Difference Between Stack Pointer and Frame Pointer

On Tue, 05 Jul 2005 14:47:59 GMT, "Richard" <nospam@thanks.com> wrote:

>> Most AVR compilers have a data stack separate from the hardware stack.
>
>I'm interested in this statement.  The IAR compiler is the only AVR compiler
>I have come across that does this, and I've never been sure why.  Any clues?

How many AVR compilers have you seen?  The only one that _doesn't_
(AFAIK) is avr-gcc.

The primary reason it that direct manipulation of the hardware stack
pointer (SP) in the AVR is non-atomic (eight bits at a time, and
interrupts must be disabled on writes to prevent ISRs from stomping
all over memory), while the data stack pointer can be kept in a 16-bit
general purpose register that supports 16-bit math.  

IOW, it makes code generation simpler, and the resulting code is both
faster an smaller.

Regards,

                               -=Dave
-- 
Change is inevitable, progress is not.