Re: [avr-gcc-list] SIGNAL and INTERRUPT overhead

[Royce Pereira]

Hi,

On Sun, 21 Aug 2005 03:04:02 +0530, Nigel Winterbottom  
<address@hidden> wrote:
> -----Original Message-----
> From:James A.R. Koehler
>
> If the consensus is that we need to be protected against ourselves by
> having all the existing prolog in the two existing interrupt service
> methods, perhaps the solution is to have a third category of interrupt
> service routine in which nothing is pushed onto the stack and the
> programmer takes full responsibility for making sure the machine is
> returned to the same state it was before the interrupt.
>
>         Jim
> ----------------------
>
> Actually this already exists in the form of applying an attribute to the
> SIGNAL or INTERRUPT name. I use it in my code as the example below shows.

> Nigel

--------------------------
What's required is a peephole optimiser that detects in the assembly  
output the registers used in the function,  or the presence of  
instructions modifying the flags etc and deletes unnecessary matching  
push/pops.

Another peephole optimisation is if a function ends like:

                rcall   label
        ret

It could be replaced with a jump to label (except if it's reti instead of  
ret). This will make the code faster, as extra push/pop of the PC is  
avoided.

Both the above is implemented in SDCC (sdcc.sourceforge.net) a freeware C  
compiler for MCS51 family, which I also use. Can these optimisations be  
implemented a AVR-Gcc?

--Thanks,

Royce.


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