[En-Nut-Discussion] How to determin size of RAM

[Ulrich Prinz]

Hi!

Is there someone who knows how to figure out the RAM memory size 
automatically?

For configuration of Nut/OS I need the available Heap. The start of the 
heap is pretty easy, as it is behind the last var in .bss segment or 
behind the stacks. For convenience a __heap_start token is added.
Fine, but how to find out about the end of the RAM?

Existing solution is to set NUT_MEMSTART and NUT_MEMSIZE manually in 
nutconf. If you omit one of them, calculation goes wrong. Dangerous!

With this piece of code the initial calculation for the heap is done:

/*!
* \brief Last memory address.
*/
#define NUTMEM_END (uptr_t)(NUTMEM_START + NUTMEM_SIZE - 1U)
extern void *__heap_start;

#define HEAP_START  &__heap_start
#define HEAP_SIZE  ((uptr_t) (NUTMEM_END - 256 - (uptr_t) (&__heap_start)))

To do it more automatically I have the following in my linker file:

MEMORY
{
     FLASH0 (rx) : ORIGIN = 0x00000000, LENGTH = 256K
     SRAM0 (rwx) : ORIGIN = 0x20000000, LENGTH = 64K
}
....
     .bss :
     {
	 PROVIDE (_sbss = .);
	 *(.bss)
	 *(COMMON)
	 . = ALIGN(4);
	 PROVIDE (_ebss = .);
	 . += 0x400;
	 PROVIDE (__exp_stack = .);
	 . += 0x400;
	 PROVIDE (_estack = .);
	 PROVIDE (__heap_start = .);
     } > SRAM0

So adding "extern void *__heap_start;" to nutinit.c is the first part of 
the action. But how to figure out the size between this and the end of 
the RAM? Is there such a thing like a variable filler to declare 
__heap_end or something to calculate something like 
origin+size-__heap_start?

Best regards
Ulrich