AVR-Chat

I now have an "official" answer from avr@atmel.com as follows:

> On new devices is the stack pointer initialized to REMEND at reset, and you don't need to do that in your code.
> Please see the datasheet of the device you're using.
> I'll update the FAQ.
> 
> Best regards
> Jan Håvard Ugelstad
> Atmel AVR Technical Support
> 

As pointed out in my original query, the "datasheet" is in conflict with
itself and should be cleaned up considerably in this area.  Looking at
other recent AVR parts datasheets (mega48/88/168 series for example),
they are all incorrect and confusing.

Thanks to everyone on this list who replied and confirmed what I thought
was true.  And in my case of code for a tiny45 bootloader (fitting into
64 words), I don't need to worry about finding two more words (besides
the two I already have) to init the stack pointer.

Don

Don AE5K wrote:
> As a longtime user of micros (since the Intel 4004), I know about the
> necessity of initializing the stack pointer in those devices which have it.
> 
> However, some of the most recent Atmel datasheets (for example
> doc2586.pdf, 2586F dated 4/06 on the tiny 25/45/85) lead me to believe
> that Atmel has gone the way of initializing the stack pointer to the top
> of SRAM at reset/powerup time.  In this doc (2586F), paragraph 5.6.1
> shows the "Initial Value" to be "RAMEND".
> 
> This is great if true, BUT in the paragraph above it (par. 5.6) it says
> "This Stack space in the data SRAM must be defined by the program before
> any subroutine calls are executed or interrupts are enabled. The Stack
> Pointer must be set to point above 0x60."
> 
> Also an answer to FAQ on the Atmel website that I read says "For all AVR
> devices with SRAM the stack pointer must be set to point at the last
> address in SRAM."  [I should note that this is not exactly true -- it
> can be set anywhere in SRAM, just as long as there is enough room in
> SRAM addresses below it to accommodate anything pushed on the stack!]
> 
> So the question is "Which is correct?"   Is the stack pointer in these
> newer devices initialized as shown so that the programmer does not need
> to do the initialization?
> 
> Regards,
> Don
>