Re: [avr-chat] avr-size .bss bigger than RAM?

[Matt.Vandewerken]

I'm not sure that you can determine how big the stack is (nor can you constrain 
it). In the AVR, the stack grows unconstrained downwards from the top of RAM. 
See here: http://www.nongnu.org/avr-libc/user-manual/malloc.html for an 
explanation of the memory sections in the AVR.

If you're running an RTOS you can often allocate/specify where the stacks for 
each process reside, and how big they are, but you can't actually constrain 
them to always fit within that space so you have to be careful to allocate 
enough space for them. 



-----Original Message-----
From: AVR-chat [mailto:address@hidden On Behalf Of Stuart Longland
Sent: Wednesday, 26 July 2017 8:11 AM
To: address@hidden
Subject: Re: [avr-chat] avr-size .bss bigger than RAM?

On 25/07/17 22:36, Rolf Pfister wrote:
> I would say it uses more than 29 bytes too much. Because data also 
> needs SRAM. And subroutine calling and interrupts will also need some 
> bytes of SRAM for the stack.
> Maybe you didn't see something going wrong yet because it didn't fill 
> all reserved data structures yet.

Right… I was a bit surprised that it would allow such a program to link.
 arm-ld complains when the data structures won't fit into the spaces allocated 
by the linker script.

I did another check, and found one of my structures occupied the full
512 bytes, so I've cut it back, .bss is now 279 bytes.

Often the code will define a big integer array somewhere and call that the 
stack, so you know exactly where it is and how big it is.  AVR though, all that 
is abstracted.

Anyone know where I can find out how much RAM is allocated for stack on AVR?
--
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
  ...it's backed up on a tape somewhere.