AVR stack problem

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I hope this is an okay group to ask this in, if not I apologise. (and
could someone point me to a better location)

I just got my deign up and running using an AVR Mega128. For some odd
reason it looks like my stack is disabled. Within AVRStudio the stack
monitor has all of the stack entries grayed out and each is labeled

How would I fix this?


Re: AVR stack problem
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for AVRstudio did you select the divice?

Re: AVR stack problem
Yes. The correct device appears to be selected.

Re: AVR stack problem
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  I am using avrstudio 3.53 and 4.0x. If you have your code
set up correctly you should see the Stackpointer being set.
should be one of the 1st instructions.

Re: AVR stack problem
It looks like everything is set up correctly. The grayed out fields on
in AVRStudio might be that limits are disabled. In any case, when I
step through my code everything seems to work, the stack pointer
changes correctly but on a return from subroutine I head off into the

I am not using external SRAM and it almost looks like the code is
trying to use it.

Any help would be greatly appreciated.

Re: AVR stack problem
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If you use a link file which assumes external RAM the stack might be
situated in external RAM.

Best Regards,
Ulf Samuelsson
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Re: AVR stack problem
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  I am using this asm code to set up the stackpointer.
   ramend is at 0FFF'h for atmega 103 and 128
    ; ************* Stack Pointer Setup Code
    ldi wl,high(ramend-5)    ; Stack Pointer Setup
    out SPH,wl        ; Stack Pointer High Byte
    ldi wl,low(ramend-5)    ; Stack Pointer Setup
    out SPL,wl        ; Stack Pointer Low Byte

this should work to init the SP

Re: AVR stack problem
I figured out that my stack pointer is being initializaed outside of my
internal SRAM  space. That should fix it. Thanks.

Re: AVR stack problem
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Have a look at:

It appears that your fuse bits are still in compatibility mode i.e.
pretending that you are using an Atmega 103.

...Well, certain odd problems arise out of the situation that the AVR
devices as shipped by Atmel often come with a default fuse bit configuration
that doesn't
match the user's expectations. Here is a list of things to care for:

. The ATmega128 ships with the fuse enabled that turns this device into
ATmega103 compatibility mode. This means that some ports are not fully
usable, and
in particular that the internal SRAM is located at lower addresses. Since by
default, the stack is located at the top of internal SRAM, a program
for an ATmega128 running on such a device will immediately crash upon the
first function call (or rather, upon the first function return).

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