Stack initialization with constant

There's a caveat. Although it works as I step through the assembler ... as soon as the program jumps to main the STACK gets overwritten and cleared to zero despite its AREA being marked NOINIT. Please does anyone have any idea why this happens and how to stop it?

There's a caveat. Although it works as I step through the assembler ... as soon as the program jumps to main the STACK gets overwritten and cleared to zero despite its AREA being marked NOINIT. Please does anyone have any idea why this happens and how to stop it?

Hmmm.

The area gets cleared by the scatter loader (executed between startup and entry to main).

This is where I have previously started using a slightly more complex scatter file. Using an UNINIT section for the segment that I din't want to be touched by the scatter loader.

OK. Thanks for the hint. I see the project's scatter file *.sct in \Obj\ folder and that I can specify a different one by unchecking the target Options/Linker/Use Memory Layout from Target Dialog checkbox.

So how do I get the STACK into an UNINIT'd section please? ... or where can I find instructions to make a new scatter file?

Sorry, I don't have much time now ... but here's a scatter file I've modified from one of the Blinky examples. I gave it a quick try and the stack is not now being cleared.

In the IDE, select this one (or the one that you'll modify accordingly).

LR_ROM1 0x00000000 0x04000000  {    ; load region size_region
  ER_ROM1 0x00000000 0x04000000  {  ; load address = execution address
   *.o (RESET, +First)
   *(InRoot$$Sections)
   .ANY (+RO)
  }

  RW_RAM1 0x20000000 0x00400000  {  ; RW data
   .ANY (+RW +ZI)
  }

  RW_STACK +0 UNINIT ALIGN 16       ; RW data - Stack <<< THIS SECTION IS WHAT I ADDED
  {
    *.o (Stack)
  }
}

Thanks very much for your generous help. It appears to work now as you described with the stack left full of 0xcccccccc.

Hi John,

Why modify the scatter file?
It's not easy to put the code in the stack initalisation?
The ram is initialized before.

__user_initial_stackheap

                 LDR     R0, =Stack_Mem            ; Test stack
                 LDR     R1, =Stack_Size           ;
                 LDR     R2, =0xCCCCCCCC           ;
Fill             STR     R2, [R0], #4              ;
                 SUBS    R1,#4                     ;
                 BNE     Fill                      ;


                LDR     R0, =  Heap_Mem
                LDR     R1, =(Stack_Mem + Stack_Size)
                LDR     R2, = (Heap_Mem +  Heap_Size)
                LDR     R3, = Stack_Mem
                BX      LR

                ALIGN

thank you for your thread, it helped me a lot.