Re: [avr-gcc-list] Support for ATMega256 and ATMega2560

[Joerg Wunsch]

Marek Michalkiewicz <address@hidden> wrote:

>  - 2 bytes are not enough for function pointers, possible solutions:

>     - require that if you take the address of a function, that
>     function must be placed in the low 64K words (special section? -
>     I don't know if the linker can do that automagically)

Perhaps by using a jump table for all indirect functions.

I'd consider this a crock though.

>     - align functions so that a few low bits of the pointer are
>     always zero, and store pointers shifted right; at runtime, shift
>     the pointer left and load the high bits into EIND, then use
>     EICALL; EIND must be saved/restored if used in interrupt
>     handlers

Hmm, that sounds even more hacky to me. :)

>     - add support for 3-byte (PSImode) pointers to GCC - this may be
>     quite a lot of work, and all pointers will have this size (not
>     just program memory pointers, because GCC core doesn't support
>     pointers of different sizes as far as I know)

I can't understand this (but then, I don't know much of the internals
of GCC).  It wouldn't even depend on ROM vs. RAM (though obviously,
ROM pointers > 16 bits size might be useful to overcome the 64 KB for
ROM constants barrier), for that purpose, only function pointers were
affected.  Why can't GCC tell a function pointer apart from a data
pointer (both, at definition and at dereferencation)?

-- 
J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/