LOAD 0x0000 0x00200000
{
  VECTORS +0 0x400
  {
    * (:gdef:__vectab_stack_and_reset, +FIRST)
    ; Additional region for other vectors would be added here
  }

  ;; Maximum of 256 exceptions (256*4bytes == 1024 == 0x400)
  CODE 0x400 FIXED
  {
    * (+RO)
  }

  DATA 0x20000000 0x00200000
  {
    * (+RW, +ZI)
  }

  ;; Heap starts at 1MB and grows upwards
  ARM_LIB_HEAP 0x20100000 EMPTY 0x100000‑0x8000
  {
  }

  ;; Stack space starts at the end of the 2MB of RAM
  ;; And grows downwards for 32KB
  ARM_LIB_STACK 0x20200000 EMPTY ‑0x8000
  {
  }
}

In Example 2.23, __vectab_stack_and_reset is a special library section that provides a convenient way for the initial values of sp and pc to be placed in the vector table starting at address 0 for Cortex‑M3 embedded applications. sp is initialized appropriately from either ARM_LIB_STACKHEAP (for the one‑region model) or ARM_LIB_STACK (for the two‑region model).

If you use a scatter file but do not specify any special region names and do not re‑implement __user_initial_stackheap(), the library generates an error message.